Toxicological Profile for Hexachlorocyclohexane (HCH)

fNTP2016T

Toxicological Profile for

Hexachlorocyclohexane (HCH)

March 2024

HEXACHLOROCYCLOHEXANE (HCH) ii

DISCLAIMER

Use of trade names is for identification only and does not imply endorsement by the Agency for Toxic

Substances and Disease Registry, the Public Health Service, or the U.S. Department of Health and Human

Services.

HEXACHLOROCYCLOHEXANE (HCH) iii

FOREWORD

This toxicological profile is prepared in accordance with guidelines developed by the Agency for Toxic

Substances and Disease Registry (ATSDR) and the Environmental Protection Agency (EPA). The

original guidelines were published in the Federal Register on April 17, 1987. Each profile will be revised

and republished as necessary.

The ATSDR toxicological profile succinctly characterizes the toxicologic and adverse health effects

information for these toxic substances described therein. Each peer-reviewed profile identifies and

reviews the key literature that describes a substance's toxicologic properties. Other pertinent literature is

also presented, but is described in less detail than the key studies. The profile is not intended to be an

exhaustive document; however, more comprehensive sources of specialty information are referenced.

The focus of the profiles is on health and toxicologic information; therefore, each toxicological profile

begins with a relevance to public health discussion which would allow a public health professional to

make a real-time determination of whether the presence of a particular substance in the environment

poses a potential threat to human health. The adequacy of information to determine a substance's health

effects is described in a health effects summary. Data needs that are of significance to the protection of

public health are identified by ATSDR.

Each profile includes the following:

(A) The examination, summary, and interpretation of available toxicologic information and

epidemiologic evaluations on a toxic substance to ascertain the levels of significant

human exposure for the substance due to associated acute-, intermediate-, and chronic-

duration exposures;

(B) A determination of whether adequate information on the health effects of each substance

is available or in the process of development to determine levels of exposure that present

a significant risk to human health of acute, intermediate, and chronic health effects; and

levels of exposure that may present significant risk of adverse health effects in humans.

The principal audiences for the toxicological profiles are health professionals at the Federal, State, and

local levels; interested private sector organizations and groups; and members of the public.

This profile reflects ATSDR’s assessment of all relevant toxicologic testing and information that has been

peer-reviewed. Staffs of the Centers for Disease Control and Prevention and other Federal scientists have

also reviewed the profile. In addition, this profile has been peer-reviewed by a nongovernmental panel

and was made available for public review. Final responsibility for the contents and views expressed in

this toxicological profile resides with ATSDR.

Christopher M. Reh, Ph.D.

Associate Director

Agency for Toxic Substances and Disease Registry

Centers for Disease Control and Prevention

HEXACHLOROCYCLOHEXANE (HCH) iv

VERSION HISTORY

Date

Description

March 2024

Final toxicological profile released

January 2023

Draft for public comment toxicological profile released

August 2005

Final toxicological profile released

July 1999

Final toxicological profile released

May 1994

Final toxicological profile released

December 1989

Final toxicological profile released

HEXACHLOROCYCLOHEXANE (HCH) v

CONTRIBUTORS & REVIEWERS

CHEMICAL MANAGER TEAM

Malcolm Williams, D.V.M., Ph.D. (Lead)

Heather Carlson-Lynch, M.S., D.A.B.T.

Melanie Buser, M.P.H.

Claire Heit, Ph.D.

Gaston Casillas, Ph.D.

Julie Melia, Ph.D., D.A.B.T.

Jennifer Rhoades, B.A.

Savannah Sierco, M.S.

ATSDR, Office of Innovation and Analytics,

Toxicology Section, Atlanta, GA

SRC, Inc., North Syracuse, NY

REVIEWERS

Interagency Minimal Risk Level Workgroup:

Includes ATSDR; National Center for Environmental Health (NCEH); National Institute for

Occupational Safety and Health (NIOSH); U.S. Environmental Protection Agency (EPA); National

Toxicology Program (NTP).

Additional reviews for science and/or policy:

ATSDR, Office of Community Health Hazard Assessment; ATSDR,

Office of Capacity Development

and Applied Prevention Science; ATSDR, Office of Science; NCEH, Division of Laboratory Sciences;

NCEH, Division of Environmental Health Science and Practice; EPA, Office of Research and

Development; EPA, Office of Water.

PEER REVIEWERS

1. Lisa Kamendulis, Ph.D.; Department of Environmental and Occupational Health; Indiana

University Bloomington; Bloomington, Indiana

2. Russell C. Cattley, VMD, Ph.D., Dipl. ACVP, Fellow IATP; Tyler & Frances Young Professor of

Pathology; Greene Hall; College of Veterinary Medicine; Auburn University, Alabama

3. Stephen M. Roberts, Ph.D.; Director, Center for Environmental & Human Toxicology; Professor,

College of Veterinary Medicine; College of Medicine, and College of Public Health and Health

Professions; University of Florida; Gainesville, Florida

These experts collectively have knowledge of toxicology, chemistry, and/or health effects. All reviewers

were selected in conformity with Section 104(I)(13) of the Comprehensive Environmental Response,

Compensation, and Liability Act, as amended.

ATSDR scientists review peer reviewers’ comments and determine whether changes will be made to the

profile based on comments. The peer reviewers’ comments and responses to these comments are part of

the administrative record for this compound.

The listing of peer reviewers should not be understood to imply their approval of the profile's final

content. The responsibility for the content of this profile lies with ATSDR.

HEXACHLOROCYCLOHEXANE (HCH) vi

CONTENTS

ISCLAIMER .............................................................................................................................................. ii

FOREWORD ............................................................................................................................................... iii

VERSION HISTORY .................................................................................................................................. iv

CONTRIBUTORS & REVIEWERS ............................................................................................................ v

CONTENTS ................................................................................................................................................. vi

LIST OF FIGURES ................................................................................................................................... viii

LIST OF TABLES ........................................................................................................................................ x

CHAPTER 1. RELEVANCE TO PUBLIC HEALTH ................................................................................. 1

1.1 OVERVIEW AND U.S. EXPOSURES ......................................................................................... 1

1.2 SUMMARY OF HEALTH EFFECTS ........................................................................................... 1

1.3 MINIMAL RISK LEVELS (MRLs) ............................................................................................ 11

CHAPTER 2. HEALTH EFFECTS ............................................................................................................ 19

2.1 INTRODUCTION ........................................................................................................................ 19

2.2 DEATH ........................................................................................................................................ 99

2.3 BODY WEIGHT ........................................................................................................................ 102

2.4 RESPIRATORY......................................................................................................................... 105

2.5 CARDIOVASCULAR ............................................................................................................... 107

2.6 GASTROINTESTINAL ............................................................................................................. 109

2.7 HEMATOLOGICAL ................................................................................................................. 110

2.8 MUSCULOSKELETAL ............................................................................................................ 113

2.9 HEPATIC ................................................................................................................................... 114

2.10 RENAL ...................................................................................................................................... 123

2.11 DERMAL ................................................................................................................................... 130

2.12 OCULAR ................................................................................................................................... 131

2.13 ENDOCRINE ............................................................................................................................. 131

2.14 IMMUNOLOGICAL ................................................................................................................. 136

2.15 NE

UROLOGICAL ..................................................................................................................... 140

2.16 REPRODUCTIVE ..................................................................................................................... 150

2.17 DEVELOPMENTAL ................................................................................................................. 163

2.18 OTHER NONCANCER ............................................................................................................. 190

2.19 CANCER .................................................................................................................................... 195

2.20 GENOTOXICITY ...................................................................................................................... 202

CHAPTER 3. TOXICOKINETICS, SUSCEPTIBLE POPULATIONS, BIOMARKERS,

CHEMICAL INTERACTIONS ............................................................................................ 209

3.1 TOXICOKINETICS ................................................................................................................... 209

3.1.1 Absorption ........................................................................................................................... 210

3.1.2 Distribution ......................................................................................................................... 212

3.1.3 Metabolism .......................................................................................................................... 215

3.1.4 Excretion ............................................................................................................................. 217

3.1.5 Physiologically Based Pharmacokinetic (PBPK)/Pharmacodynamic (PD) Models ........... 219

3.1.6 Animal-to-Human Extrapolations ....................................................................................... 221

3.2 CHILDREN AND OTHER POPULATIONS THAT ARE UNUSUALLY

SUSCEPTIBLE .......................................................................................................................... 222

3.3 BIOMARKERS OF EXPOSURE AND EFFECT ..................................................................... 225

HEXACHLOROCYCLOHEXANE (HCH) vii

3.3.1 Biomarkers of Exposure ...................................................................................................... 226

3.3.2 Biomarkers of Effect ........................................................................................................... 228

3.4 INTERACTIONS WITH OTHER CHEMICALS ..................................................................... 228

CHAPTER 4. CHEMICAL AND PHYSICAL INFORMATION ........................................................... 232

4.1 CHEMICAL IDENTITY ........................................................................................................... 232

4.2 PHYSICAL AND CHEMICAL PROPERTIES ........................................................................ 233

CHAPTER 5. POTENTIAL FOR HUMAN EXPOSURE ....................................................................... 236

5.1 OVERVIEW .............................................................................................................................. 236

5.2 PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL ................................................ 237

5.2.1 Production ........................................................................................................................... 237

5.2.2 Import/Export ...................................................................................................................... 238

5.2.3 Use ...................................................................................................................................... 239

5.2.4 Disposal ............................................................................................................................... 240

5.3 RELEASES TO THE ENVIRONMENT ................................................................................... 241

5.3.1 Air ....................................................................................................................................... 241

5.3.2 Water ................................................................................................................................... 243

5.3.3 Soil ...................................................................................................................................... 245

5.4 ENVIRONMENTAL FATE ...................................................................................................... 245

5.4.1 Transport and Partitioning ................................................................................................... 245

5.4.2 Transformation and Degradation ........................................................................................ 251

5.5 LEVELS IN THE ENVIRONMENT ......................................................................................... 256

5.5.1 Air ....................................................................................................................................... 259

5.5.2 Water ................................................................................................................................... 259

5.5.3 Sediment and Soil ............................................................................................................... 270

5.5.4 Other Media ........................................................................................................................ 270

5.6 GENERAL POPULATION EXPOSURE .................................................................................. 281

5.7 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES .............................................. 289

CHAP

TER 6. ADEQUACY OF THE DATABASE ................................................................................ 291

6.1 EXISTING INFORMATION ON HEALTH EFFECTS ........................................................... 291

6.2 IDENTIFICATION OF DATA NEEDS .................................................................................... 291

6.3 ONGOING STUDIES ................................................................................................................ 302

CHAPTER 7. REGULATIONS AND GUIDELINES ............................................................................. 303

CHAPTER 8. REFERENCES .................................................................................................................. 306

APPENDICES

APPENDIX A. ATSDR MINIMAL RISK LEVEL WORKSHEETS .................................................... A-1

APPENDIX B. LITERATURE SEARCH FRAMEWORK FOR HCH .................................................. B-1

APPENDIX C. FRAMEWORK FOR ATSDR’S SYSTEMATIC REVIEW OF HEALTH EFFECTS

DATA FOR HCH ........................................................................................................... C-1

APPENDIX D. USER’S GUIDE ............................................................................................................. D-1

APPENDIX E. QUICK REFERENCE FOR HEALTH CARE PROVIDERS ....................................... E-1

APPENDIX F. GLOSSARY .................................................................................................................... F-1

APPENDIX G. ACRONYMS, ABBREVIATIONS, AND SYMBOLS ................................................. G-1

HEXACHLOROCYCLOHEXANE (HCH) viii

LIST OF FIGURES

1-1. Health Effects Found in Animals Following Inhalation Exposure to γ-Hexachlorocyclohexane ........ 3

1-2. Health Effects Found in Animals Following Oral Exposure to α-Hexachlorocyclohexane ................. 3

1-3. Health Effects Found in Animals Following Oral Exposure to β-Hexachlorocyclohexane ................. 4

1-4. Health Effects Found in Animals Following Oral Exposure to γ-Hexachlorocyclohexane ................. 5

1-5. Health Effects Found in Animals Following Oral Exposure to Technical

Hexachlorocyclohexane ........................................................................................................................ 6

1-6. Summary of Sensitive Targets of α-Hexachlorocyclohexane (α-HCH) – Oral .................................. 12

1-7. Summary of Sensitive Targets of β-Hexachlorocyclohexane (β-HCH) – Oral .................................. 13

1-8. Summary of Sensitive Targets of γ-Hexachlorocyclohexane (γ-HCH) – Inhalation .......................... 14

1-9. Summary of Sensitive Targets of γ-Hexachlorocyclohexane (γ-HCH) – Oral ................................... 15

1-10. Summary of Sensitive Targets of Technical-Hexachlorocyclohexane (technical-HCH) – Oral ...... 16

2-1. Overview of the Number of Studies Examining α-Hexachlorocyclohexane (α-HCH) Health

Effects ................................................................................................................................................. 23

2-2. Overview of the Number of Studies Examining β-Hexachlorocyclohexane (β-HCH) Health

Effects ................................................................................................................................................. 24

2-3. Overview of the Number of Studies Examining γ-Hexachlorocyclohexane (γ-HCH) Health

Effects ................................................................................................................................................. 25

2-4. Overview of the Number of Studies Examining δ-Hexachlorocyclohexane (δ-HCH) and

Unspecified Hexachlorocyclohexanes Health Effects ........................................................................ 26

2-5. Levels of Significant Exposure to γ-Hexachlorocyclohexane (Lindane) – Inhalation ....................... 29

2-6. Levels of Significant Exposure to α-Hexachlorocyclohexane – Oral ................................................. 36

2-7. Levels of Significant Exposure to β-Hexachlorocyclohexane – Oral ................................................. 46

2-8. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral ................................................. 74

2-9. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane (HCH) – Oral ............ 90

3-1. The Proposed Metabolism of Hexachlorocyclohexane .................................................................... 216

5-1. Number of NPL Sites with Hexachlorocyclohexane Contamination ............................................... 236

6-1.

Summary of Existing Health Effects Studies on α-Hexachlorocyclohexane by Route and

Endpoint ........................................................................................................................................... 292

HEXACHLOROCYCLOHEXANE (HCH) ix

6-2. Summary of Existing Health Effects Studies on β-Hexachlorocyclohexane by Route and

Endpoint ........................................................................................................................................... 293

6-3. Summary of Existing Health Effects Studies on γ-Hexachlorocyclohexane by Route and

Endpoint ........................................................................................................................................... 294

6-4. Summary of Existing Health Effects Studies on δ-Hexachlorocyclohexane and Unspecified

Hexachlorocyclohexanes by Route and Endpoint ............................................................................ 295

HEXACHLOROCYCLOHEXANE (HCH) x

LIST OF TABLES

1. Minimal Risk Levels (MRLs) for α-Hexachlorocyclohexane ............................................................ 17

1-2. Minimal Risk Levels (MRLs) for β-Hexachlorocyclohexane ............................................................ 17

1-3. Minimal Risk Levels (MRLs) for γ-Hexachlorocyclohexane ............................................................ 18

2-1. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Inhalation ........................................ 27

2-2. Levels of Significant Exposure to α-Hexachlorocyclohexane – Oral ................................................. 31

2-3. Levels of Significant Exposure to β-Hexachlorocyclohexane – Oral ................................................. 40

2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral ................................................. 50

2-5. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane – Oral ........................ 81

2-6. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Dermal ............................................ 94

2-7. Levels of Significant Exposure to Technical Hexachlorocyclohexane – Dermal .............................. 96

2-8. Summary of Epidemiological Studies of β-Hexachlorocyclohexane (β-HCH) Exposure and

Body Weight Effects ........................................................................................................................ 103

2-9. Summary of Epidemiological Studies of β-Hexachlorocyclohexane Exposure and

Cardiovascular Effects ...................................................................................................................... 107

2-10. Summary of Epidemiological Studies of β-Hexachlorocyclohexane Exposure and Hepatic

Effects ............................................................................................................................................. 114

2-11. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and

Renal Effects .................................................................................................................................. 124

2-12. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and

Endocrine Effects ........................................................................................................................... 132

2-13. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and

Immune Effects .............................................................................................................................. 137

2-14. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and

Neurological Effects ....................................................................................................................... 142

2-15. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and

Reproductive Effects ...................................................................................................................... 151

2-16. Summary of Epidemiological Studies of α-Hexachlorocyclohexane (HCH) Exposure and

Developmental Effects ................................................................................................................... 164

2-17. Summary of Epidemiological Studies of β-Hexachlorocyclohexane Exposure and

Developmental Effects ................................................................................................................... 167

HEXACHLOROCYCLOHEXANE (HCH) xi

2-18. Summary of Epidemiological Studies of γ-Hexachlorocyclohexane Exposure and

Developmental Effects ................................................................................................................... 178

2-19. Summary of Epidemiological Studies of δ-HCH and Total HCH Exposure and

Developmental Effects ................................................................................................................... 189

2-20. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and

Other Noncancer Effects ................................................................................................................ 191

2-21. Summary of Epidemiological Studies Evaluating Possible Associations between

Hexachlorocyclohexane Exposure and Risk of Selected Cancer Types......................................... 195

2-22. Genotoxicity of Hexachlorocyclohexane Isomers In Vivo ............................................................. 202

2-23. Genotoxicity of Hexachlorocyclohexane Isomers In Vitro ............................................................ 203

4-1. Chemical Identity of Hexachlorocyclohexane Isomers .................................................................... 232

4-2. Physical and Chemical Properties of Hexachlorocyclohexane Isomers ........................................... 234

5-1. Facilities that Produce, Process, or Use γ-Hexachlorocyclohexane ................................................. 237

5-2. Releases to the Environment from Facilities that Produce, Process, or Use

Hexachlorobenzenes ......................................................................................................................... 242

5-3. γ-HCH Emissions as Reported by the 2017 National Emission Inventory ...................................... 243

5-4. Results of Experimental Bioaccumulation Studies with γ-Hexachlorocyclohexane ........................ 249

5-5. Lowest Limit of Detection Based on Standards ............................................................................... 256

5-6. Summary of Ambient Environmental Levels of HCH ..................................................................... 257

5-7. Hexachlorocyclohexanes Levels in Water, Soil, and Air of National Priorities List (NPL)

Sites .................................................................................................................................................. 258

5-8. Outdoor Air Monitoring Data for Hexachlorocyclohexanes (HCHs) ............................................... 260

5-9. Water Monitoring Data for Hexachlorocyclohexanes (HCHs) ........................................................ 264

5-10. Soil and Sediment Monitoring Data for Hexachlorocyclohexanes (HCHs) ................................... 271

5-11. Organism Monitoring Data for Hexachlorocyclohexanes (HCHs) ................................................ 275

5-12. Geometric Mean of the Serum Concentration (ng/g) of β-Hexachlorocyclohexane (β-HCH)

(2015–2016) and γ-Hexachlorocyclohexane (γ-HCH) (2011–2012) in the U.S. Population ......... 285

7-1. Regulations and Guidelines Applicable to Hexachlorocyclohexane (HCH) .................................... 303

HEXACHLOROCYCLOHEXANE (HCH) 1

CHAPTER 1. RELEVANCE TO PUBLIC HEALTH

1.1 OVERVIEW AND U.S. EXPOSURES

Hexachlorocyclohexane (HCH) is a mixture of eight isomers, four of which are of commercial

significance: alpha (α)-HCH (Chemical Abstracts Service [CAS] Registry Number 319-84-6),

beta (β)-HCH (CAS Registry Number 319-85-7), gamma (γ)-HCH (CAS Registry Number 58-89-9), and

delta (δ)-HCH (CAS Registry Number 319-86-8). Technical (or technical-grade) HCH (CAS Registry

Number 608-73-1) is not an isomer of HCH, but rather a mixture of several isomers; it consists of

approximately 60–70% α-HCH, 5–12% β-HCH, 10–15% γ-HCH, 6–10% δ-HCH, and 3–4% ε-HCH

(Kutz et al. 1991). The most well-studied isomer is γ-HCH (lindane), an organochlorine insecticide that

was used for a broad range of agricultural applications in the United States and worldwide beginning in

the 1940s. Its agricultural use began to be limited in the 1970s by the U.S. Environmental Protection

Agency (EPA), citing human health concerns, and final registrations for products containing γ-HCH were

cancelled in late 2006. Today, 1% γ-HCH prescription products, regulated by the U.S. Food and Drug

Administration (FDA), are available for lice and scabies treatment. HCH isomers exist as white solids

that can volatilize to the gas or particulate phase. HCH released to the environment can volatilize from,

or partition to, soil and can leach to groundwater. The general population may be exposed to low

amounts of HCH through inhalation of contaminated ambient air and ingestion of contaminated water

(exposure in the range of parts per trillion) or contact with contaminated soils (exposure in the range of

parts per billion). The highest exposures result from the use of γ-HCH pharmaceutical treatments.

Workers who work at facilities that use or process γ-HCH and people who live near HCH-contaminated

sites may have increased exposure.

1.2 SUMMARY OF HEALTH EFFECTS

The toxicological database for HCH includes human observational studies of pesticide workers and the

general population and studies of animals exposed by inhalation, oral administration, and dermal

application. In general, the studies of pesticide applicators with exposure to γ-HCH or technical HCH

used qualitative measures of exposure. Most general population studies used blood or tissue

concentrations of HCH isomers to assess exposure, and the samples were typically collected

simultaneously with or after outcome assessment. As such, the temporal relationship between exposure

and outcome is uncertain.

HEXACHLOROCYCLOHEXANE (HCH) 2

1. RELEVANCE TO PUBLIC HEALTH

Data pertaining to the effects in animals after inhalation or dermal exposure are limited to the γ-HCH

isomer and technical HCH. In addition, the available data on effects in animals exposed by oral

administration to α-, β-, or δ-HCH are relatively limited, compared to the information available for

γ-HCH. Figures 1-1 through 1-5 show the most sensitive effects in animals after inhalation exposure to

γ-HCH, oral exposure to α-HCH, oral exposure to β-HCH, oral exposure to γ-HCH, and oral exposure to

technical-grade HCH, respectively. The available data on δ-HCH are not adequate to identify sensitive

effects by any exposure route. As Figure 1-2 shows, the most sensitive effect of oral exposure to α-HCH

is liver toxicity. A systematic review of this endpoint resulted in the following hazard identification

conclusion:

• Hepatic effects are a presumed health effect for humans.

Figure 1-3 shows that the most sensitive effects of β-HCH in animals exposed orally are liver toxicity and

neurological effects. A systematic review of these endpoints resulted in the following hazard

identification conclusions:

• Hepatic effects are a presumed health effect for humans.

• Neurological effects are a presumed health effect for humans.

Figures 1-1 and 1-4 show that the most sensitive effects of γ-HCH in animals are developmental toxicity

and immune system effects. A systematic review of these endpoints resulted in the following hazard

identification conclusions:

• Developmental effects are a presumed health effect for humans.

• Immune system effects are a presumed health effect for humans.

Figure 1-5 shows the most sensitive effects of technical-grade HCH (a mixture of isomers) or in studies

that did not specify the HCH isomer(s). A systematic review was not conducted for the mixture.

Hepatic Effects. Data on hepatic effects of HCH isomers in humans are inadequate for hazard

identification, but studies in animals show similar liver effects induced by all the subject isomers of HCH

after inhalation, oral, and dermal exposure. Hepatic effects consisting of increased absolute and/or

relative liver weights, hepatocellular hypertrophy, necrosis, fatty degeneration, bile duct proliferation, and

nodular hyperplasia have been observed in rats, mice, and hamsters exposed by oral administration of

α-HCH for intermediate and chronic durations (Fitzhugh et al. 1950; Ito et al. 1975; Nagasaki et al. 1975;

Sumida et al. 2007; Tryphonas and Iverson 1983). Dietary administration of β-HCH for intermediate and

chronic durations has resulted in similar liver toxicity in rats and mice (Fitzhugh et al. 1950; Hanada et al.

HEXACHLOROCYCLOHEXANE (HCH) 3

1. RELEVANCE TO PUBLIC HEALTH

Figure 1-1. Health Effects Found in Animals Following Inhalation Exposure to

γ-Hexachlorocyclohexane

Concentration (ppm)

Effects in Animals

101-603

Acute: Decreased body weight and clinical signs of neurotoxicity in rats

5-10

0.5-1

Intermediate: Death in mice; histological changes in kidneys in rats

Acute: Death in mice; diarrhea in rats

Intermediate:

Diarrhea in rats; bone marrow myelogram changes in rats

Figure 1-2. Health Effects Found in Animals Following Oral Exposure to

α-Hexachlorocyclohexane

Dose (mg/kg/day) Effects in Animals

18-20

0.002 mg/kg/day Intermediate MRL

45-70

0.0009 mg/kg/day Chronic MRL

Intermediate: Histological changes in kidneys in rats; hepatoma in

female mice; decreased body weight in rats

Chronic: Hepatocellular carcinoma in rats

Intermediate: Increased liver weight and histological changes in liver in

mice; hepatoma in male mice

Chronic: Increased liver weight and histological changes in liver in rats

HEXACHLOROCYCLOHEXANE (HCH) 4

1. RELEVANCE TO PUBLIC HEALTH

Figure 1-3. Health Effects Found in Animals Following Oral Exposure to

β-Hexachlorocyclohexane

Dose (mg/kg/day) Effects in Animals

5-9

0.18-0.7

0.08 mg/kg/day Acute MRL

20-38

0.0006 mg/kg/day Intermediate MRL

60-200

Acute: Lateral recumbency and death

Acute: Ataxia and hypoactivity in rats

Intermediate: Reduced tail nerve conduction velocity in rats; immune

suppression and hepatic histopathology changes in mice

Intermediate: Death; hematology changes; histological changes in

kidneys, adrenal glands, spleen, thymus, ovaries, and testes in rats; pup

mortality in rats

Chronic: Liver tumors in mice

Intermediate: Decreased body weight gain in rats; increased liver

weight in rat pups

Intermediate: Histological changes in liver in rats

Chronic: Increased liver weight and histological changes in liver in rats

HEXACHLOROCYCLOHEXANE (HCH) 5

1. RELEVANCE TO PUBLIC HEALTH

Figure 1-4. Health Effects Found in Animals Following Oral Exposure to

γ-Hexachlorocyclohexane

Dose (mg/kg/day) Effects in Animals

0.25-1.7

0.00015-0.07

0.003 mg/kg/day Acute MRL

3-5

0.0000008 mg/kg/day Intermediate MRL

7-10

13.6-20

Acute: Death in rats; impaired development of male and female

reproductive tracts in mice

Chronic: Hepatocellular carcinoma in mice

Acute: Reduced delayed-type hypersensitivity in rats; increased

spontaneous activity in rats; hematological effects in mice

Intermediate: Female reproductive effects in rats; suppressed body

weight gain in dogs

Chronic: Increased liver weight and histological changes in liver in rats;

histological changes in kidney in rats

Acute: Histological changes in liver in rats; changes to serotonin levels

and seizures in rats

Intermediate: Decreased sperm count and motility in rats; immune

suppression in rats; cardiotoxicity in rats

Acute: Impaired development of male reproductive tract in rats

Intermediate: Histological changes in liver in rats; reproductive effects

in mink; Reduced ovulation rate in rabbits; persistent hyperactivity and

ultrastructural changes in the brains of rat pups

Intermediate: Histological changes in kidney in male rats; immune

suppression in mice; decreased body weight and cardiac histopathology

in rat pups; altered ventricular electrophysiology in rat pups

HEXACHLOROCYCLOHEXANE (HCH) 6

1. RELEVANCE TO PUBLIC HEALTH

Figure 1-5. Health Effects Found in Animals Following Oral Exposure to

Technical Hexachlorocyclohexane

Dose (mg/kg/day) Effects in Animals

2-4

0.4-0.8

50-144

Acute: Death in mice; histological changes in liver in mice

Intermediate: Liver tumors in mice

Acute: Reduced enzyme activity in the brain in rats; reproductive effects

in male rats

Intermediate: Changes in neurotransmitter levels in rat pups

Chronic:

Convulsions in mice; hepatocellular carcinoma in mice

Intermediate: Decreased body weight gain in rats; decreased vas

deferens weight and degeneration in rats; altered behavior,

ultrastructural changes in brain in rats; increased liver weight in rats

Chronic: Histological changes in liver in rats

Intermediate: Increased kidney weight in pigs; tremors, convulsions,

paralysis of limbs in rats

HEXACHLOROCYCLOHEXANE (HCH) 7

1. RELEVANCE TO PUBLIC HEALTH

1973; Ito et al. 1973, 1975; Van Velsen et al. 1986). In intermediate-duration studies of rats exposed to

γ-HCH aerosol, increased liver weights were seen without histology changes (Oldiges et al. 1983). After

oral exposure to γ-HCH for acute, intermediate, and chronic durations, liver effects in rats, mice, and

rabbits have included increased serum enzymes indicative of hepatocellular injury, increased serum lipids,

increased liver weight, hepatocellular hypertrophy, vacuolar degeneration, necrosis, and congestion (Ali

and Shakoori 1998; Amyes 1990; Attia et al. 2011; Boll et al. 1995; Cerón et al. 1995; EPA 1991a,

2000a; Fatih Fidan et al. 2008; Fitzhugh et al. 1950; Grabarczyk et al. 1990; Hfaiedh et al. 2012; Kamal

El-Dein et al. 2016; Kopec-Szlezak et al. 1989; Matsuura et al. 2005; Parmar et al. 2003; Singh and

Sharma 2011; Sumida et al. 2007; Suter 1983; Vijaya Padma et al. 2011). Centrilobular hepatocellular

hypertrophy was also reported in rats exposed to γ-HCH for 13 weeks by dermal application (EPA

1988a). In intermediate-duration studies of rats and mice exposed to δ-HCH, increased liver weight

and/or centrilobular hypertrophy were reported (Ito et al. 1973, 1975). Studies of animals exposed to

technical-grade HCH by oral or dermal administration (e.g., Dikshith et al. 1978, 1989b, 1991a, 1991c;

Fitzhugh et al. 1950; Philip et al. 1989; Trivedi et al. 2007, 2009) provide supporting evidence for hepatic

effects of HCH isomers.

Developmental Effects. Epidemiological studies examining relationships between birth outcomes and

maternal or fetal blood or tissue levels of β-HCH have reported associations with decreased birth weight

(Anand and Taneja 2020; Callan et al. 2016; Fang et al. 2019a, 2019b; Guo et al. 2014; Lopez-Espinosa et

al. 2011; Yang et al. 2020) and fetal growth restriction (Sharma et al. 2012). Studies using α- or γ-HCH

levels in maternal or fetal tissues to assess the relationship between HCH exposure and developmental

outcomes in humans have not shown consistent results and are limited by the relatively short half-life of

these isomers in the human body (see details in Section 3.1.4). No developmental toxicity studies of

animals exposed to α-HCH were located. Developmental toxicity data for β-HCH are very limited but

show increased perinatal mortality and increased liver weight of pups after exposure during gestation and

lactation or lactation only (Srinivasan et al. 1991). After oral administration of technical-grade HCH

during gestation, mice exhibited increased fetal resorptions (Dikshith et al. 1990; Srivastava and Raizada

2000) and rats have shown altered neurotransmitter levels in the brain (Nagaraja and Desiraju 1994).

Studies in a variety of species exposed to γ-HCH for acute or intermediate durations during gestation or

postnatal development have demonstrated effects on a wide range of endpoints, including birth outcomes

and development of the male and female reproductive tracts, central nervous system, heart, liver, thymus,

and spleen. Increased stillbirths, reduced neonatal viability, and decreased pup weights have been

reported in rats, mice, and mink (Beard et al. 1997; EPA 1991a, 1999c; Hassoun and Stohs 1996a;

HEXACHLOROCYCLOHEXANE (HCH) 8

1. RELEVANCE TO PUBLIC HEALTH

Matsuura et al. 2005; Sauviat et al. 2005). In male offspring of rats and mice exposed to γ-HCH via oral

administration during gestation and/or postnatal development, effects on preputial separation, serum

hormone levels, spermatogenesis, reproductive organ weights, and testicular histopathology have been

reported (Agrahari et al. 2019; Dalsenter et al. 1997a, 1997b; Di Consiglio et al. 2009; La Sala et al. 2009;

Traina et al. 2003). Female offspring of rats and mice exposed similarly exhibited effects on vaginal

opening, oogenesis, and uterine weight (La Sala et al. 2009; Maranghi et al. 2007; Matsuura et al. 2005).

Oral exposure of maternal rats and mice to γ-HCH has resulted in significant decreases in thymus and

spleen weights in the offspring (Hassoun et al. 1996; Matsuura et al. 2005), increases in pup liver weight

(Srinivasan et al. 1991), and cardiac electrophysiology and histopathology changes in pups (Sauviat et al.

2005). Developmental neurotoxicity findings in animals orally exposed to γ-HCH in utero or during

development included seizures and convulsions (Albertson et al. 1985; Johri et al. 2008); effects on motor

activity, learning, and memory (EPA 1999c; Johri et al. 2007; Rivera et al. 1998; Srivastava et al. 2019);

changes in neurotransmitter levels (Rivera et al. 1991, 1998); altered brain wave activity (Breton et al.

2005); and ultrastructural changes in the brain (Srivastava et al. 2019).

Immune System Effects. There are inadequate data on effects of HCH isomers on the immune system of

humans. No studies of immune endpoints in animals exposed to α-HCH by inhalation, oral, or dermal

routes were located. Information on immune effects of β-HCH includes a report of decreased lympho-

proliferative responses to mitogens in mice exposed via diet for 30 days (Cornacoff et al. 1988) and a

report of thymic and splenic histopathology changes (atrophy of the thymus and depletion of splenic

lymphoid tissue) in rats at doses associated with humane sacrifice due to moribund condition (Van Velsen

et al. 1986). Suppression of the immune system has been demonstrated in a small number of acute- and

intermediate-duration studies of γ-HCH administered orally to rats, mice, rabbits, and sheep. Effects seen

in these studies include reduced delayed-type hypersensitivity response (Khurana et al. 1999; Mediratta et

al. 2008) and decreased antibody titers in response to antigens (Banerjee et al. 1996; Desi et al. 1978;

Dewan et al. 1980; Koner et al. 1998; Meera et al. 1992). Decreased spleen and thymus weights and

histopathology changes in the thymus, lymph nodes, and spleen have also been seen in animals exposed

to γ-HCH (Hong and Boorman 1993; Meera et al. 1992).

Neurological Effects. The available epidemiological data on neurological effects of HCH isomers are

generally inadequate for hazard identification, but case reports support a relationship between oral and

dermal exposure to γ-HCH and seizures or convulsions in humans of all ages (Aks et al. 1995; Boffa et al.

1995; CDC 2005; Davies et al. 1983; Fischer 1994; Forrester et al. 2004; Hall and Hall 1999; Harris et al.

1969; Lee and Groth 1977; Lifshitz and Gavrilov 2002; Matsuoka 1981; Munk and Nantel 1977; Nordt

HEXACHLOROCYCLOHEXANE (HCH) 9

1. RELEVANCE TO PUBLIC HEALTH

and Chew 2000; Powell 1980; Ramabhatta et al. 2014; Ramchander et al. 1991; Solomon et al. 1995;

Starr and Clifford 1972; Storen 1955; Sudakin 2007; Wheeler 1977; Telch and Jarvis 1982; Tenenbein

1991; Wiles et al. 2015). Information on neurotoxicity of α-HCH in animals is limited to a single study

showing no effect on nerve conduction velocity in rats exposed for 30 days (Muller et al. 1981). In

addition, few data on this endpoint are available for β-HCH. Studies include reports of clinical signs of

neurotoxicity after acute durations (ataxia and hypoactivity progressing in some cases to coma)

(Cornacoff et al. 1988; Van Velsen et al. 1986) and reduced nerve conduction velocity in the tail of rats in

the isomer comparison study by Muller et al. (1981).

Neurological effects have been observed in rats and/or mice exposed to γ-HCH by inhalation, oral, and

dermal exposure routes. Inhalation exposure of rats for acute durations resulted in central nervous system

depression or restlessness, excitation, and ataxia, with spasms observed at higher concentrations (Oldiges

et al. 1980; Ullmann 1986b). In rats exposed by gavage or dietary administration of γ-HCH, seizures and

convulsions have been observed (Amyes 1990; EPA 1999a; Fitzhugh et al. 1950; Gilbert and Mack 1995;

Johri et al. 2008; Joy et al. 1982; Martinez and Martinez-Conde 1995; Martinez et al. 1991; Matsuura et

al. 2005; Parmar et al. 2003; Tusell et al. 1988; Vendrell et al. 1992a, 1992b; Woolley and Griffith 1989).

Altered neurotransmitter levels in the brain were noted in rats exposed orally for acute or intermediate

durations (Attia et al. 1991; Martinez and Martinez-Conde 1995). Clinical signs of toxicity in orally-

dosed rats have included decreased motor activity, decreased grooming behavior, increased rearing,

altered gait, and hypersensitivity to touch (EPA 1999a, 1999b). Effects on motor activity, anxiety,

cognition, and memory were demonstrated in neurobehavioral testing of rats after acute- and

intermediate-duration oral exposures to γ-HCH (Desi 1974; EPA 1999a; Llorens et al. 1990; Sahaya et al.

2007; Srivastava et al. 2019; Tilson et al. 1987); in one study, the behavioral changes were accompanied

by ultrastructural changes in the hippocampus and substantia nigra of the rats (Srivastava et al. 2019).

Clinical signs of neurotoxicity, including seizures, convulsions, hyperactivity, ataxia, and/or sedation

were reported in rats and rabbits after single or repeated dermal applications of γ-HCH (EPA 1988a;

Hanig et al. 1976; Ullmann 1986a).

Cancer. Human epidemiological data provide evidence for an association between exposure to HCH

isomers and non-Hodgkin’s lymphoma (NHL). The strongest evidence is derived from a prospective

cohort study of pesticide applicators in Iowa and North Carolina, which showed that NHL incidence

increased with duration and intensity of exposure to γ-HCH (Alavanja et al. 2014). A large, pooled case-

control study reported similar findings. Kachuri et al. (2020) pooled data across three population-based,

case-control studies in the United States and Canada (North American Pooled Project). The odds of NHL

HEXACHLOROCYCLOHEXANE (HCH) 10

1. RELEVANCE TO PUBLIC HEALTH

were increased with self-reported exposure to γ-HCH in analyses of 1,690 cases and 5,131 controls

(Kachuri et al. 2020). Additional support for the association with NHL comes from a case-control study

nested within three large prospective cohorts in Shanghai and Singapore. Bassig et al. (2020) observed a

positive association between incident NHL and blood levels of β-HCH measured approximately 7 years

prior to diagnosis. Nested case-control studies that reported no association between NHL and blood or

tissue levels of β-HCH (Brauner et al. 2012; Cantor et al. 2003) generally reported lower exposure levels

than the study by Bassig et al. (2020).

Other epidemiological studies reported positive associations between β- or γ-HCH in blood or qualitative

exposure to γ-HCH and multiple myeloma, leukemia, colorectal cancer, female breast cancer, prostate

cancer, lung cancer, thyroid cancer, brain cancer, and hepatocellular carcinoma (Arrebola et al. 2015a;

Band et al. 2011; Lee et al. 2018a; Lerro et al. 2021; Ibarluzea et al. 2004; Kumar et al. 2010; Miao et al.

2021; Purdue et al. 2007; Salimi et al. 2023; Waliszewski et al. 2005; Weber et al. 2018; Xu et al. 2010;

Yousefi et al. 2022; Zhao et al. 2012). However, the evidence for an association between HCH isomer

exposure and these cancer types is much weaker than that for NHL.

Studies in rats and mice exposed to α-, β-, γ-, and technical HCH by dietary administration have shown

increased incidences of liver tumors (Bhatt and Bano 2009; Bhatt and Nagda 2012; Hanada et al. 1973;

Ito et al. 1973, 1975, 1976; Karnik et al. 1981; Kashyap et al. 1979; Munir et al. 1983; Nagasaki et al.

1975; NCI 1977; Thakore et al. 1981; Thorpe and Walker 1973; Trivedi et al. 2007, 2009; Tryphonas and

Iverson 1983; Tsukada et al. 1979; Wolff et al. 1987). In addition, chronic dermal exposure to technical-

grade HCH resulted in liver tumors in mice (Kashyap et al. 1979). γ-HCH has been reported to induce

increased incidences of bronchiolar-alveolar adenomas and carcinomas in female mice exposed via diet

(EPA 2000a; Wolff et al. 1987).

The EPA (IRIS 1987a) listed α-HCH as a probable human carcinogen based on sufficient evidence of

carcinogenicity in animals and inadequate data in humans. The Integrated Risk Information System (IRIS

1987b) listed β-HCH as a possible human carcinogen based on evidence for benign liver tumors in

exposed mice and inadequate data in humans. Data on δ-HCH were considered inadequate to classify the

potential human carcinogenicity (IRIS 1987d). Although the IRIS (1987c) program did not evaluate the

carcinogenicity of γ-HCH, EPA’s Office of Pesticide Programs (EPA 2001, 2002) classified γ-HCH into

the category “suggestive evidence of carcinogenicity, but not sufficient to assess human carcinogenic

potential.” The Department of Health and Human Services (HHS) National Toxicology Program (NTP)

determined that γ-HCH and other HCH isomers may reasonably be anticipated to cause cancer in humans

HEXACHLOROCYCLOHEXANE (HCH) 11

1. RELEVANCE TO PUBLIC HEALTH

(NTP 2021). In 2018, the International Agency for Research on Cancer (IARC) determined that there

was sufficient evidence in both humans and animals for the carcinogenicity of γ-HCH, assigning it to

Group 1 (carcinogenic to humans). IARC (2018) concluded that γ-HCH causes NHL in humans.

1.3 MINIMAL RISK LEVELS (MRLs)

α-HCH. The inhalation database was considered inadequate for derivation of acute-, intermediate-, or

chronic-duration inhalation MRLs for α-HCH. The oral database for α-HCH was considered inadequate

for derivation of an acute-duration oral MRL, but data were adequate for derivation of intermediate- and

chronic-duration oral MRLs. As shown in Figure 1-6, hepatic effects are the most sensitive targets of

toxicity in animals exposed orally to α-HCH.

β-HCH. The inhalation database was considered inadequate for derivation of acute-, intermediate-, or

chronic-duration inhalation MRLs for β-HCH. The oral database for β-HCH was considered adequate for

derivation of acute- and intermediate-duration oral MRLs, but not for a chronic-duration oral MRL. As

shown in Figure 1-7, neurological and hepatic effects are the most sensitive targets of toxicity in animals

exposed orally to β-HCH.

γ-HCH (Lindane). The inhalation database was considered inadequate for derivation of acute-,

intermediate-, or chronic-duration inhalation MRLs for γ-HCH. Figure 1-8 shows that death and renal

and gastrointestinal effects were seen at the lowest concentrations of γ-HCH in available inhalation

studies. The oral database for γ-HCH was considered adequate for derivation of acute- and intermediate-

duration oral MRLs, but not for a chronic-duration oral MRL. As shown in Figure 1-9, developmental

and immune system effects are the most sensitive targets of toxicity in animals exposed orally to γ-HCH.

δ-HCH. The inhalation and oral databases were considered inadequate for derivation of acute-,

intermediate-, or chronic-duration inhalation or oral MRLs for δ-HCH.

Technical HCH or Unspecified Isomers of HCH. MRLs were not derived for technical-grade HCH due

to the wide variation in isomer composition of technical HCH. Figure 1-10 shows the sensitive targets in

studies of technical-grade HCH or unspecified HCH isomers.

HEXACHLOROCYCLOHEXANE (HCH) 12

1. RELEVANCE TO PUBLIC HEALTH

Figure 1-6. Summary of Sensitive Targets of α-Hexachlorocyclohexane (α-HCH) –

Oral

Available data indicate that the liver, and liver cancers, are the most sensitive targets of α-HCH

oral exposure.

Numbers in circles are the lowest LOAELs for all health effects in animals; no human data were identified.

Cancer

Hepatic

Body weight

Renal

Hepatic

Cancer

Intermediate (mg/kg/day)

Chronic (mg/kg/day)

HEXACHLOROCYCLOHEXANE (HCH) 13

1. RELEVANCE TO PUBLIC HEALTH

Figure 1-7. Summary of Sensitive Targets of β-Hexachlorocyclohexane (β-HCH) –

Oral

Available data indicate that the liver is the most sensitive target of β-HCH oral exposure.

Numbers in circles are the lowest LOAELs for all health effects in animals.

No reliable dose-response data were available for humans.

200

0.2

66.3

0.7

Acute (mg/kg/day)

Neurological

Renal

Death

Hepatic

Developmental

Body weight

Immunological

Renal

Reproductive

Neurological

Hepatic

Cancer

Intermediate (mg/kg/day)

Chronic (mg/kg/day)

HEXACHLOROCYCLOHEXANE (HCH) 14

1. RELEVANCE TO PUBLIC HEALTH

Figure 1-8. Summary of Sensitive Targets of γ-Hexachlorocyclohexane (γ-HCH) –

Inhalation

Available data indicate that the kidney is the most sensitive target of γ-HCH inhalation exposure.

Numbers in circles are the lowest LOAELs for all health effects in animals; no human data were identified.

101

603

0.5

Acute (ppm)

Intermediate (ppm)

Gastrointestinal

Death

Neurological

Body weight

Renal

Death

Gastrointestinal

Hematological

HEXACHLOROCYCLOHEXANE (HCH) 15

1. RELEVANCE TO PUBLIC HEALTH

Figure 1-9. Summary of Sensitive Targets of γ-Hexachlorocyclohexane (γ-HCH) –

Oral

Available data indicate that the developing organism is the most sensitive target of γ-HCH oral

exposure.

Numbers in circles are the lowest LOAELs for all health effects in animals; no human data were identified.

0.00015

0.012

0.07

0.8

1.7

2.5

Acute (mg/kg/day)

Developmental

Neurological

Hepatic

Reproductive

Hematological

Immunological

Death

Developmental

Immunological

Renal

Reproductive

Hepatic

Neurological

Cardiovascular

Body weight

Hepatic

Renal

Intermediate (mg/kg/day)

Chronic (mg/kg/day)

HEXACHLOROCYCLOHEXANE (HCH) 16

1. RELEVANCE TO PUBLIC HEALTH

Figure 1-10. Summary of Sensitive Targets of Technical-Hexachlorocyclohexane

(technical-HCH) – Oral

Available data indicate that the central nervous system is the most sensitive target of technical-

HCH oral exposure.

Numbers in circles are the lowest LOAELs for all health effects in animals; no human data were identified.

0.00015

0.012

0.07

0.8

1.7

2.5

Acute (mg/kg/day)

Developmental

Neurological

Hepatic

Reproductive

Hematological

Immunological

Death

Developmental

Immunological

Renal

Reproductive

Hepatic

Neurological

Cardiovascular

Body weight

Hepatic

Renal

Intermediate (mg/kg/day)

Chronic (mg/kg/day)

The MRL values for α-HCH, β-HCH, and γ-HCH are summarized in Tables 1-1, 1-2, and 1-3,

respectively, and discussed in greater detail in Appendix A.

HEXACHLOROCYCLOHEXANE (HCH) 17

1. RELEVANCE TO PUBLIC HEALTH

Table 1-1. Minimal Risk Levels (MRLs) for α-Hexachlorocyclohexane

Exposure

route

Exposure

duration

MRL

Critical effect

POD type

POD value

Uncertainty/

modifying

factor

Reference

Inhalation

No inhalation MRLs were derived for any duration.

Oral

Acute

None

–

Intermediate

0.002 mg/kg/day

Increased liver weight and

histopathology

NOAEL

2 mg/kg/day

UF: 100

MF: 10

Sumida et al.

2007

Chronic

9x10

-4

mg/kg/day

Increased liver weight and

histopathology

NOAEL

0.9 mg/kg/day

UF: 100

MF: 10

Fitzhugh et al.

1950

See Appendix A for additional information.

MF = modifying factor; NOAEL = no-observed-adverse-effect level; POD = point of departure; UF = uncertainty factor

Table 1-2. Minimal Risk Levels (MRLs) for β-Hexachlorocyclohexane

Exposure

route

Exposure

duration

MRL

Critical effect

POD type

POD value

Uncertainty/

modifying factor

Reference

Inhalation

No inhalation MRLs were derived for any duration.

Oral

Acute

0.08 mg/kg/day

Clinical signs of neurotoxicity

(ataxia, inactivity) at higher doses

NOAEL

8 mg/kg/day

UF: 100

Van Velsen

et al. 1986

Intermediate

6x10

-4

mg/kg/day

Hyalinization of centrilobular liver

cells

LOAEL

0.18 mg/kg/day

UF: 300

Van Velsen

et al. 1986

Chronic

None

–

See Appendix A for additional information.

LOAEL = lowest-observed-adverse-effect level; NOAEL = no-observed-adverse-effect level; POD = point of departure; UF = uncertainty factor

HEXACHLOROCYCLOHEXANE (HCH) 18

1. RELEVANCE TO PUBLIC HEALTH

Table 1-3. Minimal Risk Levels (MRLs) for γ-Hexachlorocyclohexane

Exposure

route

Exposure

duration

MRL

Critical effect

POD type

POD value

Uncertainty/

modifying

factor

Reference

Inhalation

No inhalation MRLs were derived for any duration.

Oral

Acute

0.003 mg/kg/day

Reduced reproductive organ

weights, sperm numbers, serum

testosterone, and increased

intromission frequency in male

offspring

LOAEL

1 mg/kg/day

UF: 300

Dalsenter

et al. 1997b

Intermediate

8x10

-7

mg/kg/day

Cardiac effects in offspring

NOAEL

7.6x10

-5

mg/kg/day

UF: 100

Sauviat et

al. 2005

Chronic

None

–

See Appendix A for additional information.

LOAEL = lowest-observed-adverse-effect level; NOAEL = no-observed-adverse-effect level; POD = point of departure; UF = uncertainty factor

HEXACHLOROCYCLOHEXANE (HCH) 19

CHAPTER 2. HEALTH EFFECTS

2.1 INTRODUCTION

The primary purpose of this chapter is to provide public health officials, physicians, toxicologists, and

other interested individuals and groups with an overall perspective on the toxicology of HCH. It contains

descriptions and evaluations of toxicological studies and epidemiological investigations and provides

conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public health. When

available, mechanisms of action are discussed along with the health effects data; toxicokinetic

mechanistic data are discussed in Section 3.1.

A glossary and list of acronyms, abbreviations, and symbols can be found at the end of this profile.

To help public health professionals and others address the needs of persons living or working near hazardous

waste sites, the information in this section is organized by health effect. These data are discussed in terms of

route of exposure (inhalation, oral, and dermal) and three exposure periods: acute (≤14 days), intermediate

(15–364 days), and chronic (≥365 days).

As discussed in Appendix B, a literature search was conducted to identify relevant studies examining health

effect endpoints. Figures 2-1, 2-2, and 2-3 provide an overview of the database of studies in humans or

experimental animals for α-, β-, and γ-HCH included in this chapter of the profile. These studies evaluate

the potential health effects associated with inhalation, oral, or dermal exposure to HCH, but may not be

inclusive of the entire body of literature. A systematic review of the scientific evidence of the health effects

associated with exposure to HCH was also conducted; the results of this review are presented in Appendix C.

Tabulated human studies of specific health endpoints are presented in the corresponding subsections of

this Chapter. Animal inhalation studies of γ-HCH are presented in Table 2-1 and Figure 2-5. There were

no inhalation studies of other HCH isomers or mixtures of isomers. Animal oral studies are presented in

Table 2-2 and Figure 2-6 (α-HCH), Table 2-3 and Figure 2-7 (β-HCH), Table 2-4 and Figure 2-8

(γ-HCH), and Table 2-5 and Figure 2-9 (δ-HCH and technical-grade HCH or unspecified isomers).

Animal dermal studies are presented in Table 2-6 (γ-HCH) and Table 2-7 (technical-grade or unspecified

isomers). There were no dermal studies of other HCH isomers.

HEXACHLOROCYCLOHEXANE (HCH) 20

2. HEALTH EFFECTS

Levels of significant exposure (LSEs) for each route and duration are presented in tables and illustrated in

figures. The points in the figures showing no-observed-adverse-effect levels (NOAELs) or lowest-

observed-adverse-effect levels (LOAELs) reflect the actual doses (levels of exposure) used in the studies.

Effects have been classified into “less serious LOAELs” or “serious LOAELs (SLOAELs).” "Serious"

effects (SLOAELs) are those that evoke failure in a biological system and can lead to morbidity or

mortality (e.g., acute respiratory distress or death). "Less serious" effects are those that are not expected

to cause significant dysfunction or death, or those whose significance to the organism is not entirely clear.

ATSDR acknowledges that a considerable amount of judgment may be required in establishing whether

an endpoint should be classified as a NOAEL, "less serious" LOAEL, or "serious" LOAEL, and that in

some cases, there will be insufficient data to decide whether the effect is indicative of significant

dysfunction. However, the Agency has established guidelines and policies that are used to classify these

endpoints (ATSDR 2018). ATSDR believes that there is sufficient merit in this approach to warrant an

attempt at distinguishing between "less serious" and "serious" effects. The distinction between "less

serious" effects and "serious" effects is considered to be important because it helps the users of the

profiles to identify levels of exposure at which major health effects start to appear. LOAELs or NOAELs

should also help in determining whether or not the effects vary with dose and/or duration, and place into

perspective the possible significance of these effects to human health. Levels of oral exposure associated

with cancer (Cancer Effect Levels, CELs) of HCH are indicated in Tables 2-2 through 2-5 and

Figures 2-6 through 2-9.

A User's Guide has been provided at the end of this profile (see Appendix D). This guide should aid in

the interpretation of the tables and figures for LSEs and MRLs.

The discussion of the available data for health effects in this chapter is organized into human and animal

data, with isomer-specific subsections on the animal data provided in the following order: α-HCH,

β-HCH, γ-HCH, δ-HCH, and technical-grade and mixtures of HCH isomers. Case reports of effects in

humans are limited to γ-HCH and technical-grade HCH and are discussed under the isomer-specific

subsections. If there are no case reports or animal data for a given isomer or for technical grade/mixtures,

there is no corresponding subsection.

Effects of HCH isomers have been evaluated in epidemiological studies and in laboratory animals

exposed under controlled conditions. Most of the human epidemiological studies used measures of HCH

isomers in blood or tissues to assess exposure, so the route is unknown; for the purpose of enumerations,

these studies are considered to reflect oral exposure (e.g., through contaminated food). In addition, there

HEXACHLOROCYCLOHEXANE (HCH) 21

2. HEALTH EFFECTS

are several case reports of health effects in humans exposed by inhalation, oral, or dermal exposure to γ-

HCH. The human data were not considered adequate for identification of sensitive target organs for any

of the HCH isomers or mixtures.

As shown in Figure 2-1 (α-HCH), there were a small number of human studies examining a handful of

endpoints; the largest number of studies were devoted to developmental endpoints. There were no

inhalation or dermal animal studies of α-HCH, and few oral studies. The available animal studies

primarily examined liver effects and cancer. Animal studies suggest that hepatic effects are a sensitive

target of α-HCH toxicity.

• Hepatic endpoints: Hepatic toxicity is a presumed health effect for humans based on a high

evidence level in animals showing increased liver weight and histopathological lesions after oral

exposure to α-HCH. No information was located on hepatic effects in humans exposed to

α-HCH.

Figure 2-2 provides an overview of the health effects data for β-HCH. For this isomer, human studies

examined a wide range of outcomes, with more studies of endocrine endpoints (thyroid hormone levels)

developmental outcomes, other noncancer endpoints (diabetes and metabolic perturbations), and cancer

than other outcomes. Animal studies are limited to oral exposures, and the endpoints examined were

largely focused on liver, kidney, body weight, nervous system, and cancer. Animal studies suggest that

neurological and hepatic effects are sensitive targets of β-HCH toxicity after acute-duration exposures and

intermediate- or chronic-duration exposures, respectively.

• Neurological endpoints: Neurotoxicity is a presumed health effect in humans based on human

and animal studies. There is a moderate level of evidence in humans suggesting associations

between serum β-HCH and risk of Parkinson disease, Alzheimer’s disease, and cognitive deficits.

There is a high level of evidence in animal studies of oral exposure showing clinical signs of

neurotoxicity in rats and mice after acute durations and reduced nerve conduction velocity in rats

after an intermediate duration. Clinical signs showed a dose-related increase in severity.

Hepatic endpoints: Hepatic toxicity is a presumed health effect for humans based on a high

level of evidence in animals showing increased liver weight and histopathology changes in rats

and mice exposed by dietary administration for intermediate and chronic durations. In humans,

there is a very low level of evidence for a minimal liver toxicity based on two cross-sectional

studies reporting no association between serum or adipose levels of β-HCH and hepatic clinical

chemistry endpoints except for increased serum bilirubin.

An overview of health effects data for γ-HCH is presented in Figure 2-3. Most of the human studies

evaluated developmental, reproductive, renal, endocrine, or cancer endpoints. Studies of occupational

exposure via pesticide application are considered to reflect primarily inhalation exposure. Most of the

HEXACHLOROCYCLOHEXANE (HCH) 22

2. HEALTH EFFECTS

animal studies used oral administration, and the available studies examined comprehensive noncancer and

cancer endpoints. The effects seen at the lowest doses in the animal studies were developmental and

immune system effects. Animal studies suggest that developmental and immune system effects are

sensitive targets of γ-HCH toxicity after acute-duration exposures (developmental) and intermediate-

duration exposures (developmental and immune system). Available studies of chronic-duration oral

exposure to γ-HCH were limited and identified effects on other systems (hepatic and renal) at much

higher doses than those associated with developmental and immune system effects in acute- and

intermediate-duration exposure studies.

• Developmental endpoints: Developmental toxicity is a presumed health effect in humans based

on human and animal evidence. There is a low level of evidence in humans based on associations

between γ-HCH in maternal or fetal blood (or tissue) and fetal growth retardation, preterm birth,

and cryptorchidism or hypospadias. There is a high level of evidence in animals based on studies

in a variety of species exposed orally to γ-HCH for acute or intermediate durations during

gestation or postnatal development demonstrating adverse effects on a wide range of

developmental endpoints, including birth outcomes and development of the male and female

reproductive tracts, central nervous system, heart, thymus, and spleen.

• Immune system endpoints: Immunotoxicity is a presumed health effect in humans based

primarily on animal evidence. There is a low level of evidence in humans based on an observed

association between asthma and plasma levels of γ-HCH in children and no evidence for

increased prevalence of monoclonal gammopathy of undetermined significance in male pesticide

applicators. There is a high level of evidence in animals based on acute- and intermediate-

duration studies of γ-HCH administered orally to rats, mice, rabbits, and sheep showing

suppression of the immune system and effects on thymus, spleen, and lymph node weights or

histology.

Figure 2-4 shows the limited health effects data available for δ-HCH and unspecified HCHs. The human

studies primarily evaluated other noncancer, developmental, reproductive, and neurological endpoints.

The small number of animal studies used oral or dermal administration and were focused on hepatic and

cancer endpoints. Data were not adequate to identify sensitive targets of δ-HCH.

HEXACHLOROCYCLOHEXANE (HCH) 23

2. HEALTH EFFECTS

Figure 2-1. Overview of the Number of Studies Examining α-Hexachlorocyclohexane (α-HCH) Health Effects*

Most studies examined the potential body weight, hepatic, and cancer effects of α-HCH

Fewer studies evaluated health effects in humans than animals (counts represent studies examining endpoint)

Cancer

Other Noncancer

Developmental

Reproductive

Neurological

Immunological

Endocrine

Ocular

Dermal

Renal

Hepatic

Musculoskeletal

Hematological

Gastrointestinal

Cardiovascular

Respiratory

Body weight

Death

Oral

100%

Exposure Route

Acute

12%

Intermediate

47%

Chronic

41%

Exposure Duration

*Includes studies discussed in Chapter 2. A total of 40 studies (including those finding no effect) have examined toxicity; most studies examined multiple

endpoints. Human studies of unknown route and/or duration were classified as chronic oral studies for the purpose of this figure.

HEXACHLOROCYCLOHEXANE (HCH) 24

2. HEALTH EFFECTS

Figure 2-2. Overview of the Number of Studies Examining β-Hexachlorocyclohexane (β-HCH) Health Effects*

Most studies examined the potential developmental, other noncancer, and cancer effects of β-HCH

More studies evaluated health effects in humans than animals (counts represent studies examining endpoint)

Cancer

Other Noncancer

Developmental

Reproductive

Neurological

Immunological

Endocrine

Ocular

Dermal

Renal

Hepatic

Musculoskeletal

Hematological

Gastrointestinal

Cardiovascular

Respiratory

Body weight

Death

Oral

100%

Exposure Route

Acute

15%

Intermediate

23%

Chronic

63%

Exposure Duration

*Includes studies discussed in Chapter 2. A total of 41 studies (including those finding no effect) have examined toxicity; most studies examined multiple

endpoints. Human studies of unknown route and/or duration were classified as chronic oral studies for the purpose of this figure.

HEXACHLOROCYCLOHEXANE (HCH) 25

2. HEALTH EFFECTS

Figure 2-3. Overview of the Number of Studies Examining γ-Hexachlorocyclohexane (γ-HCH) Health Effects*

Most studies examined the potential body weight, hepatic, and neurological effects of γ-HCH

Fewer studies evaluated health effects in humans than animals (counts represent studies examining endpoint)

Cancer

Other Noncancer

Developmental

Reproductive

Neurological

Immunological

Endocrine

Ocular

Dermal

Renal

Hepatic

Musculoskeletal

Hematological

Gastrointestinal

Cardiovascular

Respiratory

Body weight

Death

Dermal

Oral

91%

Inhalation

Exposure Route

Acute

27%

Intermediate

34%

Chronic

39%

Exposure Duration

*Includes studies discussed in Chapter 2. A total of 158 studies (including those finding no effect) have examined toxicity; most studies examined multiple

endpoints. Human studies of unknown route and/or duration were classified as chronic oral studies for the purpose of this figure.

HEXACHLOROCYCLOHEXANE (HCH) 26

2. HEALTH EFFECTS

Figure 2-4. Overview of the Number of Studies Examining δ-Hexachlorocyclohexane (δ-HCH) and Unspecified

Hexachlorocyclohexanes Health Effects*

Most studies examined the potential hepatic and cancer effects of δ-HCH and/or Unspecified HCHs

Fewer studies evaluated health effects in animals than humans (counts represent studies examining endpoint)

Cancer

Other Noncancer

Developmental

Reproductive

Neurological

Immunological

Endocrine

Ocular

Dermal

Renal

Hepatic

Musculoskeletal

Hematological

Gastrointestinal

Cardiovascular

Respiratory

Body weight

Death

Oral

94%

Dermal

Exposure Route

Intermediate

25%

Chronic

75%

Exposure Duration

*Includes studies discussed in Chapter 2. A total of 16 studies (including those finding no effect) have examined toxicity; most studies examined multiple

endpoints. Human studies of unknown route and/or duration were classified as chronic oral studies for the purpose of this figure.

HEXACHLOROCYCLOHEXANE (HCH) 27

2. HEALTH EFFECTS

Table 2-1. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Inhalation

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/m

)

Parameters

monitored

Endpoint

NOAEL

(mg/m

)

Less serious

LOAEL

(mg/m

)

Serious

LOAEL

(mg/m

)

Effects

ACUTE EXPOSURE

Oldiges et al. 1980

Rat

(Wistar)

5 M, 5 F

4 hours

0, 273, 603

LE, CS, GN,

Bd wt

603 F

Body weight loss in females

during first week of observation

Neuro

273

603

LOAEL: clinical signs of

restlessness, hyperactivity

Serious LOAEL: marked

somnolence

Ullmann 1986b

Rat

(Wistar)

5 M, 5 F

4 hours

0, 101, 378,

642, 2,104

LE, CS, BW,

Death

378

20% of rats died (LC

1,560 mg/m

)

Neuro

101

Clinical signs (sedation, curved

body position)

Klonne and Kintigh 1988

Mouse

(CD-1)

45 M, 45 F

1 week

5 days/week

6 hours/day

0, 0.3, 1, 5,

LE, CS

Death

12/45 females and 2/45 males

died during first week of 13-

week

study

INTERMEDIATE EXPOSURE

Oldiges et al. 1983

Rat

(Wistar)

12 M, 12 F

90 days

7 days/week

6 hours/day

0, 0.02, 0.1,

0.5, 5

LE, CS, BW,

FI, WI, HE,

UR, OW, HP

Bd wt

Resp

Cardio

Gastro

0.5

Diarrhea

Hemato

0.5

Bone marrow myelogram

changes (increased

reticulocytes, stem cells and

myeloblasts; decreased

lymphocytes)

Hepatic

Renal

5 F

0.5 M

Dilated tubules with protein-

containing contents; proliferated

tubules

Endocr

HEXACHLOROCYCLOHEXANE (HCH) 28

2. HEALTH EFFECTS

Table 2-1. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Inhalation

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/m

)

Parameters

monitored

Endpoint

NOAEL

(mg/m

)

Less serious

LOAEL

(mg/m

)

Serious

LOAEL

(mg/m

)

Effects

Neuro

Repro

Klonne and Kintigh 1988

Mouse

(CD-1)

45 M, 45 F

14 weeks

5 days/week

6 hours/day

0, 0.3, 1.0, 5

LE, CS, BW,

FI, WI, HE,

BC, UR,

GN, OW,

Death

1/45 males and 1/45 females

died at 1 mg/m

; 5/45 males and

15/45 females died at 5 mg/m

Bd wt

Resp

Cardio

Gastro

Hemato

Hepatic

Renal

Endocr

Repro

No histopathology changes in

reproductive organs

The number corresponds to entries in Figure 2-5; differences in levels of health effects and cancer effects between male and females are not indicated in

Figure 2-5. Where such differences exist, only the levels of effect for the most sensitive sex are presented.

BC = serum (blood) chemistry; Bd wt or BW = body weight; Cardio = cardiovascular; CS = clinical signs; Endocr = endocrine; F = female(s); FI = food intake;

Gastro = gastrointestinal; GN = gross necropsy; HE = hematology; Hemato = hematological; LE = lethality; LOAEL = lowest-observed-adverse-effect level;

M = male(s); Neuro = neurological; NOAEL = no-observed-adverse-effect level; OW = organ weight; Repro = reproductive; Resp = respiratory; UR = urinalysis;

WI = water intake

HEXACHLOROCYCLOHEXANE (HCH) 29

2. HEALTH EFFECTS

Figure 2-5. Levels of Significant Exposure to γ-Hexachlorocyclohexane (Lindane) – Inhalation

Acute (≤14 days)

HEXACHLOROCYCLOHEXANE (HCH) 30

2. HEALTH EFFECTS

Figure 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane (Lindane) – Inhalation

Intermediate (15–364 days)

HEXACHLOROCYCLOHEXANE (HCH) 31

2. HEALTH EFFECTS

Table 2-2. Levels of Significant Exposure to α-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

ACUTE EXPOSURE

Sumida et al. 2007

Rat

(Fischer-

344)

4 M

1, 3, 7, or

14 d

(GO)

0, 2, 20

BW, BC, OW

Bd wt

Hepatic

24% increase in relative liver

weight

INTERMEDIATE EXPOSURE

Fitzhugh et al. 1950

Rat

(Wistar)

10 F, 10 M

6–9 months

(F)

Males: 0, 60

Females: 0,

LE, BW, FI,

GN, OW, HP

Death

60 M

70 F

Mean survival was

35.9 weeks versus

58.3 weeks in controls

Bd wt

60 M

70 F

11–15% decrease in body

weight gain

Resp

60 M

70 F

Cardio

60 M

70 F

Gastro

60 M

70 F

Hemato

60 M

70 F

Musc/skel

60 M

70 F

Hepatic

60 M

70 F

Moderate histopathology

changes (focal necrosis,

fatty degeneration); >2-fold

increase in liver weight

Renal

60 M

70 F

Slight to moderate

histopathology changes

including tubular dilatation,

hyaline tubular casts,

glomerular fibrosis or

atrophy, pigment deposition

HEXACHLOROCYCLOHEXANE (HCH) 32

2. HEALTH EFFECTS

Table 2-2. Levels of Significant Exposure to α-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Endo

60 M

70 F

Repro

60 M

70 F

Ito et al. 1975

Rat

(W strain)

18–24 M

48 weeks

(F)

0, 35, 70

BW, OW, HP

Hepatic

Hepatocellular hypertrophy

Cancer

CEL: liver tumors after

48 weeks

Muller et al. 1981

Rat

(Wistar)

15 M

30 days

(F)

0, 5.1, 54.2,

106.2

Neuro

106.2

No reduction in motor

conduction velocity

Nagasaki et al. 1975

Rat

(Wistar)

8 M

24 weeks

(F)

0, 45

BW, OW, HP

Bd wt

15% decrease in terminal

body weight

Hepatic

Mild hypertrophy; ~2-fold

increase in absolute and

relative liver weight

Sumida et al. 2007

Rat

(Fischer-

344)

4 M

28 days

(GO)

0, 2, 20

BW, BC,

OW, HP

Bd wt

Hepatic

Increased relative liver

weight (25%); centrilobular

hepatocellular hypertrophy

Hanada et al. 1973

Mouse

(dd)

10–11 M,

10–11 F

32 weeks

(F)

M: 0, 18, 54,

108 F: 0, 20,

60, 120

BC, GN, HP

Cancer

18 M

60 F

CEL: hepatoma

HEXACHLOROCYCLOHEXANE (HCH) 33

2. HEALTH EFFECTS

Table 2-2. Levels of Significant Exposure to α-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Ito et al. 1973

Mouse

(dd)

20–40 M

24 weeks

(F)

0, 18, 45, 90

BW, OW,

GN, HP

Bd wt

Hepatic

Increased relative liver

weight (33%); hepatocellular

hypertrophy

Cancer

CEL: hepatocellular

carcinoma

Ito et al. 1976

Mouse

(DDY)

13–20 M

16–36 weeks

(F)

0, 90

BW, OW, HP

Cancer

CEL: hepatocellular

carcinoma

Nagasaki et al. 1975

Mouse

(DDY,

ICR,

DBA/2,

C57BL/6,

C3H/He)

20 M, 20 F

24 weeks

(F)

Males: 0, 90

Females: 0,

100

BW, OW, HP

Bd wt

90 M

17% decrease in terminal

body weight of male

C57BL/6 mice

Hepatic

90 M

100 F

Parenchymal cell

hypertrophy, bile duct

proliferation, oval cells;

nodular hyperplasia; 2-fold

increase in liver weight

Cancer

90 M

100 F

CEL: hepatocellular

carcinomas

Tryphonas and Iverson 1983

Mouse

(HPB)

75 M

50 weeks

(F)

0, 90

BW, GN,

OW, HP

Hepatic

Hepatomegaly;

megalocytosis

Cancer

CEL: neoplastic nodules of

the liver after 21 weeks

Tsukada et al. 1979

Mouse

(DD)

6 M

16–36 weeks

(F)

0, 90

GN HP

Cancer

CEL: hepatomas after

28 weeks

HEXACHLOROCYCLOHEXANE (HCH) 34

2. HEALTH EFFECTS

Table 2-2. Levels of Significant Exposure to α-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Nagasaki et al. 1975

Hamster

(Golden

Syrian)

6–10 M

24 weeks

(F)

0, 45

BW, OW, HP

Bd wt

14% decrease in terminal

body weight

Hepatic

20–38% increase in liver

weight; liver cell hypertrophy

CHRONIC EXPOSURE

Fitzhugh et al. 1950

Rat

(Wistar)

10 F, 10 M

107 weeks

(F)

M: 0, 0.7, 4, 7

F: 0, 0.9, 4, 9

LE, BW, FI,

GN, OW, HP

Resp

9 F

7 M

Cardio

9 F

7 M

Gastro

9 F

7 M

Hemato

9 F

7 M

Musc/skel

9 F

7 M

Hepatic

0.7 M

0.9

32% increase in relative liver

weight and very slight to

slight microscopic damage

Renal

9 F

7 M

Endo

9 F

7 M

Repro

9 F

7 M

HEXACHLOROCYCLOHEXANE (HCH) 35

2. HEALTH EFFECTS

Table 2-2. Levels of Significant Exposure to α-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Ito et al. 1975

Rat

(W strain)

18–24 M

72 weeks

(F)

0, 70, 105

BW, OW, HP

Cancer

CEL: hepatocellular

carcinoma

The number corresponds to entries in Figure 2-6; differences in levels of health effects and cancer effects between male and females are not indicated in

Figure 2-6. Where such differences exist, only the levels of effect for the most sensitive sex are presented.

Used to derive an intermediate-duration oral minimal risk level (MRL). The NOAEL of 2 mg/kg/day was divided by an uncertainty factor of 100 (10 for human

variability and 10 for animal to human extrapolation) and a modifying factor of 10 (for lack of data on developmental toxicity, immunotoxicity, and neurotoxicity),

resulting in an MRL of 0.002 mg/kg/day (2x10

-3

mg/kg/day).

Used to derive a chronic-duration oral MRL. The NOAEL of 0.9 mg/kg/day was divided by an uncertainty factor of 100 (10 for human variability and 10

for animal

to human extrapolation) and a modifying factor of 10 (for lack of data on immunotoxicity and neurotoxicity), resulting in an MRL of 0.0009 mg/kg/day

(9x10

-4

mg/kg/day).

BC = serum (blood) chemistry; Bd wt or BW = body weight; CEL = cancer effect level; (F) = feed; F = female(s); FI = food intake; GN = gross necropsy;

(GO) = gavage in oil; HP = histopathology; LE = lethality; LOAEL = lowest-observed-adverse-effect level; M = male(s); Musc/skel = muscular/skeletal;

Neuro = neurological; NOAEL = no-observed-adverse-effect level; NX = neurotoxicity; OW = organ weight; (W) = drinking water

HEXACHLOROCYCLOHEXANE (HCH) 36

2. HEALTH EFFECTS

Figure 2-6. Levels of Significant Exposure to α-Hexachlorocyclohexane – Oral

Acute (≤14 days)

HEXACHLOROCYCLOHEXANE (HCH) 37

2. HEALTH EFFECTS

Figure 2-6. Levels of Significant Exposure to α-Hexachlorocyclohexane – Oral

Intermediate (15–364 days)

HEXACHLOROCYCLOHEXANE (HCH) 38

2. HEALTH EFFECTS

Figure 2-6. Levels of Significant Exposure to α-Hexachlorocyclohexane – Oral

Intermediate (15–364 days)

HEXACHLOROCYCLOHEXANE (HCH) 39

2. HEALTH EFFECTS

Figure 2-6. Levels of Significant Exposure to α-Hexachlorocyclohexane – Oral

Chronic (≥365 days)

HEXACHLOROCYCLOHEXANE (HCH) 40

2. HEALTH EFFECTS

Table 2-3. Levels of Significant Exposure to β-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

ACUTE EXPOSURE

Srinivasan et al. 1984

Rat

(Wistar)

6 M

2 weeks

(F)

0, 72

BW, BC, UR,

Renal

Tubular degeneration,

distention of glomeruli,

swelling of tubular epithelia,

22% increase in kidney

weight, glucosuria,

increased urinary excretion

of urea and creatinine,

decreased excretion of

protein

Van Velsen et al. 1986

Rat

(Wistar)

10 F, 10 M

2 weeks

(F)

0, 8, 38

Neuro

Ataxia, hypoactivity

Cornacoff et al. 1988

Mouse

(B6C3F1)

6 F

1 weeks

(F)

0, 20, 60, 200

Death

200

Lateral recumbency leading

to humane sacrifice in 80%

of mice

Neuro

Ataxia resolving within a few

days

INTERMEDIATE EXPOSURE

Fitzhugh et al. 1950

Rat

(Wistar)

10 F, 10 M

10 weeks

(F)

Males: 0, 60

Females: 0,

LE, BW, FI,

GN, OW, HP

Death

70 F

60 M

All animals died by

10 weeks of exposure;

mean age at death was

4.4 weeks

Resp

70 F

60 M

Cardio

70 F

60 M

Gastro

70 F

60 M

HEXACHLOROCYCLOHEXANE (HCH) 41

2. HEALTH EFFECTS

Table 2-3. Levels of Significant Exposure to β-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Hemato

70 F

60 M

Musc/skel

70 F

60 M

Hepatic

70 F

60 M

Moderate to marked liver

damage including fatty

degeneration and focal

necrosis

Renal

70 F

60 M

Very slight nephritis; basal

vacuolation

Endo

70 F

60 M

Repro

70 F

60 M

Fitzhugh et al. 1950

Rat

(Wistar)

10 M, 10 F

6 months

(F)

M: 0, 7 F: 0, 9

Bd wt

7 M

9 F

11% decrease in body

weight gain among females

Ito et al. 1975

Rat

(W strain)

18–24 M

48 weeks

(F)

0, 35, 70

BW, OW, HP

Hepatic

Hepatocellular hypertrophy

Muller et al. 1981

Rat

(Wistar)

15 M

30 days

(F)

0, 66.3, 270.6

Neuro

66.3

Reduced tail nerve

conduction velocity

Srinivasan et al. 1991

Rat

(Wistar)

6 F

GDs 0–21

(F)

0, 5, 20, 40,

Death

None of the dams survived

3 weeks of treatment

Develop

48% pup mortality before

PND 5

HEXACHLOROCYCLOHEXANE (HCH) 42

2. HEALTH EFFECTS

Table 2-3. Levels of Significant Exposure to β-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Srinivasan et al. 1991

Rat

(Wistar)

6 F

GDs 0–21

and LDs 1–

28 or LDs 1–

28 only (F)

0, 5, 25

RX, DX

Develop

LOAEL: increased liver

weight in pups at 28 days of

age

Serious LOAEL: 100%

mortality before PND 5 in

pups exposed in utero

Van Velsen et al. 1986

Rat

(Wistar)

10 F, 10 M

13 weeks

(F)

Males: 0,

0.18, 0.9, 4.

22.5

Females: 0,

0.2, 1.0, 5, 25

CS, BW FI,

HE, BC, BI,

OW, HP

Death

22.5 M

25 F

50% of animals were

moribund and sacrificed

humanely

Bd wt

5 F

4.5 M

25 F

22.5 M

≥10% decrease in body

weight

Hemato

5 F

4.5 M

25 F

22.5 M

Decreased red blood cells,

leukocytes, and hemoglobin

concentrations

Hepatic

ND M

1 F

0.18

5 F

Hyalinization of centrilobular

cells in males; increased

mitoses in females

Renal

4.5 M

22.5 M

Renal medullary calcinosis

Endo

5 F

4.5 M

25 F

22.5 M

Adrenal cortical hypertrophy

Immuno

5 F

4.5 M

25 F

22.5 M

Depletion of splenic

lymphoid tissue; thymic

cortical atrophy

Repro

5 F

4.5 M

25 F

22.5 M

Atrophy of testes and

ovaries

HEXACHLOROCYCLOHEXANE (HCH) 43

2. HEALTH EFFECTS

Table 2-3. Levels of Significant Exposure to β-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Cornacoff et al. 1988

Mouse

(B6C3F1)

6 F

30 days

(F)

0, 20, 60

CS, BW, HE,

OW, HP, NX

Bd wt

Immuno

Decreased

lymphoproliferative

responses to T-cell

mitogens, decreased natural

killer cell activity

Repro

No changes in ovarian or

uterine histology

Hanada et al. 1973

Mouse

(dd)

10–11 M,

10–11 F

32 weeks

(F)

Males: 0, 20,

50, 100

Females: 0,

20, 60, 100

GN, HP

Hepatic

60 F

50 M

Nuclear irregularities in foci

of enlarged hepatocytes

Ito et al. 1973

Mouse

(dd)

20–40 M

24 weeks

(F)

0, 18, 45, 90

BW, OW, HP

Bd wt

Hepatic

18% increase in relative liver

weight with histopathology

changes (liver cell

hypertrophy) at higher doses

Thorpe and Walker 1973

Mouse

CF1

30 M, 30 F

3 months

(F)

0, 34

Death

12% of males and 25% of

females died during the first

3 months of a chronic study

HEXACHLOROCYCLOHEXANE (HCH) 44

2. HEALTH EFFECTS

Table 2-3. Levels of Significant Exposure to β-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

CHRONIC EXPOSURE

Fitzhugh et al. 1950

Rat

(Wistar)

10 F, 10 M

107 weeks

(F)

M: 0, 0.7, 7

F: 0, 0.9, 9

LE, BW, FI,

GN, OW, HP

Resp

7 M

9 F

Cardio

7 M

9 F

Gastro

7 M

9 F

Hemato

7 M

9 F

Musc/skel

7 M

9 F

Hepatic

0.7 M

0.9 F

34% increase in relative liver

weight; very slight

histopathology changes

Renal

7 M

9 F

Endo

7 M

9 F

Repro

0.7 M

9 F

7 M

Slight testicular atrophy

HEXACHLOROCYCLOHEXANE (HCH) 45

2. HEALTH EFFECTS

Table 2-3. Levels of Significant Exposure to β-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Thorpe and Walker 1973

Mouse

(CF1)

30 M, 30 F

104 weeks

(F)

0, 34

CS, GN, HP

Cancer

CEL: liver tumors in males;

unspecified tumors in

females.

The number corresponds to entries in Figure 2-7; differences in levels of health effects and cancer effects between male and females are not indicated in

Figure 2-7. Where such differences exist, only the levels of effect for the most sensitive sex are presented.

Used to derive an acute-duration oral minimal risk level (MRL). The NOAEL of 8 mg/kg/day was divided by an uncertainty factor of 100 (10 for human variability and

10 for animal to human extrapolation) resulting in an MRL of 0.08 mg/kg/day (8x10

-2

mg/kg/day).

Used to derive an intermediate-duration oral MRL. The LOAEL of 0.18 mg/kg/day was divided by an uncertainty factor of 300 (10 for human variability, 10 for animal

to human extrapolation, and 3 for use of a minimal LOAEL) resulting in an MRL of 0.0006 mg/kg/day (6x10

-4

mg/kg/day).

Bd wt or BW = body weight; CEL = cancer effect level; CS = clinical signs; Develop = developmental; DX = developmental toxicity; Endocr = endocrine; (F) = feed;

F = female(s); FI = food intake; GD = gestation day; GN = gross necropsy; Hemato = hematological; HP = histopathology; Immuno = immunological; LD = lactation

day; LOAEL = lowest-observed-adverse-effect level; M = male(s); Musc/skel = muscular/skeletal; ND = not determined; Neuro = neurological; NOAEL = no-observed-

adverse-effect level; NX = neurotoxicity; OW = organ weight; PND = postnatal day; Repro = reproductive; RX = reproductive toxicity; UR = urinalysis

HEXACHLOROCYCLOHEXANE (HCH) 46

2. HEALTH EFFECTS

Figure 2-7. Levels of Significant Exposure to β-Hexachlorocyclohexane – Oral

Acute (≤14 days)

HEXACHLOROCYCLOHEXANE (HCH) 47

2. HEALTH EFFECTS

Figure 2-7. Levels of Significant Exposure to β-Hexachlorocyclohexane – Oral

Intermediate (15–364 days)

HEXACHLOROCYCLOHEXANE (HCH) 48

2. HEALTH EFFECTS

Figure 2-7. Levels of Significant Exposure to β-Hexachlorocyclohexane – Oral

Intermediate (15–364 days)

HEXACHLOROCYCLOHEXANE (HCH) 49

2. HEALTH EFFECTS

Figure 2-7. Levels of Significant Exposure to β-Hexachlorocyclohexane – Oral

Chronic (≥365 days)

HEXACHLOROCYCLOHEXANE (HCH) 50

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

ACUTE EXPOSURE

Ali and Shakoori 1998

Rat

(Sprague-

Dawley)

3–5, NS

2 days

(F)

0, 30

Hepatic

Reduced number of cells

per field; increased cell,

nucleus, and nucleolus

size; slight cellular

disorganization

Attia et al. 1991

Rat

(Sprague-

Dawley)

9 M

6 days

(GO)

0, 3

Neuro

Increased pineal N-acetyl-

transferase, decreased

serotonin levels

Dalsenter et al. 1996

Rat

(Wistar)

15 M

1–5 days

0, 6, 30

Repro

Decreased number of

spermatids per epididymis

Dalsenter et al. 1997a

Rat

(Wistar)

15 M

GDs 15

once

(GO)

0, 30

Develop

Reduced serum

testosterone in adult

offspring

Dalsenter et al. 1997b

Rat

(BOR)

9 F

LD 9 or 14

once

(GO)

0, 6

CS, BI, OW,

HP, NX, RX

Develop

In male pups, reduced

relative testicular and

epididymis weight (~10%),

spermatid and sperm

counts (~8–10%),

testosterone levels (~30–

50%), Leydig cell numbers,

and spermatogenesis at

maturity, with no effect on

fertility

HEXACHLOROCYCLOHEXANE (HCH) 51

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Dalsenter et al. 1997b

Rat

(BOR)

9 F

LDs 9–14

(GO)

0, 1

CS, BI, OW,

HP, NX, RX

Develop

In male pups, reduced

relative testicular and

epididymis weight (~10%),

spermatid and sperm

counts (~10%), and

testosterone levels (30–

50%) at maturity, with no

effect on fertility

EPA 1999a

Rat

(CD)

10 M, 10 F

Once

(G)

0, 6, 20, 60

Neuro

6 F

20 M

20 F

60 M

LOAEL: decreased motor

activity and grooming

behavior, increased

forelimb grip strength in

females

Serious LOAEL: tremors

and convulsions in one

male

Gaines 1960

Rat

(Sherman)

89 M, 69 F

Once

(GO)

LE, CS

Death

91 F

88 M

Gilbert 1995

Rat

(Long-

Evans)

15–16 M

10 days

3 days/week

(GO)

0, 10

Neuro

Myoclonic jerks and clonic

seizures

Gilbert and Mack 1995

Rat

(Long-

Evans)

14 M

once

(GO)

0, 5, 10, 20

Neuro

Myoclonic jerks and single

clonic seizure in naive

animals

HEXACHLOROCYCLOHEXANE (HCH) 52

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Hfaiedh et al. 2012

Rat

(Wistar)

6 M

3 days

(GO)

0, 5

BC, BI, HP

Hepatic

Fatty degeneration,

vacuolation, and necrosis

of the liver

Johri et al. 2008

Rat

(Wistar)

10 M

Once

(GO)

0, 30

Neuro

Convulsions in 5/10

animals

Joy et al. 1982

Rat

(Sprague-

Dawley)

7–14 M

4 days

(GO)

0, 1, 3, 10

CS, BW,

BC, OW,

HP, NX

Neuro

LOAEL: increased kindling

acquisition

Serious LOAEL: seizures

Khera et al. 1979

Rat

(Wistar)

20 F

GDs 6–15

(GO)

0, 6.25, 12.5,

Develop

No teratogenic effects

Llorens et al. 1989

Rat

(Wistar)

9 M

Once

(GO)

0, 10, 15, 30

CS, NX

Neuro

Increased spontaneous

motor behavior

Llorens et al. 1990

Rat

(Wistar)

9 M

Once

(GO)

0, 20

CS, NX

Neuro

Increased anxiety

Martinez and Martinez-Conde 1995

Rat

(Wistar)

8 M, 8 F

Once

(GO)

0, 60

CS, NX

Neuro

Convulsions

Martinez et al. 1991

Rat

(Wistar)

7 M

Once

(GO)

0, 60

LE, CS, NX

Death

1/7 died

Neuro

Tonic-clonic seizures

HEXACHLOROCYCLOHEXANE (HCH) 53

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Mediratta et al. 2008

Rat

(Wistar)

8 M

14 days

(NS)

0, 10

Immuno

Reduced delayed-type

hypersensitivity (43%

decrease in foot pad

thickness)

Palmer et al. 1978

Rat

(CFY)

20 F

GDs 6–16

(G)

0, 5, 10, 20

Develop

Parmar et al. 2003

Rat

(Wistar)

10 M

Once

(GO)

0, 35

Neuro

Convulsions in 4/10 rats

Parmar et al. 2003

Rat

(Wistar)

10 M

5 days

(GO)

0, 2.5, 5, 10,

CS, BW, BI,

Bd wt

Rivera et al. 1991

Rat

(Wistar)

4 M, 4 F

Once

(GO)

0, 20

CS, BI, NX

Develop

Regional changes in brain

noradrenaline, serotonin,

and dopamine metabolite

levels in suckling rats

Rivera et al. 1998

Rat

(Wistar)

NS M, F

PND 15

once

(G)

0, 20

Develop

Altered acquisition of a

passive avoidance task,

decreased motor activity,

altered neurotransmitter

levels in brain

Rivera et al. 1998

Rat

(Wistar)

NS M, F

PNDs 8–14

(G)

0, 10

Develop

Altered acquisition of a

passive avoidance task,

increased motor activity,

altered neurotransmitter

levels in brain

HEXACHLOROCYCLOHEXANE (HCH) 54

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Serrano et al. 1990

Rat

(Wistar)

5 M, 5 F

PNDs 8–10

(GO)

0, 5, 10, 15,

BW, BI

Develop

Decreased myelin in

developing brain

Sharma and Singh 2010

Rat

(Wistar)

6 M

14 days

(GO)

0, 30

Repro

Markedly decreased

epididymis (27%) and

testes (68%) weights;

substantial and persistent

reductions (≥85% less than

controls) in sperm head

count, motility, and percent

live sperm; marked and

persistent increases

(4-

fold) in percent abnormal

sperm

Singh and Sharma 2011

Rat

(Wistar)

NS M

1 day

(G)

0, 60

BI, HP

Hepatic

Marked centrilobular

necrosis

Sinha and Shukla 2003

Rat

(Druckrey)

8 M

3 days

(GO)

0, 8.8

BW, OW

Bd wt

8.8

Srinivasan et al. 1984

Rat

(Wistar)

6 M

2 weeks

(F)

0, 72

BW, BC,

UR, OW, HP

Renal

10% increase in kidney

weight, distention of

glomeruli, swelling of

tubular epithelia,

glucosuria, increased

excretion of urea and

creatinine, decreased

excretion of protein

HEXACHLOROCYCLOHEXANE (HCH) 55

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Sumida et al. 2007

Rat

(Fischer-

344)

4 M

1, 3, 7, or

14 days

(GO)

0, 1, 10

BW, BC,

Bd wt

Hepatic

Tusell et al. 1988

Rat

(Wistar)

4 M

3–12 days

0, 5, 12, 20

LE, CS

Death

2/18 died on 3

day

Neuro

Convulsions after 3 days

Uphouse and Williams 1989

Rat

(CDF-

F344)

8–11 F

Once

(G)

0, 12.5, 25,

33, 50

Repro

Increased length of estrous

cycle

Woolley and Griffith 1989

Rat

(Sprague-

Dawley)

7 M

Once

(GO)

0, 30, 40, 50

CS, NX

Neuro

Seizures

Di Consiglio et al. 2009

Mouse

(CD-1)

2–10 F

GDs 9–16

(GO)

0, 25

LE, CS, BW,

BI, OW, HP,

Bd wt

Develop

Decreased sperm

concentration (20%) and

count (27%) in F1 males at

PNDs 65–69

HEXACHLOROCYCLOHEXANE (HCH) 56

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Hassoun and Stohs 1996a

Mouse

(C57BL/6J

and

DBA/2J)

NS F

GD 12

once

(GO)

0, 30, 45

LE, DX

Death

14% of dams died at

30 mg/kg and 25% died at

45 mg/kg

Develop

LOAEL: decreased fetal,

placental, and thymic

weights in C57BL/6J mice

Serious LOAEL: increased

early resorptions in

C57BL/6J mice

Hong and Boorman 1993

Mouse

(B6C3F1)

7 M

3 days

(GO)

0, 10, 20, 40

CS, BW,

HE, OW HP

Bd wt

Hemato

Transient reductions in

marrow progenitor cell

numbers

Immuno

LOAEL: decreased thymus

weights

Serious LOAEL: atrophy of

thymic cortex

Hong and Boorman 1993

Mouse

(B6C3F1)

7 M

10 days

(GO)

0, 10, 20

CS, BW,

HE, OW HP

Bd wt

Hemato

Transient decrease in

marrow progenitor cell

numbers

Immuno

Decreased relative thymus

and spleen weights

La Sala et al. 2009

Mouse

(CD-1)

NS F

3 days

(GO)

0, 15, 30

Develop

Decreased numbers of

primordial germ cells in

male and female offspring

Liu and Morgan 1986

Mouse

(DBA/2)

6 F

10 days

LE, CS, BC

Death

6/6 died

HEXACHLOROCYCLOHEXANE (HCH) 57

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Maranghi et al. 2007

Mouse

(CD)

12 F

GDs 9–16

(GO)

0, 15

BW, FI, BI,

OW, HP, DX

Bd wt

Repro

Develop

Early vaginal patency;

increased absolute (17%)

and relative (13%) uterine

weight at PND 22;

decreased oocyte diameter

(21%) in primary follicles at

PND 60 in F1 females

Scascitelli and Pacchierotti 2003

Mouse

(CD-1)

16–29 F

3 days

(GO)

0, 15, 25

Repro

Increase in degenerating

two-cell embryos following

preovulatory exposure

Sinha and Shukla 2003

Mouse

Swiss

8 M

3 days

(GO)

0, 5.9

BW, OW

Bd wt

5.9

Traina et al. 2003

Mouse

(CD-1)

10–24 F

GDs 9–16

(GO)

0, 15, 25

BW, DX

Bd wt

Develop

14% decrease in sperm

count in F1 offspring with

more severe effects

observed at higher dose

Palmer et al. 1978

Rabbit

(New

Zealand)

13 F

GDs 6–18

(G)

0, 5, 10, 20

Develop

HEXACHLOROCYCLOHEXANE (HCH) 58

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

INTERMEDIATE EXPOSURE

Ahmed et al. 2008

Rat

(Wistar)

10 M

4 weeks,

7 days/week

(GO)

0, 30

CS, BW, FI,

Bd wt

Ali and Shakoori 1998

Rat

(Sprague-

Dawley)

3–5 NS

15 days

(F)

0, 18

Hepatic

Reduced number of cells

per field; increased cell,

nucleus, and nucleolus

size; vacuoles in the

cytoplasm and granulation;

apparent fatty degeneration

Amyes 1990

Rat

(Wistar)

15 M, 15 F

Up to

52 weeks

(F)

Males: 0,

0.07, 0.7, 7,

Females: 0,

0.08, 0.8, 8,

LE, CS, BW,

FI, WI, HE,

BC, BI, UR,

GN, OW,

HP, NX

Death

32 F

Statistically significant

decreased survival

Bd wt

32F

28 M

Hemato

32F

28 M

Hepatic

0.8 F

0.7 M

8 F

7 M

Periacinar hepatocytic

hypertrophy

Renal

32 F

0.07 M

Hyaline droplets, interstitial

chronic nephritis, and

regeneration in proximal

tubules

Neuro

32 F

Convulsions in

11/55 females

HEXACHLOROCYCLOHEXANE (HCH) 59

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Anand et al. 1995

Rat

(albino)

NS M

6 weeks

(G)

0, 3

BW, BC, OF

Cardio

Tachycardia (~30%

increase in heart rate);

increased blood pressure,

plasma calcium levels, and

myocardial calcium influx;

decreased Ca, K-ATPase

activity; ECG changes

Andrews and Gray 1990

Rat

(Long-

Evans)

NS M

10 weeks

7 days/week

(G)

0, 10, 20

BW, OW,

Bd wt

Renal

Increased kidney weight;

hyaline droplet

accumulation and tubular

regeneration

Musc/skel

Decreased femur medullary

area

Arisi et al. 1994

Rat

(Wistar)

4–12 M

90 days

(F)

0, 90

Neuro

Tonic convulsions

Chadwick et al. 1988

Rat

(Fischer-

344)

6–12 F

15 weeks

(GO)

0, 5, 10, 20,

LE, BW, FI,

BI, OW

Death

2/12 died at 20 mg/kg/day;

7/12 died at 40 mg/kg/day

Repro

Delayed vaginal opening,

disrupted ovarian cycling

Desi 1974

Rat

(Wistar)

8–10 NS

40 days

(F)

0, 2.5, 5, 10,

NX, OW,

OF, HP

Hepatic

Neuro

2.5

Significantly altered

Skinner box behavior

HEXACHLOROCYCLOHEXANE (HCH) 60

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Dewan et al. 1980

Rat

(Charles

Foster)

5 M, 5 F

35 days

0, 6.25, 25

Immuno

6.25

Immunosuppression

(decreased antibody titers)

EPA 1991a

Rat

(CD)

30 M, 30 F

2 generation

s; 70 days

prior to

mating until

sacrifice

0, 0.09, 1.7,

13.1

CS, BW, FI,

HP, RX, DX

Bd Wt

1.7 F

13.1 M

13.1 F

Decreased body weight

gain during gestation in F0

females

Hepatic

0.09 M

13.1 F

1.7 M

In F1 males: hepatocellular

hypertrophy

Renal

0.09 M

13.1 F

1.7 M

In F0 and F1 males:

Increased kidney weights;

nephritis, tubular cell

regeneration, hyaline

droplets, tubular necrosis

Repro

13.1

Develop

13.1

Reduced F1 and F2 pup

weight and viability;

delayed tooth eruption and

hair growth in F2

EPA 1999b

Rat

(CD)

10 M, 10 F

13 weeks

(F)

Males: 0,

1.4, 7.1, 28.1

Females: 0,

1.6, 7.9, 30.2

Death

30.2 F

3/10 females died during

the study

Neuro

7.1 M

7.9 F

28.1 M

30.2 F

Increased rearing, walking

on tiptoes, hypersensitivity

to touch, and hunched

posture

HEXACHLOROCYCLOHEXANE (HCH) 61

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

EPA 1999c

Rat

(Wistar)

10 M, 10 F

GD 6 to

LD 10

(F)

Gestation:

0.8–0.9, 4.2–

4.6, 8.0–

10.5,

Lactation:1.2

–1.7, 5.6–

8.3, 13.7–

19.1

Develop

1.2

5.6

Up to 18% reduction in pup

body weight and 24% lower

body weight gain during

lactation

Fatih Fidan et al. 2008

Rat

(Sprague-

Dawley)

10 M

30 days

(GO)

0, 10, 20, 40

BC, BI, HP

Hepatic

Megalocytosis; vacuolar

degeneration; severe

venous and sinusoidal

congestion; and

lymphocytic infiltration

Renal

Severe kidney congestion,

medullary and cortical

hemorrhage, and

degeneration and

vacuolation of proximal

convoluted tubules

Fitzhugh et al. 1950

Rat

(Wistar)

10 F, 10 M

10 months

(F)

Males: 0, 30,

60, 120

Females: 0,

30, 70, 140

LE, BW

Death

60 M

70 F

Mean age at death was

39.7 weeks versus

58.3 weeks in controls

Bd wt

60 M

70 F

120 M

140 F

13–17% decrease in body

weight gain at 6 months

Resp

120 M

140 F

Cardio

120 M

140 F

Gastro

120 M

140 F

HEXACHLOROCYCLOHEXANE (HCH) 62

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Hemato

120 M

140 F

Musc/skel

120 M

140 F

Hepatic

60 M

70 F

Slight microscopic damage

Renal

60 M

70 F

Very slight microscopic

damage

Neuro

60 M

70 F

Convulsions

Endo

120 M

140 F

Repro

120 M

140 F

Gilbert 1995

Rat

(Long-

Evans)

15–16 M

30 days

(GO)

0, 10

Neuro

Myoclonic jerks and clonic

seizures

Hfaiedh et al. 2011

Rat

(Wistar)

6 M

30 days

(W)

0, 50

BC, BI, OW,

HP, RX

Endocr

85% increase in T4, 74%

decrease in TSH

Repro

Decreased testes (52%),

epididymides (42%),

prostate gland (50%), and

seminal vesicles (5%)

weights; 56% reduced

sperm count; 37% reduced

sperm motility; 74%

decrease in FSH

Ito et al. 1975

Rat

(W strain)

18–24 M

48 weeks

(F)

0, 35

BW, OW,

Hepatic

Hepatocellular hypertrophy

HEXACHLOROCYCLOHEXANE (HCH) 63

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Johri et al. 2007

Rat

(Wistar)

13–14 F

GDs 5–21

(GO)

0, 0.0625,

0.125, 0.25

DX, BI

Develop

0.125

0.25

Persistent hyperactivity

Johri et al. 2008

Rat

(Wistar)

13 F

GDs 5–21

and PND 45

(GO)

0, 0.25

(prenatal)

and 30

(postnatal)

CS, BI

Develop

Convulsions in

8/10 animals

Koner et al. 1998

Rat

(Wistar)

8–10 M

8 weeks

(F)

0, 3.6, 7.0

Immuno

3.6

Reduced serum antibody

response to SRBC

Martinez and Martinez-Conde 1995

Rat

(Wistar)

8 M, 8 F

30 days,

every 3 days

(GO)

0, 6

CS, NX

Neuro

Decreased brain dopamine

levels

Matsuura et al. 2005

Rat

(Crj:CD

[SD] IGS)

24 M, 24 F

~10 weeks

(2-generation

; premating

to PND 21)

(F)

Males, F0: 0,

0.56, 3.4,

17.2

Males, F1:

0.74, 4.5,

23.3

Females, F0:

0, 0.88, 5.2,

26.1

Females, F1:

0.95, 5.6,

28.0

LE, CS, BW,

FI, BC, BI,

GN, OW,

HP, RX, DX,

Death

26.1 F

2 F0 females died

Bd wt

26.1 F

17.2 M

Hepatic

0.88 F

0.56 M

5.2 F

3.4 M

Hepatocellular hypertrophy

in F0 and F1 male and

female parents

Renal

26.1 F

0.56 M

Basophilic tubules and

hyaline droplets in the

proximal tubules

Endocr

5.2 F

3.4 M

26.1 F

17.2 M

Decreased absolute and

relative pituitary weights in

F0 and F1 females; altered

serum thyroid hormone

levels; thyroid follicular cell

hypertrophy in F0 females

and F1 males

HEXACHLOROCYCLOHEXANE (HCH) 64

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Neuro

28 F

Convulsions in two F1

females

Repro

26.1 F

17.2 M

Develop

0.95

5.6

26.1

LOAEL: 10% decrease in

F2 female offspring body

weight at PND 4

Serious LOAEL: 49%

decrease in F2 offspring

viability (PNDs 0–4); 8–

29% decreases in male

and female F1 and F2

offspring weights on

PNDs

0, 4, and 21; delayed

sexual maturation

(preputial separation in

males and vaginal opening

in females) in F1

generation

Mediratta et al. 2008

Rat

(Wistar)

8 M

21 days

(NS)

0, 10

BC, IX

Immuno

Decreased anti-SRBC

antibody titer (32%)

Mudawal et al. 2018

Rat

(Wistar)

6 M

3 weeks

7 days/week

(NS)

0, 2.5

BI, NX, DX

Neuro

2.5

Decreased conditioned

avoidance, alternations,

and locomotor activity;

ultrastructural changes in

the hippocampus and

substantia nigra in adult

animals

Muller et al. 1981

Rat

(Wistar)

15 M

30 days

(F)

0, 1.3, 12.3,

25.4

Neuro

12.3

25.4

Reduced tail nerve

conduction velocity

HEXACHLOROCYCLOHEXANE (HCH) 65

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Parmar et al. 2003

Rat

(Wistar)

10 M

15 or 21

days

(GO)

0, 2.5

CS, BW, BI,

Bd wt

2.5

Prasad et al. 2016

Rat

(Wistar)

6 M

15, 30, or

45 days

(GO)

0, 20

BC, BI, GN,

Renal

Severe corticomedullary

and glomerular congestion,

intertubular hemorrhage,

severe tubular

degeneration,

desquamation of tubular

epithelium, cystic dilatation,

mononuclear cell infiltrate,

necrosis, and atrophic

glomeruli

Sahaya et al. 2007

Rat

(Wistar)

10 M

6 weeks,

7 days/week

(NS)

0, 15

BI, NX

Neuro

Impaired neurocognition

(decreased step-down

latency in passive

avoidance test and

prolonged transfer latency

in elevated plus maze)

Saradha and Mathur 2006

Rat

(Wistar)

4 M

45 days

(GO)

0, 1, 5, 50

BW, OW,

Repro

LOAEL: decreased sperm

count (~27%) and motility

(~25%)

Serious LOAEL: d

ecreased

sperm count (~40%),

motility (~40%), and

viability (~15%); decreased

epididymal weight (~10%)

HEXACHLOROCYCLOHEXANE (HCH) 66

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Sauviat et al. 2005

Rat

(Sprague-

Dawley)

NS F

~13 weeks

(W)

0, 0.000076,

0.00015,

0.00030

GN, OW,

Develop

0.000076

0.00015

0.0003

LOAEL: altered ventricular

electrophysiology

Serious LOAEL: 21%

decrease in pup body

weight; altered heart

morphometry and

electrophysiology; cardiac

histopathology

(hypertrophy in left

ventricular area,

unorganized collagen

bundles and layers,

fibroblast destruction)

Sharma and Singh 2010

Rat

(Wistar)

6 M

28 days

(GO)

0, 30

Repro

Decreased cauda

epididymis (32%) and

testes (70%) weights;

≥89% decreases in sperm

head count, motility, and

percent live sperm; 4-fold

increase in percent

abnormal sperm

Srinivasan et al. 1991

Rat

(Wistar)

6 F

GDs 0–21

and

LDs 1–28 or

LDs 1–28

(F)

0, 25

Develop

Increased pup relative liver

weights

Srivastava et al. 2019

Rat

(Wistar)

25 F

GDs 5–21

(GO)

0, 0.25

Develop

0.25

Ultrastructural changes in

the brain (moderately

distorted mitochondria and

demyelinated neurons)

HEXACHLOROCYCLOHEXANE (HCH) 67

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Srivastava et al. 2019

Rat

(Wistar)

6 M

21 days

(GO)

0, 2.5

Neuro

2.5

Reduced locomotor activity

and spatial memory;

ultrastructural changes in

the hippocampus and

substantia nigra (swollen

mitochondria with

disintegrated cristae,

shortened fuzzy synapse,

disintegrated myelin layer,

and autophagosomes)

Sumida et al. 2007

Rat

(Fischer-

344)

4 M

28 days

(GO)

0, 1, 10

BW, BC,

OW, HP

Bd wt

Hepatic

Suter 1983

Rat

(Wistar)

15 M, 15 F

12 weeks

(F)

0, 0.02, 0.08,

0.4, 2.0, 10

LE, CS, BW,

FI, HE, UR,

OW, HP

Hemato

Hepatic

0.4

Centrilobular hypertrophy

Renal

0.4 F

0.4 M

2 F

Basophilic proximal

tubules; proximal tubular

distention, hyaline droplet

formation; and minimal to

moderate interstitial

nephritis in males; slight

epithelial cell necrosis in

proximal convoluted

tubules in both sexes

HEXACHLOROCYCLOHEXANE (HCH) 68

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Vijaya Padma et al. 2011

Rat

(Wistar)

6 F

30 days

(GO)

0, 100

BC, BI, HP

Hepatic

100

“Extensive” liver injuries

consisting of vacuolar

degeneration of

hepatocytes and “massive”

degradation of the central

vein

Renal

100

Glomerular degeneration

and shrinkage;

degeneration of proximal

and distal tubules

Vijaya Padma et al. 2013

Rat

(Wistar)

6 M

30 days

(GO)

0, 100

BC, BI, OW,

Cardio

100

Histopathology changes

(inflammatory cells and

separated muscle fibers)

Yang et al. 2014; Zhang et al. 2016

Rat

(Sprague-

Dawley)

7–9 F

4 weeks,

7 days/week

(GO)

0, 4, 8

BW, BC,

OW, HP

Bd wt

Repro

Low columnar endometrial

glandular epithelial cells in

the uterus

Yuksel et al. 2009

Rat

(Sprague-

Dawley)

10 M

30 days

(GO)

0, 10, 20, 40

CS, BC, GN,

OW, HP, RX

Death

1/10 rats died at

20 mg/kg/day and

1/10 died at 40 mg/kg/day

Banerjee et al. 1996

Mouse

(Hissar)

NS M

3–12 weeks

0, 1.8, 5.4, 9

Immuno

1.8

5.4

Immunosuppression

(decreased splenic plaque-

forming colonies) after

6 weeks; decreased

antibody titers at

9 mg/kg/day

HEXACHLOROCYCLOHEXANE (HCH) 69

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Hanada et al. 1973

Mouse

(dd)

10–11 M,

10–11 F

32 weeks

Males: 0, 18,

54, 108

Females: 0,

20, 60, 120

BC, GN, HP

Cancer

120

CEL: hepatoma

Ito et al. 1973

Mouse

(dd)

20–40 M

24 weeks

(F)

0, 18, 45, 90

BW, OW,

Bd wt

Hepatic

Relative liver weight

increase of 33% and

centrilobular hypertrophy

Meera et al. 1992

Mouse

(Swiss

albino)

6 F

24 weeks

(F)

0, 0.012,

0.12, 1.2

CS, HP, IX

Immuno

0.012

1.2

LOAEL: changes in cell-

and humoral-mediated

immune system

Serious LOAEL:

histopathology changes in

thymus consisting of

marked decrease in cortical

lymphocytes, many

necrosed cells in medulla,

congestion of blood

vessels, and severe loss of

cortex and medulla

distinction

Nagda and Bhatt 2011

Mouse

(Swiss)

8–10 M

60 days

(GO)

0, 40

BI, OW, HP

Repro

10% decrease testes

weight; histopathology

changes in testes

(shrunken and distorted

seminiferous tubules,

sparse Leydig cells, and

oligospermia)

HEXACHLOROCYCLOHEXANE (HCH) 70

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Thorpe and Walker 1973

Mouse

(CF1)

30 M, 30 F

3 months

(F)

0, 68

Death

10% of males and 20% of

females died in first

3 months of chronic study

Rivett et al. 1978

Dog

(Beagle)

1 M, 1 F

7 weeks

0.9, 2, 4, 7

CS, BW,

HE, BC, UR,

GN, OW,

Bd wt

Decreased body weight

gain

Desi et al. 1978

Rabbit

(NS)

6 M

5–6 weeks

5 days/week

(C)

0, 1.5, 3, 6,

LE, OF, IX

Death

“Numerous” deaths

Lindenau et al. 1994

Rabbit

(hybrid)

5 F

12 weeks

3 days/week

(GO)

0, 0.8

CS, BC, BI

Repro

0.8

Reduced ovulation rate

Seiler et al. 1994

Rabbit

(New

Zealand)

5 F

12–15 weeks

3 days/week

(GO)

0, 0.8

DX, RX

Repro

0.8

Develop

0.8

Beard and Rawlings 1998

Mink

(NS)

8–10 F

generations

(F)

0, 1

CS, BW, FI,

GN, OW,

HP, RX, DX

Repro

Reduced litter size in F2

females (~40% lower than

controls); reduced testis

size (11–13% shorter

length and 34–36% lower

mass) in F3 males

HEXACHLOROCYCLOHEXANE (HCH) 71

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Beard et al. 1997

Mink

(NS)

10 F

12 weeks

3 weeks

premating to

8 weeks

postpartum

(F)

0, 1

CS, BW, FI,

BC, GN,

OW, HP,

RX, DX

Repro

Reduced mating receptivity

and whelping rate

Beard et al. 1997

Mink

(NS)

15 F

17 weeks

6 weeks

premating to

10 weeks

postpartum

(F)

0, 1

CS, BW, FI,

BC, GN,

OW, HP,

RX, DX

Repro

Reduced whelping rate and

increased post-

implantation

embryo loss

CHRONIC EXPOSURE

Ali and Shakoori 1998

Rat

(Sprague-

Dawley)

3–5, NS

18 months

(F)

0, 9

Hepatic

Increased cell, nucleus,

and nucleolus size;

extensive cytoplasmolysis;

slight cytoplasmic

degeneration; increasing

nuclear distortion

Fitzhugh et al. 1950

100

Rat

(Wistar)

10 F, 10 M

107 weeks

(F)

Males: 0,

0.4, 0.7, 4, 7,

Females: 0,

0.4, 0.9, 4, 9,

LE, BW, FI,

GN, OW,

Resp

Cardio

Gastro

Hemato

Musc/skel

Hepatic

9 F

7 M

Increased relative liver

weight (35%); very slight

microscopic liver damage

Renal

9 F

7 M

Very slight microscopic

kidney damage

HEXACHLOROCYCLOHEXANE (HCH) 72

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Endo

Repro

EPA 2000a

101

Mouse

(CD-1)

50 M, 50 F

78 weeks

(F)

Males: 0,

1.3, 5.2, 20.5

Females: 0,

1.8, 7.1, 26.8

LE, BW, FI,

GN, OW,

Bd wt

20.5 M

26.8 F

Resp

20.5 M

26.8 F

Hemato

20.5 M

Hepatic

5.2 M

26.8 F

20.5 M

Centrilobular hepatocyte

hypertrophy

Renal

20.5 M

26.8 F

Endocr

20.5 M

26.8 F

Neuro

20.5 M

26.8 F

Cancer

26.8 F

CEL: bronchiolar-alveolar

adenomas and carcinomas

Herbst et al. 1975; Weisse and Herbst 1977

102

Mouse

(NMRI)

50 M, 50 F

80 weeks

(F)

Males: 0,

2.1, 4.1, 8.2

Females: 0,

2.0, 3.9, 7.8

BW, GN, HP

Bd wt

8.2 M

7.8 F

Hepatic

8.2 M

7.8 F

NCI 1977

103

Mouse

(B6C3F1)

50 M, 50 F

80 weeks

(F)

0, 13.6, 27.2

CS, BW, BI,

Cancer

13.6 M

CEL: hepatocellular

carcinoma

Thorpe and Walker 1973

104

Mouse

(CF1)

30 M, 30 F

104 weeks

(F)

0, 68

CS, GN, HP

Cancer

CEL: liver and other

unspecified tumors in both

sexes

HEXACHLOROCYCLOHEXANE (HCH) 73

2. HEALTH EFFECTS

Table 2-4. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Wolff et al. 1987

105

Mouse

(F-1

hybrid)

24–96 F

24 months

(F)

0, 27.2

CS, BW, BI,

Cancer

27.2

CEL: hepatocellular

carcinoma, lung tumors

Rivett et al. 1978

106

Dog

(Beagle)

4 M, 4 F

104 weeks

(F)

0, 0.83, 1.60,

2.92

CS, BW,

HE, BC, UR,

GN, OW,

HP, NX

Bd wt

2.92

Hepatic

2.92

Livers were dark but

without histopathology

changes

Hemato

2.92

Ocular

2.92

The number corresponds to entries in Figure 2-8; differences in levels of health effects and cancer effects between male and females are not indicated in

Figure 2-8. Where such differences exist, only the levels of effect for the most sensitive sex are presented.

Used to derive an acute-duration oral minimal risk level (MRL). The LOAEL of 1 mg/kg/day was divided by an uncertainty factor of 300 (3 for use of a minimal

LOAEL, 10 for human variability, and 10 for animal to human extrapolation), resulting in an MRL of 0.003 mg/kg/day (3x10

-3

mg/kg/day).

Used to derive an intermediate-duration oral MRL. The NOAEL of 0.000076 mg/kg/day was divided by an uncertainty factor of 100 (10 for human variability, an

10 for animal to human extrapolation), resulting in an MRL of 0.0000008 mg/kg/day (8x10

-7

mg/kg/day).

BC = serum (blood) chemistry; Bd wt or BW = body weight; BI = biochemical changes; (C) = capsule; Cardio = cardiovascular; CEL = cancer effect level;

CS = clinical signs; Develop = developmental; DX = developmental toxicity; ECG = electrocardiogram; Endocr = endocrine; (F) = feed; F = female(s);

F0 = parental generation; F1 = first generation; F2 = second generation; F3 = third generation; FI = food intake; FSH = follicle stimulating hormone; (G) = gavage;

GD = gestation day; GN = gross necropsy; (GO) = gavage in oil;; HE = hematology; Hemato = hematological; HP = histopathology; Immuno = immunological;

IX = immunotoxicity; LD = lactation day; LD

= lethal dose, 50% kill; LE = lethality; LOAEL = lowest-observed-adverse-effect level; M = male(s);

Musc/skel = musculoskeletal; Neuro = neurological; NOAEL = no-observed-adverse-effect level; NS = not specified; NX = neurotoxicity; OF = organ function;

OW = organ weight; PND = postnatal day; Repro = reproductive; Resp = respiratory; RX = reproductive toxicity; SRBC = sheep red blood cell; T4 = thyroxine;

TSH = thyroid stimulating hormone; UR = urinalysis; (W) = drinking water; WI = water intake

HEXACHLOROCYCLOHEXANE (HCH) 74

2. HEALTH EFFECTS

Figure 2-8. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Acute (≤14 days)

HEXACHLOROCYCLOHEXANE (HCH) 75

2. HEALTH EFFECTS

Figure 2-8. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Acute (≤14 days)

HEXACHLOROCYCLOHEXANE (HCH) 76

2. HEALTH EFFECTS

Figure 2-8. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Intermediate (15–364 days)

HEXACHLOROCYCLOHEXANE (HCH) 77

2. HEALTH EFFECTS

Figure 2-8. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Intermediate (15–364 days)

HEXACHLOROCYCLOHEXANE (HCH) 78

2. HEALTH EFFECTS

Figure 2-8. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Intermediate (15–364 days)

HEXACHLOROCYCLOHEXANE (HCH) 79

2. HEALTH EFFECTS

Figure 2-8. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Chronic (≥365 days)

HEXACHLOROCYCLOHEXANE (HCH) 80

2. HEALTH EFFECTS

Figure 2-8. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Oral

Chronic (≥365 days)

HEXACHLOROCYCLOHEXANE (HCH) 81

2. HEALTH EFFECTS

Table 2-5. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

ACUTE EXPOSURE

Joseph et al. 1992a

Technical HCH

Rat

(CFT-

Wistar)

6 M

Once

(GO)

0–4,000

Death

2,428

Sahoo et al. 1999

Technical HCH

Rat

(Wistar)

10 M

7 days

0, 10, 20

BI, NX

Neuro

Reduced brain ATPase

activities; 12% reduction in

brain acetylcholinesterase

activity; increased motor

activity at 20 mg/kg/day

Samanta et al. 1999

Technical HCH

Rat

(Wistar)

10 M

7 days

(GO)

0, 10, 20

BW, BC, BI,

OW, HP

Repro

54% reduction in total sperm

count in adult rats;

increased frequency of

damaged sperm and sperm

with anomalous heads

Dikshith et al. 1990

Technical HCH

Mouse

(Swiss

albino)

6 F

GD 9

once

(GO)

0, 5, 25, 50,

100, 200

BW, DX

Repro

Increased fetal resorptions

Philip et al. 1989

Technical HCH

Mouse

(NS)

1 or 5 days

(GO)

0, 50

Hepatic

Marked damage including

severe congestion of portal

vessels and central vein,

severe fatty changes in

periportal cells

Renal

A few cases of interstitial

hemorrhaging in medulla,

cystic dilation of tubules,

hyaline casts

HEXACHLOROCYCLOHEXANE (HCH) 82

2. HEALTH EFFECTS

Table 2-5. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Ravinder et al. 1989, 1990

Technical HCH

Mouse

(Swiss

albino)

10 M

2 weeks

(F)

0, 72, 144

BI, OW, OF

Death

144

14% mortality

Hepatic

>2-fold increase in relative

liver weight, hepatocellular

hypertrophy, mild

centrilobular degeneration,

focal necrosis in a few

specimens

INTERMEDIATE EXPOSURE

Anand et al. 1991

Technical HCH

Rat

(NS)

45 M

90 days

6 days/week

(GO)

0, 50

BI, NX

Neuro

Increased dopamine and

decreased norepinephrine in

brain; behavioral changes;

increased brain wave

frequency

Dikshith et al. 1989a

Technical HCH

Rat

(NS)

10 M

30 days

(GO)

0, 60

CS, HE, BC,

BI, OW, HP

Hemato

Hepatic

65% increase in liver weight

Renal

Repro

Dikshith et al. 1991a

Technical HCH

Rat

(NS)

20 M

360 days

(F)

0, 0.04, 0.4,

2, 20, 40

BW, FI, BC,

BI, OW, OF,

Death

0.4

4/20 deaths

Hepatic

Focal necrosis, enlargement

of hepatocytes, nuclear

pyknosis, vacuolation,

margination

Renal

Debris cells in lumen,

glomerular degeneration

Neuro

0.04

0.4

Tremors, convulsions, hind

limb paralysis

HEXACHLOROCYCLOHEXANE (HCH) 83

2. HEALTH EFFECTS

Table 2-5. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Repro

Testicular necrosis and

degeneration

Dikshith et al. 1991b

Technical HCH

Rat

(NS)

12 M, 12 F

90 days

(GO)

0, 5, 25

LE, BW, BI,

BC, OW, HP,

Death

33% mortality in females

and 50% mortality in males

Fitzhugh et al. 1950

Technical HCH

Rat

(Wistar)

10 F, 10 M

6 months

(F)

Males: 0, 7,

Females: 0,

9, 70

LE, BW

Death

60 M

70 F

Decreased mean age at

death (32.9 versus

58.3 weeks in controls)

Bd wt

7 M

9 F

70 F

60 M

LOAEL: 16% decrease in

body weight of females

Serious LOAEL: 26%

decrease in body weight of

males

Resp

60 M

70 F

Cardio

60 M

70 F

Gastro

60 M

70 F

Hemato

60 M

70 F

Hepatic

60 M

70 F

Moderate liver damage

Renal

60 M

70 F

Slight kidney damage

Musc/skel

60 M

70 F

Endo

60 M

70 F

Repro

70 F

60 M

Moderate testicular atrophy

HEXACHLOROCYCLOHEXANE (HCH) 84

2. HEALTH EFFECTS

Table 2-5. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Gautam et al. 1989

Technical HCH

Rat

(Charles

Foster)

10 M

180 days

(GO)

0, 3, 6

Bd wt

17% decrease in body

weight gain

Repro

6% decrease in vas

deferens weight,

degeneration of inner

muscle and cell layers of

vas deferens

Gopal et al. 1992

Technical HCH

Rat

(NS)

50 M

120 days

(GO)

0, 50

CS, NX

Neuro

Increased motor activity,

decreased resting

stereotypic time

Joseph et al. 1992c

Technical HCH

Rat

(CFT-

Wistar)

4 M

7 weeks

(F)

0, 90

HE, BC

Hemato

Decreased white blood cell

counts

Ito et al. 1975

Delta HCH

Rat

(W strain)

18–24 M

48 weeks

0, 35, 70

BW, OW, HP

Hepatic

Hepatocellular hypertrophy

Mudawal et al. 2018

Technical HCH

Rat

(Wistar)

6 M

3 weeks

7 days/week

(NS)

0, 2.5

BI, NX, DX

Neuro

2.5

Statistically significant

decreases in conditioned

avoidance, alternations, and

locomotor activity;

ultrastructural changes in

the hippocampus and

substantia nigra in adult

animals

Nagaraja and Desiraju 1994

Technical HCH

Rat

(Wistar)

6–8 F

PNDs 2–60

(GO)

0, 10, 20

CS, BW, BI

Develop

Alterations in levels of

dopamine, serotonin, and

noradrenaline in pup brains

HEXACHLOROCYCLOHEXANE (HCH) 85

2. HEALTH EFFECTS

Table 2-5. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Nagaraja and Desiraju 1994

Technical HCH

Rat

(Wistar)

6–7 F

90 days

(F)

0, 20

CS, BW, BI

Bd wt

Significantly decreased

(23%) terminal body weight

Neuro

Increased GABA levels,

increased GAD activity,

decreased glutamate levels

Roy Chowdhury and Gautam 1990

Technical HCH

Rat

(Charles

Foster)

5–10 M

180 days

(G)

0, 3, 6

BW, OW, HP

Repro

LOAEL: detachment of

germinal cells from

peritubular membrane of

seminiferous tubules,

atrophy of Leydig cells, and

intertubular edema

Serious LOAEL: “complete

degeneration” of testicular

tissue

Sahoo et al. 1999

Technical HCH

Rat

(Wistar)

10 M

15 or 30

days

7 days/week

0, 10, 20

BI, NX

Neuro

Reduced brain ATPase

activity; 39% decrease in

acetylcholinesterase activity

after 15 days, with reduced

grooming behavior at

20 mg/kg/day after 30 days

Samanta et al. 1999

Technical HCH

Rat

(Wistar)

10 M

15 or 30

days

(GO)

0, 10, 20

BW, BC, BI,

OW, HP

Repro

58–65% reduction in total

sperm count in adult rats;

increased frequency of

damaged sperm and sperm

with anomalous heads

Bhatt and Bano 2009

Technical HCH

Mouse

(Swiss)

6–18 M

2, 4, or

6 months

(F)

0, 90

BI, HP

Cancer

CEL: Liver tumors

HEXACHLOROCYCLOHEXANE (HCH) 86

2. HEALTH EFFECTS

Table 2-5. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Bhatt and Nagda 2012

HCH Not further specified

Mouse

(Swiss)

18–20 M

2, 4, or

6 months

(F)

0, 90

BI, HP

Hepatic

Hepatocyte degeneration,

vacuolation, fatty changes;

hypertrophy, and

hyperplasia after 4 months

Cancer

CEL: liver tumors

Ito et al. 1973

Delta HCH

Mouse

(dd)

20–40 M

24 weeks

(F)

0, 18, 45, 90

BW, OW, HP

Bd wt

Hepatic

23% increase in relative liver

weight and centrilobular

hypertrophy

Karnik et al. 1981

Technical HCH

Mouse

(Swiss)

6 NS

2–8 months

(F)

0, 90

OW, OF

Hepatic

100% increase in liver

weight; glycogen

accumulation, smooth

endoplasmic reticulum

proliferation

Cancer

CEL: hepatocellular

carcinoma

Nigam et al. 1979

Technical HCH

Mouse

(Swiss)

6 M

3 months

(F)

0, 90

BW, OW, HP

Repro

Increased (27%) relative

testis weight, degeneration

of seminiferous tubules,

shrunken and edematous

tubules (some completely

hyalinized); decreased

(sparse) and damaged

spermatocytes

HEXACHLOROCYCLOHEXANE (HCH) 87

2. HEALTH EFFECTS

Table 2-5. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Philip et al. 1989

Mouse

(NS)

15 d

(GO)

0, 50

Hepatic

Marked damage consisting

of congestion of portal

vessels and central vein,

granular degeneration

Renal

Marked damage consisting

of congestion of blood

vessels and glomeruli,

vacuolation of epithelial cells

in glomeruli, fatty changes,

cystic dilation of the tubules,

and interstitial hemorrhaging

Thakore et al. 1981

Technical HCH

Mouse

(Swiss)

6 NS

2–8 months

(F)

0, 90

BW, BI, OW

Cancer

CEL: hepatocellular

carcinoma

Trivedi et al. 2007, 2009

Technical HCH

Mouse

(Swiss)

6 M

1–8 months

(F)

0, 90

BC, BI, GN,

Hepatic

“Severe” liver damage after

6 months

Cancer

CEL: liver tumors

Wang et al. 2006

Technical HCH

Pig

(Duroc X

Landrace

X Large

white)

12 M, 12 F

90 days

(F)

0, 0.4, 0.8

BW, FI, BC,

BI, OW, IX

Bd wt

0.8

Hepatic

0.8

No effect on liver weight;

<30% increases in serum

ALT and ALP

Renal

0.4

0.8

24% increase in relative

kidney weight

HEXACHLOROCYCLOHEXANE (HCH) 88

2. HEALTH EFFECTS

Table 2-5. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

CHRONIC EXPOSURE

Fitzhugh et al. 1950

Technical HCH

Rat

(Wistar)

10 F, 10 M

107 weeks

(F)

Males: 0, 0.7,

4, 7

Females: 0,

0.4, 0.9, 4, 9,

LE, BW, FI,

GN, OW, HP

Resp

7 M

9 F

Cardio

7 M

9 F

Gastro

7 M

9 F

Hemato

7 M

9 F

Musc/skel

7 M

9 F

Hepatic

0.7 M

0.9 F

Very slight microscopic

damage

Renal

7 M

9 F

Endo

7 M

9 F

Repro

7 M

9 F

Kashyap et al. 1979

Technical HCH

Mouse

(Swiss)

30 M, 30 F

80 weeks

(GO)

0, 10

CS, BW, FI,

GN, HP

Neuro

Convulsions

Cancer

CEL: hepatocellular

carcinoma

Kashyap et al. 1979

Technical HCH

Mouse

(Swiss)

30 M, 30 F

80 weeks

(F)

0, 17

CS, BW, FI,

GN, HP

Neuro

Convulsions

Cancer

CEL: hepatocellular

carcinoma

HEXACHLOROCYCLOHEXANE (HCH) 89

2. HEALTH EFFECTS

Table 2-5. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane – Oral

Figure

key

Species

(strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Munir et al. 1983

Technical HCH

Mouse

(Swiss)

10–37 M

20 months

(F)

0, 21.3, 42.5,

BW, OW, HP

Cancer

21.3

CEL: hepatocellular

carcinoma

The number corresponds to entries in Figure 2-9; differences in levels of health effects and cancer effects between male and females are not indicated in

Figure 2-9. Where such differences exist, only the levels of effect for the most sensitive sex are presented.

ALP = alkaline phosphatase; ALT= alanine aminotransferase; BC = serum (blood) chemistry; Bd wt or BW = body weight; BI = biochemical changes;

CEL = cancer effect level; CS = clinical signs; Develop = developmental; DX = developmental toxicity; (F) = feed; F = female(s); FI = food intake; (G) = gavage;

GABA = gamma-aminobutyric acid; GAD =glutamate decarboxylase; GD = gestation day; GN = gross necropsy; (GO) = gavage in oil; HCH = hexachlorocyclo-

hexane; HE = hematology; Hemato = hematological; HP = histopathology; IX = immunotoxicity; LD

= lethal dose, 50% kill; LE = lethality; LOAEL = lowest-

observed-adverse-effect level; M = male(s); Musc/skel = muscular/skeletal; Neuro = neurological; NOAEL = no-observed-adverse-effect level; NS = not specified;

NX = neurotoxicity; OF = organ function; OW = organ weight; PND = postnatal day; Repro = reproductive; (W) = drinking water

HEXACHLOROCYCLOHEXANE (HCH) 90

2. HEALTH EFFECTS

Figure 2-9. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane (HCH) – Oral

Acute (≤14 days)

HEXACHLOROCYCLOHEXANE (HCH) 91

2. HEALTH EFFECTS

Figure 2-9. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane (HCH) – Oral

Intermediate (15–364 days)

HEXACHLOROCYCLOHEXANE (HCH) 92

2. HEALTH EFFECTS

Figure 2-9. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane (HCH) – Oral

Intermediate (15–364 days)

HEXACHLOROCYCLOHEXANE (HCH) 93

2. HEALTH EFFECTS

Figure 2-9. Levels of Significant Exposure to δ- and Technical Hexachlorocyclohexane (HCH) – Oral

Chronic (≥365 days)

HEXACHLOROCYCLOHEXANE (HCH) 94

2. HEALTH EFFECTS

Table 2-6. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Dermal

Species

(strain)

No./group

Exposure

parameters

Doses

Parameters

monitored

Endpoint

NOAEL

Less serious

LOAEL

Serious

LOAEL

Effects

ACUTE EXPOSURE

Gaines 1960

Rat

(Sherman)

100 M, 70 F

Once

(GO)

LE, CS

Death

900 F

1,000 M

Hanig et al.

1976

Rabbit

(New Zealand)

2–6 M

Once

0, 60 mg/kg

LE, CS

Death

Deaths among weanlings

Neuro

Convulsions

Ullmann 1986a

Rat

(Wistar)

5 M, 5 F

24 hours

once

0, 250, 600,

1,000,

2,000 mg/kg

LE, CS, BW,

Death

600

2/10 died at 600 mg/kg;

=1,000 mg/kg

Neuro

600

1,000

2,000 F

LOAEL: sedation, curved body

position

Serious LOAEL: severe sedation

and spasms in one female

Ullmann 1986c

Rabbit

(New Zealand)

3 M, 3 F

Once

0, 40 mg/kg

LE, CS, BW

Ocular

Mild eye irritation

INTERMEDIATE EXPOSURE

Dikshith et al. 1973

Rat (I.T.R.C.)

30 F

25 days

180 mg/kg/day

Dermal

180

Mild dermatitis

HEXACHLOROCYCLOHEXANE (HCH) 95

2. HEALTH EFFECTS

Table 2-6. Levels of Significant Exposure to γ-Hexachlorocyclohexane – Dermal

Species

(strain)

No./group

Exposure

parameters

Doses

Parameters

monitored

Endpoint

NOAEL

Less serious

LOAEL

Serious

LOAEL

Effects

EPA 1988a

Rat

(Crl:(WI)BR)

13–23 M, 13–

23 F

13 weeks

5 days/week

6 hours/day

0, 10, 60,

400 mg/kg/day

LE, CS, BW,

FI, HE, BC,

UR, GN, OF,

HP, NX

Death

400 F

23 deaths out of 49

Bd wt

400

Resp

Rapid respiration or wheezing

Hemato

400

Hepatic

Centrilobular hypertrophy,

increased absolute liver weight

(8%) in females

Renal

10 M

60 F

60 M

Basophilic tubules in males

Neuro

60 F

LOAEL: hyperactivity

Serious LOAEL: ataxia, tremors,

convulsions

BC = serum (blood) chemistry; Bd wt or BW = body weight; CS = clinical signs; F = female(s); FI = food intake; GN = gross necropsy; HE = hematology;

HP = histopathology; LE = lethality; LD

= lethal dose, 50% kill; LOAEL = lowest-observed-adverse-effect level;; M = male(s); Neuro = neurological; NOAEL = no-

observed-adverse-effect level; NR = not reported; NS = not specified; NX = neurotoxicity; OF = organ function; Resp = respiratory; UR = urinalysis

HEXACHLOROCYCLOHEXANE (HCH) 96

2. HEALTH EFFECTS

Table 2-7. Levels of Significant Exposure to Technical Hexachlorocyclohexane – Dermal

Species (strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

ACUTE EXPOSURE

Dikshith et al. 1978

Guinea pig

(NS)

24 M

5–12 days

0, 100, 200,

500

Death

200

24/24 deaths

INTERMEDIATE EXPOSURE

Dikshith et al. 1991c

Rat

(Wistar)

6 F

15–30 days

0, 100

LE, BW, BC,

BI, OW, HP

Death

100

Two deaths by day 15 and 2

by day 30

Hepatic

100

Severe liver injury including

hypertrophy, fatty

degeneration, nuclear

pyknosis of hepatocytes,

diffuse and focal liver

necrosis, and bile duct

proliferation

Renal

100

Mild to severe tubular

epithelial cell necrosis and

glomerular atrophy

Dermal

100

Hyperkeratosis, epidermal cell

vacuolization, thickening of

collagen fibers

Neuro

100

Tremors, degenerative

changes in the cerebellum

Dikshith et al. 1989b

Rabbit

(NS)

8 M

30 days

0, 25

LE, CS, BW,

BC, BI, UR,

OW, HP

Death

6/24 deaths

Hepatic

Hepatocyte degeneration,

pycnotic nuclei, enlarged liver,

altered ALT, AST, LDH, and

ALP activities

HEXACHLOROCYCLOHEXANE (HCH) 97

2. HEALTH EFFECTS

Table 2-7. Levels of Significant Exposure to Technical Hexachlorocyclohexane – Dermal

Species (strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Renal

Altered epithelial lining of

proximal convoluted tubules,

loss of brush borders of

tubules, atrophy of glomerular

capsules

Dermal

Thickened epidermis,

hyperkeratinization, and

infiltration of mononuclear

cells

Neuro

Convulsions, tremor, and

paralysis; changes in Purkinje

cells of cerebellum including

loss of dendrites and presence

of deciduomatous cell body

Repro

Severe effects on germinal

cells of testes, including

vacuolation, cytoplasmic

changes, cell sloughing, and

multinucleated giant cells

Dikshith et al. 1978

Guinea pig

(NS)

24 M

30 days

0, 100, 200,

500

BW, BC, BI,

OW, HP

Hepatic

100

38% increase in liver weight,

hepatic hypertrophy, pyknotic

nuclei in cytoplasm, focal fatty

inclusions, increased ALT and

ALP activity

Renal

100

Repro

100

Degeneration of seminiferous

tubules, necrosed

spermatogenic cells,

multinucleated giant cells, and

no active sperm in lumen

HEXACHLOROCYCLOHEXANE (HCH) 98

2. HEALTH EFFECTS

Table 2-7. Levels of Significant Exposure to Technical Hexachlorocyclohexane – Dermal

Species (strain)

No./group

Exposure

parameters

Doses

(mg/kg/day)

Parameters

monitored

Endpoint

NOAEL

(mg/kg/day)

Less

serious

LOAEL

(mg/kg/day)

Serious

LOAEL

(mg/kg/day)

Effects

Mathur et al. 1992

Guinea pig

(NS)

6 NS

30 days

0, 100

BI, HP

Hepatic

100

Increased enzyme activity and

fatty and degenerative

changes

Renal

100

increased enzyme activity and

histopathological changes

Mathur et al. 1993

Guinea pig

(NS)

6 M

15, 30 days

0, 100

BI, HP

Dermal

100

Dermal histopathology:

hyperkeratinization,

mononuclear infiltration,

sloughing

CHRONIC EXPOSURE

Kashyap et al. 1979

Mouse

(Swiss)

30 M, 30 F

80 weeks

2 days/week

0, 2.4

BW, FI, GN,

HP, CS

Cancer

2.4

CEL: liver tumors

Prasad et al. 1995

Rat

(Wistar)

10 M

120 days

0, 50, 100

CS, BI, OF,

Repro

Decreased sperm count (57%

relative to vehicle control) and

motility (38%), increased

percent abnormal sperm

(>5-fold), alterations in

testicular enzyme activity

ALP = alkaline phosphatase; ALT= alanine aminotransferase; AST = aspartate aminotransferase; BC = serum (blood) chemistry; BW = body weight; BI =

biochemical changes; CEL = cancer effect level; CS = clinical signs; F = female(s); FI = food intake; GN = gross necropsy; HP = histopathology; LDH = lactate

dehydrogenase; LE = lethality; LOAEL = lowest-observed-adverse-effect level; M = male(s); Neuro = neurological; NOAEL = no-observed-adverse-effect level;

NS = not specified; OF = organ function; OW = organ weight; Repro = reproductive; RX = reproductive toxicity; UR = urinalysis

HEXACHLOROCYCLOHEXANE (HCH) 99

2. HEALTH EFFECTS

2.2 DEATH

Human fatalities have been reported for γ-HCH but not for other isomers or for mixtures of isomers.

Studies reporting deaths associated with γ-HCH are described below in the subsection on γ-HCH.

α-HCH. In a long-term study where Wistar rats were administered α-HCH in the diet, mean age of death

was significantly decreased to 35.9 weeks in animals administered 60–70 mg/kg/day compared to

58.3 weeks in control animals (Fitzhugh et al. 1950). No inhalation or dermal studies of mortality in

animals were identified for α-HCH.

β-HCH. Mortalities have occurred in rats and mice exposed to β-HCH in the diet for acute and

intermediate exposure durations, often after showing signs of pronounced neurotoxicity. In the first week

of a 30-day study, 80% of female mice receiving 200 mg/kg/day β-HCH in feed exhibited ataxia

progressing to lateral recumbent position and were humanely sacrificed (Cornacoff et al. 1988). No

deaths were observed in male rats exposed to 72 mg/kg/day β-HCH in food for 2 weeks (Srinivasan et al.

1984). However, maternal mortality occurred in a developmental study in rats (Srinivasan et al. 1991), in

which all dams exposed to 80 mg/kg/day β-HCH in feed died within 3 weeks of treatment (during

gestation). Similarly, in the first 2 weeks of a 13-week dietary study, two male and three female rats

exposed to doses of 38 mg/kg/day exhibited ataxia and hypoactivity, progressing within 3 days to coma

and leading to their humane sacrifice

(Van Velsen et al. 1986). Subsequently, five males and six females

in this dose group became moribund and were euthanized later in the study (timing not reported) (Van

Velsen et al. 1986). In a dietary study where Wistar rats were administered β-HCH, mean age of death

for both males and females administered 60–70 mg/kg/day was 4.4 weeks compared to 58.3 weeks in

control animals (Fitzhugh et al. 1950). All animals exposed to β-HCH at this dose died by 10 weeks of

exposure (Fitzhugh et al. 1950). Finally, in a chronic study in which CF1 mice were administered

34 mg/kg/day β-HCH for up to 104 weeks, 12% of males and 25% of females died within the first

3 months (Thorpe and Walker 1973). Survival of the remaining animals did not differ from controls. No

inhalation or dermal studies of mortality in animals were identified for β-HCH.

No information on the causes or mechanisms of death in animals exposed to β-HCH was located,

although neurotoxicity preceded death in most instances. There appears to be substantial variability in

susceptibility to the lethal effects of β-HCH, as demonstrated by the chronic study by Thorpe and Walker

Because the deaths occurred after the end of 2 weeks, they were considered to occur as a result of intermediate-

duration exposure.

HEXACHLOROCYCLOHEXANE (HCH) 100

2. HEALTH EFFECTS

(1973), in which animals that survived the first 3 months did not have any reductions in subsequent

survival.

γ-HCH (Lindane). γ-HCH was once used in insecticide vaporizer and fumigator devices, resulting in

human inhalation and dermal exposure to unspecified levels. Occasional deaths associated with the use of

this product for several months or years have been reported, but it is not clear that γ-HCH was responsible

for the deaths (Loge 1965). Two cases of pulmonary edema resulting in fatalities were reported in

toddlers inhaling and ingesting unknown quantities of γ-HCH-containing pesticidal powder (McQueen et

al. 1968). Following an accidental chemical spill from storage tanks in India, seven deaths occurred in

the area, with the cause of death reported as asphyxia (Jain et al. 2022). Sampling near the spill revealed

γ-HCH in water and soil at levels that exceeded permissible concentrations. All deaths were in

individuals within 200 m of the site. Sixteen survivors exhibited symptoms including headache, nausea,

and breathlessness.

Case reports of deaths in humans, often in children or suicidal adults, following ingestion of γ-HCH in

tablets (doses unknown) intended for γ-HCH vaporizers have been reported (Storen 1955; Sunder Ram

Rao et al. 1988). A single acute, whole-body dermal application of 1% γ-HCH in lotion to a 2-month-old

infant for scabies treatment resulted in death (Davies et al. 1983). Autopsy identified pulmonary and

epicardial petechiae and a concentration in the brain of 110 ppb γ-HCH. The death of an elderly woman

was reported following a 6-hour dermal application of γ-HCH-containing lotion (approximately 40 mg

total γ-HCH) to the head for the treatment of scabies (Katsumata and Katsumata 2003). No data were

reported for blood or tissue levels of γ-HCH. A 66-year-old man died after being treated for scabies in a

hospital with a 1% γ-HCH lotion applied dermally from neck to toes (Sudakin 2007). Eight hours after

application, the man exhibited worsening of mental status and hypoxemia. Over the next 2 hours, his

neurological symptoms increased in severity to include seizure and myoclonic jerks, and were

accompanied by severe hypoxemia, tachycardia, diaphoresis, hypotension, and respiratory acidosis. The

man remained in intensive care and subsequently died after 50 days in the hospital. The autopsy

attributed the cause of death to hypoxic ischemic encephalopathy from γ-HCH poisoning. The dose of

γ-HCH was not estimated, and neither blood nor tissue levels of γ-HCH were measured during

hospitalization or at autopsy (Sudakin 2007).

In an acute animal study of rats exposed nose-only to γ-HCH aerosol for 4 hours, the LC

was

determined to be 1,560 mg/m

(Ullmann 1986b); the lowest concentration associated with lethality was

378 mg/m

. No rats exposed whole body to γ-HCH for 4 hours up to a concentration of 603 mg/m

died

HEXACHLOROCYCLOHEXANE (HCH) 101

2. HEALTH EFFECTS

throughout the 14-day observation period (Oldiges et al. 1980). In the beginning of a 14-week study,

12/45 female and 2/45 male mice that were exposed to 10 mg/m

of γ-HCH dust aerosol via whole body

(6 hours/day) died during the first week (Klonne and Kintigh 1988). In this study, the concentration was

decreased from 10 to 5 mg/m

after the first week; additional deaths occurred at 5 mg/m

(two males and

three females) and 1 mg/m

(one male and one female), but there were no deaths at 0.3 mg/m

. One

unexplained death in a control mouse was also reported (Klonne and Kintigh 1988).

Studies in laboratory animals have reported deaths after acute-duration oral administration of γ-HCH

doses ≥20 mg/kg/day (Chadwick et al. 1988; Fitzhugh et al. 1950; Gaines 1960; Hassoun and Stohs

1996a; Liu and Morgan 1986; Martinez et al. 1991; Matsuura et al. 2005; Thorpe and Walker 1973;

Tusell et al. 1988; Yuksel et al. 2009). In studies of rats administered a single dose of γ-HCH via gavage,

values of 88 mg/kg in males and 91 mg/kg in females were obtained (Gaines 1960). One of seven

male rats died following a single administration of γ-HCH at a dose of 60 mg/kg via gavage (Martinez et

al. 1991), while 2/18 rats died within the third day of exposure to doses of 20 mg/kg/day (Tusell et al.

1988). Acute exposure-duration studies in mice showed similar lethal doses in some strains. Pregnant

DBA/2J and C57BL/6J mice both exhibited mortality (14–25%) upon single gavage doses of 30 and

45 mg/kg, respectively, administered on gestation day (GD) 12 (Hassoun and Stohs 1996a). In another

study, no mortality was reported in nonpregnant adult female C57BL/6 mice; however, six of six DBA/2

mice died after 20 mg γ-HCH/kg was administered by daily gavage for up to 10 days (Liu and Morgan

1986).

In intermediate- and chronic-duration studies, the doses inducing lethality were similar to those seen after

acute-duration exposure. Two F0 female rats exposed to doses of 26.1 mg/kg/day in a 2-generation

reproductive toxicity study died, but the times of death were not reported (Matsuura et al. 2005). In F344

rats administered γ-HCH for up to 15 weeks, 2/12 animals died at 20 mg/kg/day and 7/12 died at

40 mg/kg/day (Chadwick et al. 1988). When groups of 10 Sprague-Dawley rats were administered 20 or

40 mg/kg/day γ-HCH by gavage for 30 days, one animal in each group died during week 3 (Yuksel et al.

2009). The age at death in Wistar rats was significantly decreased to 39.7 weeks in animals administered

60–70 mg/kg/day, compared to 58.3 weeks in control animals (Fitzhugh et al. 1950). In a 2-year study

with interim sacrifices, dietary administration of technical-grade γ-HCH at a dose of 32 mg/kg/day

resulted in significantly decreased survival when compared with controls (Amyes 1990).

Acute dermal exposure to γ-HCH resulted in death. Dermal LD

values in rats exposed to γ-HCH once

and observed for 10 days were 1,000 mg/kg in males and 900 mg/kg in females (Gaines 1960). In an

HEXACHLOROCYCLOHEXANE (HCH) 102

2. HEALTH EFFECTS

acute dermal study in which male and female rats were exposed to γ-HCH for 24 hours, mortality rates

across both sexes were 0, 20, 40, and 30% at 250, 600, 1,000, and 2,000 mg/kg, respectively (Ullmann

1986a). Weanling rabbits were more sensitive to γ-HCH treatment than young adults, as seen by

increased mortality rates accompanied by excitement and convulsions after a single whole-body treatment

with a 1% solution at a dose of 60 mg/kg γ-HCH (Hanig et al. 1976). Significant mortality (47%) was

seen in female rats, but not male rats, exposed dermally to γ-HCH at 400 mg/kg/day for 6 hours/day,

5 days/week, for 13 weeks (EPA 1988a). No studies regarding chronic dermal exposure to γ-HCH were

located.

Technical HCH or Unspecified Isomers of HCH. Joseph et al. (1992a) reported an LD

of 2,428 mg/kg

in male rats administered a single gavage dose of technical-grade HCH (72.8% α-HCH, 12.6% γ-HCH,

7.95% δ-HCH, 5% β-HCH). Technical-grade HCH administered to rats for 90 days resulted in increased

mortality: 6/12 males and 4/12 females exposed to 5 mg/kg/day died, and a 58% increase in mortality

(incidence not reported) was observed at 25 mg/kg/day (Dikshith et al. 1991b). When Wistar rats were

administered technical-HCH in the diet as part of a chronic study, age at death was significantly

decreased to 32.9 weeks in animals administered 64 mg/kg/day compared to 58.3 weeks in control

animals (Fitzhugh et al. 1950). Exposure to low levels (0.4 mg/kg/day) of technical-grade HCH in the

diet for 360 days resulted in deaths of 4/20 rats (Dikshith et al. 1991a).

Dikshith et al. (1978) reported that guinea pigs dermally exposed to 200 mg technical-grade HCH/kg died

within 5–12 days. Four of 20 rats died from dermal exposure to technical-grade HCH at 100 mg/kg/day

for 15–30 days (Dikshith et al. 1991c). Rabbits treated with 25 mg/kg/day technical-grade HCH for

30 days by skin painting on shaved dorsal, ventral, or thigh areas exhibited no deaths in the group

exposed by dorsal application, but two of eight rabbits died in the group exposed by ventral application,

and four of eight died in the group exposed by thigh application (Dikshith et al. 1989b).

2.3 BODY WEIGHT

Epidemiological Studies. Studies of body weight effects in humans include three studies of β-HCH;

these are summarized in Table 2-8. In a cohort of women residing in an agricultural area of California,

serum levels of β-HCH were associated with increased body mass index (BMI), waist circumference,

body fat percent, and obesity when measured over the 3 years after serum collection (Warner et al. 2018).

A cross-sectional study of surgical patients in Spain provided support for an association between β-HCH

(measured in serum or adipose tissue) and increased BMI (Arrebola et al. 2014). In another cross-

HEXACHLOROCYCLOHEXANE (HCH) 103

2. HEALTH EFFECTS

sectional study in adults from Seoul, South Korea, serum levels of β-HCH were associated with increased

BMI (Seo et al. 2022).

Table 2-8. Summary of Epidemiological Studies of β-Hexachlorocyclohexane

(β-HCH) Exposure and Body Weight Effects

Reference, study type, and

population

Biomarker

Concentration

Outcome evaluated

Result

Arrebola et al. 2014

Cross-sectional, 298 noncancer

surgical patients >16 years old,

Spain

Serum or

adipose

19.60±28.74 ng/g

lipid (mean)

BMI

↑

Warner et al. 2018

Cohort, 468 women >18 years old,

residing in agricultural area of

California, United States

Serum

>5.2 ng/g lipid

(median)

BMI

↑

Waist circumference

↑

Body fat %

↑

Obesity

↑

Seo et al. 2022

Cross-sectional, 880 adults, ages

20–80 years, South Korea

Serum

40.4 ng/g lipid

BMI

↑

BMI exhibited a quadratic association with β-HCH, increasing at low concentrations and then decreasing at higher

concentrations.

↑ = association with increase; BMI = body mass index

Data on body weight changes in animals exposed by inhalation or dermal contact were limited to γ-HCH.

α-HCH. Sumida et al. (2007) reported no body weight changes in male rats administered α-HCH via

gavage at 20 mg/kg/day for up to 28 days. In rats exposed for 24 weeks to 45 mg/kg/day in feed, terminal

body weight was decreased by 15% (Nagasaki et al. 1975); food intake was not reported. Significantly

decreased body weight gain in the absence of changes in food intake was also seen in rats treated with

60–70 mg/kg/day of α-HCH in the diet for 6 months (Fitzhugh et al. 1950). In studies of several mouse

strains given 90 mg/kg/day α-HCH in feed for 24 weeks, a significant (17%) decrease in terminal body

weight was observed in male C57BL/6 mice, but not in other strains (dd, DDY, ICR, DBA/2, or C3H/He)

or in females of any strain (Ito et al. 1973; Nagasaki et al. 1975). These authors conducted a similar

experiment in male hamsters given 45 mg/kg/day in feed for 24 weeks. Terminal body weight was 14%

lower than controls in the hamsters (Nagasaki et al. 1975).

β-HCH. Intermediate-duration oral studies of body weight effects after exposure to β-HCH exposure

showed effects in rats, but not in mice. Body weight decreases of at least 10% were observed in Wistar

HEXACHLOROCYCLOHEXANE (HCH) 104

2. HEALTH EFFECTS

rats administered dietary β-HCH at a dose of 22.5 mg/kg/day in males or 25 mg/kg/day in females for

13 weeks; however, at this dose, half of the animals were sacrificed moribund prior to study termination

(Van Velsen et al. 1986). No body weight effects were observed at doses up to 5 mg/kg/day in males or

females (Van Velsen et al. 1986). After 6 months of β-HCH administration in the diet, body weight gain

was decreased by 11% in female Wistar rats exposed to 9 mg/kg/day (Fitzhugh et al. 1950); body weight

data for the lower dose group were not reported. No effect on body weight was observed in mice

administered β-HCH at doses of 60 mg/kg/day for 30 days (Cornacoff et al. 1988) or 90 mg/kg/day for

24 weeks (Ito et al. 1973).

γ-HCH (Lindane). Limited information is available on body weight effects of γ-HCH in animals exposed

by inhalation. In Wistar rats exposed for 4 hours to 603 mg/m

γ-HCH, females lost weight for the first

post-exposure observation week. Neither mice nor rats exposed to γ-HCH aerosols at concentrations up

to 5 mg/m

for 6 hours each day (5 or 7 days/week) for 13–14 weeks exhibited any change in body weight

(Oldiges et al. 1983; Klonne and Kintigh 1988).

No effects on body weight were observed in rats administered acute-duration oral doses ranging from

8.8 to 15 mg/kg/day (Parmar et al. 2003; Sinha and Shukla 2003; Sumida et al. 2007) or in mice at doses

ranging from 5.9 to 40 mg/kg/day (Di Consiglio et al. 2009; Hong and Boorman 1993; Maranghi et al.

2007; Serrano et al. 1990; Sinha and Shukla 2003). One study of Wistar rat dams exposed to

≥8 mg/kg/day exhibited decreased body weight gain (25% less than controls) on GDs 6–20; decreased

food consumption was seen at the same dose (EPA 1999c). Body weights of pregnant mice administered

15–25 mg/kg/day γ-HCH via gavage during gestation were not affected (Maranghi et al. 2007; Traina et

al. 2003). In a 7-week study of beagle dogs given γ-HCH in the diet, Rivett et al. (1978) reported

suppression of body weight gain at 7 mg/kg/day; however, only two dogs per group were used in this

study.

In intermediate-duration studies, there were no effects on body weight in rats administered γ-HCH via

gavage at doses between 2.5 and 30 mg/kg/day for 15–28 days (Ahmed et al. 2008; Andrews and Gray

1990; Parmar et al. 2003; Sumida et al. 2007; Yang et al. 2014; Zhang et al. 2016) or up to

26.1 mg/kg/day for about 10 weeks in a 2-generation reproductive toxicity study (Matsuura et al. 2005).

In another 2-generation reproductive toxicity study (EPA 1991a), body weight gain decreased, without

changes in food intake, in high-dose (13.1 mg/kg/day) F0 parental females during gestation. Mice

exposed to γ-HCH in feed for 24 weeks exhibited no body weight changes at doses up to 90 mg/kg/day

(Ito et al. 1973).

HEXACHLOROCYCLOHEXANE (HCH) 105

2. HEALTH EFFECTS

Significantly decreased body weight gain was seen after 6 months in rats treated with 120–140 mg/kg/day

γ-HCH in feed as part of a chronic-duration study, but this dose was also associated with significantly

reduced survival (Fitzhugh et al. 1950). Beagle dogs given doses up to 2.92 mg/kg/day γ-HCH in feed

displayed no changes in body weight over the 102-week exposure duration (Rivett et al. 1978).

Technical HCH or Unspecified Isomers of HCH. Wistar rats administered technical-grade HCH via

gavage at doses up to 20 mg/kg/day for 7 days exhibited no effect on body weight (Samanta et al. 1999).

Swiss albino mice had significantly decreased body weight after administration of a single dose of

100 mg/kg technical-grade HCH via gavage in oil (Dikshith et al. 1990). Significantly decreased body

weight gain has been observed in rats treated orally with 3 or 20 mg/kg/day technical-grade HCH for up

to 6 months (Gautam et al. 1989; Nagaraja and Desiraju 1994; Roy Chowdhury and Gautam 1990). Rats

administered technical-grade HCH via gavage at a dose of 50 mg/kg/day for 30 days exhibited a 21%

body weight loss (Khanna et al. 1990). In an 80-week study, Swiss mice administered technical-grade

HCH at 17 mg/kg/day exhibited no changes in body weight or body weight gain, despite decreased food

consumption (Kashyap et al. 1979). After 6 months of technical-grade HCH administration, no effect on

body weight was observed at 7–9 mg/kg/day, but body weight was decreased by 16% in female rats

exposed to 70 mg/kg/day and by 26% in males exposed to 60 mg/kg/day (Fitzhugh et al. 1950). No effect

on body weight was observed in mice chronically administered technical-grade HCH at 10 mg/kg/day by

gavage or 17 mg/kg/day in the diet (Kashyap et al. 1979).

2.4 RESPIRATORY

α-HCH. No studies were located regarding respiratory effects in humans after exposure to α-HCH. In

rats exposed via diet to α-HCH doses up to 70 mg/kg/day for an average of 9 months or up to

9 mg/kg/day for 2 years, there were no histopathology findings in the lungs (Fitzhugh et al. 1950).

β-HCH. In a cross-sectional study in southern Ghana, vegetable farmers who reported pesticide use

showed a significant, positive association between serum levels of β-HCH and respiratory symptoms of

cough, phlegm production, and wheezing (Quansah et al. 2016). In another cross-sectional study in

Ghana, children (up to 5 years old) of vegetable farmers who had accompanied their parents to the farm

showed an association between urine concentrations of β-HCH and lower (but not upper) respiratory tract

infections (Akyeampong et al. 2022). Rats given doses up to 70 mg/kg/day for up to 10 weeks or up to

9 mg/kg/day for 2 years exhibited no microscopic pathology in the lungs (Fitzhugh et al. 1950).

HEXACHLOROCYCLOHEXANE (HCH) 106

2. HEALTH EFFECTS

γ-HCH (Lindane). In a cross-sectional study of vegetable farmers in southern Ghana who used

pesticides, no association was observed between serum levels of γ-HCH and respiratory symptoms

(cough, phlegm production, and wheezing) (Quansah et al. 2016). In humans, mucous membrane

irritation of the nose and throat was observed after acute exposure to the HCH products dispensed by an

overheated γ-HCH vaporizer (Conley 1952). Exposure levels were not reported, and dermal exposure

may also have occurred, although the observed irritation was probably due to direct action upon the

mucous membranes. An acute dermal poisoning of a 2-month-old infant exposed to a whole-body

application of 1% γ-HCH lotion resulted in death. The autopsy revealed pulmonary petechiae (Davies et

al. 1983).

No respiratory effects and no histopathology changes in the nasal cavities or lungs were observed in rats

exposed to γ-HCH aerosol (up to 5 mg/m

) 6 hours/day for 90 days (Oldiges et al. 1983) or in mice

similarly exposed for 14 weeks (Klonne and Kintigh 1988). Mononuclear cell infiltrates in peribronchial

and perivascular regions of the lung were observed in male mice administered 0.25 mg/kg/day γ-HCH by

gavage in groundnut oil for 61 days (Tewari et al. 2017). Bronchoalveolar lavage (BAL) from the treated

mice contained increased total leukocyte counts and neutrophil percentages.

In rats, dietary exposure to γ-HCH at doses up to 140 mg/kg/day for ~10 months or 30 mg/kg/day for

2 years resulted in histopathology changes in the lungs (Fitzhugh et al. 1950). Slight dyspnea was

reported in rats exposed dermally for 24 hours to 1,000 or 2,000 mg/kg γ-HCH on a shaved patch of

dorsal skin (Ullmann 1986a). The dyspnea was severe in one female administered the high dose. Rapid

respiration or wheezing was noted in rats exposed dermally to ≥10 mg /kg/day γ-HCH for 13 weeks (EPA

1988a).

δ-HCH. No association between serum concentrations of δ-HCH and respiratory symptoms was

observed in a cross-sectional study of vegetable farmers using pesticides in southern Ghana (Quansah et

al. 2016). In another cross-sectional study in Ghana, children of vegetable farmers who had accompanied

their parents to the farm showed a positive association between urine concentrations of δ-HCH and acute

lower respiratory tract infections in children below the age of 5 years (Akyeampong et al. 2022). No

association was observed with upper respiratory tract infections.

HEXACHLOROCYCLOHEXANE (HCH) 107

2. HEALTH EFFECTS

Technical HCH or Unspecified Isomers of HCH. Neither intermediate- nor chronic-duration dietary

exposure to technical HCH resulted in lung histopathology changes in rats given doses up to

70 mg/kg/day for 6 months or 9 mg/kg/day for 2 years (Fitzhugh et al. 1950).

2.5 CARDIOVASCULAR

Epidemiological Studies. Epidemiological studies of associations between cardiovascular effects in

humans and biomarkers of exposure to β-HCH have been conducted. Table 2-9 provides a summary of

the epidemiological data pertaining to cardiovascular effects and exposure to β-HCH in humans.

Arrebola et al. (2015a) observed an association between serum β-HCH concentrations and incident

hypertension in a cohort of 297 surgical patients followed for 10 years. A positive association between

serum β-HCH concentrations and hypertension was seen among surgical patients with a BMI >26.3,

whereas no association was observed in those with a BMI <26.3 (Arrebola et al. 2015a). In cross-

sectional studies, no association was reported between blood β-HCH concentrations and hypertension in a

study of 1,615 Inuit adults in Greenland (Valera et al. 2013b), while an inverse association with

hypertension was reported in a smaller study of Inuit adults in Quebec (Valera et al. 2013a). No

association with peripheral artery disease was observed in a cross-sectional study of U.S. adult

participants in the National Health and Nutrition Examination Survey (NHANES) (1999–2004) (Min et

al. 2011). Epidemiological studies of cardiovascular effects and exposure to other HCH isomers were not

located, but there are case reports of these effects in humans accidentally or intentionally exposed to

γ-HCH.

Table 2-9. Summary of Epidemiological Studies of β-Hexachlorocyclohexane

Exposure and Cardiovascular Effects

Reference, study type, and

population

Outcome

evaluated

Biomarker

Mean concentration

(unless otherwise noted)

Result

Arrebola et al. 2015a

Cohort, 297 noncancer surgical

patients >16 years old, Spain,

follow-up 10 years

Hypertension

Serum

11.2 ng/g lipid (median) (BMI

>26.3 kg/m

)

↑

6.6 (BMI <26.3kg/m

)

↔

Valera et al. 2013a

Cross-sectional, 315 Inuit

≥18 years, Quebec, Canada

Hypertension

Plasma

0.13 μg/L lipid (GM)

↓

Valera et al. 2013b

Cross-sectional, 1,614 Inuit aged

≥18 years, Greenland

Hypertension

Plasma

27.0 μg/kg lipid (GM)

↔

HEXACHLOROCYCLOHEXANE (HCH) 108

2. HEALTH EFFECTS

Table 2-9. Summary of Epidemiological Studies of β-Hexachlorocyclohexane

Exposure and Cardiovascular Effects

Reference, study type, and

population

Outcome

evaluated

Biomarker

Mean concentration

(unless otherwise noted)

Result

Min et al. 2011

Cross-sectional, 2,032 adults

>40 years old, NHANES (1999–

2004)

PAD

Serum

15.37 ng/g lipid (obese with

PAD)

10.05 (non-obese with PAD)

10.90 (obese without PAD)

7.92 (non-obese without PAD)

↔

↑ = association with increase; ↓ = association with decrease (inverse association); ↔ = no association;

GM = geometric mean; NHANES = National Health and Nutrition Examination Survey; PAD = peripheral artery

disease

Data regarding cardiovascular effects in animals are limited to the γ-HCH isoform.

α-HCH. No histopathology changes were noted in the hearts of rats given α-HCH via the diet at doses up

to 70 mg/kg/day for ~9 months or up to 9 mg/kg/day for 2 years (Fitzhugh et al. 1950).

β-HCH. There were no microscopic lesions in the heart when rats were exposed by dietary

administration to β-HCH doses up to 70 mg/kg/day for up to 10 weeks or up to 9 mg/kg/day for 2 years

(Fitzhugh et al. 1950).

γ-HCH (Lindane). Autopsy findings in a 2-month-old infant who expired after whole-body application

of 1% γ-HCH lotion were minimal but revealed epicardial petechiae (Davies et al. 1983). In a suicide

attempt, a 56-year-old man intentionally ingested approximately 12 ounces of an insecticide containing

20% γ-HCH (Wiles et al. 2015). Cardiac symptoms of premature atrial and ventricular contractions, and

atrial fibrillation after 3–5 days were observed. The man died on day 12 by committing suicide by means

unrelated to γ-HCH, and no cardiac abnormalities were noted at autopsy.

There were no treatment-related changes to cardiac histopathology findings in rats or mice exposed by

inhalation to γ-HCH concentrations up to 5 mg/m

for 13–14 weeks (Klonne and Kintigh 1988; Oldiges et

al. 1983). Evidence for cardiac effects comes from studies of animals exposed orally. Increased serum

levels of lactate dehydrogenase (LDH) and creatine phosphokinase and cardiac histopathological changes

including separated muscle fibers and inflammatory cells were observed in male rats administered 100

mg/kg/day γ-HCH by gavage in olive oil for 30 days (Vijaya Padma et al. 2013). Rats receiving gavage

doses of 3 mg/kg/day γ-HCH for 6 weeks exhibited tachycardia, increased blood pressure and plasma

calcium levels, an increase in myocardial calcium influx, and decreased calcium-potassium-ATPase

HEXACHLOROCYCLOHEXANE (HCH) 109

2. HEALTH EFFECTS

activity. Electrocardiographic changes included increased ST segment and T-wave amplitude and

reduced R-R interval and P-wave (Anand et al. 1995). Rats exposed to γ-HCH in utero exhibited

alterations in cardiac electrophysiology and histopathology; see Section 2.17 for details. Fitzhugh et al.

(1950) reported no histopathology findings in the hearts of rats given γ-HCH in feed at doses up to

140 mg/kg/day for 10 months or 30 mg/kg/day for 2 years.

Mechanisms. Oxidative stress may contribute to the cardiovascular effects of γ-HCH. Lipid peroxidation

was increased and antioxidant enzyme activities (superoxide dismutase, catalase, glutathione peroxidase,

and glutathione) were reduced in cardiac tissue from male rats treated with 8.8 mg/kg/day γ-HCH via

gavage for 3 weeks (Kamal El-Dein et al. 2016). Serum lipid and creatine phosphokinase levels were

also increased at this dose. Pre-treatment with the antioxidant α-lipoic acid attenuated the γ-HCH-

induced effects on serum lipids, CPK, lipid peroxidation and antioxidant enzyme activities in the heart.

Technical HCH or Unspecified Isomers of HCH. Kashyap (1986) reported electrocardiogram (ECG)

abnormalities in 15% of 45 factory workers involved in the production of technical-grade HCH; exposure

concentrations were not reported, and dermal exposure may have occurred. Technical HCH administered

to rats in feed did not induce cardiac histopathology changes at doses up to 70 mg/kg/day for 6 months or

9 mg/kg/day for 2 years (Fitzhugh et al. 1950).

2.6 GASTROINTESTINAL

Data on gastrointestinal effects in humans were limited to γ-HCH. No studies were located regarding

gastrointestinal effects in animals following dermal exposure to any of the HCH isomers.

α-HCH. There were no microscopic gastrointestinal lesions in rats given α-HCH via the diet at doses up

to 70 mg/kg/day for ~9 months or up to 9 mg/kg/day for 2 years (Fitzhugh et al. 1950).

β-HCH. Dietary administration of β-HCH doses up to 70 mg/kg/day for up to 10 weeks or up to

9 mg/kg/day for 2 years did not result in histopathology changes in the gastrointestinal tracts of rats

(Fitzhugh et al. 1950).

γ-HCH (Lindane) Lindane exposures reported to the Texas poison control network between 1998 and

2002 were reviewed by Forrester et al. (2004). Ingestion was the primary exposure route (79%), and

reported symptoms included vomiting, nausea, and abdominal pain (doses were not specified). Vomiting

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and diarrhea occurred in a child (Ramchander et al. 1991) and a woman (Hall and Hall 1999) who were

exposed to 1% γ-HCH applied to the skin to treat rash or scabies.

Rats exposed to 5 mg/m

γ-HCH aerosol for 6 hours/day, 7 days/week exhibited persistent diarrhea

beginning after 2 weeks of exposure and continuing for nearly 3 weeks; exposure to 1 mg/m

did not

induce diarrhea (Oldiges et al. 1983). No gross necropsy or histopathology changes were observed in the

gastrointestinal tracts of these rats (Oldiges et al. 1983). In mice exposed to concentrations up to

5 mg/mg

for 14 weeks, no gastrointestinal effects were noted, and there were no gross or microscopic

changes to the gastrointestinal tract at necropsy (Klonne and Kintigh 1988). Microscopic examination of

the stomach, small intestine, and colon showed no treatment-related changes in rats given γ-HCH via feed

for 10 months at up to 140 mg/kg/day or 2 years at up to 30 mg/kg/day (Fitzhugh et al. 1950).

Technical HCH or Unspecified Isomers of HCH. Fitzhugh et al. (1950) did not observe any effects of

treatment on the gastrointestinal tract of rats given technical HCH via diet for 6 months (up to

70 mg/kg/day) or 2 years (up to 9 mg/kg/day).

2.7 HEMATOLOGICAL

Epidemiological Studies. In a cross-sectional study of adolescents and adults living near a former HCH

production facility in Brazil, an increase in eosinophilia was associated with serum β-HCH levels (Freire

et al. 2015). The results of a case-control study showed a positive association between serum levels of

α-HCH and childhood aplastic anemia, but no association with serum β- or γ-HCH (Ahamed et al. 2006).

α-HCH. Dietary administration of α-HCH doses up to 70 mg/kg/day for up to 9 months or up to

9 mg/kg/day for 2 years did not result in histopathology changes in the spleen or bone marrow of rats

(Fitzhugh et al. 1950).

β-HCH. Exposure to β-HCH at doses of 22.5–25 mg/kg/day in the diet for 13 weeks in rats resulted in

statistically significant decreases in numbers of red blood cells and white blood cells, as well as reduced

hemoglobin and packed cell volume values (Van Velsen et al. 1986). At this dose, 50% of the exposed

animals were sacrificed moribund. Extramedullary hematopoiesis was observed in males and females

surviving for 13 weeks at 23-26 mg/kg/day, but not in the early decedents. There were no histopathology

findings in the spleen or bone marrow of rats given β-HCH in the diet for up to 10 weeks at 70 mg/kg/day

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or 2 years at 9 mg/kg/day (Fitzhugh et al. 1950). No other data on hematological effects in animals

exposed to β-HCH were located.

γ-HCH (Lindane). Hematological effects have been reported in case reports of humans following

exposure to γ-HCH. Hypochromic anemia was reported in a 2.5-year-old boy who was exposed to

γ-HCH in a home in which a pesticide vaporizer was operated. Air γ-HCH concentrations measured in

the basement and living room of the house were 2.4–5.5 μg/m

; however, the actual concentration the

child was exposed to, and the duration of exposure were not determined (Morgan et al. 1980). Aplastic

anemia was reported in a boy exposed to γ-HCH used as an insecticide in his home and in a man exposed

at work (Rugman and Cosstick 1990). In both cases, the anemia was reversible and was not present in

other family members. The levels and routes of exposure are not known, although they are presumed to

be inhalation and dermal. Aplastic anemia was also documented in a man who applied γ-HCH to his skin

for 3 weeks for treatment of scabies (Rauch et al. 1990).

A woman who committed suicide by drinking γ-HCH was found to have disseminated intravascular

coagulation (a condition where abnormal blood clotting occurs in blood vessels throughout the body)

during the period when serum γ-HCH levels were elevated (Sunder Ram Rao et al. 1988). Reduced

hemoglobin and hematocrit values and a nearly complete absence of red blood cell precursors in bone

marrow were reported in a 2-year-old boy exposed to a family dog that was dipped regularly in mange

treatment containing 12% γ-HCH (Vodopick 1975).

In an inhalation study of rats exposed to 5 mg/m

γ-HCH aerosol for 90 days, bone marrow myelogram

changes were observed, including increased reticulocytes in males and females, increased stem cells and

myeloblasts in males, and decreased lymphocytes in females (Oldiges et al. 1983). No changes to blood

parameters were noted in this study (Oldiges et al. 1983). Mice exposed to concentrations of γ-HCH up

to 5 mg/m

for 14 weeks exhibited no hematological changes or effects on bone marrow smears (Klonne

and Kintigh 1988).

Hong and Boorman (1993) reported significant suppression in bone marrow cellularity, erythrocyte

precursors, and granulocyte-macrophage progenitor cells, and residual progenitor cell damage in male

B6C3F

mice given 20 or 40 mg γ-HCH/kg/day by gavage in corn oil for 3 days. In a similar experiment,

dose-dependent decreases in bone marrow cellularity, granulocyte-macrophage progenitor cells, and

pluripotent bone marrow stem cells were noted following 10 days of exposure to 10 or 20 mg

γ-HCH/kg/day (Hong and Boorman 1993). No effects on blood leukocytes were reported in male mice

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administered 0.25 mg/kg/day γ-HCH by gavage in oil for 61 days (Tewari et al. 2017). No hematological

effects were noted in rats exposed to 10 mg γ-HCH/kg/day in the diet for 12 weeks (Suter 1983) or in

beagle dogs exposed to 2.92 mg/kg/day γ-HCH in the diet for 104 weeks (Rivett et al. 1978). No

histopathology changes were observed in the spleen or bone marrow of rats exposed to γ-HCH in feed for

up to 10 months at 140 mg/kg/day or up to 2 years at 30 mg/kg/day (Fitzhugh et al. 1950).

Technical HCH or Unspecified Isomers of HCH. The results of a case-control study of childhood

aplastic anemia indicated no association between this disease and serum levels of total-HCH (including

α-, β-, γ-, and δ-HCH) (Ahamed et al. 2006). Hematological abnormalities, including alterations in

polymorphonuclear leukocyte count, lymphocyte count, reticulocyte count, and prothrombin time have

been reported following chronic human occupational exposure to γ-HCH (Brassow et al. 1981). Exposure

concentrations were not specified in these studies and concomitant dermal exposure probably occurred.

Granulocytopenia, aplastic anemia, and pancytopenia have been reported in several case reports of

individuals following exposure to γ-HCH and other pesticides such as DDT in the home, during the

handling of the pesticide, or from a nearby formulating plant (Danopoulos et al. 1953; Friberg and

Martensson 1953; Gewin 1939; Loge 1965; Mendeloff and Smith 1955). Exposure concentrations were

not reported, dermal exposure was likely, and in many cases, there was concomitant exposure to other

pesticides. Excessive dermal exposure to HCH was reported to result in aplastic anemia and bone

marrow hyperplasia in a woman who bathed her dog once a week for 2 years with a preparation that

reportedly contained 2% HCH (Woodliff et al. 1966).

No hematological effects were seen in rats following oral exposure to 60 mg/kg/day technical-grade HCH

for 30 days (Dikshith et al. 1989a). In a study evaluating the influence of vitamin A on the toxicity of

technical-grade HCH, significant decreases in total white blood cell counts and clotting time were

reported in rats fed vitamin A-deficient diets containing technical-grade HCH at a dose level of

90 mg/kg/day for 7 weeks (Joseph et al. 1992c). In a similar study, rats fed a vitamin A-supplemented

diet containing the same dose level of technical-grade HCH for 7 weeks exhibited a significant reduction

in total white blood cell count, but not red blood cell count (Joseph et al. 1992c). No treatment-related

histopathology changes were seen in the spleen or bone marrow of rats after 6 months of dietary exposure

to technical HCH at 70 mg/kg/day or 2 years of dietary exposure at 9 mg/kg/day (Fitzhugh et al. 1950).

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2.8 MUSCULOSKELETAL

Data regarding musculoskeletal effects in humans were limited to oral exposure to γ-HCH (see γ-HCH

subsection below).

α-HCH. There were no microscopic lesions in the leg muscles or bones of rats given α-HCH via the diet

at doses up to 70 mg/kg/day for ~9 months or up to 9 mg/kg/day for 2 years (Fitzhugh et al. 1950).

β-HCH. Dietary administration of β-HCH at doses up to 70 mg/kg/day for up to 10 weeks or up to

9 mg/kg/day for 2 years did not induce histopathology changes in the leg muscles or bones of rats

(Fitzhugh et al. 1950).

γ-HCH (Lindane) Ingestion of a single dose of approximately 15–30 mL γ-HCH powder (was associated

with seizures and limb muscle weakness and necrosis in an adult man (Munk and Nantel 1977); a muscle

biopsy conducted 15 days after ingestion showed no evidence of denervation or neuropathy. Widespread

striatal muscle necrosis was seen in a woman who died 11 days after intentionally ingesting 8 ounces of a

20% γ-HCH solution (Sunder Ram Rao et al. 1988). A suicidal 21-year-old male developed

rhabdomyolysis as indicated by muscle pain, muscle tenderness, proteinuria, myoglobinuria, elevated

serum levels of aspartate aminotransferase (AST), potassium, creatinine, and creatinine protein kinase

(CPK) 1–3 days following ingestion of a single unknown dose of γ-HCH (Shah et al. 2013). The man

recovered after 3 weeks of clinical care.

Microscopic examination of skeletal muscle in mice and rats (as well as femur in mice) exposed by

inhalation to concentrations up to 5 mg/m

for 13–14 weeks did not show any treatment-related effects

(Klonne and Kintigh 1988; Oldiges et al. 1983). Decreased medullary area in the femur bone was found

in young rats treated with 20 mg/kg/day of γ-HCH by gavage for 10 weeks (Andrews and Gray 1990).

Fitzhugh et al. (1950) reported no treatment-related histopathology changes in the leg muscles or bones of

rats exposed via diet for 10 months at doses up to 140 mg/kg/day or for 2 years at 30 mg/kg/day.

Technical HCH or Unspecified Isomers of HCH. No microscopic lesions were observed in the leg

muscles or bones of rats given dietary technical HCH doses up to 70 mg/kg/day for 6 months or

9 mg/kg/day for 2 years (Fitzhugh et al. 1950).

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2.9 HEPATIC

Epidemiological Studies. Human epidemiological data pertaining to HCH exposure and hepatic effects

(see Table 2-10) are limited to two cross-sectional studies of β-HCH (Arrebola et al. 2014; Freire et al.

2015). No association between serum lipids and serum or adipose concentrations of β-HCH was

observed in a study of 298 non-surgical cancer patients in Spain (Arrebola et al. 2014). In a study of

adolescents and adults residing near a former HCH production facility in Brazil, serum β-HCH was

associated with increased risk of elevated total and indirect serum bilirubin in females, but not in males

(Freire et al. 2015). There were no associations between serum β-HCH and risk of elevated direct serum

bilirubin or serum enzymes (Freire et al. 2015).

Table 2-10. Summary of Epidemiological Studies of β-Hexachlorocyclohexane

Exposure and Hepatic Effects

Reference, study type, and

population

Outcome evaluated

Biomarker

Mean

concentration

Result

Arrebola et al. 2014

Cross-sectional, 298 noncancer

surgical patients >16 years old,

Spain

Measures of serum lipids

(total triglycerides, HDL,

LDL, and total cholesterol)

Serum or

adipose

19.60±28.74 ng/g

lipid (biomarker

not reported)

↔

Freire et al. 2015

Cross-sectional, 339 males and

375 females, age >14 years

residing near former HCH

production facility, Brazil

Elevated total and

indirect serum bilirubin

Serum

Males: 3.72 µg/g

lipid

Females:

3.09 µg/g lipid

M: ↔

F: ↑

Elevated direct serum

bilirubin

M: ↔

F: ↔

Elevated serum AST, ALT,

GGT

M: ↔

F: ↔

↑ = association with increase; ↔ = no association; ALT = alanine aminotransferase; AST = aspartate

aminotransferase; GGT = γ-glutamyl transferase; HCH = hexachlorocyclohexane; HDL = high-density lipoprotein;

LDL = low density lipoprotein

α-HCH. Hepatic effects have been observed in rats, mice, and hamsters after intermediate- and chronic-

duration oral exposures to α-HCH. Increases in absolute and relative liver weight, coupled with

hepatocellular hypertrophy and/or hyperplasia, have been observed in F344 rats at doses of at least

20 mg/kg/day for 28 days (Sumida et al. 2007) and in Wistar rats at doses of 45 mg/kg/day for 24 weeks

(Nagasaki et al. 1975) or 35 mg/kg/day for 48 weeks (Ito et al. 1975). Rats receiving 60–70 mg/kg/day

α-HCH in the diet as part of a chronic study died early (mean survival 35.9 weeks compared with

58.3 weeks in controls); at necropsy, these animals exhibited 2-fold increases in liver weight and

histopathology changes of moderate severity, including focal necrosis and fatty degeneration (Fitzhugh et

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al. 1950). Hypertrophied liver cells were reported in mice fed 18 mg/kg/day α-HCH for 24 weeks (Ito et

al. 1973). More severe effects, including hepatomegaly, bile duct proliferation, oval cells, nodular

hyperplasia, megalocytosis, and a doubling of liver weight, were observed in several strains of mice

(DDY, ICR, DBA/2, C57BL/6, C3H/He, and HPBC57BL) given feed containing 90 mg/kg/day for at

least 21 weeks (Nagasaki et al. 1975; Tryphonas and Iverson 1983). This dose (90 mg/kg/day) yielded a

significant increase in hepatocellular carcinomas in all but the C57BL/6 strain of mouse (Nagasaki et al.

1975; Tryphonas and Iverson 1983). Nagasaki et al. (1975) also conducted an experiment using male

Syrian hamsters exposed to α-HCH in the diet for 24 weeks. In hamsters, a 38% increase in relative liver

weight, with increased liver cell hypertrophy, was observed at 45 mg/kg/day.

Chronic (107 weeks) exposure to α-HCH in feed resulted in dose-related increases in the severity of liver

histopathology changes in rats (Fitzhugh et al. 1950). Very slight to slight microscopic damage in the

liver, along with ≥32% increase in relative liver weight, was seen at ≥4 mg/kg/day (Fitzhugh et al. 1950).

The microscopic changes were described as “characteristic of certain chlorinated cyclic compounds”

without further detail. Rats at the highest dose in this study (60–70 mg/kg/day) exhibited reduced

survival (mean <1 year); these animals exhibited more severe liver effects, as described above with the

intermediate-duration studies.

Both rats and mice exposed to α-HCH have developed liver cancers. Hepatocellular carcinomas were

reported in rats administered 70 mg/kg/day in the diet for 48 or 72 weeks (Ito et al. 1975), and liver

cancers were observed in mice given 18–90 mg α-HCH/kg/day for 16–36 weeks (Hanada et al. 1973; Ito

et al. 1973, 1976; Nagasaki et al. 1975; Tryphonas and Iverson 1983; Tsukada et al. 1979) (see

Section 2.19). Hamsters exposed to 45 mg/kg/day for 24 weeks did not develop liver tumors (Nagasaki et

al. 1975).

Mechanisms: Little information is available on potential mechanisms of α-HCH-induced hepatotoxicity

but is possible that oxidative stress and/or mitotic disturbances may be involved. Administration of

1.8 mg/kg/day α-HCH in the diet to rats for 15 or 30 days resulted in increases in lipid peroxidation and

microsomal superoxide production in the liver (Barros et al. 1991). In male Donryu rats, a 3-week dietary

exposure to α-HCH resulted in mitotic disturbances including an increased mitotic rate and an increased

frequency of polyploid hepatic cells (Hitachi et al. 1975).

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β-HCH. Hepatic effects have been observed in intermediate-and chronic-duration studies of β-HCH in

rats and mice exposed via the diet. Moderate to marked liver damage, including fatty degeneration and

focal necrosis, was reported in rats that died prematurely (within 10 weeks of study initiation) after

dietary exposure to doses of 60–70 mg/kg/day (Fitzhugh et al. 1950). In a comprehensive 13-week study

of rats (Van Velsen et al. 1986), dose-related increases in hepatic effects were seen at all doses

(≥0.18 mg/kg/day) in males. At 0.18 mg/kg/day, the effects consisted of hyalinization of centrilobular

cells; at ≥4.5 mg/kg/day, increased mitoses in females, periportal fat accumulation in both sexes, and

isolated instances of focal necrosis in males were observed. Relative liver weights were increased by

10% or more at 1.0 mg/kg/day in females and 4.5 mg/kg/day in males (Van Velsen et al. 1986). At the

highest dose in this study (22.5–25 mg/kg/day), liver weights were doubled; at this dose, 50% of the

animals were sacrificed moribund before the end of the study (Van Velsen et al. 1986). Liver cell

hypertrophy was reported in rats fed 35 mg/kg/day in the diet for 48 weeks or 70 mg/kg/day for 24 weeks

(Ito et al. 1975). In mice, exposure for 24 weeks to 18 mg/kg/day in the diet resulted in an 18% increase

in liver weight, and liver cell hypertrophy at higher doses (≥45 mg/kg/day) (Ito et al. 1973). Mice

exposed to 50–60 mg/kg/day in the diet for 32 weeks exhibited hepatic foci of degeneration (Hanada et al.

1973).

Chronic dietary exposure of rats to lower doses of β-HCH resulted in increased liver weight and dose-

related histopathology changes in the liver (Fitzhugh et al. 1950). At 0.7–0.9 mg/kg/day, a 34% increase

in liver weight and slight microscopic changes described as “characteristic of certain chlorinated cyclic

compounds” were observed.

Liver tumors were not reported in mice exposed to β-HCH for 24–32 weeks (Hanada et al. 1973; Ito et al.

1973) or in rats exposed for 24–48 weeks (Ito et al. 1975); however, Thorpe and Walker (1973) reported

liver cancer in mice fed 34 mg/kg/day for 26 months.

γ-HCH (Lindane). Two case reports of intentional ingestion of γ-HCH have documented increases in

serum liver enzymes; neither report provided an estimate of the associated dose of γ-HCH. A 30-year-old

male farmer from rural India ingested a single dose of approximately 50 mL of 2% γ-HCH solution in a

suicide attempt (Paul et al. 2013). Six hours after the ingestion, the man went to the emergency

department where initial examination and laboratory tests were normal. Nausea was noted on the second

day, and abdominal tenderness and increased serum levels of bilirubin, AST, and alanine

aminotransferase (ALT) were observed on day 5. Treatment with hemodialysis for acute kidney injury

spontaneously reduced the hepatic enzymes and the man recovered after 3 weeks. A 56-year-old man

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ingested approximately 12 ounces of an insecticide containing 20% γ-HCH intentionally in a suicide

attempt (Wiles et al. 2015). Hepatic enzymes (AST, ALT, alkaline phosphatase [ALP], and γ-glutamyl

transferase [GGT]) were increased after 3 days. The man died on day 12 after committing suicide by

other means; at autopsy, no gross or microscopic abnormalities were noted.

Rats exposed to γ-HCH aerosol (5 mg/m

for 6 hours/day) exhibited increased hepatic cytochrome P450

concentration after 90 consecutive days, but this level returned to control values after a 4-week recovery

period (Oldiges et al. 1983). Statistically significant, but modest, increases in absolute and relative liver

weights (up to 12%) were observed at this exposure concentration, but there were no concomitant effects

of treatment on serum chemistry or liver histopathology in the rats (Oldiges et al. 1983). Mice exposed to

the same concentration 5 days/week for 14 weeks exhibited no changes in clinical chemistry, liver

weights, or liver histology (Klonne and Kintigh 1988).

Hepatic effects have been documented in rats and mice exposed to γ-HCH via oral administration for

acute, intermediate, and chronic durations. At lower doses, effects include increased serum enzymes,

increased liver weight, and hepatocellular hypertrophy. Higher doses and/or longer exposure durations

result in liver effects of increasing severity, including vacuolar degeneration, necrosis, and congestion.

Acute-duration oral studies in rats show increases in liver weight as well as histopathology changes in

animals exposed to γ-HCH. In male Wistar rats, a single gavage dose of 60 mg/kg/day resulted in marked

centrilobular hepatic necrosis (Singh and Sharma 2011), and fatty degeneration, vacuolation, and necrosis

were observed after gavage doses of 5 mg/kg/day for 3 days (Hfaiedh et al. 2012). Ultrastructural

changes observed in the liver of Sprague-Dawley rats (sex not specified) after 2 days of exposure to

30 mg/kg/day in feed were reduced number of cells per field; increased cell, nucleus, and nucleolus size;

and slight cellular disorganization (Ali and Shakoori 1998). Although no histopathological examinations

were performed, no significant increase in liver weight was noted in Sprague-Dawley rats exposed to

10 mg γ-HCH/kg/day for a minimum of 4 days (Joy et al. 1982). A significant increase (15% relative to

controls) in absolute, but not relative, liver weight was observed in rats exposed to 15 mg γ-HCH/kg/day

for 5 days (Parmar et al. 2003). A significant, but modest, increase (6% relative to controls) in relative

liver weight was observed in a small group of male F344 rats given 10 mg/kg/day γ-HCH by gavage for

7 days, but not in a group similarly exposed for 14 days (Sumida et al. 2007). Histopathology evaluations

of these animal were not reported.

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Increases in serum enzymes indicative of hepatotoxicity have been reported in rats exposed once to

12 mg/kg/day (Attia et al. 2011) or for 3 days to 5 mg/kg/day (Hfaiedh et al. 2012). Male Wistar rats fed

13.5 mg γ-HCH/kg/day in their diet for 12 days exhibited decreased activities of liver enzymes (malic

enzyme, glucose-6-phosphate dehydrogenase, phosphogluconate dehydrogenase, citrate cleavage enzyme,

and fatty acid synthase) and increased levels of serum triglycerides (Boll et al. 1995). Significantly

increased liver microsomal 7-ethoxycoumarin-O-dealkylase activity was found in Osborne-Mendel rats

exposed to 11.2 mg/kg/day γ-HCH and in CF1 and B6C3F1 strain mice exposed to 23.6 and

50.5 mg/kg/day in the diet for 3 days (Oesch et al. 1982).

The most common histopathology finding in the livers of rats and mice exposed to oral doses of γ-HCH

for intermediate durations is hepatocellular hypertrophy. A dose-dependent increased incidence of liver

centrilobular hypertrophy was reported in Wistar rats dosed with ≥0.4 mg γ-HCH/kg/day in the diet for

12 weeks (Suter 1983). In multigeneration reproductive toxicity studies in rats, hepatocellular

hypertrophy reportedly occurred at increased incidence in F0 and F1 male and female Sprague-Dawley rat

parents exposed to 3–6 mg/kg/day (Matsuura et al. 2005) and in F1 male CD rat parents exposed to

1.7 mg/kg/day (EPA 1991a). In both studies, no hepatic effects were seen at a dose of about 1 mg/kg/day

γ-HCH (EPA 1991a; Matsuura et al. 2005). Rats exposed to 35 mg/kg/day γ-HCH for 48 weeks in the

diet exhibited hepatocellular hypertrophy (Ito et al. 1975). Similar findings were reported in a study of

Wistar rats given ≥7–8 mg γ-HCH/kg/day in the diet for up to 52 weeks, in which a dose-related increase

in periacinar hepatocytic hypertrophy was seen (Amyes 1990). In mice, administration of 90 mg

γ-HCH/kg/day in the diet for 24 weeks was reported to result in centrilobular hypertrophy and a

significant increase (33%) in relative liver weight (Ito et al. 1973).

In other intermediate-duration studies, more severe lesions have been noted in the liver. An early study

(Ortega et al. 1957) reported the development of liver cell “lipospheres” in rats fed 2.5 mg γ-HCH/kg/day

in the diet for 32 weeks; in older literature, these changes were described as spherical cytoplasmic

inclusions of a fatty nature. Ali and Shakoori (1998) reported ultrastructural changes in the livers of

Sprague-Dawley rats exposed for 15 days to a dose of 18 mg/kg/day in food. Findings observed in the

treated animals included reduced number of cells per field; increased cell, nucleus, and nucleolus size;

vacuoles in the cytoplasm; and apparent fatty degeneration. At a dose of 20 mg/kg/day γ-HCH

administered by daily gavage for 30 days, liver histopathology changes in Sprague-Dawley rats included

megalocytosis, vacuolar degeneration, venous and sinusoidal congestion, and lymphocytic infiltration

(Fatih Fidan et al. 2008). At 100 mg/kg/day for the same duration, the livers of Wistar rats showed

vacuolar degeneration of hepatocytes and marked degradation of the central vein (Vijaya Padma et al.

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2011). Focal degeneration of hepatocytes was noted in rabbits given γ-HCH at a dose of 7 mg/kg/day by

gavage for 4 weeks (Grabarczyk et al. 1990; Kopec-Szlezak et al. 1989).

Two intermediate-duration studies reported no liver effects in rats exposed to γ-HCH. Sumida et al.

(2007) observed no treatment-related hepatic effects (clinical chemistry, liver weight, or histopathology)

in F344 rats exposed for 28 days at 10 mg/kg/day via gavage. The lack of effect in this study may

indicate a lower sensitivity of F344 rats to hepatic effects of this isomer, but also could be a reflection of

the very small numbers of animals tested (four males per group). In an older study focused on

neurotoxicity testing, groups of eight Wistar rats given 50 mg/kg/day for 40 days in feed exhibited

increased liver weight, but normal liver function test results and histology (Desi 1974).

In addition to histopathology changes, intermediate-duration oral exposure to γ-HCH has resulted in

increased liver weights. Rats exposed to 2.5 mg γ-HCH/kg/day for 21 days showed a significant increase

(13% higher than controls) in absolute, but not relative, liver weight (Parmar et al. 2003). Treatment of

female rats with ≥10.6 mg γ-HCH/kg/day or of male and female mice with ≥21.1 mg/kg/day in the diet

for 3 months resulted in significant increases in absolute and relative liver weights; histopathological

examinations were not performed (Oesch et al. 1982). Increased absolute and relative liver weights

occurred at doses (≥3–5 mg/kg/day) associated with increased incidences of hepatocellular hypertrophy in

parental animals exposed to γ-HCH in the diet in a 2-generation reproduction toxicity study (Matsuura et

al. 2005). Exposure of dd strain mice to dietary doses of 90 mg/kg/day for 24 weeks resulted in a 33%

increase in relative liver weight (Ito et al. 1973).

Increased liver weights have also been reported in offspring of rats exposed to γ-HCH during gestation

and/or lactation (Srinivasan et al. 1991). Additional details are provided in Section 2.17 (Developmental).

Increases in serum enzymes and lipids indicating hepatic effects have been observed in rats and rabbits

exposed for intermediate durations to γ-HCH. Significant increases in serum AST, ALT, GGT, ALP,

and/or LDH were observed in Wistar rats exposed to 100 mg/kg/day for 4 weeks (Etim et al. 2006; Vijaya

Padma et al. 2011). Increased serum levels of AST, LDH, cholesterol, total triglycerides, free fatty acids,

and total phospholipids were observed in male Sprague-Dawley rats administered 8.8 mg/kg/day γ-HCH

by gavage in water for 3 weeks (Kamal El-Dein et al. 2016). Rabbits treated with 4.21 mg γ-HCH/kg/day

by gavage for 28 days exhibited significant increases in plasma ALP and ALT activities immediately

following initiation of dosing; these activities returned to control levels by day 14 (Cerón et al. 1995).

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The plasma level of AST activity also increased immediately following dosing and remained elevated up

to 7 days postexposure (day 35) (Cerón et al. 1995).

Oral exposure to γ-HCH for intermediate durations has resulted in induction of hepatic cytochrome P450

levels in rats and mice. Significant increases in hepatic microsomal cytochrome P450 levels were found

in Wistar rats fed diets containing 1.8 mg/kg/day γ-HCH for 15 or 30 days (Barros et al. 1991). A dose-

and time-dependent increase of P450 and P450-dependent enzyme levels was observed in the liver of rats

exposed to γ-HCH (Parmar et al. 2003). P450 content was significantly increased in rats exposed to

10 mg γ-HCH/kg/day for 5 days, and in rats exposed to 2.5 mg γ-HCH/kg/day for 15 and 21 days. There

was no significant increase in P450 content in rats exposed to <10 mg γ-HCH/kg/day for 5 days. Several

P450-dependent enzymes, 7-ethoxyresorufin-O-deethylase (EROD), 7-pentoxyresorufin-O-dealkylase

(PROD), and N-nitrosodimethylamine demethylase (NDMA-d), were significantly increased in rats

exposed to 5 mg γ-HCH/kg/day for 5 days or 2.5 mg γ-HCH/kg/day for 15 and 21 days (Parmar et al.

2003). Increases in liver microsomal mixed-function oxidase activity were observed in rats exposed to

≥10.6 mg γ-HCH/kg/day and mice exposed to ≥21.1 mg/kg/day in the diet for 3 months (Oesch et al.

1982).

Hepatotoxicity has been documented in animals exposed by oral administration to γ-HCH for chronic

durations. After Sprague-Dawley rats were exposed for 18 months to γ-HCH at a dose of 9 mg/kg/day in

feed, the following microscopic findings were observed in the liver: increased cell, nucleus, and nucleolus

size; extensive cytoplasmolysis; slight cytoplasmic degeneration; and increasing nuclear distortion (Ali

and Shakoori 1998). Chronic exposure of rats to 7–9 mg/kg/day γ-HCH in the diet for 107 weeks resulted

in increased liver weight (35% higher than controls) and very slight microscopic liver damage described

as “characteristic of certain chlorinated cyclic compounds” (Fitzhugh et al. 1950). At higher doses, liver

necrosis and fatty degeneration were observed (Fitzhugh et al. 1950). Male CD-1 mice exposed to

20.5 mg/kg/day γ-HCH via feed for 78 weeks exhibited centrilobular hepatocyte hypertrophy (EPA

2000a). No liver lesions were observed by light or electron microscopy in NMRI mice given

~8 mg/kg/day for 80 weeks (Herbst et al. 1975; Weisse and Herbst 1977). At gross necropsy, the livers of

dogs exposed to 2.9 mg/kg/day for 104 weeks were noted to be dark, but no histopathology changes were

reported (Rivett et al. 1978).

Increased incidences of liver tumors (hepatomas, hepatocellular carcinomas) have been observed in mice

exposed via diet to γ-HCH for intermediate and chronic durations at γ-HCH doses as low as

HEXACHLOROCYCLOHEXANE (HCH) 121

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13.6 mg/kg/day (Hanada et al. 1973; NCI 1977; Thorpe and Walker 1973; Wolff et al. 1987). These

studies are discussed further in Section 2.19 (Cancer).

One study of dermal exposure to γ-HCH reported also reported liver effects. Centrilobular hepatocellular

hypertrophy was reported in male and female rats exposed to γ-HCH ≥60 mg /kg/day by dermal

application for 6 hours/day, 5 days/week, for 13 weeks (EPA 1988a).

Mechanisms. There is some evidence that oxidative stress may contribute to the hepatic effects of

γ-HCH. Significant increases in hepatic microsomal superoxide anion production and cytoplasmic

superoxide dismutase activity and lipid peroxidation were found in the livers of Wistar rats fed diets

containing 1.8 mg/kg/day γ-HCH for 15 or 30 days (Barros et al. 1991). Groups of 10 male rats (strain

not reported) were administered a single dose of γ-HCH (98% purity) in corn oil at a dose of 0 or

12 mg/kg and then sacrificed 24 hours later in a study aimed at evaluating the ameliorating effects of co-

treatment with the antioxidants, nigella sativa oil and omega 3 fatty acids. Co-treatment with nigella

sativa oil and omega 3 fatty acids attenuated the effects of γ-HCH on lipid parameters, clinical chemistry

parameters, lipid peroxidation, and antioxidant enzyme activities (Attia et al. 2011). The mitigating

effects of nigella sativa oil and omega 3 fatty acids could have resulted from their antioxidant activity or

from effects on the absorption or metabolism of γ-HCH.

δ-HCH. Liver cell hypertrophy was observed in rats fed with 70 mg/kg/day of δ-HCH in the diet for

48 weeks (Ito et al. 1975). Similarly, mice exposed for 24 weeks to 90 mg/kg/day δ-HCH in feed

exhibited a 23% increase in relative liver weight and centrilobular hypertrophy (Ito et al. 1973).

Unspecified HCH Isomers or Mixtures of HCH Isomers. In humans, statistically significant increases in

the blood levels of the enzymes LDH (33%), leucine aminopeptidase (45%), and γ-glutamyl

transpeptidase (174%) were reported in 19 individuals occupationally exposed to technical-grade HCH

for over 10 years in an HCH-formulating plant (Kashyap 1986) compared to a control group of workers.

The HCH isomer concentrations in serum were 10-fold higher in the exposed group than in the control

group of workers. Both inhalation and dermal exposure probably occurred.

Increases in liver weight, serum enzymes and lipids, and liver histopathology changes have been observed

in animals exposed to technical-grade HCH by oral administration for acute durations. Technical-grade

HCH was reported to cause increases in liver weight and serum enzyme activities (e.g., ALP,

aminotransferases) in male Swiss mice given 72 mg/kg in the diet for 2 weeks (Ravinder et al. 1989).

HEXACHLOROCYCLOHEXANE (HCH) 122

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Other effects seen in the mice included significantly increased serum triglycerides, phospholipids, and

cholesterol, as well as hypertrophy of hepatocytes with enlargement of nuclei, centrilobular degeneration,

and focal necrosis (Ravinder et al. 1990). Statistically significant decreases in the liver activities of AST

and LDH were observed in pregnant mice administered a single dose of technical-grade HCH (5 mg/kg)

on GD 9 (Dikshith et al. 1990). Pregnant animals dosed with 25 mg/kg also experienced decreases in

liver ALT and ALP activity (Dikshith et al. 1990). Virgin mice administered a single dose of 5–

200 mg/kg technical-grade HCH had statistically significant decreases in liver activity of ALT and AST,

and increases in liver ALP activity were observed in the virgin mice at doses ≥25 mg/kg. However, with

the exception of decreased AST activity in pregnant mice, the dose-response relationships were

questionable (Dikshith et al. 1990). There were also no corresponding pathological changes in the livers

of the treated mice. However, at a higher dose (50 mg/kg/day) of technical-grade HCH administered to

mice for 1, 5, or 15 days by oil gavage, congestion of hepatic portal vessels and central vein, swollen

hepatic cells with vacuolar or parenchymatous degeneration, and fatty changes in periportal and

centrilobular cells were observed (Philip et al. 1989).

Liver enzyme level changes were seen in male, but not female, rats given 5 or 25 mg/kg/day by gavage

for 90 days; at these doses, there were significant mortalities (Dikshith et al. 1991b). A 65% decrease in

liver weight, decreased liver AST and LDH activities, and increased ALP activity were noted in male rats

given 60 mg/kg by gavage for 30 days, but animals had normal liver histology (Dikshith et al. 1989a).

Technical-grade HCH was reported to deplete the hepatic vitamin A content in male rats fed a diet

containing 90 mg/kg/day HCH for 7 weeks (Joseph et al. 1992b). No adverse hepatic effects were seen in

rats treated with 50 mg/kg/day technical-grade HCH for 30 days (Khanna et al. 1990) or in pigs exposed

to 0.8 mg/kg/day for 90 days (Wang et al. 2006). Mice fed diets containing 90 mg/kg/day of HCH for

8 months exhibited increased liver weight, glycogen accumulation, and decreased glucose-6-phosphatase

and fructose-1,6-di

phosphatase activities (Karnik et al. 1981). Enlargement of hepatocytes, nuclear

pyknosis, margination, and vacuolation were observed in rats fed 20 mg/kg/day technical-grade HCH in

the diet for 360 days (Dikshith et al. 1991a). Chronic dietary administration of technical-grade HCH to

rats at a dose of 4 mg/kg/day resulted in slight microscopic liver damage, which the study authors

described as “characteristic of certain chlorinated cyclic compounds” (Fitzhugh et al. 1950).

echnical-grade HCH was also reported to cause liver cancer in mice following exposure to

90 mg/kg/day in the diet for time periods ranging from 2 to 8 months (Bhatt and Bano 2009; Bhatt and

Nagda 2012; Karnik et al. 1981; Thakore et al. 1981; Trivedi et al. 2007, 2009) or exposure to 10–

50 mg/kg/day for 80–88 weeks (Kashyap et al. 1979; Munir et al. 1983) (see Section 2.19).

HEXACHLOROCYCLOHEXANE (HCH) 123

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Hepatic effects have been seen after dermal exposure to technical-grade HCH. Alterations in liver

histopathology, including dilation of sinusoids, focal fatty inclusions, hypertrophy of hepatocytes,

thickened blood vessels, swelling, and proliferation of epithelial cells of bile ducts, was observed in

guinea pigs treated by dermal application of 100 mg/kg/day technical-grade HCH for 30 days (Dikshith et

al. 1978). The area of the abdomen on which the HCH was applied was not covered to prevent licking, so

oral exposure may also have occurred. In rabbits exposed to 25 mg technical-grade HCH/kg/day for

30 days, there were degenerative changes in hepatocytes along with increased liver and serum ALT and

ALP (Dikshith et al. 1989b). Liver cell hypertrophy, fatty degeneration, nuclear pyknosis, and focal and

diffuse necrosis were found in female rats treated with 100 mg/kg/day technical-grade HCH for 7–

30 days, but the time that it took for these lesions to occur, the severity of changes, and the numbers of

animals affected were not reported (Dikshith et al. 1991c).

2.10 RENAL

Epidemiological Studies. Very limited human epidemiological data on renal effects of HCH isomers are

available, as shown in Table 2-11. In a cohort study of 1,545 male pesticide applicators in Iowa and

North Carolina, no association was observed between self-reported pesticide exposure and chronic kidney

disease (Shearer et al. 2021). A cohort study of 31,142 wives of pesticide applicators in Iowa and North

Carolina followed for 15 years did not observe an association between self-reported pesticide exposure

and end-stage renal disease (Lebov et al. 2015). Case-control studies of chronic kidney disease (Ghosh et

al. 2017; Siddarth et al. 2014) did not observe associations with β-HCH in blood or serum, and results

were mixed for α- and γ-HCH. Ghosh et al. (2017) reported an association between blood levels of

γ-HCH and chronic kidney disease and no association for α-HCH, while Siddarth et al. (2014) reported

the converse (association for serum α-HCH and no association for γ-HCH). No association between

serum α-, β,- γ-, or δ-HCH and hyperuricemia (or increased serum uric acid) was noted in cross-sectional

studies of 453 adults in Spain (Arrebola et al. 2019) or 880 adults in South Korea (Seo et al. 2022).

α-HCH. Fitzhugh et al. (1950) reported kidney damage (nephritis tubular dilatation, hyaline tubular

casts, glomerular fibrosis or atrophy, pigment deposition) in rats fed 60–70 mg/kg/day α-HCH for an

average of 35.9 weeks; no such effects were observed in rats fed up to 9 mg/kg/day for 107 weeks.

β-HCH. Renal effects have also been noted in rats exposed to β-HCH in the diet, often at doses

associated with profound toxicity and/or death. Srinivasan et al. (1984) reported significantly increased

HEXACHLOROCYCLOHEXANE (HCH) 124

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Table 2-11. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Renal Effects

Reference, study type, and population

Outcome evaluated

Isomer

Biomarker

Mean concentration (unless

otherwise noted)

Result

Arrebola et al. 2019

Cross-sectional, 453 working adults,

median age 35 years, Spain

Hyperuricemia

α-HCH

Serum

<LOQ ng/g lipid (all)

β-HCH

<LOQ (median)

0.12 (95

percentile)

↔

γ-HCH

<LOQ (median)

0.05 (95

percentile)

↔

Seo et al. 2022

Cross-sectional, 880 adults, ages 20–

80 years, South Korea

Serum uric acid

β-HCH

Serum

40.4 ng/g lipid

↔

α-HCH

1.24

↔

γ-HCH

1.82

↔

δ-HCH

0.17

↔

Shearer et al. 2021

Cohort, 1545 male pesticide applicators,

age ≥50 years, Iowa and North Carolina,

United States

CKD

γ-HCH

NA (self-

reported

pesticide

exposure)

Ever used versus never used

↔

Ghosh et al. 2017

Case-control, 200 cases and 100 controls,

ages 30–50 years, India

CKD of known or

unknown etiology

α-HCH

Blood

1.26 ng/g (median) (CKD, known)

1.68 (CKD, unknown)

0.7 (controls)

↔

β-HCH

2.49 (CKD, known)

2.15 (CKD, unknown)

1.7 (controls)

↔

γ-HCH

2.15 (CKD, known)

2.03 (CKD, unknown)

2.6 (controls)

↑

Siddarth et al. 2014

Case-control, 270 cases and 270 controls,

mean ages 46 and 48 years (respectively),

India

CKD

α-HCH

Serum

5.23 ng/mL (median, 3rd tertile)

0.87 (median, 1

tertile)

↑

β-HCH

5.50 (3

tertile)

0.20 (1

tertile)

↔

γ-HCH

3.89 (3

tertile)

1.86 (1

tertile)

↔

Total HCH

12.51(3

tertile)

3.63 (1

tertile)

↑

HEXACHLOROCYCLOHEXANE (HCH) 125

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Table 2-11. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Renal Effects

Reference, study type, and population

Outcome evaluated

Isomer

Biomarker

Mean concentration (unless

otherwise noted)

Result

Lebov et al. 2015

Cohort, 31,142 wives of pesticide

applicators, ≥18 years at enrollment, Iowa

and North Carolina, United States, mean

follow-up 15.4 years

End-stage renal

disease

γ-HCH

NA (self-

reported

pesticide

exposure)

Ever used versus never used

↔

Analysis was not performed because all samples were below the LOQ.

Odds ratios comparing serum levels ≥ LOQ to samples < LOQ.

Positive association associated with CKD of unknown etiology; no association with CKD of known etiology.

↑ = association with increase; ↓ = association with decrease (inverse association); ↔ = no association; CKD = chronic kidney disease; LOQ = limit of

quantification; NA = not applicable

HEXACHLOROCYCLOHEXANE (HCH) 126

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excretion of glucose in urine and increased excretion of creatinine and urea, as well as hypertrophy and

degeneration of the renal tubular epithelia in rats exposed to 72 mg/kg/day β-HCH for up to 2 weeks.

Van Velsen et al. (1986) reported significantly increased kidney weights in female rats exposed to 0.2 mg

β-HCH/kg/day for 13 weeks, but the change did not exhibit dose-dependence. In males, a significant

increase in kidney weight was observed at 4.5 mg/kg/day. At the highest dose (22.5–25 mg/kg/day), a

dose that was profoundly toxic and led to the humane sacrifice of half of the animals, males exhibited

renal calcinosis in the outer medulla. The study authors noted that renal calcinosis is common in female

rats but that this finding was unusual and therefore of significance in males (Van Velsen et al. 1986).

Fitzhugh et al. (1950) examined the renal effects of exposure to β-HCH (60–70 mg/kg/day) in rats that

died after an average of 4.4 weeks and found nephritis and basal vacuolation. At lower doses in this

study, exposure to doses up to 9 mg/kg/day for up to 2 years did not induce renal histopathology changes

(Fitzhugh et al. 1950).

γ-HCH (Lindane). Renal effects have been documented in case reports of accidental or intentional oral

exposures to γ-HCH. In a suicide attempt, a 30-year-old male farmer from rural India ingested a single

dose of approximately 50 mL of 2% γ-HCH solution (Paul et al. 2013). Six hours after the ingestion, the

man went to the emergency department. On the second day symptoms of lethargy and reduced urinary

output were noted, increasing in severity by day 5 to include additional symptoms of elevated pulse,

increased serum levels of kidney enzymes (blood urea nitrogen [BUN] and creatinine), urinary white

blood cells, red blood cells, and protein. An ultrasound of the kidneys indicated cortical echogenicity and

mild ascites. The man was treated for acute kidney injury by hemodialysis. Urine output started to

increase on day 10 and serum kidney enzymes recovered in 3 weeks, after which he was discharged in

stable condition that persisted though a 3-month follow up (Paul et al. 2013).

A suicidal 21-year-old male ingested γ-HCH (dose unknown) (Shah et al. 2013). One day after ingestion,

the man experienced reduced urine output, dark urine, pedal edema, and muscular pain lasting 2 days

before he went to a clinic. Clinical evaluation at 3 days post-ingestion showed proteinuria,

myoglobinuria, muscle tenderness, elevated serum levels of AST, potassium, creatinine, and CPK, and

metabolic acidosis indicating acute kidney injury from rhabdomyolysis. Treatment included hemodialysis

and supportive care and the man recovered after 3 weeks (Shah et al. 2013). Progressive renal failure was

seen in a woman who died 11 days after intentionally ingesting 8 ounces of a 20% γ-HCH solution

(Sunder Ram Rao et al. 1988). Myoglobin release resulting from muscle lysis in this case led to kidney

shutdown, which was the ultimate cause of death.

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Small (<10%) increases in kidney weights, in the absence of clinical chemistry, urinalysis, and

histopathology changes, were observed in female rats exposed to 5 mg/m

γ-HCH aerosol 6 hours/day for

90 consecutive days (Oldiges et al. 1983). Male rats at this concentration exhibited significantly

increased kidney weights. Dose-related increases in the incidences of kidney lesions (dilated tubules with

protein-containing contents; proliferated tubules) were observed in males, but not females, at

concentrations of 0.5 and 5 mg/m

(Oldiges et al. 1983). No renal effects (including clinical chemistry,

organ weight, and histopathology) were seen in mice exposed up to 5 mg/m

γ-HCH aerosol 6 hours/day,

5 days/week for 14 weeks (Klonne and Kintigh 1988).

In studies of animals exposed orally to γ-HCH, renal effects have largely been limited to male rats,

although many studies did not test females, and two studies reported histopathology changes in females

exposed to higher doses (Suter 1983; Vijaya Padma et al. 2011). In an acute study, male Fischer-344 rats

receiving gavage doses of 10 mg/kg/day of γ-HCH for 4 days showed histopathological changes in the

proximal tubule epithelial cells including accumulation of protein droplets, hypertrophy, necrosis,

pyknotic nuclei, cellular exfoliation, and regenerative epithelium (Dietrich and Swenberg 1990, 1991).

Significantly increased excretion of glucose in urine, and histological changes consisting of hypertrophy

and degeneration of the renal tubular epithelia, were observed in male Wistar rats exposed to

72 mg/kg/day of γ-HCH for up to 2 weeks (Srinivasan and Radhakrishnamurty 1988; Srinivasan et al.

1984).

Male Sprague-Dawley rats exposed for 30 days to γ-HCH via gavage at doses ≥20 mg/kg/day exhibited

medullary and cortical hemorrhage, and degeneration and vacuolation of proximal convoluted tubules

(Fatih Fidan et al. 2008). Similarly, after 30 days of exposure to 20 mg/kg/day, male Wistar rats showed

intertubular hemorrhage, tubular degeneration and desquamation of tubular epithelium, cystic dilatation,

mononuclear cell infiltrate, and necrosis (Prasad et al. 2016). No renal effects other than significantly

increased kidney weight were observed in rats exposed to γ-HCH doses up to 5–50 mg /kg/day in the diet

for up to 40 days (Desi 1974); histological examination of the kidney did not reveal any changes. In

female Wistar rats exposed for 30 days to daily gavage doses of 100 mg/kg/day, glomerular degeneration

and shrinkage and degeneration of the proximal and distal tubules were observed (Vijaya Padma et al.

2011).

Increased kidney weight, hyaline droplet accumulation, and tubular regeneration were observed in male

Long-Evans rats exposed for 10 weeks to 10 mg/kg/day γ-HCH via gavage (Andrews and Gray 1990). In

male rats treated with 0.4–10 mg γ-HCH/kg/day in their diets for 12 weeks, dose-dependent renal effects

HEXACHLOROCYCLOHEXANE (HCH) 128

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of increasing severity were seen, including basophilic proximal tubules and proximal tubular distention

with cell debris, as well as hyaline droplet formation, and minimal to moderate interstitial nephritis (Suter

1983). Both male and female rats exposed to doses ≥2 mg/kg/day exhibited minimal to slight epithelial

cell necrosis in the proximal tubules (Suter 1983). In a 2-generation reproductive toxicity study, no renal

effects were observed in female adult Crj:CD(SD)IGS rats exposed to doses up to 26.1 mg/kg/day

(Matsuura et al. 2005). In contrast, doses ≥0.56 mg/kg/day resulted in increased incidences and severity

of basophilic tubules and hyaline droplets in the proximal tubules of F0 and F1 parental males (Matsuura

et al. 2005). EPA (1991a) also observed renal histopathological changes characteristic of alpha-

2µ-globulin accumulation in F0 and F1 male CD rats at ≥1.7 mg/kg/day in a 2-generation reproduction

study with γ-HCH. No gross or histopathological changes were observed in kidneys of females in either

generation.

Male Wistar rats exposed for up to 52 weeks to γ-HCH in their diet exhibited hyaline droplets in the renal

proximal tubules, interstitial chronic nephritis, and regeneration in proximal tubules at doses

≥0.07 mg/kg/day; and pale kidneys, increased kidney weights and urine volumes, and higher urinary

protein excretions and tubular necrosis at 7 mg/kg/day (Amyes 1990). In contrast, no renal effects were

seen in females at doses up to 32 mg/kg/day in this study (Amyes 1990). Very slight microscopic kidney

damage (not further specified) was reported in Wistar rats exposed to 7–9 mg γ-HCH/kg/day for up to

104 weeks (Fitzhugh et al. 1950). The histopathology findings were not reported by sex, so it is not clear

whether the effects were limited to males.

Male rats treated dermally with 10 mg/kg/day γ-HCH for 13 weeks exhibited hyaline droplet formation,

and urinalysis showed increased cast formation and turbidity, proteinuria, and hematuria (EPA 1988a).

Females in the same study exhibited a slight increase in the incidence of tubular basophilia at 60

mg/kg/day.

Mechanisms. Available data suggest that the renal effects of γ-HCH may result from at least two possible

mechanisms: (1) alpha-2μ-globulin accumulation in male rats; and (2) increased oxidative stress in both

male and female rats. Dietrich and Swenberg (1990, 1991) demonstrated α-2μ-globulin staining in the

kidney cortex of male F-344 rats exposed for 4 days to 10 mg/kg/day of γ-HCH. No α-2μ-globulin

staining was detected in the kidneys of F-344 male controls, F-344 control or exposed female rats, or

exposed male NBR rats (a strain that does not synthesize α-2μ-globulin). Matsuura et al. (2005) used

immunohistochemistry staining to examine kidneys of male parental rats in a 2-generation reproductive

HEXACHLOROCYCLOHEXANE (HCH) 129

2. HEALTH EFFECTS

toxicity study, and observed that smaller hyaline droplets stained positive for α-2μ-globulin, while larger

ones did not.

Renal effects seen only in male rats that are attributable to alpha-2μ-globulin accumulation are not

relevant to human health (EPA 1991b). However, kidney effects have also been seen in female rats

(Suter 1983; Vijaya Padma et al. 2011), and other mechanisms, such as induction of oxidative stress, may

play a role in these effects. Increases in lipid peroxidation and nitric oxide, as well as depletion of

antioxidant enzyme activities (superoxide dismutase, catalase, and glutathione peroxidase) and reduced

glutathione, have been observed in the kidneys of male rats exposed by gavage to doses of ≥20 mg/kg/day

γ-HCH in intermediate-duration studies (Fatih Fidan et al. 2008; Prasad et al. 2016; Vijaya Padma et al.

2011).

Technical HCH or Unspecified Isomers of HCH. Oral exposure to technical HCH has been shown to

induce kidney effects in mice, rats, and pigs. Mice treated daily with 50 mg/kg/day technical-grade HCH

for 1, 5, or 15 days by oil gavage exhibited renal changes including congestion of blood vessels and

glomerular tufts, swollen tubules with hyaline casts, cystic dilation, fatty changes, some interstitial

hemorrhaging in the medulla, and epithelial cell vacuolation (Philip et al. 1989). No adverse effects were

seen in the kidneys of male rats treated with 50 or 60 mg/kg/day technical-grade HCH for 30 days

(Dikshith et al. 1989a; Khanna et al. 1990). Wang et al. (2006) observed a 24% increase in kidney

weights in pigs given technical-grade HCH at a dose of 0.8 mg/kg/day for 90 days; renal histopathology

was not evaluated. Nephritis, pigmentation, and basal vacuolation were observed in kidneys of rats (sex

not specified) fed 60–70 mg/kg/day technical-grade HCH in the diet for an average of 32.9–64.6 weeks

(Fitzhugh et al. 1950); poor survival (for which there was no explanation) was noted in both control and

treated animals. Tubular necrosis and glomerular degeneration were seen in male rats exposed for

360 days to 20 mg/kg/day of technical-grade HCH (Dikshith et al. 1991a).

Renal changes have been reported in animals exposed to technical-grade HCH by dermal application.

Female rats treated with 100 mg/kg/day of technical-grade HCH for 7, 15, or 30 days had necrosis and

atrophy of the renal tubules and glomeruli, although the number of animals affected and the severity of

the lesions were not reported (Dikshith et al. 1991c). Similar effects were noted in male rabbits treated

with 25 mg/kg/day technical-grade HCH for 30 days (Dikshith et al. 1989b). In both of these studies,

mortalities were seen at the doses associated with renal effects.

HEXACHLOROCYCLOHEXANE (HCH) 130

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2.11 DERMAL

γ-HCH (Lindane). A 10-year-old boy who was being treated for scabies was exposed to a 1% γ-HCH

solution by dermal application from the neck down for 8 hours/day on 3 consecutive days (Juan et al.

2004). Following the initial application, erythema developed on the neck, extending to the trunk and

axillae after 2 days. On the third day, pustules were present on his neck, trunk, arms, and thighs. He was

examined in a clinic, where symptoms of leukocytosis were noted. A biopsy of a skin lesion showed sub-

corneal and intraepidermal pustule formation with neutrophilic infiltrations and scattered eosinophils in

the dermis, suggesting acute generalized exanthematous pustulosis. After discontinuation of the γ-HCH

solution, the boy recovered within a week (Juan et al. 2004).

A 57-year-old man was admitted to the hospital and diagnosed with scabies for which he was treated with

γ-HCH lotion (concentration not reported) by dermal application to the whole body for 8 hours/day for

3 consecutive days (Yu et al. 2015). Instructions included washing/removal of the lotion after 8 hours,

but the man was only partially washed for unknown reasons. One week after exposure, multiple scattered

and coalescent polymorphic ulcerations with hemorrhagic spots and black burn-like crusted edges

developed. A skin biopsy revealed papillary edema, and acute and chronic inflammation indicating

ulcerative irritant contact dermatitis. Patch testing was performed but the results were unavailable, as the

patient died from sepsis. The time elapsed between exposure and death was not reported and it was not

clear whether the ulceration caused the sepsis (Yu et al. 2015).

In a summary of γ-HCH poisoning cases reported to the Texas poison control network (Forrester et al.

2004), commonly reported symptoms of exposure included erythema and dermal irritation or pain; the

authors did not describe symptoms by routes of exposure, which included oral and dermal. An itchy red

rash was observed in a 10-month-old boy after 7 days of twice-daily application of 1% γ-HCH for scabies

treatment (Bhalla and Thami 2004). Rashes were observed in a boy following treatment with shampoo

containing γ-HCH (Fagan 1981). No exposure level was reported, but the shampoo was rinsed over the

boy's entire body.

Mild dermatitis was observed in rats after 15 skin paintings with 180 mg/kg/day γ-HCH/kg over a period

up to 25 days (Dikshith et al. 1973). Rabbits exposed to 200 mg/kg moistened γ-HCH for 4 hours showed

no primary skin irritation or other toxic symptoms (Ullmann 1986d).

HEXACHLOROCYCLOHEXANE (HCH) 131

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Technical HCH or Unspecified Isomers of HCH. Rabbits exposed to technical-grade HCH

(25 mg/kg/day for 30 days) had hyperkeratinization of the epidermal layer and swollen collagen fibers in

the dermis, but no scoring level was provided (Dikshith et al. 1989b). Dermal treatment of rats with

100 mg/kg/day technical-grade HCH for 7–30 days resulted in hyperkeratosis, epidermal cell

vacuolization, and thickening of collagen fibers (Dikshith et al. 1991c).

2.12 OCULAR

No studies were located regarding ocular effects in humans following exposure to HCH isomers.

γ-HCH (Lindane). In a survey of γ-HCH exposures reported to the Texas poison control network,

Forrester et al. (2004) reported that ocular irritation and pain were common symptoms. The authors did

not distinguish between effects seen after oral and dermal exposures, both of which were considered in

the survey.

Mice exposed to γ-HCH aerosol (up to 5 mg/m

) 6 hours/day for 14 weeks exhibited no ophthalmic

effects (Klonne and Kintigh 1988), and histopathology of the eyes showed no changes in these mice or in

rats exposed similarly (Oldiges et al. 1983). Mild eye irritation was seen in rabbits exposed to 40 mg/kg

γ-HCH in the conjunctival sac for up to 72 hours. The irritation level was given a primary irritation score

of 0.6 out of a maximum possible cumulative score of 16 (Ullmann 1986c).

2.13 ENDOCRINE

Epidemiological Studies. Several epidemiological studies have suggested that exposure to HCH may be

associated with changes in thyroid function (see Table 2-12). In a cohort study of 21,788 male pesticide

applicators, occupational exposure to γ-HCH was associated with increased odds of hypothyroid disease

(Goldner et al. 2013). In other studies, there was suggestive evidence for associations between β-HCH in

blood and alterations in serum thyroid hormone levels, but the direction of change and affected hormones

were not consistent. A case-control study in Chinese subjects with thyroid disease found no association

between serum levels of β-HCH and thyroid disease; however, serum β-HCH levels were associated with

decreased total and free thyroxine (T4) in males and increased levels of free T4 in females (Han et al.

2019). Levels of total T4 in females was not related to serum β-HCH, nor were levels of total

triiodothyronine (T3), free T3, and thyroid-stimulating hormone (TSH) in either sex (Han et al. 2019).

HEXACHLOROCYCLOHEXANE (HCH) 132

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Table 2-12. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Endocrine

Effects

Reference, study type, and

population

Isomer

Concentration in serum (unless

otherwise noted)

Outcome evaluated

Result

Han et al. 2019

Case-control, 186 cases of

thyroid disease and 186 controls,

mean ages 46 and 44 years,

China

β-HCH

78.96 ng/g lipid (median) (cases)

65.58 (controls)

Thyroid disease

↔

Serum total T4

M: ↓

F: ↔

Serum free T4

M: ↓

F: ↑

Serum total T3, free T3, and TSH

↔

Freire et al. 2013

Cross-sectional, 303 males and

305 females >14 years old, Brazil

β-HCH

6.00 ng/mL (median) (males)

6.98 (females)

Serum total T3

↔

Serum Free T4

M: ↓

F: ↔

Serum TSH

M: ↑

F: ↔

Serum anti-thyroperoxidase

↔

α-HCH

2.52 (males)

2.60 (females)

Serum total T3, free T4, TSH, and anti-

thyroperoxidase

↔

γ-HCH

0.95 (males)

0.97 (females)

Serum total T3, free T4, TSH, and anti-

thyroperoxidase

↔

Alvarez-Pedrerol et al. 2009

Cross-sectional, 1,090 pregnant

women, Spain

β-HCH

32.3 ng/mL (median) (Sabadell [S])

<LOD (median); 22.1 (75

percentile)

(Gipuzkoa [G])

Serum total T3

S: ↓

G: ↔

Serum free T4

S: ↔

G: ↑

Dallaire et al. 2009

Cross-sectional, 623 Inuit adults

≥18 years old, Canada

β-HCH

8.33 μg/kg lipid (plasma) (mean)

Serum total T3

↓

Serum thyroxine binding globulin

↓

Serum free T4, TSH

↔

HEXACHLOROCYCLOHEXANE (HCH) 133

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Table 2-12. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Endocrine

Effects

Reference, study type, and

population

Isomer

Concentration in serum (unless

otherwise noted)

Outcome evaluated

Result

Freire et al. 2012

Cross-sectional, 193 children

<15 years old, Brazil

β-HCH

479 ng/mL (mean)

Serum total T3

↑

Serum free T4, TSH

↔

α-HCH

300

Serum total T3

↑

Serum free T4, TSH

↔

γ-HCH

77.5

Serum total T3

↑

Serum free T4, TSH

↔

Seo et al. 2022

Cross-sectional, 880 adults, ages

20–80 years, South Korea

β-HCH

40.4 ng/g lipid (mean)

Serum free T4

↓

Serum TSH

↔

γ-HCH

1.82

Serum TSH and free T4

↔

α-HCH

1.24

↔

δ-HCH

0.17

↔

Kim et al. 2013

Cross-sectional, 105 pregnant

women 22–46 years old, South

Korea

β-HCH

7.58 ng/g lipid (median)

Serum total T3, free T3, total T4, free T4,

TSH

↔

Piccoli et al. 2016

Cross-sectional, 275 farmers and

farm residents, 18–69 years old,

Brazil

β-HCH

<LOD ng/g (median)

77.87 (95

percentile)

Serum total T3

↑

Serum free T4, TSH

↔

γ-HCH

3.71 (median)

24.35 (95

percentile)

Serum total T3, free T4, TSH

↔

α-HCH

<LOD (median)

21.8 (95

percentile)

Serum total T3, free T4, TSH

↔

Yamazaki et al. 2020

Cross-sectional, 333 pregnant

women 17–48 years old, Japan

β-HCH

235.6 pg/g (late gestation or post-

partum) (75

percentile)

Serum TSH (early gestation)

↔

Serum free T4 (early gestation)

↔

HEXACHLOROCYCLOHEXANE (HCH) 134

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Table 2-12. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Endocrine

Effects

Reference, study type, and

population

Isomer

Concentration in serum (unless

otherwise noted)

Outcome evaluated

Result

Goldner et al. 2013

Cohort, 21,788 male private

pesticide applicators, Iowa and

North Carolina, United States

Lindane

NA (occupational, ever use)

Hypothyroid disease

↑

↑ = association with increase; ↓ = association with decrease (inverse association); ↔ = no association; F= female; LOD = limit of detection; M = male; NA = not

applicable; T3 = triiodothyronine; T4 = thyroxine; TSH = thyroid stimulating hormone

HEXACHLOROCYCLOHEXANE (HCH) 135

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Several cross-sectional studies evaluated effects of β-HCH on thyroid hormone levels. Decreased total

T3 and thyroxine binding globulin in serum were associated with higher plasma β-HCH levels in

Canadian Inuit adults, while there were no associations with free T4 or TSH (Dallaire et al. 2009). In a

study of pregnant women in Spain, there was an association between serum β-HCH and decreased total

T3 levels in women in the city of Sabadell, but no association was seen in women from the city of

Gipuzkoa (Alvarez-Pedrerol et al. 2009). In contrast, free T4 levels were not associated with serum

β-HCH in Sabadell women, while there was an increased association in Gipuzkoa women (Alvarez-

Pedrerol et al. 2009). No relationship between serum β-HCH levels and total T3, free T3, total T4, free

T4, or TSH was observed in pregnant women or adults of both sexes in South Korea (Kim et al. 2013) or

serum TSH and free T4 levels in pregnant women in Japan (Yamazaki et al. 2020). A cross-sectional

study in adults from South Korea observed an inverse association between serum levels of β-HCH and

serum free T4 (Seo et al. 2022). No association was observed between serum levels of β-HCH and TSH,

or between serum α-, γ-, or δ-HCH concentrations and serum TSH or free T4.

A population-based survey of residents living near an HCH production factory (operating from late 1940s

to 1955) in Brazil examined associations of serum levels of α-, β-, and γ-HCH and thyroid function in

193 children <15 years old (Freire et al. 2012) and in adolescent and adult (>14 years old) males (n=303)

and females (n=305) (Freire et al. 2013). In children, serum levels of α-, β-, and γ-HCH were associated

with increased serum total T3 levels, while no association was observed for serum free T4 or TSH levels

(Freire et al. 2012). In adults, serum levels of β-HCH were associated with decreased free T4 and

increased TSH levels in men, while no association was determined in women for either parameter.

Further, there were no associations between serum β-HCH and total T3 or anti-thyroperoxidase levels and

there were no associations between α-HCH or γ-HCH and total T3, free T4, TSH, and anti-

thyroperoxidase (Freire et al. 2013). Increased total T3 levels corresponded to serum β-HCH levels in

275 adult Brazilian farmers and farm residents, while no relationship was found with α- or γ-HCH

(Piccoli et al. 2016). In this study, there was also no association between serum α-, β-, or γ-HCH and free

T4 or TSH levels (Piccoli et al. 2016).

α-HCH. No histopathology changes were noted in the adrenal glands or thyroids of rats given α-HCH via

the diet at doses up to 70 mg/kg/day for ~9 months or up to 9 mg/kg/day for 2 years (Fitzhugh et al.

1950).

HEXACHLOROCYCLOHEXANE (HCH) 136

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β-HCH. There were no microscopic lesions in the thyroid or adrenal glands when rats were exposed by

dietary administration to β-HCH doses up to 70 mg/kg/day for up to 10 weeks or up to 9 mg/kg/day for

2 years (Fitzhugh et al. 1950).

γ-HCH (Lindane). In 13- and 14-week inhalation studies of rats and mice (respectively) exposed to

concentrations up to 5 mg/m

for 6 hours/day, there were no effects of treatment on the histology of the

pancreas, thyroid, or adrenal glands (Klonne and Kintigh 1988; Oldiges et al. 1983) or on the histology of

the pituitary in the mice (Klonne and Kintigh 1988). Wistar rats administered 50 mg/kg/day γ-HCH in

drinking water for 30 days had 84% higher serum levels of free T4 and 74% lower serum TSH compared

to controls (Hfaiedh et al. 2011). In a 2-generation reproductive toxicity study, F0 and F1 male and/or

female parental rats exposed via feed to doses of 17.2–26.1 mg/kg/day exhibited endocrine effects

including decreased absolute and relative pituitary weights (F0 and F1 females), altered serum thyroid

hormone levels, and increased incidences of thyroid follicular cell hypertrophy (F0 females and F1 males)

(Matsuura et al. 2005). Fitzhugh et al. (1950) reported no histopathology findings in the thyroid or

adrenal glands of rats given γ-HCH in feed at doses up to 140 mg/kg/day for 10 months or 30 mg/kg/day

for 2 years. No effect on adrenal gland weights or adrenal, thyroid, or parathyroid histopathology

findings in CD-1 mice given γ-HCH in the diet at doses up to 26.8 mg/kg/day for 78 weeks (EPA 2000a).

Technical HCH or Unspecified Isomers of HCH. Technical HCH administered to rats in feed did not

induce thyroid or adrenal gland histopathology changes at doses up to 70 mg/kg/day for 6 months or

9 mg/kg/day for 2 years (Fitzhugh et al. 1950).

2.14 IMMUNOLOGICAL

Epidemiological Studies. Few studies of immune system effects in humans exposed to HCH isomers

were located, and the available studies examined limited endpoints. Table 2-13 provides an overview of

the epidemiological studies. Landgren et al. (2009) followed a cohort of 678 male pesticide applicators in

the United States for 9 years and evaluated the risk of monoclonal gammopathy of undetermined

significance (MGUS). MGUS is a condition in which an abnormal protein (monoclonal or M protein)

accumulates in the blood; this condition sometimes progresses to lymphoma or multiple myeloma. There

was no increase in risk for MGUS among applicators who reported use of γ-HCH compared with those

who had never used γ-HCH (Landgren et al. 2009). Ryu et al. (2018) reported a positive association

between serum levels of β-HCH and specific T-lymphocyte frequencies (CD8+ CD57+ and CD8+

HEXACHLOROCYCLOHEXANE (HCH) 137

2. HEALTH EFFECTS

Table 2-13. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Immune

Effects

Reference, study type, and

population

Outcome evaluated

Isomer

Biomarker

Mean concentration (unless

otherwise noted)

Result

Meng et al. 2016

Case-control, 124 cases of asthma,

109 controls, children ages 3–6 years,

China

Asthma

α-HCH

Plasma

Cases: 40.73±36.01 ng/g lipid

Controls: 12.52±16.03

↑

β-HCH

Cases: 111.11±70.1

Controls: 31.49±74.02

↑

γ-HCH

Cases: 27.5±12.13

Controls: 9.34±20.21

↑

Severe asthma

α-HCH

See above

↔

β-HCH

See above

↔

γ-HCH

See above

↔

Landgren et al. 2009

Cohort, 678 male pesticide applicators

followed for at least 9 years, Iowa and

North Carolina, United States

Monoclonal gammopathy of

undetermined significance

γ-HCH

None

(occupational)

Ever versus never used

↔

Ryu et al. 2018

Cross-sectional, 95 healthy adults, age

30–69 years, Korea

T-lymphocyte frequencies:

CD8+ CD57+

β-HCH

Serum

10.7 ng/g lipid

(median of 4

quartile)

↑

CD8+ CD28-

↑

CD4+ CD57+

↔

CD4+ CD28-

↔

HEXACHLOROCYCLOHEXANE (HCH) 138

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Table 2-13. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Immune

Effects

Reference, study type, and

population

Outcome evaluated

Isomer

Biomarker

Mean concentration (unless

otherwise noted)

Result

Seth et al. 2005

Case-control, 20 patients hospitalized

with lindane poisoning and

20 unexposed age- and sex-matched

healthy subjects, India

Serum immunoglobulins and

cytokines:

γ-HCH

None

(exposure

assessed

based on

clinical

symptoms,

history, and

AChE activity)

Exposed versus unexposed

IgG, IgM, IgA, and IgE

↔

IL-2,IL-4, and TNF-α

↑

IFN-γ

↓

Wang et al. 2021a

Cross sectional, 10 women (5 from

rural and 5 from urban areas), mean

age 37 years, China

IL-8, MCP-1

α-HCH

Estimated

dietary intake

0.471 ng/kg/day

↔

β-HCH

0.185

γ-HCH

0.043

δ-HCH

0.104

Severe asthma was defined as “asthma attacks more than 10 times over the year with repeated episodes (more than 3 times) during the last month, or if severe

oxygen deficiency occurred in one attack.”

↑ = association with increase; ↓ = association with decrease (inverse association); ↔ = no association; AChE = acetylcholinesterase; Ig = immunoglobulin;

IL = interleukin; TNF = tumor necrosis factor; IFN = interferon; MCP = monocyte chemotactic protein.

HEXACHLOROCYCLOHEXANE (HCH) 139

2. HEALTH EFFECTS

CD28-) in a cross-sectional study of healthy adults over 30 years of age. In a case-control study of

children 3–6 years old, associations between asthma and increased plasma α-, β-, and γ-HCH levels were

reported (Meng et al. 2016); however, in this study, exposure (blood level) was measured after the

outcome (asthma) occurred. A small cross-sectional study of 10 women in China found no association

between any of the HCHs and serum interleukin-8 (IL-8) or monocyte chemotactic protein-1 (MCP-1)

(Wang et al. 2021a).

β-

HCH. Decreased lympho

-p

roliferative responses to mitogens were seen in mice exposed to

60 mg/kg/day β-HCH in the diet for 30 days (Cornacoff et al. 1988). There were no associated changes in

immunoglobulins, red blood cell counts, or histology of the thymus, spleen, or lymph nodes (Cornacoff et

al. 1988). Cortical atrophy of the thymus and depletion of splenic lymphoid tissue were observed in rats

fed 22.5–25 mg/kg/day β-HCH in the diet (Van Velsen et al. 1986). In this 13-week study (Van Velsen et

al. 1986), 50% of the rats exposed at this dose were sacrificed humanely before study termination (as

early as the first 3 weeks) due to moribund condition.

γ-

HCH (Lindane) Immune system parameters in blood were evaluated in a group of 20 patients seen in a

hospital in India with γ-HCH poisoning and compared with results in a group of age- and sex-matched

controls without pesticide exposure (Seth et al. 2005). The dose, route, nature, and timing of γ-HCH

exposures were not reported, and there was no effort to adjust for potential confounders. No differences

in serum immunoglobulin levels (IgG, IgM, IgA, or IgE) were seen; however, several serum cytokine

levels, including interleukin-2 (IL-2), interleukin-4 (IL-4), and tumor necrosis factor-alpha (TNF-α) were

higher in the poisoning victims, and serum IFN-γ levels were lower (Seth et al. 2005).

A 14-day exposure to 10 mg/kg/day γ-HCH in male rats previously sensitized to Keyhole Limpet

Hemocyanin (KLH) resulted in a reduction in delayed-type hypersensitivity response (measured as a 43%

decrease in foot pad thickness in response to KLH challenge) (Mediratta et al. 2008). Decreased relative

thymus weight (28% less than controls) was observed in mice gavaged with 20 mg/kg/day γ-HCH for

3 days; at 40 mg/kg/day, atrophy of the thymic cortex was seen (Hong and Boorman 1993). Another

experiment by these authors showed significant decreases in relative weights of thymus (≥7%

decrements) and spleen (≥17% decrements) in mice exposed to 10–20 mg/kg/day γ-HCH for 10 days

(Hong and Boorman 1993).

Immunosuppression, as measured by decreased antibody titers against typhoid vaccine and Salmonella

vaccine, was reported in rats exposed by gavage to doses of ≥6.25 mg/kg/day γ-HCH for 5 weeks (Dewan

HEXACHLOROCYCLOHEXANE (HCH) 140

2. HEALTH EFFECTS

et al. 1980) and in rabbits exposed by capsules 5 times each week to 1.5, 6, and 12 mg/kg/day for 5–

6 weeks (Desi et al. 1978). Humoral immune response, as indicated by serum antibody response to sheep

red blood cells (SRBC), was suppressed in rats that were exposed to γ-HCH in estimated dietary doses of

3.6 or 7 mg/kg/day for 8 weeks (Koner et al. 1998). The primary antibody response to SRBC was also

suppressed in albino mice after exposure to 9 mg/kg/day γ-HCH in the diet for 12 weeks (Banerjee et al.

1996). Suppression of secondary antibody response (response after repeat exposure) was also observed

after 3 weeks of exposure to 9 mg/kg/day γ-HCH and after 12 weeks of 5.4 mg/kg/day γ-HCH exposure

(Banerjee et al. 1996). A biphasic, dose-dependent immunological effect of γ-HCH on components of

cell- and humoral-mediated immunity, characterized by initial stimulation followed by immuno-

suppression, was reported in mice fed 0.012, 0.12, or 1.2 mg γ-HCH/kg/day for 24 weeks (Meera et al.

1992). Histological examinations in these animals revealed decreased lymphocyte populations in the

thymus and lymph nodes, a reduction in overall cellularity in the spleen, and necrosis of the thymus at

1.2 mg/kg/day. Cell-mediated immune response, as measured by delayed-type hypersensitivity reaction

to dinitrofluorobenzene antigen, was suppressed in sheep that were exposed to 1.25 ppm γ-HCH in the

diet for 6 months (Khurana et al. 1999).

Technical HCH or Unspecified Isomers of HCH. A statistically significant increase (approximately

18%) in the level of immunoglobulin M (IgM) was noted in 19 workers occupationally exposed to

technical-grade HCH during pesticide formulation, as compared to 14 nonexposed workers (Kashyap

1986). The HCH isomer concentrations in serum showed a 10-fold increase when compared to the

control group. Both inhalation and dermal exposure probably occurred, and the measurement of IgM

alone is not a reliable measure of immune function in adults.

2.15 NEUROLOGICAL

Epidemiological Studies. Epidemiological studies of neurological effects in humans exposed to HCH

isomers are summarized in Table 2-14. Most of the studies used serum or blood levels of β-HCH to

assess exposure; only Singh et al. (2012, 2013, 2014) and Xu et al. (2022) measured α- γ-, and/or δ-HCH

levels as well. A cohort study of 669 Canadian adults at least 65 years old who were followed for 10

years showed no association between blood levels of β-HCH and dementia, Alzheimer’s disease, or

cognitive deficits (Medehouenou et al. 2019). In contrast, case-control studies reported increased risks of

Parkinson’s disease, Alzheimer’s disease, and cognitive deficits with higher β-HCH levels in blood or

serum (Kim et al. 2015; Petersen et al. 2008; Richardson et al. 2009, 2011; Singh et al. 2012, 2013, 2014;

Xu et al. 2022). The study by Xu et al. (2022) also reported increased risk of Parkinson’s disease

HEXACHLOROCYCLOHEXANE (HCH) 141

2. HEALTH EFFECTS

associated with increased serum levels of α- and δ-HCH. However, in the case-control studies, exposures

were measured after the outcome occurred, so there is no clear temporal relationship between exposure

and effect. A small cross-sectional study that suffered from the same limitation reported no association

between β-HCH in serum and tremors at rest or cognitive deficits (Steenland et al. 2014).

Some studies have reported impairments in sensory function associated with HCH exposure. Serum

levels of α-HCH were associated with hearing loss in a small case-control study (87 pairs) in China

(Zhang et al. 2021), but the exposure was measured after the outcome in this study. Shrestha et al. (2021)

observed an association between γ-HCH lifetime days of use and self-reported olfactory impairment

20 years after enrollment in a very large cohort of pesticide applicators in the United States. The odds of

olfactory impairment increased with intensity-weighted days of γ-HCH use in this cohort. The absence of

an objective measure of olfactory impairment limits the conclusions that can be drawn from this study.

α-HCH. Muller et al. (1981) reported no delay in tail nerve conduction velocity in rats fed 5.1, 54.2, or

106.2 mg α-HCH/kg/day for 30 days. No other data on neurological effects of α-HCH were located.

β-HCH. Clinical signs of neurotoxicity have often preceded death in rats and mice exposed to β-HCH via

oral administration. Mice treated with 60 or 200 mg/kg/day β-HCH in the diet in a 30-day study

developed ataxia within the first week of treatment (Cornacoff et al. 1988). The animals receiving

60 mg/kg/day recovered within a few days, while those receiving 200 mg/kg/day became markedly

worse, leading to humane sacrifice of 80% of the animals in this group (Cornacoff et al. 1988). In the

first 2 weeks of a 13-week study, male and female rats exposed to 38 mg/kg/day in the diet exhibited

ataxia and hypoactivity, progressing to coma within 3 days (Van Velsen et al. 1986). The animals were

humanely sacrificed, as were five additional males and six additional females that showed similar signs

later in the study. A single study of electrophysiology was located; in this study, Muller et al. (1981)

reported a significant delay in tail nerve conduction velocity in rats fed 66.3 mg β-HCH/kg/day for

30 days. No comprehensive tests of sensitive neurotoxicity endpoints other than electrophysiology in

animals exposed to β-HCH were located.

γ-HCH (Lindane). Neurological effects have been seen in humans and animals exposed to γ-HCH by

inhalation, oral, and dermal routes. The effects range in severity from subtle neurobehavioral changes

and altered neurotransmitter levels to tremors, convulsions, and ultrastructural changes in the brain.

HEXACHLOROCYCLOHEXANE (HCH) 142

2. HEALTH EFFECTS

Table 2-14. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Neurological

Effects

Reference, study type, and population

Outcome

evaluated

Isomer

Exposure

Biomarker

Mean concentration

(unless otherwise noted)

Result

Richardson et al. 2009, 2011

Case-control, 149 cases of Parkinson’s

disease, 134 controls, four sites in Texas

and Georgia, United States

Parkinson’s disease

β-HCH

Serum

10.77–79.43 ng/mg

cholesterol

(range of medians among

cases across four sites)

↑

Petersen et al. 2008

Case-control, 79 cases of Parkinson’s

disease, 154 controls, mean ages 74 and

75 years, respectively, Faroe Islands

Parkinson’s disease

β-HCH

Serum

0.06 µg/g lipid (GM) (cases)

0.04 (controls

↑

Xu et al. 2022

Case-control, 90 cases of Parkinson’s

disease, 90 controls who were spouses of

the cases, mean ages 65.76 and 64.23,

respectively, China

Parkinson’s disease

α-HCH

Serum

80.19 ng/g lipid (cases)

1.79 ng/g lipid (controls)

↑

β-HCH

1126.4 ng/g lipid (cases)

349.88 ng/g lipid (controls)

↑

γ-HCH

583.30 ng/g lipid (cases)

39.62 ng/g lipid (controls)

↔

δ-HCH

12.09 ng/g lipid (cases)

5.82 ng/g lipid (controls)

↑

Singh et al. 2012, 2013, 2014

Case-control, 100 patients with Alzheimer’s

disease, 100 age-matched controls, Delhi,

India

Alzheimer’s disease

β-HCH

Serum

4.42±0.54 ng/mL (in cases)

↑

α-HCH

Serum

0.37±0.11 ng/mL

↔

γ-HCH

Serum

0.78±0.23 ng/mL

↔

Kim et al. 2015

Cross-sectional, 633 adults aged 60–85

years, NHANES 1999–2002, United States

Cognitive deficit

β-HCH

Blood

89.6 ng/g lipid (median of 4

quartile)

↑

Medehouenou et al. 2019

Cohort, 669 adults ≥65 years old, Canadian

Study of Health and Aging (CSHA), Canada

Dementia, Alzheimer’s disease,

cognitive deficit

β-HCH

Blood

0.13 µg/L (median) (cases)

0.12 (controls)

↔

Steenland et al. 2014

Cross-sectional, 89 adults >65 years of age,

Costa Rica

Movement disorder (tremor at

rest)

β-HCH

Serum

≥0.88 ng/mL (4

quartile

cutoff)

↔

Cognitive deficit

β-HCH

Serum

≥0.88 ng/mL (4

quartile

cutoff)

↔

HEXACHLOROCYCLOHEXANE (HCH) 143

2. HEALTH EFFECTS

Table 2-14. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Neurological

Effects

Reference, study type, and population

Outcome

evaluated

Isomer

Exposure

Biomarker

Mean concentration

(unless otherwise noted)

Result

Sullivan et al. 2018

Cohort, 159 Gulf War veterans who had

worked in pest control, mean age 48 years,

United States

Depression, fatigue scores on

mood test

γ-HCH

NA (self-

reported

exposure)

(high exposure versus low

exposure)

↑

Anger, confusion, tension

scores on mood test

↔

Zhang et al. 2021

Case-control, 87 cases and 87 age- and

gender-matched controls

, mean age

51 years, China

Hearing loss

β-HCH

Serum

27.0 ng/g lipid (cases)

(geometric mean)

29.6 ng/g lipid (controls)

↔

α-HCH

14.4 ng/g lipid (cases)

12.2 ng/ml (controls)

↑

δ-HCH

8.98 ng/g lipid (cases)

9.54 ng/g lipid (controls)

↔

Shrestha et al. 2021

Cohort, 20,409 adult, mostly male pesticide

applicators, Iowa and North Carolina, United

States

Olfactory impairment

γ-HCH

NA (self-

reported

exposure)

Quartiles of intensity-weighted

lifetime days of use

↑

↑ = association with increase; ↔ = no association; GM = geometric mean; NA = not applicable; NHANES = National Health and Nutrition Examination Survey

HEXACHLOROCYCLOHEXANE (HCH) 144

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Studies in animals exposed in utero and/or during lactation show that γ-HCH can also elicit these

neurological effects in offspring of exposed parents; neurotoxic effects in animals exposed during

development are discussed in Section 2.17.

Abnormal electroencephalographic (EEG) patterns (increased variation in the frequency and amplitude of

wave pattern or more serious changes without specific EEG signs) were recorded in 16 of 37 workers

following exposure to γ-HCH for 0.5–2 years in a fertilizer plant (Czeglédi-Jankó and Avar 1970).

Exposure concentrations were not reported; however, these EEG changes were found to correlate with

blood levels of γ-HCH. Effects on mood were examined in a cohort of 159 Gulf War veterans who had

been engaged in pesticide application (Sullivan et al. 2018). In this group, higher self-reported exposure

to γ-HCH was associated with higher scores for depression and fatigue in mood tests, while no

association was seen with anger, confusion, or tension scores on the tests (Sullivan et al. 2018).

Seizures and convulsions have been observed in individuals who accidentally or intentionally ingested

γ-HCH in insecticide pellets, liquid scabicide, or contaminated food (Davies et al. 1983; Forrester et al.

2004; Harris et al. 1969; Munk and Nantel 1977; Nordt and Chew 2000; Powell 1980; Ramabhatta et al.

2014; Starr and Clifford 1972; Storen 1955; Wiles et al. 2015). In most cases, the amount of γ-HCH

ingested could not be determined. A 56-year-old man intentionally ingested approximately 12 ounces of

an insecticide containing 20% γ-HCH in a suicide attempt (Wiles et al. 2015). Thirty minutes later, he

developed a progressive decline in consciousness and multiple seizures ensued between 3 and 14 hours

later. After 18 hours, the man was conscious and responsive, but neurological symptoms were noted

6 days later, including ataxia, slurred speech, paranoia, depression, and defects in higher mental

functioning. The man committed suicide 12 days later by other means. At autopsy, γ-HCH levels in

blood and adipose tissue were 0.248 µg/mL and 132.83 μg/g, respectively.

Several case studies of acute γ-HCH exposure to children ingesting liquid scabicide reported similar

neurological effects, including tremors and tonic/clonic seizures (Aks et al. 1995; CDC 2005; Lifshitz and

Gavrilov 2002; Wheeler 1977). One hour after a 3-year-old boy ingested approximately one teaspoon of

a 1% γ-HCH shampoo, the boy had a tonic-clonic seizure for a duration of 4–5 minutes, despite the

mother’s efforts to induce vomiting (CDC 2005). Three hours later, the boy’s condition was stable, and

he was discharged from the hospital emergency room. Ramabhatta et al. (2014) reported two cases of

neurological effects in children after accidental γ-HCH ingestion. In the first case, a 3-year-old boy was

orally administered a single dose of 10 mL of a γ-HCH lotion (due to a mix-up of prescribed oral and

dermal medications). The child had convulsions 1 hour after ingestion and recovered in 24 hours with

HEXACHLOROCYCLOHEXANE (HCH) 145

2. HEALTH EFFECTS

supportive measures. In the second case, a 6-year-old girl ingested a γ-HCH lotion (amount and

concentration not reported) and had a generalized seizure lasting 10–15 minutes. The child recovered

24 hours after clinic admission (Ramabhatta et al. 2014).

here have been many reports of human intoxication involving seizures or convulsions in adults and

children after excessive topical application of γ-HCH (Boffa et al. 1995; Fischer 1994; Hall and Hall

1999; Lee and Groth 1977; Matsuoka 1981; Ramchander et al. 1991; Solomon et al. 1995; Sudakin 2007;

Telch and Jarvis 1982; Tenenbein 1991); exposure levels were generally not quantified. Central nervous

systems symptoms of severe γ-HCH poisoning, including uncontrollable shaking and myoclonic jerking

and tonic-

onic movements of the extremities, developed in a woman following three dermal

applications of a considerable amount (not quantified) of an anti-scabies product over a period of

approximately 2 weeks (Hall and Hall 1999). Fever, tachycardia, grand mal seizure, and hallucinations

were reported in a teenager treated with a 1% γ-HCH lotion for 3 consecutive nights (Boffa et al. 1995).

Weakness of the left and right limbs, dysarthria, and dysphagia were seen in an agricultural worker

exposed by inhalation and dermal contact to unspecified levels of several organochlorine pesticides,

including γ-HCH (Fonseca et al. 1993).

A 1

0-month-old boy exposed to 1% γ-HCH by repeated dermal application to the whole body 2 times/day

for the treatment of scabies developed jerky movements, listlessness, and loss of consciousness after

7 days (Bhalla and Thami 2004). Upon examination by a medical professional after 10 days, the boy

exhibited apathy, semi-consciousness, absence of superficial reflexes, reduced response to touch, pain,

and pressure, and tremor in tongue and limbs. Use of γ-HCH was immediately discontinued and the

infant regained normal consciousness and interaction with environmental stimuli over the subsequent

2 weeks (Bhalla and Thami 2004). The study authors reported that the boy showed evidence of anemia

and malnutrition, which were described as risk factors for γ-HCH-induced neurotoxicity. A 7-year-old

boy exposed to γ-HCH by dermal application 3 times in 4 days (dose not reported) exhibited ataxia,

weakness, and burning paresthesia, and following the third application, the boy had myoclonic jerks and

tonic-clonic seizures, whereupon he was brought to the hospital (Daud et al. 2010). No details of the

extent of exposure were reported. After treatment to control the seizures, induction of diuresis, and

frequent bathing and changing of clothing, the boy was discharged after 2 days (Daud et al. 2010).

Rats exposed to various concentrations of γ-HCH aerosol via nose-only inhalation for 4 hours exhibited

concentration-related neurological effects (Oldiges et al. 1980; Ullmann 1986b). Slight-to-moderate

sedation was observed after exposure to 101 mg/m

; slight-to-severe sedation was noted after exposure to

HEXACHLOROCYCLOHEXANE (HCH) 146

2. HEALTH EFFECTS

378 mg/m

; restlessness, excitation, and ataxia were seen after exposure to ≥273 mg/m

; and spasms were

also noted at the highest concentration (2,104 mg/m

). Concentrations ≥378 mg/m

were also associated

with mortality in one study (Ullmann 1986b) but not in the other even at concentrations up to 603 mg/m

(Oldiges et al. 1980). Rats exposed to 0.02–5 mg/m

γ-HCH aerosol for 90 consecutive days exhibited a

"slightly disturbed general condition" (not further characterized) within 2 weeks (Oldiges et al. 1983). At

the end of the 90-day exposure, there were no treatment-related changes in brain weight or histology, or

on histology of the sciatic or optic nerves. Mice were exposed to similar concentrations (0.3–5 mg/m

)

for 14 weeks (5 days/week) and exhibited no clinical signs of neurotoxicity (Klonne and Kintigh 1988).

Neurotoxic effects have been reported in several species of animals exposed to γ-HCH. The most serious

effects were seizures and/or convulsions following intragastric administration of approximately 15–

60 mg/kg for ≥1 day in rats (Amyes 1990; EPA 1999a; Fitzhugh et al. 1950; Gilbert and Mack 1995;

Johri et al. 2008; Joy et al. 1982; Martinez and Martinez-Conde 1995; Martinez et al. 1991; Matsuura et

al. 2005; Parmar et al. 2003; Tusell et al. 1988; Vendrell et al. 1992a, 1992b; Woolley and Griffith 1989).

Kindling, the induction of seizures with repeated application of subthreshold electrical or chemical stimuli

to the brain, has been used as a method of investigating neurological response to γ-HCH poisoning. A

single oral dose of 5–20 mg/kg γ-HCH to either naïve or rats previously kindled by electrical stimulus

produced myoclonic jerks and clonic seizures, which increased in a dose-dependent manner and were

increased in kindled animals (Gilbert and Mack 1995). Enhanced susceptibility to kindled seizures

brought on by electrical stimulation was seen in rats exposed for 10 weeks to 10 mg/kg/day γ-HCH,

3 days/week (Gilbert 1995). Increased rates of acquisition of kindled seizures were observed following

dosing of rats with 3–10 mg γ-HCH/kg/day for 4 days (Joy et al. 1982). Single daily doses of 20 mg/kg

γ-HCH in mice significantly reduced the convulsive threshold, as measured by the dose of

pentylenetetrazol required to induce seizures 1–4 hours after treatment, but increased the convulsive

threshold 48 hours following treatment (Hulth et al. 1978). A dose of 50 mg/kg γ-HCH significantly

increased the convulsive threshold 2, 4, and 10 days following dosing (Hulth et al. 1978).

Two studies of rats showed that oral administration of γ-HCH can alter neurotransmitter levels in the

brain. Decreased levels of brain serotonin were reported in rats exposed for 6 days to a dose of

3 mg/kg/day γ-HCH (Attia et al. 1991), while 10 doses totaling 60 mg/kg γ-HCH over a period of 30 days

resulted in decreased brain dopamine levels (Martinez and Martinez-Conde 1995).

HEXACHLOROCYCLOHEXANE (HCH) 147

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Acute and subchronic neurotoxicity screening bioassays including functional observational battery, motor

activity assessments, and neuropathology were reported in unpublished Confidential Business

Information (CBI) submissions summarized by EPA (1999a, 1999b). In the acute neurotoxicity screening

study, exposure to γ-HCH caused decreased motor activity 3 hours after gavage dosing of female rats

with ≥20 mg/kg and males at 60 mg/kg (EPA 1999a). Females also had increased forelimb grip strength

and decreased grooming behavior at 20 mg/kg, and an absence of grooming behavior at 60 mg/kg. Other

effects at 60 mg/kg included clinical signs (e.g., piloerection, urine-stained fur, tremors, and/or

convulsions) in both sexes and increased hindlimb foot splay in males (EPA 1999a). A 13-week

neurotoxicity screening study in Crl:CDBR rats by the same author (EPA 1999b) showed neurological

effects in both sexes at the highest dose (28.1–30.2 mg/mg/day), including clinical signs (e.g.,

piloerection, abnormal grooming behavior), increased rearing, walking on tiptoes, hypersensitivity to

touch, hunched posture, and several deaths. There were no effects on forelimb or hindlimb grip strength,

hindlimb splay, motor activity, or neuropathology (EPA 1999b).

Neurobehavioral testing in rats exposed for acute and intermediate durations have shown effects on

activity, cognition, and memory. Increased anxiety (Llorens et al. 1990) and decreased motor activity

(EPA 1999a) were reported in rats following a single gavage dose of 20 mg/kg, and increased

spontaneous motor behavior was observed at 10 mg/kg (Llorens et al. 1989). Avoidance response latency

was significantly increased in rats administered a single dose of 15 mg/kg by gavage (Tilson et al. 1987).

Impaired neurocognition, measured as decreased step-down latency in passive avoidance test and

prolonged transfer latency in the elevated plus maze test, occurred in rats exposed for 6 weeks to a γ-HCH

dose of 15 mg/kg/day (Sahaya et al. 2007). Srivastava et al. (2019) observed behavioral changes (reduced

locomotor activity and impaired spatial memory) in rats exposed to 2.5 mg/kg/day for 21 days. A longer

exposure (40 days) at this dose (2.5 mg/kg/day) resulted in significantly altered Skinner box behavior

(operant conditioning) in a small number of rats (Desi 1974).

At a γ-HCH dose (2.5 mg/kg/day for 21 days) that induced changes in locomotor activity and spatial

memory, Srivastava et al. (2019) detected ultrastructural changes in the hippocampus and substantia nigra

of rats. Changes in the brain included swollen mitochondria with disintegrated cristae, shortened fuzzy

synapse, disintegrated myelin layer, and autophagosomes (Srivastava et al. 2019). Peripheral nerve

effects were seen in one oral study of γ-HCH. Significantly decreased nerve conduction velocity was

measured in rats exposed to 25.4 mg/kg/day for 30 days (Muller et al. 1981).

HEXACHLOROCYCLOHEXANE (HCH) 148

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While data are more limited, neurotoxicity has been documented in rats and rabbits exposed to γ-HCH via

dermal application. Clinical signs such as excitability, seizures, and convulsions were observed in rabbits

following a single topical application of 60 mg/kg γ-HCH in a 1% solution (Hanig et al. 1976); young

rabbits were more susceptible than older rabbits. Slight sedation was observed in rats exposed once for

24 hours to 1,000 mg/kg γ-HCH through shaved dorsal skin (Ullmann 1986a). One female exposed to

2,000 mg/kg in this study exhibited severe sedation and spasms (Ullmann 1986a). Aggressiveness or

hyperactivity were noted in rats exposed dermally for 13 weeks to ≥10 mg γ-HCH/kg/day, while ataxia,

tremors, and convulsions were seen in females at 60 mg/kg/day (EPA 1988a).

Mechanisms. Gavage administration of 2.5, 5, 10, or 15 mg γ-HCH/kg/day for 5 days produced a dose-

dependent increase in the activities of EROD, PROD, and NDMA-d in the brain of Wistar rats (Parmar et

al. 2003). In the same study, Parmar et al. (2003) examined the effect of metabolism on the convulsive

effect of γ-HCH in rats. A single dose of 35 mg/kg of γ-HCH induced convulsions in 4 out of 10 animals.

Pretreatment of the rats with 3-methylcholanthrene (MC), an inducer of CYP1A1/1A2, had no significant

effect in the incidence of convulsions induced by γ-HCH. However, induction of CYP 2B1/2B2 (by

pretreatment with phenobarbital) or CYP2E1 (by pretreatment with ethanol) significantly increased the

incidence of convulsions caused by γ-HCH, as did blocking of cytochrome P450-mediated metabolism

with cobalt chloride (Parmar et al. 2003). Taken together, the results suggest that the convulsive activity

is due to γ-HCH per se and/or to metabolites formed by phenobarbital- or ethanol-inducible P450

isoenzymes.

Decreased myelin was observed in rats exposed to 5 mg/kg/day by gavage for 3 days (Serrano et al.

1990). These authors also detected a significant decrease in 2',3'-cyclic nucleotide 3'-phosphodiesterase

(CNP) activity in treated animals, although no dose-response was seen. This enzyme is myelin-specific,

but its exact function in normal myelin in unknown (Serrano et al. 1990).

Increased lipid peroxidation (thiobarbituric acid reactive substances [TBARS]) and decreases in

antioxidant enzyme activities (superoxide dismutase, catalase, and glutathione peroxidase) were measured

in the brains of Wistar rats after three daily doses of 5 mg/kg/day γ-HCH; neurological endpoints were

not evaluated in these animals (Hfaiedh et al. 2012). Fatih Fidan et al. (2008) reported increased

malondialdehyde and decreased levels of reduced glutathione in the brains of rats exposed to γ-HCH

(≥10 mg/kg/day) by daily gavage for 30 days. Similarly, a 30-day exposure to doses of 50 mg/kg/day

induced lipid peroxidation (measured as TBARS) and depletion of antioxidant enzymes (glutathione

peroxidase and catalase) in the brains of rats exposed by drinking water (Hfaiedh et al. 2011). After

HEXACHLOROCYCLOHEXANE (HCH) 149

2. HEALTH EFFECTS

6 weeks of daily exposures to 15 mg/kg/day, rats exhibited increased malondialdehyde and non-protein

thiols in the brain (Sahaya et al. 2007). In contrast, no significant changes were seen in lipid peroxidation

in brain tissue from rats treated for 90 days with 90 mg γ-HCH/kg/day in food (Arisi et al. 1994).

Technical HCH or Unspecified Isomers of HCH. Paresthesia of the face and extremities, headache, and

vertigo were reported in a group of 45 workers occupationally exposed during manufacture and

formulation of technical-grade HCH for several years (Kashyap 1986); exposure concentrations were not

reported. Both inhalation and dermal exposures were possible. Heiberg and Wright (1955) reported

convulsions in a woman who had treated cattle with an insecticide containing 11% γ-HCH and 16% other

HCH isomers.

In animals exposed to technical-grade HCH by oral administration, effects like those seen with β- and

γ-HCH were seen. Behavioral and neurochemical changes were evaluated in rats that were administered

technical-grade HCH in doses of 10 or 20 mg/kg/day in oil by gavage for 7–30 days (Sahoo et al. 1999).

Assessment of open-field behavior (horizontal motor activity, vertical exploratory rearing, and grooming

activities) and brain biochemistry (ATPases and acetylcholinesterase) showed effects that included

reduced brain total ATPase and Na

-, K

-, and/or Mg

-ATPase activities after 7–30 days at

≥10 mg/kg/day, reduced brain acetylcholinesterase activity after 15 and 30 days at 20 mg/kg/day,

increased motor activity after 7 days at 20 mg/kg/day, and reduced grooming behavior after 30 days at

20 mg/kg/day (Sahoo et al. 1999). Mudawal et al. (2018) observed impairments in learning (conditioned

avoidance response and Y-maze continuous alternation test) and increased spontaneous locomotor

activity in rats given technical-grade HCH for 21 days beginning at 3, 18, or 48 weeks of age. The most

pronounced effects were observed in the aged rats. After exposure that began at 48 weeks of age, the

animals also exhibited ultrastructural changes in the hippocampus and substantia nigra when examined by

transmission electron microscopy; in contrast, similar exposure beginning at 3 or 18 weeks of age did not

result in ultrastructural changes (Mudawal et al. 2018). Increased motor activity was also observed in rats

exposed to technical-grade HCH at a level of 50 mg/kg/day for 120 days (Gopal et al. 1992).

Alterations in neurotransmitter levels, increased brain wave frequency, and behavioral changes were

reported in male rats administered 50 mg/kg/day technical-grade HCH by gavage for 1 or 3 months

(Anand et al. 1991). Exposure to 0.4 mg/kg/day technical-grade HCH for 360 days resulted in

convulsions, tremors, and paralysis in male rats after 270 days, although the number of animals affected

and the severity of the symptoms were not reported (Dikshith et al. 1991a). This study also found

degeneration of the cerebellum and cerebellar cortex in animals sacrificed after a 1-year exposure to

HEXACHLOROCYCLOHEXANE (HCH) 150

2. HEALTH EFFECTS

20 mg/kg/day. Seizures were noted in mice exposed to technical-grade HCH through feed or gavage at

levels of 10–17 mg/kg/day for 80 weeks (Kashyap et al. 1979). Damage to Purkinje cells in the

cerebellum and tremors were found in female Wistar rats treated with 100 mg/kg/day technical-grade

HCH for 7–30 days (Dikshith et al. 1991c).

Increased levels of brain catecholamines, particularly norepinephrine and dopamine, and associated signs

of toxicity such as mild tremor, lacrimation, salivation, and dyspnea were observed in female rats given

oral doses of 100 mg/kg/day of technical-grade HCH for 7 days (Raizada et al. 1993). The activity of

monoamine oxidase (MAO, an enzyme that oxidizes monoamine neurotransmitters) in the cerebrum

showed a marginal decrease, while significant increases and decreases were observed in the cerebellum

and spinal cord, respectively (Raizada et al. 1993). Rats treated with 20 mg technical-grade HCH/kg/day

in food for 90 days exhibited increased γ-aminobutyric acid (GABA) levels, increased glutamate

decarboxylase (GAD) activity, and decreased glutamate levels in the brain (Nagaraja and Desiraju 1994).

Mechanisms. As with γ-HCH, there is some evidence that oxidative stress may contribute to the

neurotoxic effects of technical-HCH. Mudawal et al. (2018) observed increased lipid peroxidation and

decreases in both antioxidant enzyme activities (superoxide dismutase and catalase) and reduced

glutathione in the hippocampus and substantia nigra of rats given 2.5 mg/kg/day technical HCH for

21 days. These changes correlated with neurobehavioral effects, as discussed above.

2.16 REPRODUCTIVE

Epidemiological Studies. Few epidemiological studies on the reproductive effects of HCH isomers were

located; the available studies are summarized in Table 2-15. With one exception (Freire et al. 2014), the

studies were conducted in populations without known sources of exposure to HCH; in these populations,

consumption of contaminated food is expected to be the primary exposure route. All these studies

measured HCH isomers in serum, fat, or follicular fluid as biomarkers of exposure, and exposure was

measured simultaneously with outcome assessment or after the outcome occurred.

Freire et al. (2014) conducted a cross-sectional study of reproductive hormone and HCH levels in the

serum of 604 people residing near a former HCH manufacturing facility in Brazil. In this population, an

inverse association between serum testosterone concentrations and serum α- and β-HCH concentrations

was observed in men. In women, increases in serum β-HCH were associated with increased serum

HEXACHLOROCYCLOHEXANE (HCH) 151

2. HEALTH EFFECTS

Table 2-15. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Reproductive

Effects

Reference, study type, and population

Outcome evaluated

Isomer

Biomarker

Mean concentration (unless

otherwise noted)

Result

Akkina et al. 2004

Cross-sectional, 219 menopausal women,

Hispanic Health and Nutrition Examination

survey (HHANES), United States

Age at menopause

β-HCH

Serum

>2.09 ng/g (> median)

↓

Buck Louis et al. 2012

Matched cohort, operative cohort:

473 women undergoing laparoscopy or

laparotomy; population-based cohort:

127

women matched on age and residence,

18–44 years old, United States

Endometriosis

β-HCH

Serum

Operative cohort, medians:

0.0063 ng/g (cases)

0.0063 (non-cases)

↔

Population cohort, medians:

0.0066 (cases)

0.0063 (non-cases)

↑

γ-HCH

Omental fat

Operative cohort, medians:

0.1991 ng/g fat (cases)

0.1200 (non-cases)

↑

Ploteau et al. 2017

Case-control, 55 cases of deep infiltrating

endometriosis and 44 controls, 18–

45 years

old, France

Deep infiltrating

endometriosis

β-HCH

Adipose

tissue

13.62 ng/g lipid (median) (cases)

14.33 (controls)

↔

Deep infiltrating

endometriosis with

ovarian

endometrioma

21.61(cases)

14.33 (controls)

↑

Upson et al. 2013

Case-control, 248 cases of endometriosis

and 538 population-based controls,

Washington, United States

Endometriosis

β-HCH

Serum

>43.06 pg/g (3

quartile)

↑

γ-HCH

>13.89 (4

quartile)

↔

Sum HCH

>0.29 mol/g (4

quartile)

↔

Ovarian

endometriosis

β-HCH

Serum

>43.06 pg/g (3

quartile)

↑

γ-HCH

>13.89 (4

quartile)

↔

Sum HCH

>0.29 mol/g (4

quartile)

↔

Al-Hussaini et al. 2018

Cross-sectional, 94 women in infertile

couples undergoing intracytoplasmic sperm

injection, 20–38 years old, Egypt

Endometrial

thickness

γ-HCH

Follicular

fluid

418.6±171.4 µg/L (mean±SD)

↑

Implantation rate

↓

HEXACHLOROCYCLOHEXANE (HCH) 152

2. HEALTH EFFECTS

Table 2-15. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Reproductive

Effects

Reference, study type, and population

Outcome evaluated

Isomer

Biomarker

Mean concentration (unless

otherwise noted)

Result

Pollack et al. 2021

Operative cohort, 339 women undergoing

laparoscopy or laparotomy, age 18-

44 years, United States

Endometriosis

β-HCH

Omental fat

0.14 ng/g (median)

↑

Serum

0.013

↔

Adipose to

serum ratio

Not reported

↑

γ-HCH

Omental fat

0.137

↑

Serum

0.019

↔

Adipose to

serum ratio

Not reported

↑

Génard-Walton et al. 2023

Case-control, 138 cases of diminished

ovarian reserve and 151 controls,

mean age

33.8 years for cases, 32.4 years for

controls, France

Diminished ovarian

reserve

β-HCH

Serum

4.1 ng/g lipid (cases) (median)

4.5 (controls)

↓

Abou Ghayda et al. 2020

Prospective cohort, 152 males enrolled in

the Russian children’s study at 8–9 years of

age and followed up at 18–23 years of age,

Russia

Semen volume

β-HCH

Serum

172 ng/g lipid (median)

↓

Sperm concentration

↔

Total sperm count

↔

Progressive motility

↔

Madrigal et al. 2021

Cross-sectional, 748 men aged ≥20 years,

NHANES 1999–2004, United States

Serum testosterone

β-HCH

Serum

22.56-1200.0 ng/g lipid (4

quartile)

↔

Serum estradiol

↔

Serum sex hormone

binding globulin

↔

Serum androstanediol

glucuronide

↔

HEXACHLOROCYCLOHEXANE (HCH) 153

2. HEALTH EFFECTS

Table 2-15. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Reproductive

Effects

Reference, study type, and population

Outcome evaluated

Isomer

Biomarker

Mean concentration (unless

otherwise noted)

Result

Miao et al. 2022

Cross-sectional, 387 men seeking semen

analysis, mean age 30.5 years, China

Sperm motility

α-HCH

Serum

0.08 ug/L

↔

β-HCH

0.85

↔

γ-HCH

0.12

↓

δ-HCH

0.70

↔

Sperm concentration,

sperm count

α-HCH

See above

↔

β-HCH

See above

↔

γ-HCH

See above

↓

δ-HCH

See above

↔

Zeng et al. 2022

Cross-sectional, 421 men seeking semen

analysis, mean age 30.6 years, China

Serum testosterone

α-HCH

Serum

0.10 ug/L (75

percentile)

↔

β-HCH

1.03

↔

γ-HCH

0.12

↔

δ-HCH

0.89

↔

Freire et al. 2014

Cross-sectional, 604 persons 15–94 years

old, residing near former HCH

manufacturing facility, Brazil

In men:

Serum testosterone

α-HCH

Serum

2.52 ng/mL (median)

↓

β-HCH

6.00

↓

γ-HCH

0.95

↔

In premenopausal women:

Serum estradiol,

progesterone,

prolactin, LH, and

FSH

α-HCH

Serum

2.77 ng/mL (median)

↔

β-HCH

6.32

↔

γ-HCH

0.89

↔

HEXACHLOROCYCLOHEXANE (HCH) 154

2. HEALTH EFFECTS

Table 2-15. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Reproductive

Effects

Reference, study type, and population

Outcome evaluated

Isomer

Biomarker

Mean concentration (unless

otherwise noted)

Result

In peri- or post-menopausal women:

Serum estradiol

α-HCH

Serum

2.43 ng/mL (median)

↔

β-HCH

11.72

↑

γ-HCH

1.07

↔

Serum LH

α-HCH

Serum

See above

↔

β-HCH

See above

↓

γ-HCH

See above

↔

Serum progesterone,

prolactin, and FSH

α-HCH

Serum

See above

↔

β-HCH

See above

↔

γ-HCH

See above

↔

Borderline significant.

↑ = association with increase; ↓ = association with decrease (inverse association); ↔ = no association; FSH = follicle-stimulating hormone; LH = luteinizing

hormone; NHANES = National Health and Nutrition Examination Survey; SD = standard deviation

HEXACHLOROCYCLOHEXANE (HCH) 155

2. HEALTH EFFECTS

estradiol and decreased serum luteinizing hormone (LH) levels among peri- and post-menopausal women,

but not premenopausal women. No associations were seen between any HCH isomer and serum

progesterone, prolactin, or follicle-stimulating hormone (FSH) in women. Serum α- and γ-HCH levels

showed no association with reproductive hormone levels in women (Freire et al. 2014).

There were no observed associations between serum levels of HCHs and serum testosterone in two cross-

sectional studies (Madrigal et al. 2021; Zeng et al. 2022), and no association between serum β-HCH and

serum estradiol, sex hormone binding globulin, or androstanediol glucuronide in one of the studies

(Madrigal et al. 2021). A decrease in semen volume at adulthood was associated with pre-pubescent

serum levels of β-HCH in a prospective cohort study of 152 Russian men (Abou-Ghayad et al. 2020).

Miao et al. (2022) observed an association between γ-HCH levels in serum and decreased sperm motility

in a cross-sectional study in China. Neither γ-HCH nor other HCH isomers in serum were associated with

changes in sperm count or concentration in this study.

In a matched cohort study of 473 women undergoing laparoscopy or laparotomy (operative cohort) and

127 women matched on age and residence (population-based cohort), both β-HCH levels in serum and

γ-HCH levels in omental fat were associated with increased risk of endometriosis (Buck Louis et al.

2012). Three case-control studies also reported associations between endometriosis and biomarkers of

β-HCH exposure. An association between deep infiltrating endometriosis with ovarian endometrioma

and β-HCH in adipose tissue was seen in a study of 99 adult women in France (55 cases and 44 controls)

(Ploteau et al. 2017). Upson et al. (2013) observed associations between serum levels of β-HCH and both

endometriosis and ovarian endometriosis in a larger study in the United States (248 cases and

538 controls). Serum concentrations of γ-HCH were not associated with endometriosis in this study

(Upson et al. 2013). Pollack et al. (2021) observed an association between incident endometriosis and

β- and γ-HCH concentrations in adipose tissue and adipose to serum concentration ratios; however, no

association was seen with β- or γ-HCH concentrations in serum. Measurements of γ-HCH in follicular

fluid from 94 women undergoing intracytoplasmic sperm injection were associated with increased

endometrial thickness and decreased implantation rate (Al-Hussaini et al. 2018).

A case-control study in France observed an inverse association between diminished ovarian reserve and

serum levels of β-HCH (Génard-Walton et al. 2023). There were no other studies of this endpoint.

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A small cross-sectional study (Akkina et al. 2004) of Hispanic women in the United States reported a

decrease in the age at menopause associated with higher serum levels of β-HCH; no other studies of this

endpoint were located.

α-HCH. No treatment-related histopathology findings were noted in the testes or uterus and ovaries of

rats given α-HCH in feed at doses up to 70 mg/kg/day for an average of 6 months or 9 mg/kg/day for

2 years (Fitzhugh et al. 1950).

β-HCH. Oral exposure to 60 mg β-HCH/kg for 30 days resulted in normal uteri and reproductive cycling

in female mice (Cornacoff et al. 1988). Atrophy of the ovaries and testes, hyperplastic and vacuolized

endometrial epithelium, degeneration of the seminiferous tubules, and disruption of spermatogenesis were

seen in rats exposed to 22.5–25 mg/kg/day β-HCH in the diet (Van Velsen et al. 1986). Half of the

animals in this group showed significant clinical signs of neurotoxicity and were humanely sacrificed

before the end of the 13-week study; abnormal reproductive organ pathology was seen in both survivors

and early decedents (Van Velsen et al. 1986). While no effects were seen upon microscopic examination

of the testes, uteri, and ovaries of rats given β-HCH in the diet at doses up to 70 mg/kg/day for up to

10 weeks, slight testicular atrophy was seen after 2 years of exposure to 7 mg/kg/day (Fitzhugh et al.

1950).

γ-HCH (Lindane). Statistically significant increases in the levels of serum LH were reported in a group

of 54 men occupationally exposed to unspecified concentrations of γ-HCH for approximately 8 years in a

γ-HCH-producing factory (Tomczak et al. 1981). Although the mean serum concentration of FSH was

increased and testosterone was decreased, these differences were not statistically significant compared to

mean values determined in a control group.

Studies of reproductive effects in animals exposed by inhalation are limited to two intermediate-duration

studies focused on systemic toxicity endpoints. Histopathology evaluation of the testes, prostate, ovaries,

and uterus of rats and mice exposed by inhalation to 5 mg/m

γ-HCH for 13–14 weeks showed no effects

of treatment (Klonne and Kintigh 1988; Oldiges et al. 1983).

In animals exposed orally for acute and intermediate durations, γ-HCH induced effects on the male

reproductive system, female reproductive system, and on mating, fertility, and early gestation endpoints,

as discussed below.

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Effects on male reproductive system. The male reproductive system appears to be sensitive to the toxic

effects of orally administered γ-HCH. Rats and mice exposed to this isomer have exhibited effects on

spermatogenesis, reproductive organ weight changes, and histopathology changes in the testes, while

altered sexual behavior was reported in sheep. The lowest dose associated with effects on the male

reproductive tract in acute-duration studies is 6 mg/kg/day (Dalsenter et al. 1996); for intermediate-

duration studies, it is 1 mg/kg/day in mink (Beard and Rawlings 1998).

In male rats, oral administration of 6 mg/kg for 5 days or a single dose of 30 mg/kg of γ-HCH resulted in

a reduction in the number of testicular spermatids and epididymal sperm of both treated groups 2 weeks

after treatment (Dalsenter et al. 1996). γ-HCH was detected in the testes of both groups 24 hours and

2 weeks after the last treatment. Histological examination by electron microscopy revealed ballooning of

the Sertoli cells with fragmentation or loss of organelles (Dalsenter et al. 1996). Sharma and Singh

(2010) administered γ-HCH (30 mg/kg/day) by gavage to Wistar rats for 14 and 28 days for evaluation of

effects on the male reproductive tract. After 14 days, the rats had markedly decreased epididymis (27%)

and testes (68%) weights. In addition, substantial and persistent reductions (≥85% less than controls) in

sperm head count, motility, and percent live sperm, and marked and persistent increases (4-fold) in

percent abnormal sperm were observed (Sharma and Singh 2010). After 28 days at this dose, the effects

on epididymis and testes weights were more pronounced, as were the changes in sperm parameters:

decreases of ≥89% compared to controls were seen in sperm head count, motility, and percent live sperm,

as well as a 4-fold increase in percent abnormal sperm (Sharma and Singh 2010). Similar results were

seen in Wistar rats given 50 mg/kg/day γ-HCH in water for 30 days (Hfaiedh et al. 2011). The weights of

the testes, epididymides, and prostate gland were decreased by 42–52% relative to controls, and the

seminal vesicle weight was reduced by 5%. Compared to control values, sperm count was diminished by

56% and sperm motility by 37% at this dose (Hfaiedh et al. 2011). In a 45-day exposure study, Saradha

and Mathur (2006) observed decreased sperm count (~7%) and motility (~15%) in male Wistar rats

administered doses of 1 mg/kg/day by gavage. At the higher dose of 5 mg/kg/day in this study, the

effects were more severe, with a 27% decrease in sperm count and ~25% decrease in sperm motility

(Saradha and Mathur 2006). In a 2-generation reproductive toxicity study in Crj:CD(SD)IGS rats given

dietary doses up to 23.3 mg/kg/day, no statistically significant treatment-related effects on sperm count,

motility, or percent abnormal sperm were noted in F0 or F1 males (Matsuura et al. 2005). Histology of

the parental male reproductive organs was also normal (Matsuura et al. 2005). Dietary exposure to up to

120 mg/day γ-HCH for 10 months or 30 mg/kg/day for 2 years or did not result in histopathology changes

in the testes of rats (Fitzhugh et al. 1950).

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Exposure to γ-HCH has also induced altered levels of reproductive hormones in male rats. When male

Wistar rats were exposed to 50 mg/kg/day γ-HCH in water for 30 days, serum FSH levels were decreased

by 74% relative to controls (Hfaiedh et al. 2011). Effects of γ-HCH on the levels of reproductive

hormones in blood of male animals appear to be more significant in younger animals compared with older

animals. Groups of 30 male Wistar rats were administered 5 mg/kg/day γ-HCH for 5 days beginning at 9,

18, or 27 weeks of age (Agrahari et al. 2019). Animals treated with γ-HCH beginning at 9 weeks of age

exhibited significantly decreased serum testosterone (39%) and growth hormone (29%), and increased

serum LH (42%) and FSH (31%), compared to controls. Similar results were observed in the group

treated at 18 weeks of age, but treatment at 27 weeks of age resulted in smaller decreases in serum

testosterone and growth hormone, and no significant effect on serum LH or FSH. No dose-related effects

on serum hormone levels were observed in F0 or F1 male parents in a 2-generation study of

Crl:CD(SD)IGS rats at doses of 17.2–26.1 mg/kg/day in diet for ~10 weeks (Matsuura et al. 2005).

One study reported male reproductive tract effects in mice exposed to γ-HCH. Nagda and Bhatt (2011)

exposed Swiss mice by gavage (40 mg/kg/day) for 60 days. At sacrifice at the end of exposure, the mice

exhibited a 10% decrease in testes weight as well as histopathology changes in the testes, including

shrunken and distorted seminiferous tubules, sparse Leydig cells, and oligospermia (Nagda and Bhatt

2011). The male reproductive effects of γ-HCH were also studied in young rams given 1 mg/kg/day in

treated feed from conception to sexual maturity (Beard et al. 1999a). The subjectively-scored sexual

behavior in the rams was significantly reduced in treated animals presented with estrous ewes (Beard et

al. 1999a).

Effects on female reproductive system. Studies examining female reproductive effects in animals exposed

to γ-HCH are more limited, but suggest effects on estrous cycling and other endpoints in a variety of

species. Oral administration of γ-HCH for acute and intermediate durations has resulted in alterations in

estrous cycling, sexual behavior, and uterine histopathology. In acute-duration studies, the lowest dose

associated with these effects was 25 mg/kg/day (Uphouse and Williams 1989); in intermediate-duration

studies, the lowest dose associated with these effects was 1 mg/kg/day (Beard and Rawlings 1999).

Increased length of estrous cycle and decreased sexual receptivity were found in female rats treated with a

single dose of γ-HCH (≥25 mg/kg) given by gavage (Uphouse and Williams 1989). Female rabbits

exposed to 0.8 mg γ-HCH/kg/day, 3 days/week for 12 weeks had a reduced ovulation rate (Lindenau et al.

1994). Histopathological changes were observed in the uteri of female Sprague-Dawley rats given

γ-HCH by gavage at a dose of 8 mg/kg/day for 4 weeks. The uterine changes were described as low

columnar endometrial glandular epithelial cells (Yang et al. 2014; Zhang et al. 2016). Delayed vaginal

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opening and disrupted ovarian cycling in female F344 rats given ≥10 mg/kg/day by gavage for 15 weeks

beginning at weaning (Chadwick et al. 1988). Finally, in estrus synchronized ewe lambs dosed with

γ-HCH in feed at 1 mg/kg/day from conception to sexual maturity, significantly shorter estrous cycle

length and reduced number and total volume of corpus lutea were observed (Beard and Rawlings 1999).

No other detrimental fertility effects were observed. No effects on maternal female reproductive organ

weights or histology were noted in CD mice exposed to 15 mg/kg/day via gavage on GDs 9–16

(Maranghi et al. 2007). In a 2-generation reproductive toxicity study in Crj:CD(SD)IGS rats, doses of

28.0 mg/kg/day in diet for ~10 weeks resulted in a significantly decreased estrus cycle length (4 days

versus 4.45 days in controls) in F1, but not F0 female adults (Matsuura et al. 2005). No effects were

observed on ovarian follicle counts at any dose in F1 females, and no changes in reproductive organ

weights or histology were observed at sacrifice of F0 or F1 female parental animals (Matsuura et al.

2005). Fitzhugh et al. (1950) observed no effects on the histopathology of the uterus or ovaries of rats

given γ-HCH via the diet for up to 140 mg/kg/day for 10 months or up to 30 mg/kg/day for 2 years.

In female Wistar rats dosed with γ-HCH by daily gavage for 4 weeks, significantly decreased serum

levels of estradiol (20 and 26%) and testosterone (28 and 37%) were observed at 4 and 8 mg/kg/day

γ-HCH, respectively (Zhang et al. 2016; Yang et al. 2014). Significant, dose-related increases in serum

LH were seen at all doses (23–44% relative to controls at doses from 0.95 to 28 mg/kg/day) in F1 females

during proestrus in a 2-generation study of Crj:CD(SD)IGS rats (Matsuura et al. 2005). Serum hormone

levels in F0 female parents were not impacted by exposure in this study. Female mink exposed to

1 mg/kg/day γ-HCH before mating and through mating, gestation, and lactation exhibited no effects on

serum estradiol or progesterone when evaluated at weaning of their kits (Beard et al. 1997). Sheep

exposed on a similar schedule to the same dose did not show changes in serum LH or FSH (Beard et al.

1999b)

Effects on mating, fertility, and early gestation. In a multigeneration reproduction study with γ-HCH,

Charles River CD rats were exposed to estimated dietary doses of 0, 0.09, 1.7, or 13.1 mg/kg/day for

2 generations (EPA 1991a). No treatment-related effects on mating, fertility, gestation survival, liveborn

indices, or mean litter sizes occurred in either generation, although developmental toxicity occurred at

13.1 mg/kg/day, as shown by reduced body weight and decreased viability in pups of both generations

and delayed maturation of F2 pups (see Section 2.17). Similar findings were noted in the 2-generation

study reported by Matsuura et al. (2005). No effects on mating, fertility, gestation length, birth index, or

gestation index were seen in Crj:CD(SD)IGS rats of either generation at doses up to 28 mg/kg/day, but

there were developmental effects on offspring body weight, viability, and sexual maturation (see

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Section 2.17). Female rabbits dosed with 0.8 mg γ-HCH/kg/day, 3 days/week for 12 weeks followed by

artificial insemination exhibited no effects on the fertilization rate or on pre- or post-implantation losses

(Seiler et al. 1994).

Mice and mink appear to be more sensitive than rats to the effects of γ-HCH on fertility and early

gestation. When mouse dams were treated with γ-HCH (6.2 mg/kg) during GDs 6–12, all fetuses were

resorbed (Sircar and Lahiri 1989). In another experiment by these authors, pregnant mice exposed to

10.8 mg/kg/day on GDs 1–4 exhibited no implantation sites. When pregnant mice were exposed to

3.6 mg/kg/day on GDs 14–19, all pups died (Sircar and Lahiri 1989). Acute preovulatory exposure to

γ-HCH caused embryonic effects in mice (Scascitelli and Pacchierotti 2003). Three consecutive daily

doses of γ-HCH in olive oil were administered to female mice either before mating (during the

preovulatory period) or immediately after mating. Oocyte maturation, ovulation, and fertilization were

evaluated by assessing percentage of vaginal plug positive females, number of embryos/female,

percentage of one-cell embryos (corresponding to unfertilized oocytes or zygotes that did not undergo

cleavage), and gross morphologic alterations of two-cell embryos. Preimplantation embryonic

development was evaluated by morphological examinations of morulae for determinations of one-cell

embryos (unfertilized eggs or zygotes that did not undergo cleavage), embryos retarded in their cleavage,

and abnormal embryos, as well as by cytological examinations of morulae for determinations of

interphase nuclei, meta-anaphases, apoptotic nuclei, micronuclei, and mitotic index. Preovulatory

exposure caused a significant increase of degenerating two-cell embryos (lysis or fragmentation of

blastomeres), but there were no exposure-related effects of post-mating treatment.

Reproductive toxicity studies in mink showed effects on sexual receptivity, whelping rate, and embryo

mortality. A 2-generation reproduction study of γ-HCH was conducted in mink that were exposed to

dietary doses of 0 or 1 mg/kg/day (Beard and Rawlings 1998). The parental (P0) generation was exposed

from 3 weeks before breeding until weaning of the offspring. Following weaning, the F1 females were

exposed throughout growth and mating (to untreated males), and subsequently throughout pregnancy and

lactation until 3 months post-lactation. The F2 females were exposed until they reached full adult body

size at 30 weeks of age. The F1 and F2 males were exposed until the time their testis development was

maximal (sexual maturity) at about 42 weeks of age. In addition to standard reproductive indices, serum

hormone levels (estradiol, testosterone) and histology of male and female reproductive tissues were

evaluated in offspring of both generations. There were no overt signs of toxicity or effects on mating

percentage. Fertility was reduced in both generations, as shown by reductions in whelping rate and litter

size, such that exposed mink produced approximately 60% fewer kits than controls. Other effects

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included reduced testis size in F2 males. In a single-generation study, female mink treated with

1 mg/kg/day γ-HCH in their diet from 3–6 weeks before mating until weaning at 8–10 weeks postpartum

showed effects on reproductive efficiency that included reduced receptivity to a second mating and

reduced whelping rate, although litter size was not affected (Beard et al. 1997). This decreased fertility

effect was primarily a result of embryo mortality after implantation.

Mechanisms. Inhibition of the formation of estradiol-receptor complex in the rat uterus cytosol was

reported in female rats administered 30 mg γ-HCH/kg/day by oral intubation for 7 days (Tezak et al.

1992). Statistically significant increases in the glycogen content of the uterus, cervix, and vagina (but no

increase in organ weight) were reported in female rats exposed to 20 mg γ-HCH/kg/day in the diet for

30 days (Raizada et al. 1980). Antiestrogenic properties were found in female rats given gavage doses of

10 mg/kg/day γ-HCH for 15 weeks (Chadwick et al. 1988). These responses were not seen at

5 mg/kg/day. Ovariectomized rats exposed for 5 days and sexually immature female rats exposed for

7 days to 40 mg γ-HCH/kg/day showed no effects on the number of estrogen and estrogen-dependent

progesterone receptors (Laws et al. 1994). Thus, γ-HCH's antiestrogenic effects in reproductive tissue do

not appear to be due to direct action on estrogen receptors or its induction of progesterone receptors.

In vitro studies have not shown binding of γ-HCH to the estrogen receptor, but one study showed that this

isomer could inhibit the activity of aromatase (the enzyme that forms estrogen in mammals) in human

placental and embryonic kidney cells transfected with the associated gene (reviewed by IARC 2018).

Technical or Unspecified HCH. Studies of reproductive toxicity in animals exposed orally to technical-

grade HCH have shown effects on the male reproductive tract of rats and mice. Dermal exposure of rats

and guinea pigs induced similar changes.

Immature (15-day-old) and mature (90-day-old) rats were administered technical-grade HCH in doses of

10 or 20 mg/kg/day in oil by gavage for 7, 15, or 30 days (Samanta et al. 1999). Exposure to

≥10 mg/kg/day for 7 days caused effects that included reduced epididymis weight in immature rats and

reduced seminal vesicle and ventral prostate weights in adult rats. Effects observed following exposure to

≥10 mg/kg/day for 7–30 days included reduced total sperm count and increased frequencies of damaged

sperm and sperm with anomalous heads in adult rats. Shivanandappa and Krishnakumari (1983) reported

testicular atrophy, degeneration of seminiferous tubules, and disruption of spermatogenesis in male rats

fed technical-grade HCH at 75 mg/kg/day for 90 days. After 180 days of exposure to 3 mg/kg/day

technical-grade HCH, male Charles Foster rats exhibited significant decreases in testes and vas deferens

HEXACHLOROCYCLOHEXANE (HCH) 162

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weights, as well as decreases in seminiferous tubule diameter and degeneration of muscle tissue in the vas

deferens (Gautam et al. 1989; Roy Chowdhury and Gautam 1990). At a higher dose of 6 mg/kg/day,

complete degeneration of testicular tissue, post-meiotic spermatogenic arrest, and degeneration of

spermatogenic cells were seen (Roy Chowdhury and Gautam 1990). Testicular degeneration was

reported in male rats exposed to 20 mg/kg/day technical-grade HCH in the diet for 360 days (Dikshith et

al. 1991a). Fitzhugh et al. (1950) observed no effects on the histopathology of the testes, uterus, or

ovaries of rats given technical HCH via the diet for up to 9 mg/kg/day for 2 years. Moderate testicular

atrophy was observed in rats given technical HCH in the diet for 6 months at a dose of 60 mg/kg/day

(Fitzhugh et al. 1950). In mice, exposure to 90 mg technical-grade HCH/kg/day (isomer composition

unknown) for 3 months led to increased testicular weight and degeneration of seminiferous tubules

(Nigam et al. 1979).

Male and female Druckrey rats were exposed via diet and drinking water to estimated total daily doses of

0, 16, or 32 mg/kg/day technical-HCH throughout 3 generations (Srivastava and Raizada 2000). There

were no exposure-related effects on reproduction in any of the 3 parental generations, and no

morphological or teratological changes in any of the offspring generations (F1b, F2b, or F3b).

In studies of dermal exposure, the backs of male rats were sprayed with 50 or 100 mg/kg/day technical-

grade HCH for 120 days and the rats were housed in separate cages to prevent licking (Prasad et al.

1995). Depletion of germ cells and impaired function of Leydig and Sertoli cells was suggested by

significant dose-related changes in activities of testicular enzymes such as sorbitol dehydrogenase,

glucose-6-P-dehydrogenase, γ-glutamyl transpeptidase, and β-glucuronidase. Significant reductions in

sperm count and motility and increased percentages of abnormal sperm were also observed in both

groups. A significant reduction in testosterone level was observed in the high-dose group. Dikshith et al.

(1978) reported testicular hypertrophy and atrophy and complete inhibition of spermatogenesis in guinea

pigs dermally treated with technical-grade HCH for 7, 15, or 30 days at doses as low as 100 mg/kg/day.

The patch of the abdomen on which the HCH was applied was not covered to prevent licking, so oral

exposure more than likely occurred.

Mechanisms. There is evidence that oxidative stress may contribute to the effects of technical-grade HCH

on the male reproductive system. Testicular oxidative stress was studied in immature (15-day-old) and

mature (90-day-old) rats that were administered technical-grade HCH in doses of 10 or 20 mg/kg/day in

oil by gavage for 7, 15, or 30 days (Samanta et al. 1999). Endpoints that were evaluated included

testicular protein and lipid peroxidation, testicular levels of antioxidant enzymes (superoxide dismutase,

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catalase, glutathione peroxidase, glutathione reductase) and non-enzymatic antioxidants (reduced

glutathione, ascorbic acid, hydrogen peroxide). Testes from immature and adult rats exposed to

≥10 mg/kg/day for 7–30 days also showed increased lipid peroxidation and changes in glutathione

peroxidase, ascorbic acid, and hydrogen peroxide levels.

2.17 DEVELOPMENTAL

Developmental effects of HCH isomers have been evaluated in human populations and in animals. These

studies are discussed below in the individual isomer subsections. However, the epidemiological studies

of all isomers share limitations that render the reported associations uncertain, especially when considered

without any supporting animal data. Epidemiological studies of developmental effects were conducted in

the general population (without occupational exposure), generally using measurements of HCH isomers

in physiological fluids or tissues of mothers and infants. In the general population, the route(s) of

exposure is unknown. In the studies discussed herein, other organochlorine compounds (such as

hexachlorobenzene, aldrin, heptachlor and its epoxide, DDT and its metabolites, polychlorinated

biphenyls, and/or polychlorinated dioxins and furans) were also present in the blood. Few of the studies

controlled for these co-exposures; thus, the role of HCH isomers in the observed effects, if any, cannot be

ascertained. In addition, the case-control studies examined levels of HCH isomers in blood and tissues

after the outcome was established, rendering the temporal association between exposure and outcome

uncertain.

α-HCH. Data on the developmental effects of α-HCH are limited to a small number of human

epidemiological studies; there are no animal studies of developmental toxicity for this isomer. Table 2-16

provides a summary of human epidemiological data on developmental effects of α-HCH. As the table

shows, the epidemiology data suggest possible associations between growth retardation and maternal or

placental levels of α-HCH. Increased risks of fetal growth restriction (defined as <10

percentile of birth

weight for gestational age, and also termed ‘intrauterine growth retardation’ in some studies) were

associated with maternal blood levels of α-HCH in two small case-control studies in India (Sharma et al.

2012; Siddiqui et al. 2003). Reduced birth weight was associated with higher levels of α-HCH in placenta

in a small cross-sectional study in India (Anand and Taneja 2020), but not with maternal serum levels of

α-HCH in a cross-sectional study in an Arctic population in Russia (Bravo et al. 2019) or with cord serum

levels in a large cross-sectional analysis of 1,028 mother-infant pairs in China (Fang et al. 2019a, 2019b).

No association between cord serum α-HCH and infant BMI through age 24 months was observed in a

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Table 2-16. Summary of Epidemiological Studies of α-Hexachlorocyclohexane (HCH) Exposure and

Developmental Effects

Reference, study type, and population

Outcome evaluated

Biomarker

Mean concentration (unless

otherwise noted)

Result

Siddiqui et al. 2003

Case-control, 30 mothers of infants with intra-

uterine growth retardation, 24 mothers of

normal weight infants, India

Intra-uterine growth

retardation

Maternal blood

5.82±3.22 ng/g (mean±SD)

(cases)

3.79±3.14 (controls)

↑

Placenta

9.91±3.89 (cases)

8.88±5.17 (controls)

Cord blood

9.84±5.12 (cases)

6.74±7.83 (controls)

Fang et al. 2019a, 2019b

Cross-sectional, 1,028 pregnant mother-

infant pairs, China

Birth weight

Cord serum

≥0.718 ng/g lipid (3

tertile)

↔

Birth length

↔

Ponderal index

↔

Gestational age

↓ (among

term births)

Anand and Taneja 2020

Cross-sectional, 90 mother-infant pairs, India

Birth weight

Placenta tissue

1.09–211.43 μg/L (range)

↓

Birth length

↔

Head circumference

↔

Ponderal index

↔

Bravo et al. 2019

Cross-sectional, 247 mother-child pairs,

Russia

Gestational age

Maternal serum

(last week of

pregnancy)

3.3 ng/g lipid (median)

↔

Birth weight

↔

Birth length

↔

Head circumference

↔

Yang et al. 2021a

Birth cohort, 1,039 mother-infant pairs

followed for 2 years after birth, China

Infant BMI at birth and

ages 6, 12, and

24 months; risk of

overweight status

Cord serum

0.35 ng/g lipid (median)

↔

HEXACHLOROCYCLOHEXANE (HCH) 165

2. HEALTH EFFECTS

Table 2-16. Summary of Epidemiological Studies of α-Hexachlorocyclohexane (HCH) Exposure and

Developmental Effects

Reference, study type, and population

Outcome evaluated

Biomarker

Mean concentration (unless

otherwise noted)

Result

Mustafa et al. 2013

Case-

control, 156 mothers with preterm births

and 150 mothers with term births, India

Preterm birth

Maternal blood

4.04±2.63 ng/g (mean±SD)

(cases)

2.93±2.59 (controls)

↑

Cord blood

1.91±2.03 (cases)

1.69±2.25 (controls)

↔

Sharma et al. 2012

Case-control, 50 cases delivering babies with

fetal growth restriction and 50 women with

healthy term infants, mean ages 23–24

years,

India

Fetal growth

restriction

Maternal blood

4.55±3.2 ng/g (mean±SD) (cases)

2.92±2.7 (controls)

↑

Cord blood

2.01±1.6 (cases)

1.90±2.3 (controls)

↔

Yin et al. 2021

Case-control, 119 mothers delivering infants

or electively terminating pregnancies with

neural tube defects and 119 controls, China

Neural tube defects

Cord tissue

0.23 ng/g (cases) (median)

0.13 (controls)

↔

↑ = association with increase; ↓ = association with decrease (inverse association); ↔ = no association; SD = standard deviation

HEXACHLOROCYCLOHEXANE (HCH) 166

2. HEALTH EFFECTS

birth cohort of 1,039 mother-infant pairs in China (Yang et al. 2021a). None of the available studies

suggested associations between biomarkers of α-HCH exposure in maternal and infant tissues and birth

length, head circumference, or ponderal index (Anand and Taneja 2020; Bravo et al. 2019; Fang et al.

2019a, 2019b).

In cross-sectional studies, a negative association between gestational age among term births and α-HCH

in cord serum was observed in a study of 1,028 mother-infant pairs in China (Fang et al. 2019a, 2019b),

but no association was seen in a smaller group of 247 mother-infant pairs in Russia (Bravo et al. 2019).

Increased risk of preterm birth was associated with higher maternal blood levels of α-HCH in a case-

control study in India (Mustafa et al. 2013).

A small case-control study in China did not observe an association between α-HCH in umbilical cord

tissue and neural tube defects (Yin et al. 2021).

β-HCH. Epidemiological studies of developmental endpoints in humans exposed to β-HCH are

summarized in Table 2-17. As the table shows, most of the studies examined metrics pertaining to fetal

growth and gestational age. The studies provide suggestive evidence for an association between β-HCH

concentrations in maternal or umbilical cord blood and reduced birth weight.

In birth cohorts of mother-infant pairs in California, Lebanon, and China, birth weight showed no

association with β-HCH in maternal serum sampled during the second trimester or maternal or cord serum

at delivery (Fenster et al. 2006, Wang et al. 2022a). An association between increased infant BMI at 1

and 2 years of age and cord serum levels of β-HCH was observed in another birth cohort in China; this

study reported no association with infant BMI at birth or 6 years of age (Yang et al. 2021a). Case-control

studies of fetal growth restriction (<10

percentile weight for gestational age) reported conflicting

findings. Siddiqui et al. (2003) reported no association of fetal growth restriction with maternal, cord

blood, or placental concentrations of β-HCH in a small (30 cases and 24 controls) study conducted in

India. However, a slightly larger study of 50 cases and 50 controls in India showed a positive association

between increased risk of fetal growth restriction and β-HCH in maternal blood (but not cord blood)

(Sharma et al. 2012).

Associations between reduced birth weight and increased maternal plasma, umbilical cord blood, or

placental tissue concentrations of β-HCH were reported in cross-sectional studies in Australia (Callan et

al. 2016), Spain (Lopez-Espinosa et al. 2011), China (Fang et al. 2019a, 2019b; Guo et al. 2014; Yang et

HEXACHLOROCYCLOHEXANE (HCH) 167

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Table 2-17. Summary of Epidemiological Studies of β-Hexachlorocyclohexane Exposure and Developmental

Effects

Reference, study type, and population

Outcome evaluated

Biomarker

Concentration

Result

Birth outcomes

Siddiqui et al. 2003

Case-control, 30 mothers of infants with intra-

uterine growth retardation, 24 mothers of

normal weight infants, India

Fetal growth restriction

(intrauterine growth

retardation)

Maternal blood

7.95±11.43 ng/g (mean±SD)

(cases)

6.55±5.43 (controls)

↔

Placenta

7.30±10.92 (cases)

7.00±7.14 (controls)

↔

Cord blood

3.03±5.22 (cases)

2.96±3.62 (controls)

↔

Callan et al. 2016

Cross-sectional, 161 mother-infant pairs,

Australia

Birth weight, proportion of

optimal birth weight

Maternal plasma

(2 weeks prior to

birth)

0.18 μg/L (mean)

↓ (boys)

↔ (girls)

Ponderal index

↔

Hjermitslev et al. 2020

Cross-sectional, 468 mother-infant pairs,

Greenland

Birth weight

Maternal serum

3.6 µg/kg lipid (median)

↔

Gestational age

↓

Fenster et al. 2006

Cohort, 385 mother-infant pairs, California,

United States

Length of gestation

Maternal serum

trimester or at

delivery)

37.2 ng/g lipid (median)

↔

Birth weight

See above

↔

Crown-heel length

See above

↔

Khanjani and Sim 2006

Cross-sectional, 815 mother-infant pairs,

Australia

Prematurity

Breast milk

0.0098±0.0286 mg/kg milk fat

(mean±SD)

↔

Previous miscarriage or still

birth

↔

Low birth weight

↔

Small for gestation age

↔

Head circumference

↔

Sex ratio

↔

Gladen et al. 2003

Cross-sectional, 197 mother-infant pairs,

Ukraine

Birth weight

Breast milk

860 ng/g milk fat (3

tertile)

↔

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Table 2-17. Summary of Epidemiological Studies of β-Hexachlorocyclohexane Exposure and Developmental

Effects

Reference, study type, and population

Outcome evaluated

Biomarker

Concentration

Result

Lopez-Espinosa et al. 2011

Cross-sectional, 494 mothers-infant pairs,

Spain

Birth weight

Cord serum

0.085 ng/mL (median)

↓

(marginal)

Birth length

↔

Head circumference

↔

Fang et al. 2019a, 2019b

Cross-sectional, 1,028 pregnant mother-

infant

pairs, China

Birth weight

Cord serum

≥12.64 ng/g lipid (3

tertile)

↓ (boys)

Birth length

↔

Ponderal index

↓ (boys)

Gestational age

↔

Wang et al. 2022a

Cohort, 1,522 mother-child pairs, China

Birth weight

Cord serum

0.65 ug/L (mean)

↔

Birth length

↔

Head circumference

↓

Yang et al. 2021a

Birth cohort, 1,039 mother-infant pairs

followed for 2 years after birth, China

Infant BMI at ages 12 and

24 months

Cord serum

8. 42 ng/g lipid (median)

↑

Infant BMI at birth and age

6 months

↔

Risk of overweight status

↑ (girls)

↔ (boys)

Guo et al. 2014

Cross-sectional, 81 mother-

infant pairs, China

Birth weight

Maternal serum at

birth

73.96 (median)

↓

Cord serum

35.29 (median)

↓

Anand and Taneja 2020

Cross-sectional, 90 mother-infant pairs, India

Birth weight

Placenta tissue

1.10–678.74 μg/L (range)

↓

Birth length

↔

Head circumference

↔

Ponderal index

↔

Mustafa et al. 2013

Case-

control, 156 mothers with preterm births

and 150 mothers with term births, India

Preterm birth

Maternal blood

5.07±3.40 ng/g (mean±SD)

(cases)

4.03±3.40 (controls)

↔

Cord blood

2.10±1.83 (cases)

1.84±2.10 (controls)

↔

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Table 2-17. Summary of Epidemiological Studies of β-Hexachlorocyclohexane Exposure and Developmental

Effects

Reference, study type, and population

Outcome evaluated

Biomarker

Concentration

Result

Tan et al. 2009

Cross-sectional, 41 mother-infant pairs,

Singapore

Birth weight

Cord blood

85.4±173 ng/g lipid (mean±SD)

↔

Birth length

↑

Head circumference

↑

Gender

↔

Tyagi et al. 2016

Cross-sectional, 30 mothers with preterm

births and 30 mothers with term births, India

Preterm birth

Maternal blood

6.42±2.158 ng/mL (mean±SD)

(cases)

3.06±2.05 (controls)

↑

Bravo et al. 2019

Cross-sectional, 247 mother-child pairs,

Russia

Gestational age

Maternal serum (last

week of pregnancy)

38 ng/g lipid (median)

↔

Birth weight

↔

Birth length

↔

Head circumference

↔

Yang et al. 2020

Cohort, 102 healthy pregnant women, mean

age 28 years, China

Birth weight

Maternal serum

7.44 ng/mL (mean)

↓

Yang et al. 2021b

Case-control, 89 infants with orofacial clefts

and 129 controls, China

Orofacial cleft

Cord tissue

0.74 ng/g dry weight (cases)

0.66 (controls)

↔

Sharma et al. 2012

Case-control, 50 cases delivering babies with

fetal growth restriction and 50 women with

healthy term infants, mean ages 23–

24 years,

India

Fetal growth restriction

Maternal blood

3.97±3.9 ng/g (mean±SD)

(cases)

↑

Cord blood

2.67±2.4 (cases)

↔

Torres-Arreola et al. 2003

Case-

cohort, 100 mothers with preterm births,

133 controls with full-term births, Mexico

Preterm birth

(<37 weeks)

Maternal serum at

birth

>76.53 ng/g (3

tertile)

↔

HEXACHLOROCYCLOHEXANE (HCH) 170

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Table 2-17. Summary of Epidemiological Studies of β-Hexachlorocyclohexane Exposure and Developmental

Effects

Reference, study type, and population

Outcome evaluated

Biomarker

Concentration

Result

Pierik et al. 2007

Case-control nested in birth cohort,

219 mothers of children with cryptorchidism,

564 controls, United States

Cryptorchidism within first

year of life

Maternal serum

trimester)

>3.41 µg/L (90

percentile)

↔

Desalegn et al. 2021

Case-cohort, 641 mother-male infant pairs,

Norway

Cryptorchidism

Breast milk

4.43 ng/g (median)

↑

Warembourg et al. 2016

Cross-sectional, 282 newborns, France

Umbilical cord blood free

testosterone, sex hormone

binding globulin, anti-

Müllerian

hormone, estradiol,

aromatase index

Cord blood

11.27 ng/g lipid (median)

↔

Debost-Legrand et al. 2016

Cross-sectional, 268 mother-infant pairs,

France

Umbilical cord serum insulin,

adiponectin

Cord serum

>0.061μg/L (4

quartile)

↔

Yin et al. 2021

Case-control, 119 mothers delivering infants

or electively terminating pregnancies with

neural tube defects and 119 controls, China

Neural tube defects

Cord tissue

1.81 ng/g dry weight (cases)

(median)

0.93 (controls)

↑

Postnatal development

Namulanda et al. 2016

Case-control, 218 girls with early menarche

(<11.5 years of age), 230 controls, England

Early menarche

Maternal serum

47.4 ng/g lipid (median)

↔

Marks et al. 2021

Nested case-control, 218 cases of early

menarche (<11.5 years of age),

230 controls, United Kingdom

Early menarche

Maternal serum

45.3 ng/g lipid (cases) (median)

47.5 (controls)

↔

Lam et al. 2014, 2015

Cohort, 350 boys 8–9 years old, followed for

8 years, Russia

Age of pubertal onset

Serum at cohort entry

1.3–14 ng/g (4

quartile)

↔

Age of sexual maturity

↑

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Table 2-17. Summary of Epidemiological Studies of β-Hexachlorocyclohexane Exposure and Developmental

Effects

Reference, study type, and population

Outcome evaluated

Biomarker

Concentration

Result

Garcia-Villarino et al. 2022

Birth cohort, 201 mother-child pairs with

children followed at 8 years of age, Spain

Anogenital index at

8 years of age

Maternal serum

27.23 ng/g lipid (Median)

↓ (boys)

↔ (girls)

Cupul-Uicab et al. 2013

Birth cohort, 1,915 children followed

until age

7 years, United States

Childhood obesity or

overweight and obese

Maternal serum

trimester)

≥2.12 μg/L (4

quartile)

↔

Lauritzen et al. 2018

Cohort, 412 mother-child pairs followed until

child age of 5 years, Norway and Sweden

Childhood obesity at

5 years old (BMI, triceps

skinfold, subscapular

skinfold, overweight)

Maternal serum

trimester)

Norway:

21.2 ng/g lipid (median)

Sweden:

25 ng/g lipid (median)

↔

Mendez et al. 2011

Birth cohort, 518 mother-infant pairs

followed

for 14 months, Spain

Rapid infant growth during

first 6 months; elevated BMI

at 14 months

Maternal serum (1

trimester)

≥47.28 ng/g lipid

quartile)

↔

Salo et al. 2019

Case-control, 40 cases with autoantibodies

and 11 control children up to 6 years old,

Finland

Diabetes-associated

autoantibodies

Cord plasma

>LOQ (not specified)

↔

Alvarez-Pedrerol et al. 2008a

Cross-sectional, 21 newborn infants, Spain

Neonatal plasma TSH

(3 days postpartum)

Cord serum

0.48 ng/mL (geometric mean)

(group with TSH ≥10 mU/L)

0.24 (group with TSH

<10 mU/L)

↑

Alvarez-Pedrerol et al. 2008b

Cross-sectional, 259 children 4 years old,

Spain

Serum free T4, TSH at age

4 years

Serum (child)

≥0.305 ng/mL (4

quartile)

↔

Serum total T3 at age

4 years

≥0.191 ng/mL (3

quartile)

↓

Ribas-Fito et al. 2003

Cross-sectional, 98 newborn infants, Spain

Neonatal plasma TSH

≥10 mU/l

Cord serum

0.54 ng/mL (median)

↑

Lopez-Espinosa et al. 2010

Cross-sectional, 453 newborn infants, Spain

Postpartum (≥2 days)

neonatal serum TSH

Cord serum

>104 ng/g lipid (90

percentile)

↑

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Table 2-17. Summary of Epidemiological Studies of β-Hexachlorocyclohexane Exposure and Developmental

Effects

Reference, study type, and population

Outcome evaluated

Biomarker

Concentration

Result

Yamazaki et al. 2020

Cross-sectional, 333 mother-child pairs,

Japan

Serum free T4 or TSH in

infants 7–43 days old

Maternal serum

235.6 pg/g (75

percentile)

↔

Li et al. 2014

Cross-sectional, 247 pregnant women,

Yanchen City, China

Umbilical cord serum free

T3, free T4, TSH

Cord serum

13.336 ng/g (median)

↔

Wang et al. 2022b

Birth cohort, 228 mother-child pairs, China

Total or free T3, total or free

T4, TSH in cord serum

Cord serum

0.48 ug/L (median)

↔

Sunyer et al. 2008

Cross-sectional, 52 children, 4 years old,

Spain

Urinary porphyrins (child)

Serum (child)

>0.37 ng/mL

↔

Neurodevelopmental endpoints

Lenters et al. 2019

Birth cohort, 1,199 mother-child pairs,

Norway

ADHD by 13 years of age

Breast milk

4.367 ng/g lipid (median)

↑

Kokroko et al. 2020

Cohort, 256 mother child pairs, United States

IQ at 7 years old (Wechsler

Intelligence Scale for

Children)

Maternal serum during

pregnancy

33.3 ng/g lipid (geometric

mean)

↔

Braun et al. 2014

Cohort, 175 mother-child pairs, Ohio, United

States

Social responsiveness scale

score, children aged 4 and

5 years

Maternal serum

<LOD (median)

1.9 ng/g lipids (75

percentile)

↔

Jeddy et al. 2018

Cohort, 400 mother-daughter pairs, England

Communication

development: nonverbal

communication, social

development, verbal

comprehension, vocabulary

comprehension in daughters

at 15 and 38 months

Maternal serum

>56.15 ng/g lipid (3

tertile)

↔

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Table 2-17. Summary of Epidemiological Studies of β-Hexachlorocyclohexane Exposure and Developmental

Effects

Reference, study type, and population

Outcome evaluated

Biomarker

Concentration

Result

Wang et al. 2021b

Birth cohort, 242 mother-child pairs, China

Language development at

18 months of age

Cord blood

0.51 ug/L (median)

↔

Motor development at

18 months of age

↓

Cognitive development at

18 months of age

↔

Lee et al. 2007

Cross-sectional, 278 children aged 12–

15 years, NHANES, United States

Learning disability

Serum (child)

17.9 ng/g lipid (median)

↔

Attention deficit disorder

↔

Fabisiková et al. 2012

Cross-sectional, 143 mother-infant pairs,

Slovakia

Bayley mental development

index at 10 months of age

Serum (child)

0.01–82.9 ng/g lipid (range)

↔

Bayley psychomotor

development index at

10 months of age

↔

Sisto et al. 2015

Cohort, 351 infants enrolled at birth, Slovakia

Cochlear deficits

measured as altered

distortion product

otoacoustic emissions at

45 months of age

Cord blood

9.84±8.09 ng/g lipid

↑

Serum at 6 months old

12.24±12.9

↓

Serum at 16 months old

13.36±16.06

↓

Serum at 45 months old

7.70±9.21

↓

Kornvig et al. 2021

Birth cohort, 102 mother-child pairs,

Greenland

Problematic child behavior

at 3–5 years of age

Maternal serum

3.50 ug/kg lipid (median)

↔

Abnormal hyperactivity at 3–

5 years of age

↔

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Table 2-17. Summary of Epidemiological Studies of β-Hexachlorocyclohexane Exposure and Developmental

Effects

Reference, study type, and population

Outcome evaluated

Biomarker

Concentration

Result

Cheslack-Postava et al. 2022

Nested case-control, 359 cases of ADHD

and 359 sex-, age- and birthplace-matched

controls, Finland

ADHD

Maternal serum

↑

A significant increase in working memory IQ score was observed but is not shown here as it is not considered adverse.

A significant decrease in SRS score, corresponding to lower autism-related behaviors, was observed but is shown here as it not considered adverse.

↑ = association with increase; ↓ = association with decrease (inverse association); ↔ = no association; ADHD = attention deficit hyperactivity disorder;

BMI = body mass index; IQ = intelligence quotient; LOD = limit of detection; NHANES = National Health and Nutrition Examination Survey; SD = standard

deviation; T3 = triiodothyronine, T4 = thyroxine; TSH = thyroid-stimulating hormone

HEXACHLOROCYCLOHEXANE (HCH) 175

2. HEALTH EFFECTS

al. 2020), and India (Anand and Taneja 2020), but not in cross-sectional studies in Greenland

(Hjermitslev et al. 2020) or Russia (Bravo et al. 2019).

Studies evaluating whether β-HCH concentrations in maternal or infant blood were associated with

preterm birth or gestational age have yielded mixed results. Tyagi et al. (2016) reported a positive

association between risk of preterm birth and β-HCH in maternal blood in a small cross-sectional study in

India, but no association was reported in a case-control study in India (Mustafa et al. 2013) or in a case-

cohort study in Mexico (Torres-Arreola et al. 2003). In 468 mother-infant pairs in Greenland, decreased

gestational age was associated with maternal serum levels of β-HCH (Hjermitslev et al. 2020), but no

association was seen in cross-sectional studies in China (Fang et al. 2019a, 2019b) or Russia (Bravo et al.

2019) or between gestation length and β-HCH in maternal blood in a cohort study in the United States

(Fenster et al. 2006).

No association between umbilical cord levels of β-HCH and orofacial clefts were observed in a case-

control study in China (Yang et al. 2021b). A case-control study in China identified a positive association

between umbilical cord tissue levels of β-HCH and neural tube defects (Yin et al. 2021).

A case-control study nested in a birth cohort in the United States observed no association between

maternal serum concentrations of β-HCH and cryptorchidism or hypospadias (Pierik et al. 2007), but a

case-cohort study of 641 mother-male infant pairs in Norway showed a positive association between

breast milk concentrations of β-HCH and cryptorchidism (Desalegn et al. 2021). Cross-sectional studies

in France reported no association between β-HCH in umbilical cord blood and reproductive hormone

levels (Warembourg et al. 2016), or insulin and adiponectin concentrations in umbilical cord (Debost-

Legrand et al. 2016).

As shown in Table 2-17, serum and cord blood levels of β-HCH were associated with increased serum

levels of TSH in cross-sectional studies conducted in Spain (Alvarez-Pedrerol et al. 2008a, 2008b; Lopez-

Espinosa et al. 2010; Ribas-Fito et al. 2003) but not in a similar study in China (Li et al. 2014). No

association between maternal serum levels of β-HCH and concentrations of free T4 or TSH in infants

from 1 to 6 weeks old (Yamazaki et al. 2020), or between cord serum β-HCH and concentrations of T4,

T3, or TSH in cord serum in a birth cohort in China (Wang et al. 2022b).

In British case-control studies nested in birth cohorts, there was no association between maternal serum

levels of β-HCH and early menarche (Namulanda et al. 2016, Marks et al. 2021). A cohort of 332 mother-

HEXACHLOROCYCLOHEXANE (HCH) 176

2. HEALTH EFFECTS

child pairs found an inverse association between β-HCH levels in serum and anogenital index in boys at

8 years of age (Garcia-Villarino et al. 2022). In a cohort study of 350 boys in Russia, serum levels of

β-HCH were associated with a higher age at sexual maturity (Lam et al. 2014, 2015).

Studies examining neurodevelopmental effects in relationship to maternal or cord serum, breast milk, or

infant or child blood levels of β-HCH are shown in Table 2-17. In general, these studies showed no

associations with IQ, problematic behavior, social responsiveness, communication, or mental and

psychomotor development (see Table 2-17). A birth cohort study in China reported diminished motor

development at 18 months of age with higher β-HCH in cord blood, but no effect on language or

cognitive development (Wang et al. 2021b). Lenters et al. (2019) showed an association between breast

milk concentrations of β-HCH and diagnosis of attention deficit hyperactivity disorder (ADHD) at

approximately 13 years of age. Similarly, β-HCH in maternal serum was associated with ADHD in a

nested case-control study in Finland (Cheslack-Postava et al. 2022).

Sisto et al. (2015) reported an association between serum concentrations of β-HCH in children (obtained

at birth [cord serum] and 6, 16, and 45 months of age) and cochlear deficits (measured as altered

distortion product otoacoustic emissions [DPOAEs] measured at 45 months of age). DPOAEs have been

established as an objective diagnostic tool for assessing the function of cochlear outer hair cells. In this

study, the investigators controlled for co-exposure confounding by evaluating the association between

β-HCH and cochlear function both with and without potentially ototoxic co-exposures. Cord serum

β-HCH concentration was positively associated with the amplitude of otoacoustic emissions across a

range of f2 frequencies, while analyses using β-HCH concentrations from serum samples at 6, 16, and

45 months of age yielded inverse associations with the amplitude of otoacoustic emissions and at

inconsistent frequencies. Significant inverse associations with β-HCH concentrations were seen at low

frequencies in analyses of 6-month blood samples, and at higher frequencies in analyses of 16-month

blood samples. In analyses using the 45-month blood samples, a significant inverse association between

β-HCH concentration and amplitude of otoacoustic emissions was seen for only 1 of 11 frequencies

tested. The study authors suggested that increased exposure during lactation might account for the change

from positive to inverse association between birth and 6 months of age, and indeed, the maximum serum

concentration of β-HCH almost doubled between these two measurements. Sisto et al. (2015) also

assessed tonotopicity (specificity of the effect on different regions of the basal membrane in the organ of

Corti, which correspond to effects on different frequencies), observing that the strength of the association

with each compound varied by noise frequency.

HEXACHLOROCYCLOHEXANE (HCH) 177

2. HEALTH EFFECTS

Limited data are available on developmental effects of β-HCH in animals. Dietary exposure of pregnant

rats to 20 or 25 mg/kg/day of β-HCH during gestation caused increased perinatal mortality, with deaths of

48 or 100% of the pups within 5 days of birth; exposure to 5 mg/kg/day did not influence perinatal

survival (Srinivasan et al. 1991). In another experiment by these authors, a dose 5 mg/kg/day of β-HCH

during gestation and lactation or during lactation only resulted in increased liver weights of pups when

measured at 28 days of age (Srinivasan et al. 1991).

γ-HCH (Lindane). Epidemiological studies of developmental endpoints in humans exposed to γ-HCH

are summarized in Table 2-18. Two case-control studies in India reported associations between maternal

and cord blood levels of γ-HCH and fetal growth restriction (Sharma et al. 2012; Siddiqui et al. 2003). In

a birth cohort of 385 mother-infant pairs in California, birth weight and length were not associated with

γ-HCH concentration in maternal serum collected during the second trimester and at delivery (Fenster et

al. 2006). Birth weight, birth length, and ponderal index showed no association with γ-HCH in cord

serum in a cross-sectional study of 1,028 infants in China (Fang et al. 2019a, 2019b). Higher BMI in

6-month-old infants was associated with increased γ-HCH in cord serum in a cohort in China; however,

BMI at 12 and 24 months of age was not associated with γ-HCH levels (Yang et al. 2021a).

Gestation length was not associated with γ-HCH concentration in maternal serum in a birth cohort of

385 mother-infant pairs in an agricultural area of California (Fenster et al. 2006). Gestational age was

inversely associated with γ-HCH in cord serum in a cross-sectional study of 1,028 infants in China (Fang

et al. 2019a, 2019b). A case-control study in India observed an increased risk of preterm birth associated

with maternal, but not cord blood levels of γ-HCH (Mustafa et al. 2013).

The concentration of γ-HCH in the placenta was associated with an increased risk of male reproductive

tract abnormalities (cryptorchidism or hypospadias observed at birth and 1 month of age) in a case-control

study nested within a birth cohort in Spain (Fernandez et al. 2007). No association between γ-HCH in

maternal serum and anogenital index at age 8 years was observed in a birth cohort of 201 mother-child

pairs in Spain (Garcia-Villarino et al. 2022).

No associations between levels of γ-HCH in umbilical cord tissue and orofacial cleft or neural tube

defects were observed in case-control studies in China (Yang et al. 2021b; Yin et al. 2021).

A cross-sectional study of 220 male newborns in Spain showed no association between placental γ-HCH

and TSH levels in umbilical cord serum (Freire et al. 2011).

HEXACHLOROCYCLOHEXANE (HCH) 178

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Table 2-18. Summary of Epidemiological Studies of γ-Hexachlorocyclohexane Exposure and Developmental

Effects

Reference, study type, and population

Outcome evaluated

Biomarker

Concentration

Result

Siddiqui et al. 2003

Case-control, 30 mothers of infants with

intrauterine growth retardation, 24 mothers of

normal weight infants, India

Intrauterine growth

retardation

Maternal blood

6.30±7.51 ng/g (mean±SD)

(cases)

2.65±2.15 (controls)

↑

Placenta

8.71±4.57 (cases)

6.86±4.46 (controls

↔

Cord blood

9.23±10.31 (cases)

4.23±4.59 (controls)

↑

Fenster et al. 2006

Cohort, 385 mother-infant pairs, California,

United States

Length of gestation

Maternal serum

trimester and

at delivery)

1.0 ng/g lipid (median)

↔

Birth weight

↔

Crown-heel length

↔

Fang et al. 2019a, 2019b

Cross-sectional, 1,028 pregnant mother-infant

pairs, China

Birth weight

Cord serum

≥1.125 ng/g lipid (3

tertile)

↔

Birth length

↔

Ponderal index

↔

Gestational age

↓

Yang et al. 2021a

Birth cohort, 1,039 mother-infant pairs followed

for 2 years after birth, China

Infant BMI at age 6 months

Cord serum

0.70 ng/g lipid (median)

↑

Infant BMI at birth and

ages 12 and 24 months;

risk of overweight status

↔

Mustafa et al. 2013

Case-control, 156 mothers with preterm births

and 150 mothers with term births, India

Preterm birth

Maternal blood

2.63±2.46 ng/g (mean±SD)

(cases)

1.52±1.83 (controls)

↑

Cord blood

0.988±1.31 (cases)

0.887±1.24 (controls)

↔

HEXACHLOROCYCLOHEXANE (HCH) 179

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Table 2-18. Summary of Epidemiological Studies of γ-Hexachlorocyclohexane Exposure and Developmental

Effects

Reference, study type, and population

Outcome evaluated

Biomarker

Concentration

Result

Sharma et al. 2012

Case-control, 50 cases delivering babies with

fetal growth restriction and 50 women with

healthy term infants, mean ages 23–24 years,

India

Fetal growth restriction

Maternal blood

7.06±6.7 ng/g (mean±SD)

(cases)

2.58±3.9 (controls)

↑

Cord blood

3.59±3.8 (cases)

1.44±2.1 (controls)

↑

Yang et al. 2021b

Case-control, 89 infants with orofacial clefts and

129 controls, China

Orofacial cleft

Cord tissue

0.01 ng/g dry weight (cases)

(median)

0.15 (controls)

↔

Yin et al. 2021

Case-control, 119 mothers delivering infants or

electively terminating pregnancies with neural

tube defects and 119 controls, China

Neural tube defects

Cord tissue

9.92 ng/g dry weight (cases)

(median)

7.19 (controls)

↔

Fernandez et al. 2007

Case-control (nested), 50 newborn boys with

cryptorchidism or hypospadias, 114 boys without

malformations, Spain

Cryptorchidism or

hypospadias

Placenta

0.9±0.8 ng/g lipid (mean±SD)

(cases)

0.7±1.0 (controls)

↑

Garcia-Villarino et al. 2022

Birth cohort, 201 mother-child pairs with children

followed to 8 years of age, Spain

Anogenital index at 8 years

of age

Maternal serum

2.49 ng/g lipid (median)

↔

Freire et al. 2011

Cross-sectional, 220 mother-infant son pairs,

Spain

Umbilical cord serum TSH

Placenta

0.25 ng/g placenta (median)

↔

↑ = association with increase; ↓ = association with decrease (inverse association); ↔ = no association; SD = standard deviation; TSH = thyroid-stimulating

hormone

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The effects of oral exposure to γ-HCH on development in animals have been extensively studied,

primarily in rats and mice. Developmental effects of γ-HCH in these species include reduced viability

and pup body weight; perturbation of male and female reproductive tract development; alterations in the

developing liver, thymus, spleen, and heart; and developmental neurotoxicity.

Birth outcomes. Effects of γ-HCH administered orally to animals include stillbirths, reduced viability,

and decreased body weight; in addition, some studies have suggested delays in developmental milestones.

There is no evidence for teratogenic effects in animals exposed orally to γ-HCH.

In Wistar rats exposed from GD 6 through lactation to doses of 0, 0.8–0.9, 4.2–4.6, or 8.0–

10.5 mg/kg/day during gestation and 0, 1.2–1.7, 5.6–8.3, or 13.7–19.1 mg/kg/day during lactation, effects

observed at 8.0 to 19.1 mg/kg/day included increased stillbirths (live birth index of 77% compared to

99% in controls), and increased neonatal mortality (postnatal day [PND] 4 viability index of 71%

compared to 89% in controls) (EPA 1999c). In a 2-generation reproductive toxicity study of rats, a dose

of 13.1 mg/kg/day γ-HCH in food resulted in significant reductions in the pup survival on lactation day

(LD) 4; for the F1 and F2 pups, survival was 81 and 85%, respectively, compared with ≥96% for the

controls (EPA 1991a). In another 2-generation rat study, F0 dams exhibited normal lactation and

maternal behavior, but six F1 dams exposed to 26–28 mg/kg/day γ-HCH showed abnormal lactation and

retrieving behavior, leading to death of nearly all their offspring by PND 4, and a significant (49%)

reduction in the F2 PND 0–4 viability index for this group (Matsuura et al. 2005). In rats, dietary

exposure to 25 mg/kg/day of γ-HCH during gestation (GDs 0–21) did not result in changes in numbers of

litter or pup survivals (Srinivasan et al. 1991). When minks were treated with 1 mg/kg/day γ-HCH in

their diet (Beard et al. 1997), the proportion of embryos lost after implantation was increased.

Reduced pup body weights have been reported in rats and mice exposed to γ-HCH during gestation and/or

lactation. Sauviat et al. (2005) observed a 21% reduction in body weight on PND 42 in rats exposed to

0.0003 mg/kg/day γ-HCH in drinking water during gestation, lactation, and growth; body weight was not

affected at 0.00015 mg/kg/day. Exposure of female Wistar rats from GD 6 through lactation to doses

≥4.2 mg/kg/day resulted in decreased pup body weights (up to 18% less than controls at the mid-dose and

up to 20% less than controls at the high dose), and body weight gains (16–24% less than controls at the

mid-dose, and up to 40% less than controls at the high dose) in both sexes during LDs 1–11 (EPA 1999c).

Similarly, body weights of the pups of both generations were significantly lower than controls in

2-generation studies of γ-HCH in rats exposed via feed at doses of 13.1 mg/kg/day (EPA 1991a) and

26.1 mg/kg/day (Matsuura et al. 2005). In the latter study, F2 female offspring also exhibited a 10%

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reduction in body weight at 5.6 mg/kg/day (Matsuura et al. 2005). Administration of 30 mg/kg to

pregnant C57BL/6J mice and 45 mg/kg to pregnant DBA/2J mice on GD 12 resulted in significant

decreases in fetal and placental weights (Hassoun and Stohs 1996a).

No malformations were observed in the fetuses of pregnant C57BL/6J or DBA/2J mice dosed with 30 and

45 mg/kg/day γ-HCH by gastric intubation on GD 12, even though both doses caused maternal deaths

(Hassoun and Stohs 1996a). A dose-related increase in the incidence of fetuses with an extra 14th rib was

reported in CFY rats exposed to 5, 10, or 20 mg/kg γ-HCH by gavage during GDs 6–15; statistical

significance was attained only at 20 mg/kg (Palmer et al. 1978). The incidence of fetuses with an extra

13th rib was statistically increased in rabbits exposed to 20 mg/kg γ-HCH by gavage during GDs 6–18

(Palmer et al. 1978). In both rats and rabbits, the incidences of extra ribs were within or just greater than

the ranges recorded for the control groups, and therefore, may not be sufficient evidence of teratogenicity

of γ-HCH. Maternal toxicity (reduced body weight gain and food consumption) occurred at doses

≥10 mg/kg/day in the rats, but not in rabbits (highest tested dose 20 mg/kg/day) (Palmer et al. 1978). No

effects on embryonic development were seen in rabbits treated by gavage with 0.8 mg/kg/day γ-HCH

3 times/week for 12–15 weeks before artificial insemination (at week 15) and throughout gestation (Seiler

et al. 1994).

In a 2-generation study of γ-HCH in CD rats exposed via feed to a dose of 13.1 mg/kg/day, the onset and

completion of tooth eruption and completion of hair growth were delayed by 10.5, 11.6, and 24% in the

high-dose F2 pups, respectively, compared to controls (EPA 1991a). In contrast, doses up to 26–

28 mg/kg/day in a 2-generation reproductive toxicity study of Crj:CD(SD)IGS rats did not influence

offspring developmental landmarks (pinna unfolding, incisor eruption, or eye opening) (Matsuura et al.

2005).

Male reproductive system development. Studies in rats and mice exposed to γ-HCH via oral

administration during gestation and lactation show effects on the developing male reproductive system,

including effects on serum hormone levels, spermatogenesis, reproductive organ weights, and testicular

histopathology; effects on sexual behavior and fertility have not been seen in these studies. Serum

testosterone was reduced in 7-month-old male rats exposed to 30 mg/kg/day γ-HCH on GD 15 (Dalsenter

et al. 1997a) and in PND 65 male rats exposed to 6 mg/kg/day on LD 9 or 14 or 1 mg/kg/day on LDs 9–

14 (Dalsenter et al. 1997b).

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Lactational exposure of rats to 6 mg/kg/day on LD9 or 14 resulted in significantly reduced spermatid and

sperm counts (~8–10%) at PND 140 (Dalsenter et al. 1997b). In rats exposed to 1 mg/kg/day on LDs 9–

14, reduced spermatid numbers at PNDs 65 and 140 (29 and 12.8% less than controls, respectively) and

reduced sperm number at PND 140 (13.2%) were observed (Dalsenter et al. 1997b). Similarly, CD-1

mice that were administered 15 or 25 mg/kg/day doses of γ-HCH in olive oil by gavage on GDs 9–16

showed reduced sperm count at ≥15 mg/kg/day on PND 60 and reduced sperm concentration at

25 mg/kg/day on PNDs 60–69 and 100 (Traina et al. 2003; Di Consiglio et al. 2009). La Sala et al.

(2009) reported decreased numbers of primordial germ cells in male CD1 mouse embryos exposed to

≥15 mg/kg/day on days 8.5–11.5 post-coitum and collected on day 12.5.

Exposure of rats to 1 mg/kg/day on LDs 9–14 resulted in statistically significant reductions in relative

testicular weight at PND 140 and relative epididymis weight at PND 65 (Dalsenter et al. 1997b). In

another experiment by these authors, a single dose of 6 mg/kg/day on LD 9 or 14 resulted in 10%

reductions in relative testicular weights on PNDs 66 and 140 (Dalsenter et al. 1997b). Traina et al. (2003)

observed reduced absolute (8%) and relative (10%) testicular weights in male mouse offspring of dams

exposed to 15 mg/kg/day during GDs 9–16, but not at 25 mg/kg/day; in addition, no change in testes

weight was evident in 25 mg/kg/day F1 males sacrificed on PND 100. No change in testis weight was

observed in PND 50 or 100 mouse offspring exposed in utero to 25 mg/kg/day γ-HCH on GDs 9–16 (Di

Consiglio et al. 2009).

Gestational or lactational exposure to γ-HCH also resulted in histopathology changes in male

reproductive organs. Dalsenter et al. (1997b) reported that microscopic examination of the testes in male

rat pups exposed to 6 mg/kg/day on LD 9 or 14 showed large areas of normal tissue, but some areas had

distinct changes ranging from small alterations to a pronounced effect, including necrotic changes and

reductions in Leydig cell numbers and spermatogenesis. However, there were no significant effects on

sexual behavior or fertility in the group exposed to 1 mg/kg/day on LDs 9–14 or to 6 mg/kg on LD 9 or

14 (Dalsenter et al. 1997b). In CD-1 mice administered 15 or 25 mg/kg/day doses of γ-HCH by gavage

on GDs 9–16, testicular histological alterations (increased number and size of Leydig cells) were seen

along with increased number of epididymal sperm with chromatin abnormalities at ≥15 mg/kg/day on

PND 60 and altered testicular germ cell distribution at 25 mg/kg/day on PNDs 60 and 100 (Traina et al.

2003). A multigeneration study in mink exposed to 1 mg/kg/day γ-HCH in the diet observed that testis

size was reduced in F3 males, although there were no effects on testicular development in the second

generation (Beard and Rawlings 1998).

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Agrahari et al. (2019) showed that gestational exposure to γ-HCH could influence reproductive hormone

levels in male offspring. Pregnant Wistar rats were administered γ-HCH by gavage in corn oil at doses of

0 or 0.25 mg/kg/day on GDs 5–21. Serum hormone levels were evaluated in male offspring at 9, 18, and

27 weeks of age. In offspring evaluated at 9 weeks of age, decreased serum levels of testosterone (16%

compared to controls) and growth hormone (15%) were observed, while serum LH (22%) and FSH (18%)

levels were significantly increased. Offspring evaluated at 18 and 27 weeks of age exhibited no

statistically significant changes in serum hormone levels (Agrahari et al. 2019). In other groups of male

offspring that were exposed similarly during gestation and then treated by gavage with 5 mg/kg/day for

5 days at 9, 18, or 27 weeks of age, significant hormone level changes were seen in all groups, including

decreased testosterone and growth hormone, and increased LH and FSH (Agrahari et al. 2019).

The results of another study with γ-HCH, reported only as an abstract, indicate that the male reproductive

system may be a particularly sensitive target of developmental toxicity in rats (Pages et al. 2000). Male

Sprague-Dawley rats were exposed to γ-HCH in drinking water for 12 weeks from the beginning of

gestation, lactation, or weaning at concentrations that provided estimated doses of 0.000075, 0.00015, or

0.0003 mg/kg/day. Body weight gain, plasma testosterone, sperm number, and sperm mobility values

were approximately 18, 38, 40, and 52% reduced compared to controls, respectively, in groups exposed to

0.0003 mg/kg/day during gestation or lactation. The pup rate was normal when treated males were mated

with untreated females, but newborn mortality was higher when treated males were exposed to treated

females. Given the lack of a complete report, the results of this study cannot be regarded as conclusive.

A multigeneration reproduction toxicity study in Crj:CD(SD)IGS rats exposed to γ-HCH via diet showed

a delay of 1.5 days in preputial separation in F1 animals exposed to 26.1 mg/kg/day (Matsuura et al.

2005). In contrast, the mean day of preputial separation was not affected by treatment in Wistar rat pups

exposed to doses up to 10.5–19.1 mg/kg/day from GD 6 through lactation (EPA 1999c) or in mouse pups

exposed to doses up to 25 mg/kg/day during GDs 9–16 (Traina et al. 2003).

Female reproductive system development. There are few data on the effects of γ-HCH on development of

the female reproductive tract, but available studies show effects in mice exposed during gestation to oral

doses of 15 mg/kg/day. La Sala et al. (2009) exposed CD-1 mice to 15 or 30 mg/kg/day γ-HCH by

gavage for 3 days during gestation (days 8.5–11.5 post-coitum) and collected embryos 1 day after the last

dose. The female embryos exhibited reduced numbers of primordial germ cells in the ovaries at both

doses (La Sala et al. 2009). In female pups of CD mice exposed to 15 mg/kg/day γ-HCH on GDs 9–16

and sacrificed on PND 22, significant increases in uterine weight (13–17% higher than controls) were

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observed, while those pups sacrificed on PND 60 exhibited decreased oocyte diameter (21%) in primary

follicles (Maranghi et al. 2007). Exposed female pups also developed vaginal patency earlier than

controls; by PND 33, 93% of female pups exposed to 15 mg/kg/day and 36% of control females exhibited

complete vaginal opening (Maranghi et al. 2007). No effect on vaginal opening was observed in Wistar

rat pups exposed to doses as high as 10.5–19.1 mg/kg/day from GD 6 through lactation (EPA 1999c) or in

CD-1 mouse pups exposed on GDs 9–16 to doses up to 25 mg/kg/day (Traina et al. 2003). In contrast,

vaginal opening was delayed by 1.4 days in Crj:CD(SD)IGS rats exposed to 26.1 mg/kg/day γ-HCH via

diet in a multigeneration reproductive toxicity study (Matsuura et al. 2005).

Systemic development. Oral exposure to γ-HCH during gestation and/or lactation has resulted in

significant effects on liver, thymus, and spleen weights in the offspring, and on cardiac development.

Srinivasan et al. (1991) observed significant increases in pup relative liver weight when rat dams were

exposed to 25 mg/kg/day during gestation and lactation or during lactation only (LDs 0–28). When

administered by gavage on GD 12 to pregnant C57BL/6J mice, a dose of 30 mg/kg γ-HCH resulted in

significant decreases in fetal thymic weight; fetal body weight was also reduced (Hassoun et al. 1996). At

doses of 26–28 mg/kg/day administered in feed to rats through 2 generations, treatment-related decreases

in absolute and relative thymus (13–31%) and spleen (13–32%) weights were observed in both

generations (Matsuura et al. 2005).

Development of the heart was examined in a study of female Sprague-Dawley rats exposed to very low

doses (0.000076, 0.00015, or 0.0003 mg/kg/day) of γ-HCH in drinking water (0.5, 1, and 2 μg/L,

respectively) prior to mating; during mating, gestation, and lactation; and for 3 weeks post-weaning

(Sauviat et al. 2005). The pups were sacrificed at 6 weeks of age for evaluation of heart weight,

morphometry, and lipid content and electrophysiology of dissected left ventricular papillary muscles.

Heart weights and lipid content of exposed rats did not differ from control. Morphometry analysis

showed that hearts of pups in the 0.0003 mg/kg/day group had a 9% increase in heart width (relative to

controls), but no significant change in length, with a corresponding 9% decrease in length-to-width ratio.

At this dose, offspring heart morphology was described as rounder and “cherry like.” The study authors

reported that hearts of treated offspring showed hypertrophied areas with thinning of the left ventricular

wall and few developed papillary muscles. Histopathological examination in offspring exposed to

0.0003 mg/kg/day showed that the heart tissue muscle bundles and layers were unorganized and

dissociated, with large hemorrhagic interspaces and dispersion of cell nuclei, destruction of fibroblasts,

and dispersion and disorganization of collagen bundles, compared to control heart muscle.

Histopathology was not assessed in the groups exposed to 0.000076 or 0.00015 mg/kg/day.

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Electrophysiology changes were also evident in the dissected left ventricular muscles of exposed pups.

Action potential durations were unchanged at 0.000076 mg/kg/day, but the plateau was shortened

moderately at 0.00015 mg/kg/day, and significantly shortened at 0.0003 mg/kg/day. At

0.0003 mg/kg/day, the slow repolarizing phase was also significantly shortened. The effects of γ-HCH on

action potential durations were mitigated by addition of quinidine or E-4031 (blockers of the rapid

delayed rectifier potassium current or I

) to the test solution, indicating that γ-HCH may act directly on

the I

Sauviat et al. (2005) noted that the I

channel is involved in long QT syndrome (a disorder that

increases the risk of cardiac arrhythmias).

These authors conducted a related study examining whether the cardiac effects could be induced by

paternal exposure to γ-HCH in drinking water (Sauviat et al. 2007). In this study, male rats were exposed

to a concentration of 2 μg/L for an unspecified “chronic” duration prior to mating with untreated females.

The lack of information on exposure duration in the males precluded estimation of doses. In offspring

sacrificed at 6 weeks of age, there were no effects on heart weight or shape or electrophysiology, but there

were histopathology changes in the hearts similar to those reported by Sauviat et al. (2005) at the same

water concentration.

Developmental neurotoxicity. Convulsions and seizures have been observed in offspring of rats exposed

to γ-HCH during gestation and/or lactation. Johri et al. (2008) observed convulsions in 8/10 male rat

pups that had been exposed during gestation (GDs 5–21) to 0.25 mg/kg/day γ-HCH and then received a

single gavage dose of 30 mg/kg on PND 45. In pups exposed only during gestation, no convulsions were

observed (Johri et al. 2008). Epileptiform seizures were reported in male rats fed milk from dams that

were gavaged with 20 mg/kg/day γ-HCH on PNDs 3–15 (Albertson et al. 1985).

In a developmental neurotoxicity study, Han Wistar rats were exposed to 0, 10, 50 or 120 ppm γ-HCH in

the diet from GD 6 through LD 10 (EPA 1999c). Reported daily maternal dose levels were 0, 0.8–0.9,

4.2–4.6, or 8.0–10.5 mg/kg/day during gestation, and 0, 1.2–1.7, 5.6–8.3, or 13.7–19.1 mg/kg/day during

lactation. The F1 offspring were evaluated for functional observational battery, motor activity, auditory

startle response, learning and memory, and brain endpoints (weight, histology, and morphometrics) on

postpartum days 11 and 65. The offspring showed increased motor activity (both sexes) and decreased

habituation of motor activity (females) at the two highest dose levels. Reduced auditory startle response

habituation was observed at the high dose in both sexes on day 28 and day 60 postpartum (EPA 1999c).

No significant changes in brain weight, morphometry, or histology were detected in the pups. This study

was classified as an unacceptable developmental neurotoxicity study by EPA (2000a) because there was

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no laboratory validation of the neurobehavioral tests and the number of animals (six per dose level) was

insufficient.

Increased motor activity was also reported in rat pups exposed during gestation only. Exposure on

GDs 5–21 to doses ≥0.25 mg/kg/day resulted in increased locomotor activity (increases in distance

traveled, ambulatory time, horizontal count, stereotypic time, and stereotypic movement burst) in 3-week-

old rat pups, and some of the changes (increased distance traveled) persisted through 9 weeks of age

(Johri et al. 2007). At a dose of 0.125 mg/kg/day, distance traveled was increased at 3 weeks of age, but

not at subsequent evaluations (Johri et al. 2007). Srivastava et al. (2019) observed no significant changes

in spontaneous locomotor activity or spatial memory (Y-maze activity) in 12-week-old male rat pups

whose mothers were exposed by gavage from GD 5 through GD 21 to 0.25 mg/kg/day γ-HCH. However,

other groups of pups similarly exposed in utero and then rechallenged at 12 weeks of age with 21 daily

gavage doses of 2.5 mg/kg/day γ-HCH exhibited significantly reduced spontaneous locomotor activity

(reductions in distance travelled, moving time, numbers of rearings, and stereotypic counts, along with

significantly increased resting time) and spatial memory effects (significant reduction in percent

alterations in Y-maze testing) (Srivastava et al. 2019). Acquisition of a passive avoidance task was

improved in 15-day-old rat pups that were treated with γ-HCH by gavage as either a single 20 mg/kg dose

or 7-day repeated 10 mg/kg/day doses (Rivera et al. 1998). Exposure to the single 20 mg/kg dose resulted

in a decrease in motor activity, while repeated exposure to the lower dose increased motor activity in this

study (Rivera et al. 1998).

Neurobehavioral testing of F1 offspring exposed to doses up to 26–28 mg/kg/day in a 2-generation

reproductive toxicity study showed no effects in tests of reflex, sensory function, surface righting reflex,

corneal reflex, startle response, pain response, or mid-air righting reflex at 4–6 weeks of age (Matsuura et

al. 2005). In addition, no effects were observed in the open field test, rotarod test, or pole climbing test

(Matsuura et al. 2005).

tudies of neurotransmitter levels in rats exposed to γ-HCH showed that the effects depended on the

treatment schedule and brain region (Rivera et al. 1991, 1998). In suckling Wistar rats treated once with

20 mg/kg γ-HCH by gavage at PNDs 8, 15, 22, or 29, regional changes in brain noradrenaline, serotonin,

and the dopamine metabolite, 3,4-dihydroxyphenyl- acetic acid (DOPAC) levels were seen, with

differential effects depending on age at the time of exposure (Rivera et al. 1991). Similarly, Rivera et al.

(1998) observed different patterns (e.g., ratios of 5-HIAA/serotonin and DOPAC/dopamine) in brain

monoaminergic levels in rat pups after exposure on PND 15 to a single 20 mg/kg dose or 7 consecutive

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daily doses of 10 mg/kg/day γ-HCH. The patterns suggested that monoaminergic turnover was increased

by the single dose but decreased by repeated exposure at lower doses (Rivera et al. 1998).

A study of rats exposed to γ-HCH in drinking water at very low doses (0.000055–0.00011 mg/kg/day) for

12 days prior to mating and through gestation and lactation examined effects of treatment on wake-sleep

cycle in male offspring at 14 weeks of age (Breton et al. 2005). Sleep cycle was analyzed by EEG in

three phases: wakefulness, slow wave sleep, and paradoxical sleep, and there were no treatment-related

changes in the sleep cycle. Spectral electrocorticographic analysis showed slight changes in brain activity

relative to controls (increased relative energy in the 11–15 Hz frequency during wakefulness and slow

wave sleep, and increased activity in the 7–15 Hz range in all sleep phases) in both exposure groups, but

the changes did not show dose-dependence. No histopathological effects were reported in the brain at any

dose (Breton et al. 2005).

Srivastava et al. (2019) examined transmission electron ultrastructural microscopy of the brains in

15-week old male rat pups whose mothers were exposed by gavage from GD 5 through GD 21 to

0.25 mg/kg/day γ-HCH. Although neurobehavioral changes were not seen in these pups, ultrastructural

changes were detected in the hippocampus and substantia nigra of exposed pups, including moderately

distorted mitochondria, demyelinated neurons, and autophagic vesicles with damaged cytoplasmic

contents (Srivastava et al. 2019). In another experiment by these authors, electron microscopy of the

hippocampus and substantia nigra showed loss of mitochondrial integrity (loss of cristae and number),

severe loss of synaptic structure, severe demyelination, and highly condensed nuclei with cytoplasmic

content showing necrotic effects after similar prenatal exposure followed by a rechallenge exposure at

12 weeks of age (21 days at 2.5 mg/kg/day) (Srivastava et al. 2019).

Mechanisms. Superoxide production, lipid peroxidation, and deoxyribonucleic acid (DNA) single-strand

breaks were increased in fetal and placental tissues, and lipid peroxidation markers were increased in

maternal sera and amniotic fluid 48 hours after administration of a single dose of 30 mg/kg γ-HCH to

pregnant mice on GD 12 (Hassoun and Stohs 1996b; Hassoun et al. 1996). Significant increases in lipid

peroxidation also occurred in fetal livers collected on GD 18. Thus, it was suggested that fetotoxic effects

of γ-HCH may be due to induced oxidative stress, enhanced lipid peroxidation, and DNA-single strand

breaks in mice.

There is evidence that the developmental neurotoxicity effects of γ-HCH may be mediated by metabolites

and involve alterations in the blood-brain barrier. Johri et al. (2007) detected dose-dependent increases in

brain cytochrome P450 (CYP1A1, 1A2, 2B1, 2B2, and 2E1) protein expression and mRNA, and CYP-

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dependent enzyme (EROD, PROD, and NDMA-d) activities in F1 offspring exposed to 0.0625–

0.25 mg/kg/day γ-HCH. The enzyme changes persisted longer at the high dose, correlating with the

effects on locomotor activity and suggesting that metabolites of γ-HCH may be responsible for this effect

(Johri et al. 2008). γ-HCH exposure causes functional impairment of the developing blood brain barrier

in young rats (Gupta et al. 1999). The integrity (impermeability) of the blood brain barrier was studied by

assessing uptake of sodium fluorescein (a micromolecular tracer dye) into the brain of neonatal rats

following single or repeated acute gavage doses of γ-HCH. The brain uptake index of fluorescein was

significantly increased in 10-day-old pups treated with a single 2 mg/kg dose (72 and 23% higher than

controls after 2 hours and 3 days, respectively), as well as in those treated with 2 mg/kg/day for 8 days

(50% higher than controls 7 days after the first exposure, with recovery 20 days after the first exposure).

The effect appeared to be age-related because the brain uptake index was lower when rats were

administered a single 2 mg/kg dose at 15 days of age (20% higher than controls after 2 hours) or a higher

dose of 4 mg/kg/day for 3 days as adults (no effect on brain permeability).

δ-HCH. Epidemiological studies that have examined relationships between δ-HCH in maternal or fetal

blood or tissues and developmental outcomes are shown in Table 2-19. A small case-control study in

India reported positive associations between fetal growth restriction and higher δ-HCH concentrations in

maternal and umbilical cord blood, but not with concentrations in placenta (Siddiqui et al. 2003). No

association between infant birth size and δ-HCH in placental tissue was observed in a cross-sectional

study in India (Anand and Taneja 2020). No studies of developmental outcomes in animals exposed to

δ-HCH by any exposure route were located.

Technical HCH or Unspecified Isomers of HCH. A dose-related increase in fetal resorptions was seen

in pregnant female mice treated once with 25–200 mg/kg technical-grade HCH by gavage on GD 9, but

fetal development was normal (Dikshith et al. 1990). Srivastava and Raizada (2000) further studied the

prenatal effect of orally administered technical-grade HCH. While mice exposed to HCH during the

preimplantation period (GDs 2–6) did not show fetolethality, exposure during the post-implantation

period (GDs 6–12) to 25 and 50 mg/kg/day HCH produced significant increases in resorption of fetuses,

inhibition of maternal serum progesterone levels, and higher levels of HCH in fetal tissues. Oral exposure

to Benesan (a pesticidal formulation containing 50% γ-HCH) given at doses of 6.25, 12.5, or

25 mg/kg/day by gavage on GDs 6–15 failed to produce teratogenic effects in rats (Khera et al. 1979).

Alterations in levels of brain dopamine, serotonin, GABA, glutamate, glutamate decarboxylase, and

noradrenaline were seen in various areas of the brains of female rat pups treated with 10 mg technical-

grade HCH/kg/day for 60 days beginning at birth (Nagaraja and Desiraju 1994).

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Table 2-19. Summary of Epidemiological Studies of δ-HCH and Total HCH Exposure and Developmental Effects

Reference, study type, and

population

Outcome

evaluated

Isomer

Biomarker

Mean concentration (unless

otherwise noted)

Result

Siddiqui et al. 2003

Case-control, 30 mothers of infants with

fetal growth restriction (intrauterine

growth retardation), 24 mothers of normal

weight infants, India

Fetal growth

restriction

δ-HCH

Maternal blood

2.14±1.94

↑

Placenta

2.92±3.99

↔

Cord blood

4.51±4.63

↑

Anand and Taneja 2020

Cross-sectional, 90 mother-infant pairs,

India

Birth weight

δ-HCH

Placenta tissue

1.18–24.4μg/L (range)

↔

Birth length

↔

Head circumference

↔

Ponderal index

↔

Yin et al. 2021

Case-control, 119 mothers delivering

infants or electively terminating

pregnancies with neural tube defects and

119 controls, China

Neural tube defects

δ-HCH

Cord tissue

0.81 ng/g dry weight (cases)

(median)

0.57 (controls)

↔

↑ = association with increase; ↔ = no association; HCH = hexachlorocyclohexane

HEXACHLOROCYCLOHEXANE (HCH) 190

2. HEALTH EFFECTS

2.18 OTHER NONCANCER

Epidemiology Studies. Several case-control studies (Berg et al. 2021; Charles et al. 2022; Daniels et al.

2018; Han et al. 2020; Li et al. 2016; Rylander et al. 2015; Tawar et al. 2022; Tyagi et al. 2021; Zong et

al. 2018) and cross-sectional studies (Arrebola et al. 2013; Everett and Matheson 2010; Gasull et al. 2012;

Schwarz et al. 2021; Ukropec et al. 2010) evaluated associations between diabetes and exposure to HCH

isomers (see Table 2-20). There were no associations with serum levels of α-, γ-, or δ-HCH isomers and

type 2 diabetes reported in a case-control study of 723 cases of Chinese type 2 diabetes patients compared

to control subjects, while higher mean serum levels of β-HCH and with total HCH levels were associated

with type 2 diabetes (Li et al. 2016); significant interactions with several ADIPOQ (gene encoding

adiponectin) genotypes were reported for the β-HCH isomer. No association was observed with type 2

diabetes and serum levels of β-HCH or γ -HCH in case-control studies in Norway (Berg et al. 2021;

Charles et al. 2022) or in a case-cohort study in France (Magliano et al. 2021). However, nested case-

control studies reported an association between serum and plasma β-HCH levels and increased incidences

of type 2 diabetes in American nurses (Zong et al. 2018), Norwegian women (Rylander et al. 2015), and

in Chinese adults (Han et al. 2020). One nested case-control study comparing South Asians and European

whites living in London determined a significant association between plasma concentrations of β-HCH

and increased prevalence of diabetes in a Tamil-descent population, while an elevated, but not significant,

association was reported in a Telugu-descent population with much higher plasma concentrations of

β-HCH (Daniels et al. 2018). Tawar et al. (2022) conducted a case-control study in India and reported a

positive association between levels of δ- HCH in adipose tissue and type 2 diabetes, but no association

between α-, β-, or γ-HCH and type 2 diabetes was observed.

In cross-sectional studies evaluating β-HCH, there was no association between the prevalence of diabetes

and levels in adipose tissue (Arrebola et al. 2013), and no association between diabetes and pre-diabetes

and serum levels (Everett and Matheson 2010; Gasull et al. 2012; Schwarz et al. 2021). Another cross-

sectional study similarly found no association with diabetes; however, an association was seen between

serum β-HCH and increased incidence of pre-diabetes (Ukropec et al. 2010). Additionally, a cross-

sectional study using NHANES data reported an association with serum β-HCH and increased incidence

of diabetes without nephropathy, but no association in adults with both diabetes and nephropathy (Everett

and Thompson 2015). There was no relationship between serum β-HCH and insulin sensitivity and

secretion indicators (Lee et al. 2017), nor were there associations with leptin and insulin levels and insulin

resistance (Burns et al. 2014).

HEXACHLOROCYCLOHEXANE (HCH) 191

2. HEALTH EFFECTS

Table 2-20. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Other

Noncancer Effects

Reference, study type, and population

Outcome

evaluated

Isomer

Biomarker

Concentration

Result

Arrebola et al. 2013

Cross-sectional, 386 patients undergoing

noncancer-related surgery, Spain

Type 2 diabetes

β-HCH

Adipose

>16.81 ng/g lipid

↔

Berg et al. 2021

Case-control, 44 cases of Type 2 diabetes and

44 age-matched controls, mean age 52 years,

Norway

Type 2 diabetes

β-HCH

Serum

12.8 ng/g lipid (cases) (median,

prediagnostic sample)

13.9 (controls)

↔

γ-HCH

3.36 (cases)

4.39 (controls)

↓

Charles et al. 2022

Nested case-control, 116 cases of Type 2

diabetes, 139 controls, mean ages 48 and

45 years, respectively, Norway

Type 2 diabetes

β-HCH

Serum

14.0-36.7 ng/g lipid (cases) (mean,

prediagnostic samples)

12.9-31.8 (controls)

↔

Han et al. 2020

Case-control, 158 cases of Type 2 diabetes,

158 controls, China

Type 2 diabetes

β-HCH

Serum

1351 pg/mL (cases) (GM)

695 (controls)

↑

Magliano et al. 2021

Case-cohort, 200 cases of type 2 diabetes and

553 controls, mean ages 51 and 47 years,

respectively, France

Type 2 diabetes

β-HCH

Serum

811 ng/L (cases) (median)

513 (controls)

↔

γ-HCH

18.4 ng/L (cases) (median)

14.7 (controls)

↔

Li et al. 2016

Case-control, 723 cases and 723 controls, mean

age 62 years, China

Type 2 diabetes

α-HCH

Serum

0.012 ng/mL (cases) (GM)

0.011 (controls)

↔

β-HCH

0.575 (cases)

0.266 (controls)

↑

γ-HCH

0.020 (cases)

0.018 (controls)

↔

δ-HCH

0.068 (cases)

0.060 (controls)

↔

Total HCH

↑

HEXACHLOROCYCLOHEXANE (HCH) 192

2. HEALTH EFFECTS

Table 2-20. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Other

Noncancer Effects

Reference, study type, and population

Outcome

evaluated

Isomer

Biomarker

Concentration

Result

Zong et al. 2018

Nested case-control, 793 cases and 793 controls

participating in Nurse Health Study II, age 32–

52 years, United States

Type 2 diabetes

β-HCH

Serum

14.3 ng/g lipid (median) (cases)

9.84 (controls)

↑ (trend)

Rylander et al. 2015

Nested case-control, 106 cases and 106 control

women, age 30–70 years, Norway

Type 2 diabetes

β-HCH

Plasma

20.3 ng/g lipid (mean) (cases)

10.0 (controls)

↑

Daniels et al. 2018

Nested case-control, 73 adults of Tamil descent

and 47 adults of Telugu descent, >21 years old,

United Kingdom

Diabetes in Tamil

population

β-HCH

Plasma

≥50.58 ng/g lipid

↑

Diabetes in Telugu

population

≥369.30 ng/g lipid

↔

Everett and Matheson 2010

Cross-sectional, 3,414 adults ≥20 years old,

NHANES, United States

Diabetes

β-HCH

Serum

>9.36 ng/g lipid

↔

Pre-diabetes

↔

Gasull et al. 2012

Cross-sectional, 886 adults 18–74 years, Spain

Diabetes

β-HCH

Serum

>1.547 ng/mL (4

quartile cutoff)

↔

Pre-diabetes

↔

Ukropec et al. 2010

Cross-sectional, 2,047 adults 21–75 years old,

Slovakia

Diabetes

β-HCH

Serum

83–781 ng/g lipid (5th quintile)

↔

Pre-diabetes

↑

Schwarz et al. 2021

Cross-sectional, 200 adults 75–76 years old,

Germany

Known diabetes

β-HCH

Serum

0.12 ug/L (median)

↔

Newly diagnosed

diabetes

0.10

↔

Pre-diabetes

0.08

↔

Everett and Thompson 2015

Cross-sectional, 2,992 adults ≥20 years old,

NHANES (1999–2004), United States

Diabetes without

nephropathy

β-HCH

Serum

≥0.1018 ng/g

↑

Diabetes with

nephropathy

β-HCH

Serum

≥0.1018 ng/g

↔

HEXACHLOROCYCLOHEXANE (HCH) 193

2. HEALTH EFFECTS

Table 2-20. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Other

Noncancer Effects

Reference, study type, and population

Outcome

evaluated

Isomer

Biomarker

Concentration

Result

Tawar et al. 2022

Case-control, 70 cases of type 2 diabetes and

70 age-, gender-, and BMI- matched controls,

mean ages 43.65 (control) and 44.9 (cases)

years, India

Type 2 diabetes

α-HCH

Adipose

tissue

0.90 ng/g (cases)

0.41 (controls)

↔

β-HCH

1.25 (cases)

0.89 (controls)

↔

γ-HCH

1.17 (cases)

0.86 (controls)

↔

δ-HCH

2.70 (cases)

0.79 (controls)

↑

Lee et al. 2017

Cross-sectional, 200 adults >30 years old, Korea

Insulin sensitivity

and secretion

indicators

β-HCH

Serum

157.97 pg/mL (4

quartile cutoff)

↔

Burns et al. 2014

Cohort, 318 boys, age 8–9 years, Russia

Leptin

β-HCH

Serum

165 ng/g lipid (median)

↔

Insulin

↔

Insulin resistance

↔

Gasull et al. 2018

Cross-sectional, 860 adults 18–74 years old,

Spain

Unhealthy

metabolic

phenotype

β-HCH

Serum

≥0.671 ng/mL (4th quartile)

↑

Reina-Pérez et al. 2023

Cross-sectional, 117 adult surgical patients,

median age 44 years, Spain

Metabolic

syndrome

γ-HCH

Adipose

tissue

11.44 ng/g (median)

↑

Elevated waist

circumference

↑

Elevated blood

pressure

↑

Elevated fasting

blood glucose,

triglycerides, or

HDL cholesterol

↔

HEXACHLOROCYCLOHEXANE (HCH) 194

2. HEALTH EFFECTS

Table 2-20. Summary of Epidemiological Studies of Hexachlorocyclohexane (HCH) Exposure and Other

Noncancer Effects

Reference, study type, and population

Outcome

evaluated

Isomer

Biomarker

Concentration

Result

Zhang et al. 2023

Cross-sectional, 1,996 adult residents of Wuhan,

mean age 44.8 years, China

Metabolic

syndrome

β-HCH

Serum

34.5 ng/g lipid (median)

↑

Lee et al. 2016

Cohort, 214 children 7–9 years old, Korea

Measures of

metabolic

syndrome

β-HCH

Serum

6.13 ng/g lipid (median)

↔

Mustieles et al. 2017

Cross-sectional and 10-year longitudinal,

387 noncancer surgical patients (at baseline),

median age 52 years; 154 without metabolic

disease at baseline followed for 10 years, median

age 42 years, Spain

Metabolically

compromised

baseline

β-HCH

Adipose

tissue

10.6 ng/g lipid (median)

↑

Metabolically

compromised

follow up

6.9

↑

Wang et al. 2021a

Cross sectional, 10 women, mean age 37 years,

China

Serum lipoprotein

a, total cholesterol,

triglycerides, high-

and low-density

lipoprotein

cholesterol

α-HCH

Estimated

dietary

intake

0.471 ng/kg/day

↔

β-HCH

0.185

↔

γ-HCH

0.043

↔

δ-HCH

0.104

↔

Significant interactions with several ADIPOQ genotypes.

Unhealthy metabolic phenotype was defined as exhibiting two or more of the following: hypertension, hypertriglyceridemia, low HDL cholesterol, hyperglycemia,

insulin resistance, or systemic inflammation.

Metabolically compromised was defined as exhibiting one or more of the following: type 2 diabetes, hypertension, hypertriglyceridemia, or low HDL cholesterol.

↑ = association with increase; ↓ = association with decrease (inverse association); ↔ = no association; GM = geometric mean; HDL = high-density lipoprotein;

NHANES = National Health and Nutrition Examination Survey

HEXACHLOROCYCLOHEXANE (HCH) 195

2. HEALTH EFFECTS

Gasull et al. (2018) reported a positive association between unhealthy metabolic phenotypes (defined as

exhibiting at least two of the following: hypertension, hypertriglyceridemia, low high-density lipoprotein

(HDL) cholesterol, hyperglycemia, insulin resistance, or systemic inflammation) and serum β-HCH

levels. A study of adult noncancer surgical patients also showed an association between β-HCH levels in

adipose tissue and increased likelihood of being metabolically compromised (exhibiting type 2 diabetes,

hypertension, hypertriglyceridemia, or low HDL cholesterol) at baseline and at a 10-year follow-up

(Mustieles et al. 2017). A cross-sectional study of 1,996 adults in China reported a positive association

between β-HCH in serum and metabolic syndrome (Zhang et al. 2023). There was no association

between serum β-HCH levels and measures of metabolic syndrome in a cohort of 214 Korean children

between 7 and 9 years of age (Lee et al. 2016).

In a cross-sectional study of surgical patients in Spain, associations between metabolic syndrome,

elevated waist circumference, and elevated blood pressure with γ-HCH levels in adipose tissue were

observed (Reina-Pérez et al. 2023). In a small cross-sectional study of 10 women in China, Wang et al.

(2021) reported no association between any of the HCH isomers and serum levels of lipids.

2.19 CANCER

Epidemiological Studies. Epidemiological studies of HCH isomers and cancer are shown in Table 2-21.

Studies shown in the table include only those that accounted for at least one potential confounding

variable (i.e., studies reporting only univariate analyses were excluded). In addition, only the most recent

analysis of a given cohort or case-control population is shown in the table.

Table 2-21. Summary of Epidemiological Studies Evaluating Possible

Associations between Hexachlorocyclohexane Exposure and

Risk of Selected Cancer Types

Cancer type

Isomer

Association

No association

Non-Hodgkin’s lymphoma

Beta (β)

Bassig et al. 2020; Viel et

al. 2011

Brauner et al. 2012; Cantor et al.

2003; Cocco et al. 2008

Gamma (γ)

Alavanja et al. 2014

;

Kachuri et al. 2020

Cocco et al. 2008; De Roos et al.

2021; Viel et al. 2011

Multiple myeloma

Beta (β)

Weber et al. 2018

Gamma (γ)

Presutti et al. 2016

HEXACHLOROCYCLOHEXANE (HCH) 196

2. HEALTH EFFECTS

Table 2-21. Summary of Epidemiological Studies Evaluating Possible

Associations between Hexachlorocyclohexane Exposure and

Risk of Selected Cancer Types

Cancer type

Isomer

Association

No association

Leukemia

Alpha (α)

Rafeeinia et al. 2023;

Beta (β)

Rafeeinia et al. 2023;

Cocco et al. 2008

Gamma (γ)

Purdue et al. 2007;

Rafeeinia et al. 2023

Colon/colorectal

Αlpha (α)

Howsam et al. 2004

Beta (β)

Lee et al. 2018a

Howsam et al. 2004; Park et al. 2021

Gamma (γ)

Howsam et al. 2004; Purdue et al.

2007

Female breast cancer

Alpha (α)

Miao et al. 2021

Beta (β)

Arrebola et al. 2015b

Miao et al. 2021;

Waliszewski et al. 2005

Hoyer et al. 1998; Lopez-Carrillo et

al. 2002; McCready et al. 2004;

Raaschou-Nielsen et al. 2005

;

Ward

et al. 2000; Wielsoe et al. 2017; Xu

et al. 2010

Gamma (γ)

Ibarluzea et al. 2004

Hoyer et al. 1998; Miao et al. 2021

Delta (δ)

Miao et al. 2021

Prostate cancer

Alpha (α)

Pi et al. 2016

Beta (β)

Kumar et al. 2010; Xu et

al. 2010

Aronson et al. 2010; Lim et al. 2017;

Pi et al. 2016; Sawada et al. 2010

Gamma (γ)

Band et al. 2011

Barry et al. 2011; Koutros et al.

2011; Pi et al. 2016

Lung cancer

Gamma (γ)

Purdue et al. 2007

Hepatocellular carcinoma

Beta (β)

Zhao et al. 2012

Bladder cancer

Gamma (γ)

Purdue et al. 2007

Endometrial cancer

Beta (β)

Sturgeon et al. 1998

Melanoma

Gamma (γ)

Purdue et al. 2007

Soft tissue sarcoma

Gamma (γ)

Pahwa et al. 2011

Pancreatic cancer

Beta (β)

Porta et al. 2022

Brain cancer

Alpha (α)

Yousefi et al. 2022

Beta (β)

Yousefi et al. 2022

Gamma (γ)

Yousefi et al. 2022

Testicular germ cell tumors

Beta (β)

McGlynn et al. 2008

HEXACHLOROCYCLOHEXANE (HCH) 197

2. HEALTH EFFECTS

Table 2-21. Summary of Epidemiological Studies Evaluating Possible

Associations between Hexachlorocyclohexane Exposure and

Risk of Selected Cancer Types

Cancer type

Isomer

Association

No association

Thyroid cancer

Alpha (α)

Salimi et al. 2023

Beta (β)

Salimi et al. 2023

Deziel et al. 2021; Lerro et al. 2018

Gamma (γ)

Lerro et al. 2021; Salimi

et al. 2023

Statistically significant positive association.

No statistically significant positive association.

Follicular B-cell subtype.

Statistically significant inverse association.

Among post-menopausal women only.

The available studies provide evidence for an association between exposure to HCH and NHL, and

suggestive evidence for associations with some other cancer types (see Table 2-21). The strongest

evidence for an association between HCH exposure and NHL comes from a prospective cohort study of

54,306 pesticide applicators (the Agricultural Health Study) in Iowa and North Carolina (Alavanja et al.

2014). Cohort members were enrolled between 1993 and 1997 and followed through 2011. At

enrollment and 5 years later, the subjects filled out questionnaires about use of specific pesticides,

including frequency and duration of γ-HCH use. A total of 523 incident cases of NHL were observed

over 803,140 person-years of follow up. The risk of incident NHL was increased with total days of

γ-HCH exposure and with intensity-weighted total days of exposure after adjustment for confounders

identified in the NHL literature and for herbicide use. Analysis by subtype of NHL showed the increased

risk with HCH exposure to be limited to the follicular B-cell subtype (Alavanja et al. 2014).

Three case-control studies nested within prospective cohort studies of populations without known sources

of HCH exposure examined associations between NHL and prediagnostic blood or adipose tissue levels.

In an analysis of 167 cases and 167 controls from three prospective cohort studies (>150,000 subjects) in

Shanghai and Singapore, Bassig et al. (2020) observed a positive association between NHL and blood

levels of β-HCH measured approximately 7 years prior to diagnosis. In contrast, Cantor et al. (2003)

observed no association between NHL and exposure among 74 cases and 157 controls from a large cohort

(25,802 participants) in Maryland. In this study, serum concentrations of β-HCH were measured in 1974,

and cases were identified through 1994. Importantly, the blood concentrations of β-HCH were markedly

higher in the study by Bassig et al. (2020) (median among cases was 5,670 ng/g lipid) than in the study by

Cantor et al. (2003) (mean among cases was 139.9 ng/g lipid). Finally, Brauner et al. (2012) did not

HEXACHLOROCYCLOHEXANE (HCH) 198

2. HEALTH EFFECTS

observe a significant association between NHL and β-HCH in adipose tissue among 256 cases and

256 referents in a cohort of 57,053 participants in Denmark. Adipose samples were collected at

enrollment between 1993 and 1997 and cases were identified through 2008; the median adipose

concentration of β-HCH among cases was 59 ng/g. A large, pooled case-control study provides support

for the association between NHL and HCH exposure. Kachuri et al. (2020) pooled data across three

population-based, case-control studies in the United States and Canada (North American Pooled Project).

The odds of NHL were increased with self-reported exposure to γ-HCH in analyses of 1,690 cases and

5,131 controls (Kachuri et al. 2020). In contrast, another pooled case-control study that included

4,373 cases and 4,373 controls from studies in the United States, Canada, and Italy, found no association

between self-reported exposure to γ-HCH and increased odds of NHL or any individual subtype (De Roos

et al. 2021).

Other epidemiological studies have reported positive associations between β- or γ-HCH in blood or

qualitative exposure to γ-HCH and multiple myeloma, leukemia, colorectal cancer, female breast cancer,

prostate cancer, lung cancer, thyroid cancer, brain cancer, and hepatocellular carcinoma (see Table 2-21).

However, the evidence for these cancer types is relatively weak. In an earlier analysis of cancer incidence

in the Agricultural Health Study (cohort of 57,311 pesticide applicators), increased risks of incident

leukemia and lung cancer were observed among subjects with any self-reported use of γ-HCH compared

with those who never used it (Purdue et al. 2007). In a case-control study of children in Iran, Rafeeinia et

al. (2023) reported an association between serum levels of α-, β-, and γ-HCH and acute lymphoblastic

leukemia (ALL). Lerro et al. (2021) examined incident thyroid cancer in subjects in the Agricultural

Health Study cohort and observed an increase in the hazard ratio among subjects who reported ever use of

lindane (compared with those reporting no lindane use) after a relatively brief follow-up period of 5 years

after enrollment. Band et al. (2011) reported an association between γ-HCH exposure assessed through a

job-exposure matrix and increased risk of prostate cancer in a study of 1,153 cases and 3,999 controls.

Many of the studies reporting positive associations between multiple myeloma, colorectal cancer,

hepatocellular carcinoma, breast cancer, prostate cancer, or thyroid cancer and HCH exposures (Arrebola

et al. 2015b; Ibarluzea et al. 2004; Kumar et al. 2010; Lee et al. 2018a; Miao et al. 2021; Salimi et al.

2023; Waliszewski et al. 2005; Weber et al. 2018; Xu et al. 2010; Zhao et al. 2012) are case-control

studies in which exposure was assessed using concentrations of HCH in blood or adipose samples

collected after disease onset. The lack of temporal relationship between exposure and outcome render

these studies of uncertain utility for hazard identification.

HEXACHLOROCYCLOHEXANE (HCH) 199

2. HEALTH EFFECTS

Epidemiological studies published to date have not shown any associations between exposure to HCH

and cancers of the bladder, endometrium, pancreas, and testicular germ cells, or melanoma and soft tissue

sarcoma (see Table 2-21).

α-HCH. Increased incidences of neoplastic nodules in the liver, hepatomas, and/or hepatocellular

carcinomas were reported in several strains of mice exposed to doses between 13 and 95 mg/kg/day for

16–36 weeks (Hanada et al. 1973; Ito et al. 1973, 1976; Nagasaki et al. 1975; Tryphonas and Iverson

1983; Tsukada et al. 1979). No evidence of liver carcinogenicity was reported in Wistar rats exposed to

45 mg/kg/day α-HCH in the diet for 24 weeks (Nagasaki et al. 1975), but a dose of 70 mg/kg/day for

48 weeks resulted in liver tumors (Ito et al. 1975). Ito et al. (1975) also reported an increased incidence

of hepatocellular carcinomas in male rats exposed to α-HCH in the diet at ≥70 mg/kg/day for 72 weeks.

In studies of α-HCH tumor promotion, mixed results were observed. In rats, administration of

35 mg/kg/day of α-HCH in the diet for 65 weeks inhibited the induction of liver tumors by

0.07 mg/kg/day of aflatoxin B

(Angsubhakorn et al. 1981). A study of γ-glutamyltranspeptidase-positive

liver foci in rats pretreated with the tumor initiator N-nitrosomorpholine showed that administration of

α-HCH at 20 mg/kg/day in food for 49 weeks increased the volume fraction of positive foci, largely by

reducing apoptosis (Luebeck et al. 1995). Schröter et al. (1987) reported significant increases in the

number and areas of preneoplastic hepatic foci in female Wistar rats treated with doses ≥2 mg/kg/day in

the diet.

β-HCH. Animal studies of β-HCH carcinogenicity are limited by short duration of exposure, concurrent

mortality, and/or reporting limitations. β-HCH did not increase liver tumor incidences in Wistar rats

exposed to 35 or 70 mg/kg/day in the diet for 24 or 48 weeks (Ito et al. 1975), but this study was

hampered by significant mortality. No increase in liver tumor incidence was noted in dd mice exposed to

18–120 mg/kg/day in the diet for 24 or 32 weeks (Hanada et al. 1973; Ito et al. 1973). However, in a

longer study, Thorpe and Walker (1973) reported an increased incidence of hepatocellular carcinomas in

male CF1 mice and a significant increase in other (unspecified) tumors in female CF1 mice exposed to

34 mg/kg/day in the diet for 104 weeks. In this study, significant mortality occurred early in the study

(12% of males and 25% of females died within 3 months).

β-HCH, at a single oral dose of 100 mg/kg/day, did not induce an increase in the number or size of

preneoplastic hepatic foci in a two-stage study using female Wistar rats dosed with phenobarbital as a

promoting agent (Schröter et al. 1987). However, a significant increase in preneoplastic hepatic foci was

HEXACHLOROCYCLOHEXANE (HCH) 200

2. HEALTH EFFECTS

noted in rats exposed for 20 weeks to doses ≥3 mg/kg/day β-HCH in the diet after initiation with

N-nitrosomorpholine (Schröter et al. 1987).

γ-HCH (Lindane). In Wistar rats, exposure to 25 mg γ-HCH/kg/day in the diet for 24 or 48 weeks did

not result in any liver tumors (Ito et al. 1975); however, the abbreviated exposure duration and high

mortality in the control and treatment groups preclude conclusions as to carcinogenicity under this

experimental protocol. Mice (dd strain) exposed to as much as 90 mg γ-HCH/kg/day in the diet for 24

weeks did not exhibit any increased tumor incidences when compared to controls (Ito et al. 1973). An

increased incidence of malignant hepatomas was reported in male dd mice exposed to 108–120

mg/kg/day in the diet for 32 weeks (Hanada et al. 1973). In that study, survival to study end at the

carcinogenic dose was very low, so the magnitude of the effect may be underestimated.

Chronic-duration studies have shown increased incidences of tumors in mice, but not rats, exposed to γ-

HCH. No statistically significant increases in endocrine, thyroid, pituitary, adrenal gland, liver, or ovary

tumors were observed in male and female Osborne-Mendel rats fed 10.8–33 mg/kg/day in the diet for 80

weeks (NCI 1977) or in Wistar rats fed 0.07–32 mg γ-HCH/kg/day in the diet for 104 weeks (Amyes

1990); however, poor survival rates limit the significance of these results. Liver tumors have been

reported in CF1 and B6C3F1 mice exposed to 13.6–68 mg/kg/day in the diet for 80 to 104 weeks (NCI

1977; Thorpe and Walker 1973). In contrast, EPA (2000a) did not observe an increase in liver tumor

incidence in CD-1 mice exposed to doses up to 26.8 mg/kg/day for 78 weeks. Female mice, but not male

mice, in this study exhibited increased incidences of lung adenomas at the high dose (26.8 mg/kg/day)

(EPA 2000a). Increased incidences of hepatocellular adenomas and carcinomas were also observed in

obese mottled yellow A

/a and lean pseudoagouti A

/a (YSxVY) F1 mice exposed to 27.2 mg/kg/day in

the diet for 96 weeks, but not in lean black a/a (YSxVY) F1 mice (Wolff et al. 1987). The obese mottled

yellow and lean pseudoagouti strains have a dominant mutation at the agouti locus (Avy) that increases

their susceptibility to strain-specific neoplasms. Incidences of benign lung adenomas were also increased

in female obese mottled yellow A

/a and lean pseudoagouti A

/a (YSxVY)F1 mice exposed to

27.2 mg/kg/day for 24 months (Wolff et al. 1987).

In mice, dermal exposure to a 0.5% solution of γ-HCH in acetone applied twice a day for 60 days was

reported to result in no treatment-related tumors (Orr 1948). Limitations of this study include less-than-

lifetime exposure and study duration, testing of only one dose, and potential for ingestion of some of the

compound from the skin.

HEXACHLOROCYCLOHEXANE (HCH) 201

2. HEALTH EFFECTS

δ-HCH. δ-HCH did not induce a significant increase in liver tumors in male Wistar rats exposed to doses

up to 70 mg/kg/day in the diet for 48 weeks (Ito et al. 1975) or in male dd mice exposed to doses up to

90 mg/kg/day in the diet for 24 weeks (Ito et al. 1973). However, these studies were of relatively short

exposure durations, and organs other than the liver were not evaluated for histopathology.

Technical HCH or Unspecified Isomers of HCH. Ito et al. (1973) examined the carcinogenicity of pairs

of HCH isomers in dd mice exposed to 45 mg/kg/day of each isomer in the diet (total HCH dosage of

90 mg/kg/day) for 24 weeks. Exposure to β-HCH with γ- or δ-HCH, or to γ-HCH together with δ-HCH

did not result in hepatocellular carcinomas. However, when any of these isomers was administered with

α-HCH, an increased incidence of hepatocellular carcinomas was observed.

Thakore et al. (1981) reported the appearance of neoplastic nodules in the livers of Swiss mice following

dietary exposure to technical-grade HCH at 90 mg/kg/day for 6 months. Increased incidences of

hepatocellular carcinoma were reported in Swiss mice exposed to 90 mg/kg/day in the diet for 6–

8 months (Bhatt and Bano 2009; Bhatt and Nagda 2012; Trivedi et al. 2007, 2009); to 21.3–85 mg/kg/day

in the diet for 20 months (Munir et al. 1983); and to 10 or 17 mg/kg/day through gavage or the diet,

respectively, for 80 weeks (Kashyap et al. 1979). Dermal application of 2.4 mg technical-grade

HCH/kg/day by skin painting on Swiss mice for 80 weeks resulted in nonsignificant increases in the

incidences of hyperplastic and preneoplastic areas in the liver and hepatic tumors (Kashyap et al. 1979).

The EPA (IRIS 1987a) listed α-HCH as a probable human carcinogen based on sufficient evidence of

carcinogenicity in animals and inadequate data in humans. IRIS (1987b) lists β-HCH as a possible human

carcinogen based on evidence for benign liver tumors in exposed mice and inadequate data in humans.

Data on δ- and ε-HCH were considered inadequate to classify the potential human carcinogenicity (IRIS

1987d, 1987e). Although the IRIS (1987c) program did not evaluate the carcinogenicity of γ-HCH,

EPA’s Office of Pesticide Programs (EPA 2001, 2002) classified γ-HCH into the category “suggestive

evidence of carcinogenicity, but not sufficient to assess human carcinogenic potential.”

The HHS NTP determined that γ-HCH and other HCH isomers may reasonably be anticipated to cause

cancer in humans (NTP 2021). In 2018, IARC determined that there was sufficient evidence in both

humans and animals for the carcinogenicity of γ-HCH, assigning it to Group 1 (carcinogenic to humans).

IARC (2018) concluded that γ-HCH causes NHL in humans.

HEXACHLOROCYCLOHEXANE (HCH) 202

2. HEALTH EFFECTS

Mechanisms. IARC (2018) conducted an extensive review of the available data on mechanisms of HCH

carcinogenicity using the 10 key characteristics of carcinogens (Smith et al. 2016) as a framework. Their

analysis noted that the metabolism of γ-HCH yields several intermediates and metabolites, but that to

date, those involved in carcinogenesis have not yet been identified. In vitro data in rat liver microsomes

have shown the formation of a stable epoxide, indicating that γ-HCH can form electrophilic metabolites

(reviewed by IARC 2018). Based on the available in vivo and in vitro data, IARC (2018) concluded that

there was strong evidence that γ-HCH induces immunosuppression and oxidative stress, and moderate

evidence for genotoxicity and modulation of receptor-mediated effects. Section 2.14 provides details on

the in vivo evidence for immunosuppression in animals exposed orally to γ-HCH; little to no data are

available for immune system effects of other isomers. Several in vivo studies reported increased measures

of oxidative stress in the heart, liver, kidney, central nervous system, testes, and maternal or fetal tissues

after oral exposure to γ-HCH; these studies are described in the Mechanisms subsections of Sections 2.5,

2.9, 2.10, 2.15, 2.16, and 2.17. In vivo studies of estrogen-mediated effects are described under

Mechanisms in Section 2.16. Genotoxicity studies of HCH isomers are summarized in Section 2.20.

2.20 GENOTOXICITY

Numerous in vivo and in vitro studies have assessed the genotoxic potential of HCH and its isomers (α-,

β-, and γ-HCH). Genotoxicity testing results for HCH isomers are summarized below. Results of in vivo

and in vitro genotoxicity studies are presented in Tables 2-22 and 2-23, respectively.

Table 2-22. Genotoxicity of Hexachlorocyclohexane Isomers In Vivo

Species (test system)

Endpoint

Results

Isomer

Reference

Mammalian cells

Human (peripheral blood)

DNA damage

–

Alpha, beta

Varona-Uribe et al. 2016

Human (peripheral blood)

Comet assay

–

Alpha, beta

Varona-Uribe et al. 2016

Human (peripheral

lymphocytes)

Micronucleus test

–

Alpha, beta,

and gamma

Jonnalagadda et al. 2012

Mouse (bone marrow)

Micronucleus test

Gamma

Yaduvanshi et al. 2012

Human (peripheral

lymphocytes)

Chromosomal

aberrations

Alpha, beta,

and gamma

Jonnalagadda et al. 2012

Rat (bone marrow)

Chromosomal

aberrations

Beta

Shimazu et al. 1972

Human (peripheral

lymphocytes)

Chromosomal

aberrations

–

Gamma

Kiraly et al. 1979

Syrian hamster (bone

marrow)

Chromosomal

aberrations

–

Gamma

Dzwonkowska and

Hubner 1986

HEXACHLOROCYCLOHEXANE (HCH) 203

2. HEALTH EFFECTS

Table 2-22. Genotoxicity of Hexachlorocyclohexane Isomers In Vivo

Species (test system)

Endpoint

Results

Isomer

Reference

Mouse

Micronuclei

–

Gamma

Jenssen and Ramel 1980

Mouse (bone marrow)

Chromosomal

aberrations

Gamma

Kumar et al. 1995

Rat (liver)

Mitotic disturbances

Alpha

Hitachi et al. 1975

Mouse (liver)

DNA binding

(+)

Alpha/

gamma

Iverson et al. 1984

Mouse (germ cells)

Dominant lethal

Technical

Lakkad et al. 1982

Human (MGMT tumor

suppressor gene in

colorectal cancer cells)

Hypermethylation

–

Alpha, beta,

and gamma

Abolhassani et al. 2019

Human (P16 tumor

suppressor gene in

colorectal cancer cells)

Hypermethylation

–

Αlpha and

beta

Abolhassani et al. 2019

Human (P16 tumor

suppressor gene in

colorectal cancer cells)

Hypermethylation

Gamma

Abolhassani et al. 2019

Human (Leukocyte DNA)

DNA hypomethylation

Beta

Itoh et al. 2014

Human (tumor suppressor

gene E-cadherin [CDH1] in

peripheral blood

mononuclear cells)

Methylation

(+)

Beta

Lee et al. 2018b

– = negative result; + = positive result; (+) = weakly positive result; DNA = deoxyribonucleic acid

Table 2-23. Genotoxicity of Hexachlorocyclohexane Isomers In Vitro

Species (test system)

Endpoint

Results

Isomer

Reference

With

activation

Without

activation

Prokaryotic organisms

Salmonella typhimurium

TA100, TA98, TA1535,

TA1537, TA1538

(reversion assay)

Gene mutation

–

Gamma

Moriya et al. 1983

S. typhimurium TA98,

TA100, TA102

(Salmonella/microsome

mutagenicity assay)

Gene mutation

–

Gamma

Yaduvanshi et al.

2012

Escherichia coli (WP2/spot

test)

Gene mutation

–

Gamma

Nagy et al. 1975

E. coli (WP2 hcr)

(reversion assay)

Gene mutation

–

Gamma

Moriya et al. 1983

Bacillus subtilis (rec assay)

DNA damage

–

Gamma

Shirasu et al. 1976

HEXACHLOROCYCLOHEXANE (HCH) 204

2. HEALTH EFFECTS

Table 2-23. Genotoxicity of Hexachlorocyclohexane Isomers In Vitro

Species (test system)

Endpoint

Results

Isomer

Reference

With

activation

Without

activation

Eukaryotic organisms

Fungi and plant cells:

Saccharomyces cerevisiae

Gene mutation

–

Gamma

Shahin and von

Borstel 1977

S. cerevisiae (transformed

reporter strain HLYRGI)

DNA damage

Gamma

Schmitt et al. 2005

Nostoc muscorum

Gene mutation

–

Gamma

Kar and Singh 1979a

Allium cepa

Mitotic

disturbances

Gamma

Nybom and Knutsson

1947

Mammalian cells

Human (peripheral

lymphocytes)

Micronuclei

–

Alpha

Ennaceur 2017

Human (peripheral

lymphocytes)

Micronuclei

Beta

Ennaceur 2017

Human (peripheral

lymphocytes)

Micronuclei

Gamma

Ennaceur 2017

Human (mammary

carcinoma MCF-7)

Micronuclei

Gamma

Kalantzi et al. 2004

Human (prostate carcinoma

PC-3)

Micronuclei

Gamma

Kalantzi et al. 2004

Human (SV-40 fibroblasts)

Unscheduled

DNA synthesis

–

Gamma

Ahmed et al. 1977

Human (peripheral

lymphocytes)

Unscheduled

DNA synthesis

Gamma

Rocchi et al. 1980

Rat (primary hepatocytes)

Unscheduled

DNA synthesis

–

Gamma

Cifone 1990

Human (mammary

carcinoma MCF-7)

DNA damage

–

Gamma

Kalantzi et al. 2004

Human (prostate carcinoma

PC-3)

DNA damage

–

Gamma

Kalantzi et al. 2004

Human (ovary surface

epithelial cells)

DNA damage

Beta

Shah et al. 2020

Human hepatocytes

DNA

fragmentation

Alpha

Mattioli et al. 1996

Rat (primary cultures)

DNA

fragmentation

Alpha

Mattioli et al. 1996

Mouse (hepatocytes)

DNA

fragmentation

–

Alpha

Mattioli et al. 1996

Chinese hamster lung (CHL)

cells

Chromosomal

aberrations

(+)

Gamma

Ishidate and

Odashima 1977

Chinese hamster ovary

(CHO) cells

Chromosomal

aberrations

–

Gamma

NTP 1984

HEXACHLOROCYCLOHEXANE (HCH) 205

2. HEALTH EFFECTS

Table 2-23. Genotoxicity of Hexachlorocyclohexane Isomers In Vitro

Species (test system)

Endpoint

Results

Isomer

Reference

With

activation

Without

activation

CHO cells

Sister chromatid

exchange

–

Gamma

NTP 1984

CHO cells

Chromosomal

aberrations

–

Gamma

Murli 1990

Human (peripheral

lymphocytes)

Sister chromatid

exchange

Technical

Rupa et al. 1989d

Human (peripheral

lymphocytes)

Chromosomal

aberrations

Technical

Rupa et al. 1989d

Calf (thymus DNA)

DNA binding

(+)

Alpha/

gamma

Iverson et al. 1984

– = negative result; + = positive result; (+) = weakly positive result; DNA = deoxyribonucleic acid; NT = not tested

Several studies in humans evaluated the genotoxicity of HCH. Several studies examined the genotoxicity

of hexachlorocyclohexane in agricultural workers exposed to mixtures of pesticides. In rice field workers

exposed to pesticide mixtures, there was no association between peripheral blood levels of α-HCH or β-

HCH and DNA damage measured by comet assay (Varona-Uribe et al. 2016). The frequency of

micronuclei in peripheral lymphocytes in agricultural workers exposed to a complex mixture of pesticides

including HCH was not significantly different compared to unexposed workers, while the frequency of

chromosomal aberrations was significantly increased in exposed workers (Jonnalagadda et al. 2012). In

addition, a correlation between chromosomal aberrations per cell and HCH level was reported

(Jonnalagadda et al. 2012).

In workers occupationally exposed primarily to γ-HCH by inhalation in a pesticide production factory, no

appreciable increase in the frequency of chromosome aberrations was observed compared to the factory

employee control group (Kiraly et al. 1979). In colorectal cancer patients, serum levels of the α-HCH

isomer were not associated with changes in the methylation status of CpG islands of MGMT and

P16 tumor suppressor genes in colorectal cancer cells (Abolhassani et al. 2019). γ-HCH was not

associated with methylation status of the MGMT tumor suppression gene; however, hypermethylation

was found in the P16 tumor suppressor gene (Abolhassani et al. 2019). There was no significant

association between serum levels of β-HCH and methylation status of MGMT and P16 tumor suppressor

genes (Abolhassani et al. 2019); however, serum β-HCH was associated with a slight increase in

methylation of the tumor suppressor gene E-cadherin [CDH1] in peripheral blood mononuclear cells of

HEXACHLOROCYCLOHEXANE (HCH) 206

2. HEALTH EFFECTS

healthy Korean subjects (Lee et al. 2018b). There was a decreased level of global methylation associated

with β-HCH serum levels in human leukocyte DNA of Japanese women (Itoh et al. 2014).

Other studies are available regarding genotoxic effects (chromosomal aberrations, sister chromatid

exchanges) in humans exposed to a wide variety of pesticides, including HCH, when they were used on

farms (Rupa et al. 1988, 1989a, 1989b, 1989c). The specific effects of HCH, apart from the effects due to

other exposures, are not evident from these studies.

α-HCH. Both in vivo and in vitro assays for genotoxicity of α-HCH are available. α-HCH was observed

to bind to liver DNA in HPB mice following intraperitoneal administration (Iverson et al. 1984).

In human peripheral lymphocytes, in vitro exposure to α-HCH did not increase the frequency of

micronuclei in a cytokinesis-block micronucleus assay (Ennaceur 2017). Exposure to α-HCH produced

DNA fragmentation in primary cultures of rat and human hepatocytes, but not in mouse hepatocytes;

DNA repair was not induced in hepatocytes from all three species tested (Mattioli et al. 1996). α-HCH

was observed to bind to calf thymus DNA with metabolic activation (Iverson et al. 1984).

β-HCH. Limited in vivo and in vitro assays for the genotoxicity of β-HCH are available. In animals,

chromosomal aberrations were induced in bone marrow cells of Long-Evans rats following intraperitoneal

exposure to β-HCH in a study reported only as an abstract (Shimazu et al. 1972). In vitro exposure to

β-HCH increased the frequency of micronuclei at cytotoxic concentrations in human peripheral

lymphocytes in a cytokinesis-block micronucleus assay (Ennaceur 2017). β-HCH also induced DNA

damage in ovary surface epithelial cells (Shah et al. 2020).

γ-HCH (Lindane). γ-HCH has been tested in several in vivo and in vitro genotoxicity assays. The

incidence of chromosomal abnormalities (breaks and gaps with or without acentric fragments) in bone

marrow cells was increased in mice exposed to 1.6 mg γ-HCH/kg body weight/day by gavage for 7 days

(Kumar et al. 1995). In a mouse bone marrow micronucleus test, the frequency of micronucleated-

polychromatic erythrocytes was increased, and the frequency of polychromatic erythrocytes was

decreased in bone marrow cells (Yaduvanshi et al. 2012). γ-HCH was negative in a micronucleus assay

in CBA mice (Jenssen and Ramel 1980). Intraperitoneal exposure of Syrian hamsters did not induce

chromosome aberrations in bone marrow cells (Dzwonkowska and Hubner 1986). γ-HCH was observed

to bind to liver DNA in mice following intraperitoneal administration (Iverson et al. 1984).

HEXACHLOROCYCLOHEXANE (HCH) 207

2. HEALTH EFFECTS

γ-HCH did not induce gene mutations in Salmonella typhimurium (TA100, TA98, TA1535, TA1537, and

TA1538) or Escherichia coli (WP2) with or without a metabolic activation system (Moriya et al. 1983) or

in E. coli without metabolic activation in a WP2 spot test (Nagy et al. 1975). γ-HCH was also negative in

an Ames Salmonella/microsome mutagenicity assay in S. typhimurium (TA98, TA100, TA102) with and

without metabolic activation (Yaduvanshi et al. 2012). Exposure to γ-HCH did not produce DNA

damage in Bacillus subtilis in a rec assay, although a mammalian metabolic activation system was not

present (Shirasu et al. 1976). γ-HCH was not mutagenic in Nostoc muscorum algae (Kar and Singh

1979a). Mitotic disturbances (c-mitosis, which is characterized by spindle breakdown as that produced by

colchicine) and chromosome aberrations were observed in onion root tip cells exposed to commercial

γ-HCH (Nybom and Knutsson 1947). In yeast, exposure to γ-HCH did not induce mutations in

Saccharomyces cerevisiae (XV185-14C) in a reversion study (Shahin and von Borstel 1977) but did

induce DNA damage in transformed reporter strain HLYRGI (Schmitt et al. 2005).

In mammalian cells, γ-HCH induced a marginal increase in the frequency of chromosome aberrations

(including chromosomal gaps) in Chinese hamster ovary (CHO) cells (without metabolic activation),

which was interpreted by the authors of the study as providing suggestive, but not conclusive, evidence of

an effect (Ishidate and Odashima 1977). Another study reported negative results in cytogenetic tests

(chromosomal aberrations and sister chromatid exchange) in CHO cells exposed to γ-HCH without

metabolic activation (NTP 1984). In addition, γ-HCH was reported to be negative for chromosomal

aberrations in CHO cells with and without metabolic activation (Murli 1990).

In a cytokinesis-block micronucleus assay, exposure of human peripheral lymphocytes to γ-HCH induced

micronuclei and binucleated cells with micronucleus (BNMN) at a concentration of 100 µg/L, with

significant cytotoxicity at that concentration (Ennaceur 2017). γ-HCH exposure in human mammary

carcinoma MCF-7 and human prostate carcinoma PC-3 cell lines increased the frequency of micronuclei

in both cell lines in the absence of DNA damage or cytotoxicity, suggesting a clastogenic effect (Kalantzi

et al. 2004). In a microgel single cell assay, DNA damage was observed in cultures of rat nasal and

gastric mucosa cells and human nasal mucosa cells following exposure to

γ-HCH (Pool-Zobel et al. 1994).

γ-HCH was found to induce unscheduled DNA synthesis in human peripheral lymphocytes without

metabolic activation (Rocchi et al. 1980), while it was inactive for inducing unscheduled DNA synthesis

in human SV-40 fibroblasts, both with and without activation (Ahmed et al. 1977). In rat primary

hepatocytes tested without metabolic activation mammalian cells, γ-HCH did not induce unscheduled

DNA synthesis (Cifone 1990). γ-HCH was observed to bind to calf thymus DNA when tested with

exogenous metabolic activation (Iverson et al. 1984).

HEXACHLOROCYCLOHEXANE (HCH) 208

2. HEALTH EFFECTS

Technical HCH or Unspecified HCH Isomers. Technical-grade HCH has been tested for genotoxic

effects in one in vivo and one in vitro study. When male Swiss mice were exposed to technical-grade

HCH prior to mating, dominant-lethal mutations were induced, as evidenced by the number of dead

implantations per pregnant female (Lakkad et al. 1982). Cultured human lymphocytes showed a dose-

dependent increase in chromosomal aberrations (gaps, breaks, and fragments) with significant increases at

0.1 μg/mL technical-grade HCH for 48-hour treatment and at 0.05 and 0.1 μg/mL for 72-hour treatment

(Rupa et al. 1989d). In addition, sister chromatid exchanges increased in a dose-dependent manner with

the high dose (0.1 μg/mL) producing the only significant result. These results suggest mild mutagenic

activity at high doses in humans (Rupa et al. 1989d).

HEXACHLOROCYCLOHEXANE (HCH) 209

CHAPTER 3. TOXICOKINETICS, SUSCEPTIBLE POPULATIONS,

BIOMARKERS, CHEMICAL INTERACTIONS

3.1

TOXICOKINETICS

Human studies of HCH isomers provide limited quantitative information on absorption, metabolism,

distribution, and excretion. Toxicokinetics have been studied in rodents, with most quantitative

information derived from studies conducted in mice and rats. An overview of these data is provided

below.

• Absorption of HCH isomers has been demonstrated in humans by increased serum levels of the

isomers following inhalation, oral, or dermal exposure.

• N

o animal data are available from the inhalation route to quantify the extent or rate of absorption.

Technical-grade HCH has been shown to be well absorbed from the gastrointestinal tract of

animals (>90% recovery).

• The distribution of HCH isomers in humans and animals is primarily to the adipose tissue but

also to the brain, kidney, muscle, blood, and other tissues. β-HCH accumulates to a much greater

extent than other HCH isomers.

• HCH isomers have been measured in the placenta and umbilical cord blood of humans, indicating

that transplacental exposure to fetuses is likely to occur. HCH isomers have also been detected in

breast milk.

• The primary urinary metabolites are chlorophenols and 1,2,4-trichlorocyclohexane-4,5-epoxide.

The conversion occurs mainly by the action of hepatic CYP enzymes.

• HCH isomer metabolites are primarily excreted through the urine as conjugates of mercapturic

acid, glucuronide, and sulfate.

• A rat physiologically based pharmacokinetic (PBPK) model simulated the toxicokinetics of

γ-HCH. Predicted concentrations in blood, brain, muscle, and fat after a single intraperitoneal

injection and chronic-duration oral dosing compared adequately well with experimental results;

however, the model is not validated via biological evaluation of kinetic parameters.

• A human PBPK model was developed to simulate toxicokinetics of β-HCH in pregnant mothers

and infants exposed during gestation and lactation. The model was validated by comparing

predicted concentrations in breast milk, cord blood, and infant blood to concentrations measured

in mothers and infants from a Canadian Inuit population. Correlations between model-predicted

and measured values for β-HCH were relatively weak because measured concentrations were near

the limit of detection.

• A human dermal PBPK model for

γ-HCH was developed by modifying a flow-limited PBPK

model to include a skin patch compartment for the exposure location. A comparison of model

simulations in which the optimized diffusion constants were varied illustrated the importance of

HEXACHLOROCYCLOHEXANE (HCH) 210

3. TOXICOKINETICS, SUSCEPTIBLE POPULATIONS, BIOMARKERS, CHEMICAL INTERACTIONS

considering protein binding of γ-HCH, when predicting the steady-state dermal permeability

constant (K

3.1.1 Absorption

α-, β-, γ-, and δ-HCH have been detected in the blood serum, adipose tissue, and semen of occupationally

and environmentally exposed individuals, indicating that absorption takes place following inhalation

exposure (Baumann et al. 1980; Czeglédi-Jankó and Avar 1970; Kashyap 1986; Nigam et al. 1986;

Quintana et al. 2004; Saxena et al. 1980, 1981a, 1981b). Human case reports of accidental poisoning

indicate that HCH is also absorbed following oral exposure. High blood concentrations of γ-HCH have

been demonstrated following oral exposure in these cases (Berry et al. 1987; Harris et al. 1969; Khare et

al. 1977; Munk and Nantel 1977; Nantel et al. 1977; Powell 1980; Starr and Clifford 1972).

Dermal absorption of γ-HCH has been demonstrated in several studies that examined absorption from

anti-scabies lotion or head lice shampoo (EPA 2002; Feldmann and Maibach 1974; Franz et al. 1996;

Ginsburg et al. 1977; Lange et al. 1981). Maximum serum levels in healthy volunteers and scabies

patients were reported within 4–6 hours following whole-body application (Lange et al. 1981). However,

the maximum serum levels of γ-HCH in scabies patients were greater than those reported for normal

volunteers. Studies involving a single topical application of γ-HCH to the forearm, which was left for

24 hours before washing, indicate that at least 9% of the applied dose was absorbed; maximum absorption

occurred during the first 12 hours after application of γ-HCH to the skin, but absorption continued for at

least 5 days (Feldmann and Maibach 1974). In infants and children dermally treated with 1% γ-HCH

lotion, maximum blood concentrations of γ-HCH were observed in 6 hours, and averaged 0.028 μg/mL

for the group infested with scabies and 0.024 μg/mL for the non-infested group (Ginsburg et al. 1977).

The maximum blood level measured in children aged 33–64 months treated with 1% topical γ-HCH

lotion was 64 μg/L (EPA 2002). Children aged 3.5–18 years treated for head lice with 1% γ-HCH

shampoo had a maximum γ-HCH blood level of 6.13 μg/L (EPA 2002). HCH isomers are bioavailable

from soil and can be absorbed dermally (Duff and Kissel 1996). In an in vitro study using abdominal skin

obtained from human cadavers, γ-HCH exhibited mean 24-hour dermal absorption values from 0.45 to

2.35% varying with different soil types and soil loadings of 1, 5, and 10 mg/cm

The absorption of γ-HCH through the skin was studied following application of two different preparations

to the forearm of volunteers (Dick et al. 1997a). The mean peak plasma concentrations of γ-HCH

following exposure to 120 mg γ-HCH/mL acetone and a 3 mg γ-HCH/mL formulation containing white

spirit (a petroleum-based solvent) were 0.91 and 0.47 ng/mL, respectively, although the preparation in

HEXACHLOROCYCLOHEXANE (HCH) 211

3. TOXICOKINETICS, SUSCEPTIBLE POPULATIONS, BIOMARKERS, CHEMICAL INTERACTIONS

acetone contained a 40-fold higher concentration of γ-HCH. The proportion of the applied dose absorbed

into the systemic circulation in 6 hours was 5% for the dose applied in acetone and 60% of the applied

dose in white spirit-based formulation. Thus, the white spirit enhanced the absorption of γ-HCH relative

to acetone as the vehicle. About 30% of the applied dose for the white-spirit based formulation was

observed in the stratum corneum at 6 hours of exposure and decreased by 90% at 24 hours. Fifteen

percent of the applied dose for the acetone-based application was in the stratum corneum. The absorption

of γ-HCH through human skin was also assessed in an in vitro study (Dick et al. 1997b). γ-HCH

absorption was reported to be 15–25% in 24 hours for the two formulations that contained white spirit as

the predominant solvent, 3% in 24 hours from an aqueous spray dilution, and <1% in 24 hours for the

acetone preparation.

No information is available on the absorption of α-, β-, γ-, and δ-HCH following inhalation exposure in

experimental animals. γ-HCH is readily absorbed from the gastrointestinal tract of mice and rats (Ahdaya

et al. 1981; Turner and Shanks 1980). Ahdaya et al. (1981) demonstrated that half of the administered

dose was absorbed from the gastrointestinal tract of fasting mice approximately 14 minutes after

administration of radiolabeled γ-HCH by stomach tube. Although this study demonstrates the rapid

absorption of γ-HCH from the gastrointestinal tract, the use of fasted animals prevents an assessment of

the effect of stomach contents on the rate of absorption. Turner and Shanks (1980) studied the rate of

absorption of γ-HCH from the gastrointestinal tract and intestinal lymphatic system using rat intestinal

loop preparations. Prepared loops were injected with γ-HCH, and the blood and lymph were sampled for

30 minutes. γ-HCH was readily absorbed from the intestine into the blood; however, only a small amount

of γ-HCH entered the lymphatic system from the intestine. The extent of oral absorption of technical-

grade HCH has been estimated to be 95.8% in rats within 4 days following the administration of single

doses of the substance (Albro and Thomas 1974). Variation of the dosages from 30 to 125 mg/kg had no

effect on the percent absorption. The overall degree of absorption of technical-grade HCH administered

in the feed for 14 days was similar (94.9%), but the average absorption values of α-, β-, γ-, and δ-HCH

were 97.4, 90.7, 99.4, and 91.9%, respectively (Albro and Thomas 1974). HCH isomers in contaminated

soil were shown to be bioaccessible in an in vitro gastrointestinal model (Tao et al. 2009).

Dermal absorption of γ-HCH was demonstrated in rats and rabbits (Bosch 1987a, 1987b). Male rats

treated dermally with radiolabeled γ-HCH (20% emulsifiable concentrate) on a 4.9 cm

shaved dorsal

area exhibited absorption of radiolabel, which increased with time of exposure (Bosch 1987a). After

4 hours, 10.1, 5.3, and 2.0% were absorbed from doses of 0.06, 0.6, and 6 mg/cm

/kg, respectively. After

24 hours, 27.7, 20.9, and 5.1% were absorbed from doses of 0.06, 0.6, and 6 mg/cm

/kg, respectively.

HEXACHLOROCYCLOHEXANE (HCH) 212

3. TOXICOKINETICS, SUSCEPTIBLE POPULATIONS, BIOMARKERS, CHEMICAL INTERACTIONS

Male rabbits treated dermally with radiolabeled γ-HCH (20% emulsifiable concentrate) in a 28.3-cm

shaved dorsal area absorbed, after 4 hours, 29.6, 18.3, and 7.3% radiolabel from doses of 0.005, 0.05, and

0.5 mg/cm

/kg, respectively, and, after 24 hours, 55.7, 40.0, and 16.6% from the same respective doses

(Bosch 1987b). In weanling rabbits, levels of γ-HCH in the blood after a single application of a 1%

solution (60 mg γ-HCH/kg) were 1.67 and 2.48 μg/mL in two rabbits that had been shaved and depilated,

then stripped to remove the keratin layer (Hanig et al. 1976). In contrast, a blood level of only

0.67 μg/mL was seen in a rabbit that had only been shaved and depilated, indicating that absorption

increases with loss of skin integrity.

Dermal absorption of γ-HCH was evaluated in human skin grafted onto a nude mouse model and the

results were compared to an in vivo rat model and in vitro rat and human models (Capt et al. 2007). The

maximum percent absorbed, which included the amount directly absorbed and present in the skin and

stratum corneum, was comparable for the human skin grafted onto a nude mouse (20.7% of applied dose)

and the in vitro human skin model (24.5%). Data for the rat in vivo and in vitro models appeared to

overestimate the potential human absorption. The maximum percent absorbed was 39.8% in the rat in

vivo model and 62.5% in the rat in vitro model.

3.1.2 Distribution

Occupational studies provide information on the distribution of HCH isomers following inhalation

exposure in humans. Air concentrations of α-HCH (0.002–1.99 mg/m

), β-HCH (0.001–0.38 mg/m

), and

γ-HCH (0.004–0.15 mg/m

) were associated with concurrent mean blood serum levels in workers of 69.6,

190.3, and 36.9 μg/L, respectively (Baumann et al. 1980). Serum total HCH concentrations of 0.14–

0.60 ppm were found in workers with unknown levels of exposure to technical-grade HCH (Nigam et al.

1986). HCH isomers have also been detected in adipose tissues of occupational workers and the general

population (Arrebola et al. 2013, 2014; Baumann et al. 1980; Kim et al. 2014; Mustieles et al. 2017;

Pestana et al. 2011; Ploteau et al. 2017; Quintana et al. 2004; Siddiqui et al. 1981). Accumulation of

β-HCH has been shown to increase approximately linearly with time of exposure (Baumann et al. 1980).

In a national EPA survey, adipose tissue samples collected from surgical procedures or autopsies between

1969 and 1983 showed β-HCH concentrations >0.37 ppm lipid in the highest quartile (Quintana et al.

2004).

Case reports of poisoning confirm that γ-HCH is distributed to the central nervous system. γ-HCH was

detected in the cerebrospinal fluid of a young boy following ingestion of an unknown quantity of γ-HCH

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(Davies et al. 1983). γ-HCH was also detected in brain tissue (110 ppb) and heart blood (33.3 ppb)

collected during the autopsy of an infant who was treated with a whole-body application of a 1% γ-HCH

lotion after a hot bath (Davies et al. 1983).

HCH isomers have been measured in the placenta and/or umbilical cord blood of humans, indicating that

transplacental exposure to fetuses is likely to occur (Alvarado-Hernandez et al. 2013; Anand and Taneja

2020; Anand and Taneja 2020; Anand et al. 2019; Dewan et al. 2013; Fukata et al. 2005; Hernik et al.

2016; Herrero-Mercado et al. 2010, 2011; Junque et al. 2020; Lopez-Espinosa et al. 2007; Morello-Frosch

et al. 2016; Saxena et al. 1981a; Shen et al. 2007; Siddiqui et al. 2003; Vizcaino et al. 2011; Yin et al.

2019; Yu et al. 2013). Placental transfer of HCH isomers was analyzed using matched maternal serum,

cord serum, and placenta samples in mother-infant pairs (Yin et al. 2019; Zhang et al. 2018). β-HCH was

the predominant isomer measured in each sample type. An analysis of concentration ratios for all HCH

isomers suggests that the rate of transfer from the placenta to cord blood is slower than for maternal

serum to the placenta (Yin et al. 2019). Transfer data for the two enantiomers of α-HCH suggests that

placental transfer may involve both simple diffusion and active transport (Yin et al. 2019). Experiments

using an in vitro placenta model (human choriocarcinoma derived BeWo cells in a confluent, polarized

monolayer) confirm that multiple mechanisms are likely involved in transplacental transfer of HCH

isomers (Yin et al. 2020). Maternal serum concentrations of β-HCH were shown to increase between the

first trimester of pregnancy and delivery, possibly due to mobilization of fat stores or changes in blood

volume at different stages of pregnancy (Junque et al. 2020). Concentrations in cord blood serum were

correlated with maternal serum concentrations at delivery in this study.

HCH isomers have also been detected in human breast milk (Bedi et al. 2013; Chen et al. 2018; Dewan et

al. 2013; Dimitriadou et al. 2016; Elserougy et al. 2013; Fytianos et al. 1985; Hernik et al. 2016; Kao et

al. 2019; Minh et al. 2004; Shen et al. 2007; Yalcin et al. 2015). α-, β-, and γ-HCH have been found to be

bioconcentrated and excreted in breast milk of women who have been exposed to technical-grade HCH in

pesticide residues (Nair et al. 1996). All four of the HCH isomers (α, β, γ, and δ) discussed in this profile

have been detected in human semen following environmental exposure (Szymczynski and Waliszewski

1981).

In a study of Wistar rats exposed to air concentrations of 0.02–5 mg/m

γ-HCH for 90 days, male rats

exhibited higher serum γ-HCH levels than females, but females had higher liver, brain, and fat levels

(Oldiges et al. 1983). The organ levels of γ-HCH were dose-dependent but had returned to baseline levels

after a 4-week recovery period. Oral animal studies provide more detailed information on the distribution

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of HCH or its isomers (Chand and Ramachandran 1980; Eichler et al. 1983; Srinivasan and

Radhakrishnamurty 1983). γ- and β-HCH are primarily stored in the fat of rats acutely exposed for 5, 10,

or 15 days (Srinivasan and Radhakrishnamurty 1983). The overall distribution of γ-HCH was greatest in

fat, followed by brain, kidney, muscle, lungs, heart, spleen, liver, and blood. γ-HCH has also been found

in the adrenal glands of rats (Lahiri et al. 1990; Sulik et al. 1988). In an experiment lasting 12 days, the

accumulation of γ-HCH in the brain of rats dosed with 5 or 12 mg/kg/day by gavage began to decline

after 8 days. This reduction was not observed in rats given 20 mg/kg/day (Tusell et al. 1988).

In the brain of rats, α-HCH has been found to accumulate preferentially in the white matter, an area

containing lipid-rich myelin, as opposed to gray matter (Portig et al. 1989). However, the same brain

distribution pattern was not noted for γ-HCH in mice, even though α- and γ-HCH are equally lipophilic.

Differences in distribution of γ- and α-HCH are most likely due to stereospecificity, because only the

+-enantiomer of α-HCH was shown to accumulate in white matter (Portig et al. 1989). A comparison of

the enantiomeric fractions in the blood, liver, and brain of mice following administration of a single

gavage dose of α-HCH, demonstrated enrichment of the +-enantiomer in the brain, but not in the liver or

blood (Yang et al. 2010). Enantioselective transport across the blood-brain barrier was also demonstrated

in rabbits exposed orally or dermally to α-HCH (Xue et al. 2010). Toxicokinetic modeling from this

study suggested that enrichment of the +-enantiomer in blood was due to a faster elimination rate for the

–-enantiomer in rabbits (Xue et al. 2010). In mice, gavage exposure to 5.9 mg/kg/day γ-HCH for 3 days

was shown to increase the permeability of the blood-brain barrier, as measured by increased fluorescein

dye uptake (Sinha and Shukla 2003). Similar effects were not observed in rats given 8.8 mg/kg/day for

3 days (Sinha and Shukla 2003).

The distribution pattern for β-HCH was found to be in the following order: fat > kidney > lungs > liver >

muscle > heart > spleen > brain > blood. β-HCH accumulates in tissues to a greater degree than γ-HCH

except in the brain, where the γ-HCH accumulates at a higher concentration (Srinivasan and

Radhakrishnamurty 1983). This accumulation increases with increasing dose and treatment period for

β-HCH more so than for γ-HCH. The greater accumulation of β-HCH in tissues is expected since this

isomer is known to be metabolized more slowly. In addition, γ-HCH is known to induce the liver

cytochrome P-450 mixed-function oxygenase system (CYP), and thus, self-induced metabolism is an

important factor that minimizes the accumulation of γ-HCH residues in animal tissues.

The preferential accumulation of HCH in fatty tissues is also observed following intermediate- and

chronic-duration exposure of rats to HCH isomers in the diet (overall distribution: fat > liver > serum)

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(Amyes 1990; Chand and Ramachandran 1980; Dikshith et al. 1991c; Fitzhugh et al. 1950) or exposure to

α- or γ-HCH by gavage (overall distribution: fat > kidney > liver > brain > blood) (Eichler et al. 1983).

HCH has been shown to accumulate in amniotic fluid, placenta, and fetal tissues after oral treatment of

pregnant mice (Srivastava and Raizada 2000). In rats gavaged with γ-HCH on LDs 9 or 14, γ-HCH levels

were higher in their milk than plasma (Dalsenter et al. 1997b). Levels of γ-HCH in the offspring of those

rats were approximately twice as high in kidneys and liver than in brain and testes.

Some information on the distribution of γ-HCH is available from studies in which laboratory animals

were exposed by dermal application (Bosch 1987a, 1987b; Hanig et al. 1976; Solomon et al. 1977a,

1977b). A study on the distribution of γ-HCH in guinea pigs following acute dermal exposure indicates

that accumulation of γ-HCH in the brain is greater than in the blood after single and multiple topical

applications (Solomon et al. 1977a, 1977b); the levels in both tissues increased with the number of

applications. Following dermal treatment of rats with 50 or 100 mg/kg/day technical-grade HCH for

120 days, α-, β-, γ-, and δ-HCH were accumulated in testicular tissue and sperm in a dose-related manner

(Prasad et al. 1995). β-HCH was present at the highest concentration in testicular tissue and sperm.

3.1.3 Metabolism

The metabolism of γ-HCH is illustrated in Figure 3-1. Angerer et al. (1983) determined that

chlorophenols were the primary urinary metabolites of γ-HCH excreted by workers involved in γ-HCH

production. In the study, glucuronides and sulfates of chlorophenols were cleaved by acidic hydrolysis of

urine samples. The metabolites 2,3,5-, 2,4,6-, and 2,4,5-trichlorophenol accounted for almost 57.7% of

the γ-HCH metabolites identified in the urine collected during the last 2 hours of the workers' shifts.

Other urinary metabolites identified included other trichlorophenols, dichlorophenols, tetrachlorophenols,

and dihydroxychlorobenzenes. Pentachlorophenol has also been identified as a urinary metabolite in

humans following occupational exposure (Engst et al. 1979). In vitro investigations indicate that human

liver microsomes convert γ-HCH by dechlorination, dehydrogenation, dehydrochlorination, and

hydroxylation to five primary metabolites: 3,6/4,5-hexachlorocyclohexene, pentachlorocyclohexene,

2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, and pentachlorobenzene (Fitzloff et al. 1982). Similar in

vitro studies have demonstrated that an epoxide forms during the metabolism of pentachlorocyclohexene.

This stable halogenated hydrocarbon epoxide metabolite may be responsible for the mutagenic and

carcinogenic effects of γ-HCH (Fitzloff and Pan 1984).

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Figure 3-1. The Proposed Metabolism of Hexachlorocyclohexane

(Cl)n

3,4,5-PCCOL

3,4,6,5-PCCH

1,2,3,4-TTCB

cis B-PCCH

Oxide

1,2,4-TCB

2,4,5-TCB

3,6,4,5-PCCH

1,2,4-TCB

2,3,5-TCB

Glucuronide and Sulfate Conjugates

Mercapturic Acid Conjugates

3,4,6,5-TCCH

1,2,4,6-TCCOL

2,4,5,6-TCCOL

HCH

PCCHA

2,4,6-TCP

3,6/4,5-HCCH

HCCOL

2,3,4,5-TTCP

1,2,4-TCB

PCB

HCB

HCCHD

PCCOL

1,2,4-TCB-5,b-epoxide

1,2,4-TCB-

5,b-epoxide

3,6/4,5-HCCH = 3,6/4,5-hexachlorocyclohexene; HCB = hexachlorobenzene; HCCHD = hexachlorocyclohexadiene;

HCCOL = hexachlorocyclohexenol; HCH = hexachlorocyclohexane; PCB = pentachlorobenzene;

PCCH = pentachlorocyclohexene; PCCHA = pentachlorocyclohexane; PCCOL = pentachlorocyclohexenol;

TCB = trichlorobenzene; TCCH = tetrachlorobenzene; TCCOL = tetrachlorocyclohexenol; TCP = trichlorophenol;

TTCP = tetrachlorophenol

Sources: Chadwick et al. 1985; Fitzloff and Pan 1984; Fitzloff et al. 1982

In animals, γ-HCH appears to be transformed by hepatic enzymes to form chlorophenols, chlorobenzenes,

chlorocyclohexanes, chlorocyclohexenes, chlorocyclohexenols, and conjugates of mercapturic acid,

glucuronide, and sulfate (Chadwick and Freal 1972a; Chadwick et al. 1978a; Engst et al. 1979; Kujawa et

al. 1977). These metabolites have been identified in various tissues and in the urine of laboratory

animals. Metabolites found in the liver of rats following intermediate exposure to γ-HCH via gavage or

diet include di-, tri-, tetra-, and pentachlorobenzenes; pentachlorocyclohexenes; and pentachloro-

2-cyclohexen-1-ol (Chadwick and Freal 1972a; Kujawa et al. 1977). Metabolites identified in the blood

of these rats include di-, tri-, tetra-, and pentachlorophenols and pentachloro-2-cyclohexen-1-ol (Kujawa

et al. 1977). Di-, tri-, and tetrachlorophenols; pentachlorocyclohexenes; and pentachloro-2-cyclohexen-

1-ol have been identified in samples of kidney, spleen, heart, and brain tissue from rats fed γ-HCH

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(Kujawa et al. 1977). Metabolites found in the urine include tri-, tetra-, and pentachlorophenol;

pentachloro-2-cyclohexen-1-ol; and isomers of tetrachloro-2-cyclohexen-1-ol (Chadwick and

Freal 1972a; Chadwick et al. 1978c; Kujawa et al. 1977). The metabolism of γ-HCH in the intestine was

reported to be very minor, or the metabolites were completely absorbed. No metabolites were detected in

the feces or in the adrenal gland (Kujawa et al. 1977). In vitro preparations using rat liver slices have also

found that γ-HCH is converted to hexachlorobenzene (Gopalaswamy and Aiyar 1984). However, these

findings have not been confirmed in in vivo experiments.

The major urinary metabolites formed in rats, following intermediate oral exposure to α- or β-HCH, were

identified as tri- and tetrachlorophenols; pentachlorocyclohexene was also identified as a metabolite of

γ-HCH in kidney tissue (Macholz et al. 1982a, 1982b).

The toxicity of γ-HCH appears to be dependent on CYP enzymes. Intermediate exposure to γ-HCH

resulted in greater toxicity in DBA/2 (D2) mice than in C57BL/6 (B6) mice; the DBA/2 (D2) mice are

considered unresponsive to microsomal enzyme induction by aromatic hydrocarbons (Liu and Morgan

1986). Increased toxicity was associated with higher blood and brain concentrations in D2 mice than in

B6 mice at the time of sacrifice. In addition, D2 mice were found to have more 2,4,6-trichlorophenol in

the liver, kidney, and spleen than the less-susceptible B6 mice. The inability of D2 mice to undergo

enzyme induction to increase the rate of detoxification led to γ-HCH’s enhanced toxicity in this strain.

Other investigators have demonstrated the importance of the hepatic microsomal enzymes in the toxicity

of γ-HCH (Baker et al. 1985; Chadwick and Freal 1972a; Chadwick et al. 1981; Chand and

Ramachandran 1980; Tanaka et al. 1979). Chadwick et al. (1981) demonstrated that pretreatment of rats

with inducers of hepatic enzymes significantly influenced the metabolism and excretion of γ-HCH and its

metabolites by altering specific metabolic pathways; excretion of γ-HCH metabolites in the urine

increased nearly 4-fold following pretreatment with Aroclor 1254 or phenobarbital. Following

pretreatment with Aroclor 1254, a 7-fold increase in expired metabolites was observed. Naphthoflavone

had no effect on the excretion rate.

3.1.4 Excretion

Humans excrete HCH isomers and their metabolites in urine, breast milk, sweat, and semen (Angerer et

al. 1981; Genuis et al. 2016). Analysis of urine from humans occupationally exposed to HCH showed the

presence of chlorinated phenols and all isomers of di-, tri-, and tetrachlorophenol (Angerer et al. 1981).

In another study, the elimination of β-HCH (a byproduct of γ-HCH production studied due to its long

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half-life in humans) was investigated in a group of 40 former workers of a γ-HCH-producing plant by

analyzing at least two blood specimens from different time points between 1952 and 1980. The median

half-life of β-HCH was 7.2 years, calculated by concentrations in whole blood, and 7.6 years, calculated

by concentrations in extractable lipids (Jung et al. 1997), assuming first-order kinetics for excretion.

Nonmetabolized γ-HCH was excreted in the urine and feces of healthy volunteers and scabies patients

acutely exposed to a 0.3% γ-HCH emulsion by whole-body application. The cumulative excretion of

nonmetabolized γ-HCH was almost the same in the healthy volunteers and the scabies patients (Zesch et

al. 1982). The elimination of γ-HCH was studied following application of two different preparations to

the forearm of volunteers (Dick et al. 1997a). The elimination half-life was between 50 and 111 hours for

the acetone-based application, and 25–58 hours for the white-spirit based formulation. Absorbed γ-HCH

was excreted in the urine as conjugates of 2,4,6-, 2,3,5-, and 2,4,5-trichlorophenol. Only 0.01–0.15% of

the dose was excreted in the urine in 72 hours following dermal exposure for 6 hours. In a study in which

children infested with scabies and their noninfested siblings were treated dermally with 1% γ-HCH lotion,

the blood level was found to diminish rapidly after application, with a half-life of 17.9 hours in infested

children and 21.4 hours in noninfested children (Ginsburg et al. 1977).

The excretion kinetics of β-HCH into breast milk were studied by monitoring breast milk concentrations

in lactating mothers after birth (Song et al. 2018; Waliszewski et al. 2009). In 40 lactating women, breast

milk concentrations of β-HCH decreased by approximately 30%, from 95 µg/kg fat on the 4

day after

birth to 66 µg/kg fat on PND 30 (Waliszewski et al. 2009). Song et al. (2018) monitored monthly breast

milk concentrations in 40 lactating women during the first 6 months after birth. The average breast milk

concentrations of β-HCH decreased from 127 µg/kg lipid 1 month after birth to 84.8 µg/kg lipid 6 months

after birth, representing a 32% reduction over this time period. The excretion profile for β-HCH in milk

lipids followed zero-order kinetics and the mean excretion rate was approximately 7% per month.

Excretion of γ-HCH and its metabolites in laboratory animals has been well documented. Data indicate

that the major route of elimination is via the urine following intermediate- and chronic-duration oral

feeding in mice (Chadwick et al. 1985). Very little is eliminated in exhaled air (Ahdaya et al. 1981;

Chadwick et al. 1985) or in feces (Chadwick et al. 1985) following acute-, intermediate-, and chronic-

duration oral administration in rodents. Because of its high lipid solubility, γ-HCH is excreted through

the dam’s milk (Dalsenter et al. 1997b).

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Very little γ-HCH is excreted unaltered. Various phenylmercapturic acid derivatives have been detected

in the urine of rats, formed by the conjugation of γ-HCH metabolites with glutathione subsequent to

dechlorinations and dehydrochlorinations (Allsup and Walsh 1982; Kurihara et al. 1979). In vitro

investigations using rat liver cells indicate that glutathione conjugation is lower for β-HCH compared to

γ- and α-HCH, which are readily conjugated (Fitzloff and Pan 1984; Fitzloff et al. 1982). Γ-HCH

metabolites are excreted in the form of phenylmercapturic acids and glucuronide and sulfate conjugates

(Chadwick et al. 1978a).

In male rats treated dermally with radiolabeled γ-HCH, 0.28, 0.08, and 0.02% radiolabel was excreted in

urine within 4 hours after doses of 0.06, 0.6, and 6 mg/cm

/kg, respectively (Bosch 1987a). After

24 hours, 4.4, 3.2, and 0.6% radiolabel had been excreted in urine from the same respective doses. In a

similar study with male rabbits, 3.8, 2.6, and 1.3% radiolabel was excreted in urine within 4 hours after

doses of 0.005, 0.05, and 0.5 mg/cm

/kg, respectively (Bosch 1987b). After 24 hours, 25.5, 11.6, and

6.8% radiolabel had been excreted in urine from the same respective doses.

3.1.5 Physiologically Based Pharmacokinetic (PBPK)/Pharmacodynamic (PD) Models

Models are simplified representations of a system with the intent of reproducing or simulating its

structure, function, and behavior. PBPK models are more firmly grounded in principles of biology and

biochemistry. They use mathematical descriptions of the processes determining uptake and disposition of

chemical substances as a function of their physicochemical, biochemical, and physiological

characteristics (Andersen and Krishnan 1994; Clewell 1995; Mumtaz et al. 2012a; Sweeney and Gearhart

2020). PBPK models have been developed for both organic and inorganic pollutants (Ruiz et al. 2011)

and are increasingly used in risk assessments, primarily to predict the concentration of potentially toxic

moieties of a chemical that will be delivered to any given target tissue following various combinations of

route, dose level, and test species (Mumtaz et al. 2012b; Ruiz et al. 2011; Sweeney and Gearhart 2020;

Tan et al. 2020). PBPK models can also be used to more accurately extrapolate from animal to human,

high dose to low dose, route to route, and various exposure scenarios and to study pollutant mixtures (El-

Masri et al. 2004). Physiologically based pharmacodynamic (PBPD) models use mathematical

descriptions of the dose-response function to quantitatively describe the relationship between target tissue

dose and toxic endpoints (Clewell 1995).

DeJongh and Blaauboer (1997) simulated the toxicokinetics of γ-HCH in rats with a PBPK model. A

five-compartment model was constructed: (1) the liver, serving as the metabolizing organ; (2) blood;

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(3) fat; (4) brain; and (5) a lumped compartment representing all other tissues, consisting mainly of

muscle tissue. Values for the physiological parameters and tissue-blood partition coefficients were

obtained from the literature. The model was calibrated on a dataset from the literature on the disposition

of γ-HCH from blood in vivo after single oral dosage and first-order biotransformation and

gastrointestinal absorption constants for γ-HCH were obtained.

The model was validated by simulating the disposition of γ-HCH in vivo after single intraperitoneal and

chronic-duration oral dosing and comparing these simulations with experimental results. Simulated

γ-HCH concentrations in fat, brain, and muscle compared well with measured values obtained after single

intraperitoneal exposure in rats. Simulated levels in blood were slightly higher than measured levels after

oral and intraperitoneal exposure.

A human PBPK model was developed to assess pre- and postnatal exposure to β-HCH and other neutral

persistent organic pollutants (Verner et al. 2009). The infant portion of the model was added to a

previously published maternal model (Verner et al. 2008) that consisted of nine compartments (liver,

brain, adipose tissue, richly perfused tissues, poorly perfused tissues, mammary tissue, uterus, placenta,

and fetus). Β-HCH was assumed to be completely absorbed from contaminated food and absorption was

entered as a direct input to the maternal liver. Excretion into breast milk was modeled as an output from

mammary tissue. The infant portion of the model consisted of five compartments, including liver, brain,

adipose tissue, richly perfused tissues, and poorly perfused tissues. The infant liver was modeled as

receiving β-HCH directly from breast milk for the first year of life (100% absorption was assumed) with

subsequent first-pass metabolism. The brain was included as a potential target organ of toxicity and

adipose tissue was considered the primary site for β-HCH storage. The initial body burden in the infant

was equivalent to lipid-adjusted levels of β-HCH in maternal blood at delivery. Distribution between

compartments in both the maternal and infant models was derived using blood flow and tissue:blood

partition coefficients. Metabolism was parameterized by transforming a published physiological half-life

of 7.6 years into a liver volume-adjusted intrinsic clearance value. Intrinsic clearance values based on

hepatic metabolism were assumed to be the same in mothers and infants. Model parameters described by

Verner et al. (2008) for the maternal model were adjusted for blood lipids during pregnancy, breast milk

lipid content, and excreted volume in breast milk. Parameters for the infant model described infant

physiology as a function of sex, age, body weight, and body height, and included sex-specific organ

volumes and blood flows and tissue:blood and milk:blood partition coefficients.

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The model was validated by comparing predicted concentrations in breast milk, cord blood, and infant

blood to concentrations measured in mothers and infants from a Canadian Inuit population. Correlations

between model predictions and measured values for β-HCH were relatively weak (r=0.35 for cord blood;

r=0.7 for breast milk; r=0.62 for infant blood) because measured concentrations were near the limit of

detection. A sensitivity analysis was performed using Monte Carlo simulations based on variability in

breast milk consumption, fraction of lipids in breast milk, and fraction of lipids in infant adipose tissue for

PCB-153 and p,p’-DDT. Variability was estimated to be approximately 2.5-fold between the 5

and

percentiles. Predicted blood concentrations were highly variable for β-HCH, with only 66% of

individual values falling within the 2.5-fold range of variation.

A human dermal PBPK model for γ-HCH was developed by modifying a flow-limited PBPK model to

include a skin patch compartment for the exposure location (Sawyer et al. 2016). Optimized dermal

absorption parameters were calculated for γ-HCH by adjusting diffusion equations for binding to protein

and lipids and these parameters were included in the PBPK model to describe in vivo toxicokinetics.

Model simulations were run using the time course data from Dick et al. (1997a) where volunteers were

exposed to a 3 mg γ-HCH/mL formulation containing white-spirit for 6 hours and blood samples were

analyzed for γ-HCH for up to 80 hours after exposure. A comparison of model simulations in which the

optimized diffusion constants were varied illustrated the importance of considering protein binding of

γ-HCH, when predicting the steady-state dermal permeability constant (K

3.1.6 Animal-to-Human Extrapolations

Extrapolating animal toxicity data to predict human risk from HCH exposure appears to be reasonable

since similar effects are seen in both species.

CYP metabolism of HCH isomers occurs in both humans and rodents. The presence of chlorophenols

and chlorobenzenes in urine of workers occupationally exposed to γ-HCH (Angerer et al. 1983; Engst et

al. 1979) was similar to observations of rats experimentally exposed to γ-HCH (Chadwick and Freal

1972a; Chadwick et al. 1978a; Engst et al. 1976; Kujawa et al. 1977). In vitro investigations indicate that

human liver microsomes convert γ-HCH to chlorocyclohexenes, chlorophenols, and chlorobenzenes

(Fitzloff et al. 1982). Both human and rat microsomes have been shown to form an identical epoxide in

vitro following γ-HCH exposure (Fitzloff and Pan 1984). An important difference in interspecies

metabolism of γ-HCH is the production of α-2μ-globulin in the male rat (Dietrich and Swenberg 1990,

1991), a protein not present in humans, which is well known for its role in renal toxicity.

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Similar clinical toxic effects resulting from HCH exposure have been observed in laboratory animals

dosed experimentally and humans experiencing occupational, therapeutic, and accidental domestic

exposures to HCH. These include neurological, hepatic, hematological, and dermatological effects.

Though reproductive, immunological, and carcinogenic effects have been reported in occupationally

exposed humans and in animals, the human studies lack both quantitative exposure data and strong causal

associations and also involve concurrent exposures to other chemicals. While rodents appear to be

adequate models for a variety of human effects of HCH exposure, care must be taken in interpreting data

from reproductive toxicity feeding studies in sheep (Beard and Rawlings 1999; Beard et al. 1999a) since

significant differences exist in the gastrointestinal physiology of ruminants and humans.

3.2 CHILDREN AND OTHER POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE

This section discusses potential health effects from exposures during the period from conception to

maturity at 18 years of age in humans. Potential effects on offspring resulting from exposures of parental

germ cells are considered, as well as any indirect effects on the fetus and neonate resulting from maternal

exposure during gestation and lactation. Children may be more or less susceptible than adults to health

effects from exposure to hazardous substances and the relationship may change with developmental age.

This section also discusses unusually susceptible populations. A susceptible population may exhibit

different or enhanced responses to certain chemicals than most persons exposed to the same level of these

chemicals in the environment. Factors involved with increased susceptibility may include genetic

makeup, age, health and nutritional status, and exposure to other toxic substances (e.g., cigarette smoke).

These parameters can reduce detoxification or excretion or compromise organ function.

Populations at greater exposure risk to unusually high exposure levels of HCH are discussed in

Section 5.7, Populations with Potentially High Exposures.

Several human studies suggest that the developing fetus may be susceptible to health effects of prenatal

exposure to HCH isomers, with reports of decreased birth weight or increased risk of fetal growth

restriction associated with higher maternal or fetal concentrations of HCH isomers (see Section 2.17).

Individuals with genetic polymorphisms that alter the metabolism and excretion of HCH isomers, may be

at increased risk of these effects. For example, polymorphism of glutathione S-transferase mu 1

(GSTM1) was shown to contribute to the risk of preterm birth or fetal growth restriction following

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exposure to β-HCH (Mustafa et al. 2013; Sharma et al. 2012). A significant interaction was also observed

between polymorphism of the CYP17 gene (A1A2) and

γ-HCH in maternal blood and the risk of preterm

birth (Sharma et al. 2013).

In human studies, serum cord blood levels of β-HCH were associated with increased serum levels of TSH

(see Section 2.17 and Table 2-16); altered thyroid hormone status may affect neurodevelopment of

infants. In addition, adverse neurodevelopmental outcomes have been associated with elevated

concentrations of total HCH or specific HCH isomers in maternal breast milk or children’s blood (Lenters

et al. 2019; Sisto et al. 2015).

Serious neurological effects and occasional deaths have been reported in children following exposure to

γ-HCH by accidental ingestion or by topical application (see Sections 2.2 and 2.15).

Studies of animals exposed to γ-HCH by oral administration demonstrate that the developing organism is

exquisitely sensitive to the toxic effects of this isomer. Developmental effects of γ-HCH observed in

studies of rats, mice, and mink include reduced viability and pup body weight; perturbation of male and

female reproductive tract development; alterations in the developing liver, thymus, spleen, and heart; and

developmental neurotoxicity (see Section 2.17). Little to no data are available for the other isomers of

HCH.

Few studies have compared effects in young and aged animals exposed by the same regimen to HCH

isomers. Weanling rabbits were more sensitive to γ-HCH treatment than young adults, as seen by higher

mortality rates accompanied by excitement and convulsions after a single whole-body treatment with a

1% solution at a dose of 60 mg/kg γ-HCH (Hanig et al. 1976). As discussed in Section 2.17, there is

evidence that γ-HCH causes functional impairment of the developing blood brain barrier in young rats

(Gupta et al. 1999). The brain uptake of fluorescein was significantly increased in 10-day-old pups

treated with a single 2 mg/kg dose, as well as in those treated with 2 mg/kg/day for 8 days. The effect

appeared to be age-related because the brain uptake index was lower when rats were administered a single

2 mg/kg dose at 15 days of age, and there was no effect on brain permeability at a higher dose of

4 mg/kg/day when administered for 3 days to adults (Gupta et al. 1999).

Following intraperitoneal dosing of dams with γ-HCH on GDs 12–17, GABAA receptors in rat fetuses

were studied with radiolabeled t-butylbicyclophosphorothionate (TBPS), a ligand that binds to the

GABAA receptor (Brannen et al. 1998). Treatment with γ-HCH significantly reduced the TBPS binding

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affinity in fetal brainstems and it was concluded that the effect could potentially lead to abnormal brain

activity, increased susceptibility to seizures, and behavioral effects. TBPS binding in brains of fetuses

was reduced when compared to adults (Brannen et al. 1998).

Effects of γ-HCH on the levels of reproductive hormones in blood of male animals appear to be more

significant in younger animals compared with older animals. Male Wistar rats treated with γ-HCH

beginning at 9 weeks of age exhibited significantly decreased serum testosterone and growth hormone

and increased serum LH and FSH (Agrahari et al. 2019). Similar results were observed in another group

exposed at 18 weeks of age, but treatment at 27 weeks of age resulted in smaller decreases in serum

testosterone and growth hormone, and no significant effect on serum LH or FSH (Agrahari et al. 2019).

Differences in oxidative effects have been observed in the testes of young (15-day-old ) versus mature

(90-day-old) rats following intraperitoneal injection with 10 or 20 mg/kg technical-grade HCH (Samanta

and Chainy 1997). Lipid peroxidation occurred to a greater extent in mature rats. However, the percent

decrease in cytosolic superoxide dismutase activity was greater in young rats, which have increased

baseline activity of the enzyme. Based on the findings of this study, it does not appear that young rats are

at increased risk of oxidative testicular damage.

Although it is unknown whether the ability to metabolize HCH specifically differs between children and

adults, some enzymes, which belong to the enzyme superfamilies involved in phase II HCH metabolism,

are developmentally regulated in humans. The development of uridine 5’-diphospho-glucuronosyl-

transferase (UDP-glucuronosyltransferase; responsible for glucuronide conjugation) depends on the

enzyme isoform, but, in general, adult activity is attained by 6–18 months of age (Leeder and Kearns

1997). Development of sulfotransferase (responsible for sulfate conjugates) activity is also substrate-

specific and is usually earlier than UDP-glucuronosyltransferase. In fact, levels of some sulfotransferases

may be greater during infancy and early childhood than during adulthood (Leeder and Kearns 1997). A

series of enzymes are involved in the production of mercapturic acid conjugates: γ-glutamyltrans-

peptidase, glutathione S-transferase, cysteinyl glycinase, and N-acetyl transferase (Sipes and Gandolfi

1991). There are two superfamilies of N-acetyltransferase, and the N-acetyltransferase 2 superfamily has

members that are developmentally regulated in humans. There is some N-acetyltransferase 2 activity in

fetuses by 16 weeks of gestation. Infants up to 2 months of age have the slow metabolizer phenotype of

this gene; the adult distribution of slow and fast metabolizer phenotypes is reached by 4–6 months of age

and full adult activity is achieved at 1–3 years of age (Leeder and Kearns 1997).

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Case-control studies have evaluated the interactive effect of exposure to HCH isomers and genetic

polymorphisms on the increased risk of cancer or diabetes (Li et al. 2013, 2016; McCready et al. 2004;

Sharma et al. 2013, 2019). The risk of breast cancer associated with higher serum levels of HCH isomers

was increased by the presence of a polymorphism in the GSTM1 gene (GSTM1 null) (Li et al. 2013;

McCready et al. 2004). Genetic polymorphisms of CYP1A1 did not influence the breast cancer risk

associated with β-HCH exposure (McCready et al. 2004). A significant interaction was demonstrated

between the GSTM1 null polymorphism and β-HCH blood levels on risk of urinary bladder cancer

(Sharma et al. 2013). Mortazavi et al. (2019) did not show a similar correlation between GSTM1 or

GSTT1 polymorphisms and bladder cancer risk associated with HCH isomers. Sharma et al. (2019)

evaluated the influence of CYP1A1, GSTM1, and GSTT1 polymorphisms on the increased risk of

epithelial ovarian cancer risk associated with HCH isomers. Significant interactions between β-HCH

blood levels and CYP1A1m1 and GSTM1 and GSTT1 null genotypes were observed for increased risk of

ovarian cancer (measured as increased cancer antigen-125 or CA-125 levels). The risk of type 2 diabetes

associated with exposure to β-HCH was elevated in individuals carrying a single-nucleotide

polymorphism in the gene encoding adiponectin (ADIPOQ) (Li et al. 2016). Serum adiponectin levels

were reduced in individuals with this polymorphism.

People with lowered convulsion thresholds due to epilepsy (treated or untreated), cerebrovascular

accidents, or head injuries may be at greater risk of the central nervous system effects of γ-HCH toxicity

and may suffer increased risk of or severity of seizures (Kramer et al. 1980; Matsuoka 1981). Exposure

to β-HCH may increase the risk of hypertension in individuals with an elevated BMI (Arrebola et al.

2015a).

3.3 BIOMARKERS OF EXPOSURE AND EFFECT

Biomarkers are broadly defined as indicators signaling events in biologic systems or samples. They have

been classified as biomarkers of exposure, biomarkers of effect, and biomarkers of susceptibility

(NAS/NRC 2006).

The National Report on Human Exposure to Environmental Chemicals provides an ongoing assessment

of the exposure of a generalizable sample of the U.S. population to environmental chemicals using

biomonitoring (see http://www.cdc.gov/exposurereport/). If available, biomonitoring data for HCH from

this report are discussed in Section 5.6, General Population Exposure.

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A biomarker of exposure is a xenobiotic substance or its metabolite(s) or the product of an interaction

between a xenobiotic agent and some target molecule(s) or cell(s) that is measured within a compartment

of an organism (NAS/NRC 2006). The preferred biomarkers of exposure are generally the substance

itself, substance-specific metabolites in readily obtainable body fluid(s), or excreta. Biomarkers of

exposure to HCH are discussed in Section 3.3.1.

Biomarkers of effect are defined as any measurable biochemical, physiologic, or other alteration within an

organism that (depending on magnitude) can be recognized as an established or potential health

impairment or disease (NAS/NRC 2006). This definition encompasses biochemical or cellular signals of

tissue dysfunction (e.g., increased liver enzyme activity or pathologic changes in female genital epithelial

cells), as well as physiologic signs of dysfunction such as increased blood pressure or decreased lung

capacity. Note that these markers are not often substance specific. They also may not be directly

adverse, but can indicate potential health impairment (e.g., DNA adducts). Biomarkers of effect caused

by HCH are discussed in Section 3.3.2.

A biomarker of susceptibility is an indicator of an inherent or acquired limitation of an organism's ability

to respond to the challenge of exposure to a specific xenobiotic substance. It can be an intrinsic genetic or

other characteristic or a preexisting disease that results in an increase in absorbed dose, a decrease in the

biologically effective dose, or a target tissue response. If biomarkers of susceptibility exist, they are

discussed in Section 3.2, Children and Other Populations that are Unusually Susceptible.

3.3.1 Biomarkers of Exposure

HCH isomers measured in human serum are generally normalized by total lipid content, based on total

cholesterol and triglycerides (e.g., ng/g lipid) (Bradman et al. 2007; Curren et al. 2014; Everett and

Matheson 2010; Kaur et al. 2020; Mørck et al. 2014). Porta et al. (2009) suggested that adjustment of

serum concentrations by total cholesterol may be more appropriate than total lipid in studies of patients

with severe disease (e.g., pancreatic cancer). Concentrations of HCH isomers have also been measured

using whole blood (Sexton and Ryan 2012; Sexton et al. 2011).

Urinary concentrations of 2,4,5- and 2,4,6-trichlorophenol (in units of µg/g creatinine) were measured as

indicators of γ-HCH exposure in the NHANES III survey (1998–2004) (Allen et al. 2006).

Pentachlorophenol was also included as a γ-HCH metabolite in some studies (Naeher et al. 2009). The

use of these phenolic urinary metabolites as exposure biomarkers is limited because these are not specific

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to γ-HCH and may result from exposure to other chlorinated benzenes or phenols (Angerer et al. 1981;

Naeher et al. 2009).

Measurement of HCH isomers in hair has also been used as an exposure biomarker and was suggested to

be a better measure of chronic exposure than blood or serum concentrations (Michalakis et al. 2012;

Tsatsakis et al. 2008). A linear relationship between exposure level and hair concentration was observed

in a 90-day gavage study in rats exposed to a mixture of pesticide including γ- and β-HCH (Appenzeller

et al. 2017).

HCH isomers have been detected in adipose tissue samples taken by biopsy or following surgical

procedures (Aulakh et al. 2007; Ociepa-Zawal et al. 2010).

There are few quantitative data to correlate levels of any of the HCH isomers in human tissue or fluids

with past exposure. A study in which children infested with scabies and their non-infested siblings were

treated dermally with 1% γ-HCH lotion found no correlation between the dose applied and the subsequent

level of γ-HCH in blood (Ginsburg et al. 1977). The blood level was also seen to diminish rapidly after

application, with a half-life of 17.9 hours in infested children and 21.4 hours in non-infested children.

In contrast, β-HCH persists in the blood for a longer period of time than the other isomers. A study of

workers in a γ-HCH -producing factory found that levels of β-HCH in blood serum were higher than

those of other isomers, and there was a significant correlation between serum levels of β-HCH and length

of employment (Baumann et al. 1980). Studies of populations with general HCH exposure have

consistently found the level of the β-isomer to be higher than those of the other isomers (Kashyap 1986;

Nigam et al. 1986; Ramachandran et al. 1984). This is probably due to the greater tendency of β-HCH to

persist and accumulate in the body, while the other isomers are more rapidly metabolized or excreted. A

survey of epidemiological studies involving workers occupationally exposed to “crude benzene

hexachloride” as much as 10–15 years prior to sampling reported serum levels of 20–348 μg/L β-HCH

(Morgan and Lin 1978). Unfortunately, none of the above studies specified exposure levels, so it is still

questionable whether blood HCH levels can be used as biomarkers to quantify exposure.

There is also a direct correlation between HCH levels in the blood and human adipose tissue and semen

(Baumann et al. 1980; Radomski et al. 1971a, 1971b; Szymczynski and Waliszewski 1981);

concentrations of β-HCH in subcutaneous adipose tissues were found to be 300 times higher than blood

levels (Baumann et al. 1980). Levels of β-HCH detected in skin lipids correlated with those found in

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human adipose tissue (Sasaki et al. 1991). Although exposure levels were not known, the results of this

study indicate that measuring β-HCH in skin lipids can be an easy means of determining relative levels or

times of individual exposure. The method of collecting the skin lipid samples was noninvasive, involving

washing the face with soap and wiping 3–4 hours later with fat-free cotton soaked in 70% ethanol. Β- and

γ-HCH have also been found in samples of human maternal adipose tissue, maternal blood, cord blood,

and breast milk in women who were exposed to unknown levels of various organochlorine pesticides in

Kenya (Kanja et al. 1992).

3.3.2 Biomarkers of Effect

No biomarkers of effect, specific for HCH isomers, have been identified in the literature. Several studies

have demonstrated increases in lipid peroxidation and depletion of antioxidants in the central nervous

system, liver, kidney, male reproductive tract, and maternal or fetal tissues in animals exposed to γ-HCH;

however, these are nonspecific effects induced by a wide range of compounds.

3.4 INTERACTIONS WITH OTHER CHEMICALS

Toxicokinetics. The metabolism of γ-HCH can be altered by exposure to other chlorinated hydrocarbon

insecticides such as DDT. Exposure to various chlorinated hydrocarbon insecticides, including γ-HCH, is

thought to produce generalized nonspecific induction of microsomal enzymes, including cytochrome

P450s. Induction of these enzymes could affect the toxicokinetics of a variety of xenobiotics that are

metabolized through microsomal oxidation. Induction of mixed-function oxidase activity by other

chlorinated hydrocarbon insecticides stimulates the oxidative degradation of γ-HCH to the

tetrachlorophenols and enhances its elimination in the urine (Chadwick and Freal 1972b). Guinea pigs

maintained on diets deficient in vitamin C and protein showed altered γ-HCH metabolism and excretion.

Vitamin C deficiency decreased the amount of γ-HCH and its metabolites excreted in the urine and

increased the amount stored in the kidney (Chadwick et al. 1972). Cadmium, which is known to inhibit

hepatic drug-metabolizing enzymes in mammals, also inhibited the metabolism of γ-HCH in adult male

Wistar rats exposed to the compound after short- and long-term pretreatment with cadmium (Chadwick et

al. 1978b). Cadmium may inhibit γ-HCH metabolism indirectly by increasing levels of zinc and reducing

levels of copper in the liver (Chadwick et al. 1978b). The addition of cadmium to the diet also increased

the concentration of γ-HCH measured in the plasma and liver (Khanna et al. 1988).

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Liver Effects. Pretreatment with γ-HCH reduced the clearance and exacerbated the liver toxicity (i.e.,

increased ALT and AST levels) of a single oral dose of 500 mg/kg acetaminophen in rats (Akhlaq et al.

2006). Acute exposure to ethanol was shown to increase the hepatotoxicity of

γ-HCH in an

intraperitoneal injection study as measured by increased ALT and AST activity (Radosavljević et al.

2008). The increase in liver weight produced by oral subchronic exposure to commercial HCH was

exacerbated by concurrent exposure to phenobarbital or carbon tetrachloride (Khanna et al. 2002).

A low-protein diet potentiated the effects of γ-HCH on reducing the weights of various organs in male

rats (Khanna et al. 1990). Serum and liver lipid content and cholesterol levels were increased in animals

fed low-protein diets. The low-protein diet increased the levels of γ-HCH found in the various organ

tissues. Histopathological changes in the liver, kidneys, and muscles following dietary exposure to a

pesticide mixture containing monocrotophos, endosulfan, and HCH were exacerbated in protein-

malnourished and diabetic rats (Benjamin et al. 2006).

Natural plant extracts (i.e., ajwain extract, Hyrtios aff. Erectus sponge extract) have been shown to reduce

rodent liver toxicity of HCH isomers administered individually (Anilakumar et al. 2009) or as a mixture

with other organochlorine compounds (Abd El-Moneam et al. 2017). The mechanisms by which these

plant extracts mitigate HCH toxicity may include antioxidant activity and/or alterations in HCH

absorption, distribution, metabolism, or elimination. Oral administration of aloe vera extract prevented

the liver toxicity of

γ-HCH in rats (measured by serum enzymes), when administered concurrently for

4 weeks (Etim et al. 2006). Intravenous administration of gadolinium chloride to hyperthyroid rats

resulted in Kupffer cell depletion and a reduction in oxidative stress and liver injury following

intraperitoneal injection of

γ-HCH (Simon-Giavarotti et al. 2002). Administration of the antioxidant plant

extract andrographolide (from Andrographis paniculate) was shown to exert a hepatoprotective effect in

mice chronically exposed to technical-grade HCH (Trivedi et al. 2007, 2009). Liver toxicity measured by

serum enzymes and histopathology and liver tumor formation occurring in mice exposed to HCH in the

diet were not seen in mice given the combined exposure to andrographolide and HCH. Measures of

oxidative stress in the mouse liver associated with HCH were also ameliorated by the combined treatment

(Trivedi et al. 2007).

Γ-HCH was shown to be an aryl hydrocarbon receptor (AhR) antagonist in rat and human hepatoma cells

(DR-H4IIE and DR-Hep-G2, respectively) and mammary gland carcinoma DR-T47-D cells. When

administered as a mixture with other organochlorine compounds, an additive response on AhR

antagonism was observed (Doan et al. 2019).

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Gupta et al. (2011) showed that

γ-HCH promoted the formation of preneoplastic lesions (glutathione-

S-transferase placental [GST-P] positive foci) in the rat liver following initiation by diethylnitrosamine.

Simultaneous treatment with the dietary flavonoid quercetin appeared to reverse this promotion resulting

in decreased apoptosis, reduced incidence of GST-P positive foci and lower expression of p53.

Immunological Effects.

Γ-HCH produced apoptosis and necrotic cell death in isolated mouse

thymocytes in vitro and a greater-than-additive effect was observed when

γ-HCH was administered in

combination with malathion or permethrin (Olgun et al. 2004). Each of these pesticides produced

oxidative stress in mouse thymocytes (increased superoxide anion and hydrogen peroxide) with a greater-

than-additive effect on superoxide anion production observed when

γ-HCH and malathion were

administered together (Olgun and Misra 2006). Hydrogen peroxide production was not significantly

higher if pesticides were given in combination.

Γ-HCH given in combination with malathion or

permethrin increased superoxide dismutase activity and decreased the activity of glutathione-peroxidase

and glutathione-reductase in mouse thymocytes, suggesting a role for oxidative stress in cytotoxicity

(Olgun and Misra 2006).

Ocimum sanctum seed oil (OSSO) antagonized the immunotoxic effects of

γ-HCH on humoral immunity

(i.e., anti-SRBC response) and delayed-type hypersensitivity (i.e., footpad thickness) (Mediratta et al.

2008).

Neurological Effects. Γ-HCH is a central nervous system stimulant, whereas the α-, β-, and δ-isomers of

HCH are mainly depressants (McNamara and Krop 1948; Smith 1991). Isomeric interactions can occur,

such that α-, β-, and δ-HCH counteract the effects of

γ-HCH; neurotoxicity is reduced when a dose of

δ-HCH is accompanied by an equal or higher dose of the other isomers. These interactions likely account

for differences in the neurotoxicity of γ-HCH and technical-grade HCH, the majority of which is

comprised of isomers other than γ-HCH (60–70% α-HCH, 5–12% β-HCH, 10–15% γ-HCH, 6–10%

δ-HCH, and 3–4% ε-HCH [Baumann et al. 1980; Kutz et al. 1991]).

Γ-HCH and dieldrin, given in combination, produced a greater-than-additive effect on reactive oxygen

species generation, caspase activation, reduced mitochondrial membrane potential, and enhanced

cytotoxicity in immortalized rat dopaminergic neuronal cells in vitro (Sharma et al. 2010). Pretreatment

with an antioxidant plant extract (Decalepis hamiltonii) for 7 days was shown to prevent lipid

peroxidation, glutathione depletion, and altered activity of antioxidant enzymes in major rat brain regions

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induced by a single dose of technical-grade HCH (Srivastava and Shivanandappa 2014). The natural

product Chaetoglobosin K (ChK) was shown to prevent or reverse the

γ-HCH-induced inhibition of gap

junction-mediated communication in rat RG-2 astroglial cells in vitro (Sidorova and Matesic 2008).

Ethanol acted as an antagonist to

γ-HCH in the central nervous system by decreasing the seizure

incidence and intensity of convulsions and prolonging the duration of the latency period in rats

(Mladenović et al. 2007). Anticonvulsant medications (e.g., diazepam, clonazepam, phenobarbital) were

also effective in reducing seizures and lethality induced by

γ-HCH in mice (Tochman et al. 2000).

Reproductive Effects. Vitamin A supplements decreased HCH-induced toxicity in the rat testes, while

deficiencies in vitamin A potentiated the toxicity (Pius et al. 1990). Combined antioxidant treatment with

vitamin C, vitamin E, and α-lipoic acid was shown to reduce

γ-HCH -induced testicular toxicity in mice

(i.e., testes weight and histopathology) (Nagda and Bhatt 2011). Daily injection of garlic extracts

following oral exposure to

γ-HCH reversed the observed male reproductive toxicity of γ-HCH alone in

rats (decreased weights of testes, epididymis, seminal vesicles and prostate, sperm effects, and altered

serum hormone levels). Injection of garlic extracts also reduced measures of oxidative stress in the rat

testes and brain (Hfaiedh et al. 2011). Oral administration of the antioxidant, curcumin, either before,

concurrently, or after oral

γ-HCH dosing for 14 or 28 days, protected against male reproductive toxicity

including decreased testes and epididymis weight and effects on sperm count, morphology, and motility

(Sharma and Singh 2010). Curcumin also reduced the testicular levels of superoxide dismutase, catalase,

and glutathione-transferase; however, testicular glutathione content was not affected.

Soy isoflavones in the diet have been shown to alter uterine morphology (i.e., increased hyperplasia) and

expression of Erα in the rat (Yang et al. 2014; Zhang et al. 2016). These effects were reduced by

simultaneous gavage administration of

γ-HCH.

Developmental Effects. Cadmium interacts with γ-HCH to cause significant embryotoxic and teratogenic

effects in the developing rat fetus when administered together at a dosage that, for either toxin alone, is

insufficient to cause any deleterious effects on development (Saxena et al. 1986).

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CHAPTER 4. CHEMICAL AND PHYSICAL INFORMATION

4.1

CHEMICAL IDENTITY

HCH consists of eight isomers (Safe 1993). Only γ-HCH, α-HCH, β-HCH, and δ-HCH are of

commercial significance and considered in this profile. The pesticide lindane refers to products that

contain >99% γ-HCH. The α-, β-, and δ-isomers, as well as technical-grade HCH are not synonymous

with γ-HCH (Farm Chemicals Handbook 1993). Technical-grade HCH (CAS Registry Number

608-73-1) is not an isomer of HCH, but rather a mixture of several isomers; it consists of approximately

60–70% α-HCH, 5–12% β-HCH, 10–15% γ-HCH, 6–10% δ-HCH, and 3–4% ε-HCH (Kutz et al. 1991).

Information regarding the chemical identities of α-, β-, γ-, and δ-HCH is located in Table 4-1.

Table 4-1. Chemical Identity of Hexachlorocyclohexane Isomers

Characteristic

α-Hexachlorocyclohexane

β-Hexachlorocyclohexane

Synonym(s) and

registered trade name(s)

1-alpha, 2-alpha, 3-beta, 4-alpha,

5-beta, 6-beta-benzene-trans-

hexachloride; alpha-1,2,3,4,5,6-hexa-

chlorocyclohexane; alpha-benzene

hexachloride; alpha-BHC; alpha-

HCH; alpha-hexachloran; alpha-

hexachlorane; alpha-hexachloro-

cyclohexane; alpha-lindane;

benzenehexachloride-alpha-isomer;

cyclohexane 1,2,3,4,5,6-(alpha, DL);

cyclohexane 1,2,3,4,5,6-hexachloro,

alpha-; cyclohexane

1,2,3,4,5,6-hexachloro-, alpha-

isomer; cyclohexane, alpha-

1,2,3,4,5,6-hexachloro; ENT 9232

1-alpha, 2-beta, 3-alpha, 4-beta,

5-aplha, 6-beta-hexachlorocyclo-

hexane; beta 1,2,3,4,5,6-hexachloro-

cyclohexane; beta-benzenehexa-

chloride; beta-BHC; beta HCH; beta-

hexachloran; beta-hexachloro

benzene;

beta-lindane; cyclohexane,

1,2,3,4,5,6-hexachloro-, beta-; cyclo-

hexane, 1,2,3,4,5,6-hexachloro-, beta-

isomer; cyclohexane, 1,2,3,4,5,6-hexa-

chloro-, trans-; cyclohexane, beta-

1,2,3,4,5,6-hexachloro-; ENT 9233;

trans-alpha-benzenehexachloride

Chemical formula

SMILES

C1(C(C(C(C(C1Cl)Cl)Cl)Cl)Cl)Cl

Chemical structure

CAS Registry Number

319-84-6

319-85-7

HEXACHLOROCYCLOHEXANE (HCH) 233

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-1. Chemical Identity of Hexachlorocyclohexane Isomers

Characteristic

γ-Hexachlorocyclohexane

δ-Hexachlorocyclohexane

Synonym(s) and registered

trade name(s)

Lindane; 1-alpha, 2-alpha, 3-beta,

4-alpha, 5-alpha, 6-beta-hexachloro-

cyclohexane; benzene hexachloride-

gamma-isomer; BHC; cyclohexane

1,2,3,4,5,6-hexachloro-gamma-

isomer; ENT 7796; gamma-benzene

hexachloride; gamma-BHC; gamma-

hexachlorocyclohexane; gamma-

1,2,3,4,5,6-hexachlorocyclohexane;

gamma-HCH; gamma-

lindane; HCH;

HCCH; hexachlorocyclohexane,

gamma-isomer; 1,2,3,4,5,6-hexa-

chlorocyclohexane, gamma-isomer,

Etan 3G (Diachem S.P.A.); Forlin;

Gamaphex; Isotox (Chevron

Chemical Co.); Germate Plus

(Gustafson Inc.); Gamma-Mean 400

and Gamma Mean L. (Oregon-

California Chemicals, Inc.); Hammer

(Exsin Industries); Lindagam;

Novigam; Silvanol; Kwell

1-alpha,2-alpha,3-alpha, 4-beta,

5-alpha, 6-beta-hexachlorocyclo-

hexane; cyclohexane,

1,2,3,4,5,6-hexachloro-, delta-

isomer; cyclohexane, delta-

1,2,3,4,5,6-hexachloro-; delta-

(AEEEEE)- 1,2,3,4,5,6-hexachloro-

cyclohexane; delta-benzenehexa-

chloride; delta-BHC; delta-HCH;

delta-1,2,3,4,5,6-hexachlorocyclo-

hexane; delta-lindane; ENT 9234

Chemical formula

SMILES

C1(C(C(C(C(C1Cl)Cl)Cl)Cl)Cl)Cl

Chemical structure

CAS Registry Number

58-89-9

319-86-8

All information obtained from NLM 2021.

CAS = Chemical Abstracts Service; SMILES = Simplified molecular-input line-entry system

4.2 PHYSICAL AND CHEMICAL PROPERTIES

Information regarding the physical and chemical properties of α-, β-, γ-, and δ-HCH is located in

Table 4-2.

HEXACHLOROCYCLOHEXANE (HCH) 234

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-2. Physical and Chemical Properties of Hexachlorocyclohexane Isomers

Property

α-Hexachloro-

cyclohexane

(CAS 319-84-6)

β-Hexachloro-

cyclohexane

(CAS 319-85-7)

γ-Hexachlorocyclo-

hexane

(CAS 58-89-9)

δ-Hexachloro-

cyclohexane

(CAS 319-86-8)

Molecular weight

290.83

Color

Brownish to white

No data

White

No data

Physical state

Crystalline solid

;

monoclinic prisms

Crystalline solid

a,d

Crystalline solid

;

monoclinic prisms

Fine plates

a,c

Melting point

159–160°C

314–315°C

112.5°C

a,e

141–142°C

Boiling point

288°C at

760 mmHg

60°C at 0.5 mmHg

323.4°C at

760 mmHg

60°C at 0.36 mmHg

Density (g/cm

)

1.87 at 20°C

1.89 at 19°C

No data

Odor

Phosgene-like odor

No data

Slightly musty odor

No data

Odor threshold:

Water

0.88 ppm for

unspecified purity

0.00032 mg/kg

12 mg/kg

No data

Air

No data

Solubility:

Water

10 ppm

; 69.5 mg/L

at 28°C

5 ppm

17 ppm

; 7.3 mg/L at

25°C

10 ppm

Organic

solvents

Soluble in alcohol

;

1.8 g/100 g in

ethanol

; 6.2 g/100 g

in ether

1.1 g/100 g in

ethanol; 1.8 g/100 g

in ether; 1.9 g/100 g

in benzene

6.4 g/100 g in

ethanol; 20.8 g/100 g

in ether; 28.9 g/100 g

in benzene

24.4 g/100 g in

ethanol;

35.4 g/100 g in

ether; 41.4 g/100 g

in benzene

Partition coefficients:

Log K

3.8

3.78

3.72

4.14

Log K

3.57

3.0

; 3.57

3.8

Vapor pressure

4.5x10

-5

mmHg at

25°C

3.6x10

-7

mmHg at

20°C

4.2x10

-5

mmHg at

20°C

;

9.4x10

-6

mmHg at

20°C

3.5x10

-5

mmHg at

25°C

Henry’s law

constant

6.86x10

-6b

4.5x10

-7m,n

3.5x10

-6b

2.1x10

-7o,p

Autoignition

temperature

No data

Not flammable

No data

Flashpoint

No data

Approximately 150°F

(closed cup)

No data

HEXACHLOROCYCLOHEXANE (HCH) 235

4. CHEMICAL AND PHYSICAL INFORMATION

Table 4-2. Physical and Chemical Properties of Hexachlorocyclohexane Isomers

Property

α-Hexachloro-

cyclohexane

(CAS 319-84-6)

β-Hexachloro-

cyclohexane

(CAS 319-85-7)

γ-Hexachlorocyclo-

hexane

(CAS 58-89-9)

δ-Hexachloro-

cyclohexane

(CAS 319-86-8)

Flammability

limits

No data

Not flammable

No data

Conversion

factors

ppm to mg/m

in air (20°C): ppm x 4.96 = mg/m

;

mg/m

to ppm in air (20°C): mg/m

x 0.20 = ppm

Explosive limits

No data

CAS = Chemical Abstracts Service

Lide 1991.

NLM 2021.

Kirk and Othmer 1985.

IARC 1979.

Budavari et al. 1989.

Weiss 1986.

Fazzalari 1978.

Verschueren 1983.

Clayton and Clayton 1981.

Kurihara et al. 1973.

Hollifield 1979.

Hansch and Leo 1995.

Rippen et al. 1982.

Veith et al. 1979.

Pankow et al. 1984.

EPA 1982a.

Same for all isomers.

HEXACHLOROCYCLOHEXANE (HCH) 236

CHAPTER 5. POTENTIAL FOR HUMAN EXPOSURE

5.1 OVERVIEW

HCH isomers have been identified in at least 312 of the 1,868 hazardous waste sites that have been

proposed for inclusion on the EPA National Priorities List (NPL) (ATSDR 2022). However, the number

of sites in which HCH isomers have been evaluated is not known. The number of sites in each state is

shown in Figure 5-1. Of these sites, 308 are located within the United States, 1 is located in the Virgin

Islands, 1 is in Guam, and 2 are in Puerto Rico (not shown).

Figure 5-1. Number of NPL Sites with Hexachlorocyclohexane Contamination

• Reg

istrations of γ-HCH agricultural products have been cancelled since 2006, significantly

reducing most consumer exposure routes. The primary route of exposure is through dermal

contact from medicinal use. One percent γ-HCH shampoos or lotions are registered with the

FDA and are used for prescription treatment of lice and scabies.

• Individuals who are at risk of higher exposures to γ-HCH include those who live near

contaminated sites and anyone who improperly uses γ-HCH prescription medications .

HEXACHLOROCYCLOHEXANE (HCH) 237

5. POTENTIAL FOR HUMAN EXPOSURE

• Historically, HCH has been released to the environment during its formulation process and

through its use. HCH isomers are persistent and have been recently detected in air, water, and

soil. The general public may be exposed to low levels of HCH through inhalation of

contaminated ambient air, consumption of contaminated drinking water, or incidental ingestion of

or dermal contact with contaminated soils. HCH has not been found to be a major contaminant of

drinking water supplies.

• Once released to the environment, HCH can partition to all environmental media. HCH can exist

in the vapor and particulate phase in the atmosphere. HCH can volatilize from soils but is not

expected to volatilize significantly from water. HCH has low to moderate mobility in soils and

may leach to groundwater. HCH has low to moderate potential to bioaccumulate and has been

detected in aquatic organisms in the United States.

• HCH has a long atmospheric lifetime but can be removed by photodegradation with hydroxyl

radicals or wet and dry deposition. Biodegradation is believed to be the dominant decomposition

process for HCH in soil and water, although hydrolysis and photolysis may occur to a lesser

extent. The rates of degradation depend on the ambient environmental conditions.

5.2 PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL

5.2.1 Production

Table 5-1 summarizes information on companies that reported the production, import, or use of γ-HCH

for the Toxics Release Inventory (TRI) in 2021 (TRI21 2022). Most of the uses by these facilities are

considered to be ancillary, indicating purposes other than chemical processing or manufacturing.

Examples of ancillary uses as defined under TRI include cleaners, degreasers, lubricants, fuels, and waste

treatment uses. TRI data should be used with caution since only certain types of industrial facilities are

required to report. This is not an exhaustive list.

Table 5-1. Facilities that Produce, Process, or Use γ-Hexachlorocyclohexane

State

Number of facilities

Minimum amount on

site in pounds

Maximum amount on

site in pounds

Activities and uses

1,000

9,999

9, 12

10,000

99,999

9, 12

1,000

99,999

HEXACHLOROCYCLOHEXANE (HCH) 238

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-1. Facilities that Produce, Process, or Use γ-Hexachlorocyclohexane

State

Number of facilities

Minimum amount on

site in pounds

Maximum amount on

site in pounds

Activities and uses

1,000

99,999

9, 12

10,000

99,999

9, 12

Post office state abbreviations used.

Amounts on site reported by facilities in each state.

Activities/Uses:

1. Produce

2. Import

3. Used Processing

4. Sale/Distribution

5. Byproduct

6. Reactant

7. Formulation Component

8. Article Component

9. Repackaging

10. Chemical Processing Aid

11. Manufacture Aid

12. Ancillary

13. Manufacture Impurity

14. Process Impurity

Source: TRI21 2022 (Data are from 2021)

HCH does not occur as a natural substance. The manufacturing of technical-grade HCH involves the

photochlorination of benzene, which yields an isomeric mixture consisting of α-HCH, β-HCH, γ-HCH,

δ-HCH, ε-HCH, and inerts (IARC 1979); this reaction can be started by free-radical initiators such as

visual or ultraviolet light, X-rays, or γ-rays (Kirk and Othmer 1985). Treatment with methanol or acetic

acid, followed by fractional crystallization, concentrates γ-HCH to the 99.9% required in the technical-

grade of γ-HCH (IARC 1979); nitric acid is used to remove odor (NLM 2021). None of the isomers or

technical-grade HCH are currently produced in the United States. The production of γ-HCH exceeded

2.27x10

g in 1976 (NLM 2021); commercial γ-HCH production in the United States reportedly ended in

that year (EPA 1989a).

γ-HCH was available in emulsifiable and flowable concentrates, soluble concentrates/liquids, wettable

powders, dusts, ready-to-use liquids, pressurized liquids and impregnated materials, oil base and aerosol

sprays, and granules, as well as a smoke generator (Berg 1988; EPA 1985a). γ-HCH was sold separately

or in combination with fungicides, fertilizers, other insecticides, or wood preservatives (Hayes 1982).

5.2.2 Import/Export

Current data on the importation of γ-HCH were not located. Γ-HCH was not included in import/export

information submitted by manufacturers under EPA’s Chemical Data Reporting (CDR) database in the

2020 (covering 2016–2019) reporting cycle (EPA 2022a). The reporting threshold was 2,500 pounds.

HEXACHLOROCYCLOHEXANE (HCH) 239

5. POTENTIAL FOR HUMAN EXPOSURE

Γ-HCH historically was imported from France, Germany, Spain, Japan, and China (EPA 1985a).

Currently, India is the only country where γ-HCH is reportedly produced; thus, India may be the current

supplier to the United States (Vijgen et al. 2011). The U.S. imports of γ-HCH declined from 1.52x10

in 1977 to 8.53x10

kg in 1982 (NLM 2021). In 2002, it was estimated that 90 metric tons (9.0x10

kg)

of γ-HCH were imported into the United States (Hauzenberger et al. 2002). Up until 2001, it was

estimated that 500 metric tons of γ-HCH-containing pesticide products were exported annually by the

United States (primarily to Canada) (Hauzenberger et al. 2002). That export volume dropped to 25 metric

tons in 2001 and continued to decline significantly as other countries and the United States ceased the

usage of γ-HCH containing pesticides.

5.2.3 Use

γ-HCH was initially registered by the U.S. Department of Agriculture (USDA) in the 1940s and over the

years, was approved for use on a wide variety of fruit and vegetable crops (including seed treatment),

tobacco, greenhouse vegetables and ornamentals, forestry (including Christmas tree plantations), farm

animal premises, and other uses. In February 1977, EPA issued a notice of Rebuttal Presumption Against

Registration (RPAR), now called a Special Review, and continued registration of pesticide products

containing γ-HCH. EPA took this action in response to indications of γ-HCH’s potential carcinogenic

effect, possible developmental and reproductive effects, possible blood dyscrasias, and delayed toxic

effects, as well as its acute toxic effects seen in aquatic wildlife (IARC 1979). In October of 1983, EPA

issued a “Notice of Intent to Cancel Pesticide Products Containing γ-HCH.” The contentions concerning

developmental and reproductive effects were successfully challenged by industry. EPA no longer permits

the use of γ-HCH for purposes involving direct aerial application (EPA 1985b). The notice restricted

certain applications of γ-HCH on livestock, structures, and domestic pets to certified applicators or

persons under their direct supervision (EPA 1985b). In November 1993, EPA issued a “Notice of Receipt

of a Request for Amendments to Delete Uses” for several formulations of γ-HCH powder, 99.5%

technical-grade HCH, and dust concentrate, which would delete from the pesticide label most uses of

γ-HCH for agricultural crops and use on animals and humans (EPA 1993). According to the EPA’s last

Registration Eligibility Decision (RED), the last approved food/feed use of γ-HCH that was supported for

re-registration was seed treatment on barley, corn, oats, rye, sorghum, and wheat (EPA 2002). Since the

1998 and 1999 use deletions, the registrants were no longer interested in supporting the seed treatment

use on broccoli, Brussel sprouts, celery, cabbage, cauliflower, collards, kale, kohlrabi, mustard greens,

lettuce, radishes, spinach, or Swiss Chard (EPA 2002). Based on EPA estimates from 1996 to 2001,

about 233,000 pounds of γ-HCH were used annually as a seed treatment (EPA 2002). In August 2006,

HEXACHLOROCYCLOHEXANE (HCH) 240

5. POTENTIAL FOR HUMAN EXPOSURE

EPA issued “Notice of Receipt of Requests to Voluntarily Cancel Lindane Pesticide Registrations,”

which would end the use of γ-HCH as seed treatments, and notice of final orders of cancellation was

issued in December of 2006 (EPA 2006a, 2006b).

γ-HCH is available and regulated by the FDA, for the pharmaceutical treatment of scabies and head lice

(EPA 2002). A 1% γ-HCH lotion is available for the treatment of scabies, and a 1% shampoo is available

for the treatment of head lice; both are prescription use only. Both uses have been on the market since

1947, but they were labeled as a second line therapy in 1995 after a review by the FDA. The FDA has

issued revised labels for 1% γ-HCH lotion and 1% γ-HCH shampoo to be used with caution for infants,

children, and the elderly or anyone who weighs <110 pounds (50 kg), and people with other skin

conditions (FDA 2015). The products are contraindicated in premature infants and people with disorders

that cause seizures (FDA 2015). In the past, γ-HCH was used in veterinary products to control mites and

other pests, but recent data suggest that no products are currently registered in the United States for this

use (Hauzenberger et al. 2002).

5.2.4 Disposal

HCH is listed as a toxic substance under Section 313 of the Emergency Planning and Community Right to

Know Act (EPCRA) under Title III of the Superfund Amendments and Reauthorization Act (SARA)

(EPA 2020c). Disposal of wastes containing HCH is controlled by a number of federal regulations.

The recommended disposal technique for γ-HCH is incineration, at 400–500 ℃ in the presence of a

catalytic mixture of 5–10% metal chloride (copper, iron, zinc, or aluminum) on activated carbon (EPA

1975). Residence times based on this method were not reported. Other effective waste disposal methods

include treatment with strongly alkaline solution or oxidation. In a laboratory-scale study, 98.5% γ-HCH

was removed after a 6.5-hour treatment at pH 11.5 (EPA 1975). Γ-HCH can be effectively oxidized by

ozone and somewhat effectively oxidized by potassium permanganate; oxidation with chlorine or

hydrogen peroxide was ineffective (EPA 1975). EPA standard treatment for hazardous wastes containing

α-, β-, δ-, and γ-HCH is through either incineration or removal from liquid wastes by adsorption, prior to

land disposal (EPA 2014).

While current disposal techniques may be adequate, chemical and biological degradation methods may

provide increased efficiency and quality of disposal at a greatly reduced cost. Some methods utilize

various absorbents, which can be natural (ex. Agricultural solid wastes, biomass) or engineered materials

HEXACHLOROCYCLOHEXANE (HCH) 241

5. POTENTIAL FOR HUMAN EXPOSURE

(e.g., nanomaterials, activated carbon absorbents), to remove pesticides from wastewater prior to

treatment of the absorbent solid waste via microbial degradation or incineration (Saleh et al. 2020).

Microbial strains enriched from HCH-contaminated media can be employed for direct treatment of

wastewater. One laboratory-scale study was able to degrade HCH in wastewater with a consortium of

Pseudomonas, Burkholderia, Flavobacterium, and Vibrio microbial strains (Saleh et al. 2020). Another

method successfully degraded γ-HCH via UV-Fenton treatment (Saleh et al. 2020). This process is cost

effective, around $28.70 per kilogram of contaminants treated, and has shown a 90% chemical oxygen

demand (COD) reduction in studies with other organochlorine pesticides.

It’s unclear how frequently chemical or biological degradation methods are employed, but there are clear

benefits of these disposal techniques. They can be cost-effective, reliable, and can be adapted to the

variety of disposal challenges presented by the multitude of pesticides that are currently used. The use of

microbial consortia ensures that each pesticide will be degraded rapidly. These methods can also be used

for pesticide mixtures (Saleh et al. 2020).

5.3 RELEASES TO THE ENVIRONMENT

The Toxics Release Inventory (TRI) data should be used with caution because only certain types of

facilities are required to report (EPA 2022b). This is not an exhaustive list. Manufacturing and

processing facilities are required to report information to the TRI only if they employ ≥10 full-time

employees; if their facility's North American Industry Classification System (NAICS) codes is covered

under EPCRA Section 313 or is a federal facility; and if their facility manufactures (defined to include

importing) or processes any TRI chemical in excess of 25,000 pounds, or otherwise uses any TRI

chemical in excess of 10,000 pounds, in a calendar year (EPA 2022b).

5.3.1 Air

Estimated releases of 189 pounds (~0.086 metric tons) of γ-HCH to the atmosphere from 7 domestic

manufacturing and processing facilities in 2021 accounted for about 69% of the estimated total

environmental releases from facilities required to report to the TRI (TRI21 2022). These releases are

summarized in Table 5-2.

HEXACHLOROCYCLOHEXANE (HCH) 242

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-2. Releases to the Environment from Facilities that Produce, Process, or

Use γ-Hexachlorocyclohexane

Reported amounts released in pounds per year

State

Air

Water

Land

Other

Total release

On-site

Off-site

On- and off-site

γ-HCH

180

200

Total

189

273

The TRI data should be used with caution since only certain types of facilities are required to report. This is not an

exhaustive list. Data are rounded to nearest whole number.

Data in TRI are maximum amounts released by each facility.

Post office state abbreviations are used.

Number of reporting facilities.

The sum of fugitive and point source releases are included in releases to air by a given facility.

Surface water discharges, wastewater treatment-(metals only), and publicly owned treatment works (

POTWs) (metal

and metal compounds).

Class I wells, Class II-V wells, and underground injection.

Resource Conservation and Recovery Act (RCRA) subtitle C landfills; other onsite landfills, land treatment, surface

impoundments, other land disposal, other landfills.

Storage only, solidification/stabilization (metals only), other off-site management, transfers to waste broker for

disposal, unknown.

The sum of all releases of the chemical to air, land, water, and underground injection wells.

Total amount of chemical transferred off-site, including to POTWs.

RF = reporting facilities; UI = underground injection

Source: TRI21 2022 (Data are from 2021)

All isomers of HCH are considered hazardous air pollutants (HAPs) known to cause or suspected of

causing cancer or other serious human health effects or harmful environmental effects (EPA 2020a), as

regulated under the Clean Air Act. EPA's National Emission Inventory (NEI) database contains

comprehensive and detailed estimates regarding sectors part of the emissions inventory system (EIS)

which emit criteria air pollutants and HAPs for the 50 United States, Washington D.C., Puerto Rico, and

the U.S. Virgin Islands. The NEI database includes point and non-point source emissions, onroad

sources, non-road sources, and event sources such as emissions from wildfires or prescribed burning.

According to data from the 2017 NEI, 62.40 pounds of γ-HCH were released from waste disposal,

industrial solvent use, industrial processes, and fuel combustion (EPA 2020b). These data are

summarized in Table 5-3.

HEXACHLOROCYCLOHEXANE (HCH) 243

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-3. γ-HCH Emissions as Reported by the 2017 National Emission Inventory

Release sector

Emissions (pounds)

Waste disposal

54.607700078

Solvent; industrial surface coating and solvent use

5.91946

Industrial processes; ferrous metals

1.819

Industrial processes; NEC

0.04

Fuel combustion; commercial/institutional oil

0.01

NEC = not elsewhere classified

Source: EPA 2020b

Historically, the largest source of γ-HCH releases to the air resulted from agricultural use of the pesticide

γ-HCH, from aerial pesticide application or wind erosion of contaminated soils. γ-HCH may have also

been released to the atmosphere via volatilization from treated agricultural soils and plant foliage (Lewis

and Lee 1976). Evaporative loss of γ-HCH from water is not considered a significant potential source of

atmospheric γ-HCH because of its relatively high water solubility (Mackay and Leinonen 1975).

Quantitative historical estimates of the amount of γ-HCH released from these sources were not located in

the literature. Aerial applications of γ-HCH were prohibited in the United States as its use as a pesticide

was continuously restricted and eventually prohibited (EPA 1985b, 2006a, 2006b), and atmospheric

releases from agricultural sources today are not expected.

5.3.2 Water

No releases of γ-HCH to water from 7 domestic manufacturing and processing facilities required to report

to the TRI were reported in 2021 (TRI21 2022). This estimate includes releases to wastewater treatment

and publicly owned treatment works (POTWs) (TRI21 2022). These releases are summarized in

Table 5-2.

γ-HCH can be released to surface water via “down-the-drain” releases from consumer wash-off of

treatments for lice and scabies (EPA 2002). These releases would be treated by wastewater treatment and

POTWs, which did not report releases of γ-HCH to the TRI in 2021. Average γ-HCH concentrations in

wastewater treated in Los Angeles County, California, have been reported to range from 3.6x10

-5

0.03 μg/L (EPA 2002; Humphreys et al. 2008). α-HCH was not detected in 165 wastewater and

wastewater treatment effluent samples collected between 2001 and 2010 (WQP 2021). One wastewater

sample collected in 2003 contained 0.014 μg/L α-HCH (WQP 2021). β-HCH was not detected in

HEXACHLOROCYCLOHEXANE (HCH) 244

5. POTENTIAL FOR HUMAN EXPOSURE

24 wastewater samples collected between 2003 and 2009 (WQP 2021). Wastewater may be a negligible

source of hexachlorocyclohexanes to surface water and groundwater.

After soil or aerial application for agricultural use, γ-HCH could be released to surface water via surface

runoff (as the dissolved chemical or adsorbed to particulates) or via wet deposition of rain and snow

(Tanabe et al. 1982; Wheatley and Hardman 1965). Lake Ontario received 7 kg/year of α-HCH and

<2 kg/year of γ-HCH due to suspended sediment loading from the Niagara River between 1979 and 1981

(Kuntz and Warry 1983). Historically, the Great Lakes in general received 0.77–3.3 metric tons/year of

α-HCH and 3.7–15.9 metric tons/year of γ-HCH from atmospheric deposition of these contaminants

(Eisenreich et al. 1981). Because γ-HCH is no longer allowed to be used for agricultural purposes, these

are not expected to be significant sources of releases today.

Further from agricultural areas, urban stormwater runoff has historically resulted in releases of HCH to

water in the range of parts per billion to parts per trillion. In 1982, α- and γ-HCH were detected in

samples of urban stormwater runoff from Denver, Colorado, and Washington, D.C., at 0.0027–0.1 and

0.052–0.1 μg/L in 20 and 11%, respectively, of the 86 samples collected; β-HCH was detected only in

runoff from Washington, D.C., in 5% of the samples at a concentration of 0.1 μg/L (Cole et al. 1984). In

urban runoff samples collected in the Canadian Great Lakes Basin, γ-HCH was detected at mean

concentrations of 0.0065 μg/L and 0.0035 mg/kg in the aqueous and sediment portions, respectively; the

mean annual loading of the compound in runoff in the basin was reported to be 4.1 kg/year (Marsalek and

Schroeter 1988). Stormwater samples collected in 2007, just after the ban on γ-HCH for agricultural use,

showed concentrations between 6.0x10

-5

and 0.14 μg/L α-HCH and 3.8x10

-4

and 0.0976 μg/L β-HCH

(WQP 2021).

γ-HCH could be released to groundwater via soil leachate after agricultural application or from improper

disposal at contaminated sites. Available adsorption data indicate that γ-HCH has a low to moderate

mobility in soils, and the results of monitoring studies suggest that γ-HCH does migrate to groundwater

(Page 1981; Sandhu et al. 1978). Groundwater samples were collected from a packaging and

reformulating pesticide facility in Florida, which had disposed of γ-HCH wastes in unlined trenches until

1996. Ground water concentrations for the site ranged from 30 to 420 μg/L for α-, γ-, and δ-HCH

(Chartrand et al. 2015).

HEXACHLOROCYCLOHEXANE (HCH) 245

5. POTENTIAL FOR HUMAN EXPOSURE

5.3.3 Soil

Estimated releases of 56 pounds (~0.025 metric tons) of γ-HCH to soil from 7 domestic manufacturing

and processing facilities in 2021, constituting about 20% of the estimated total environmental releases

from facilities required to report to the TRI (TRI21 2022). No additional quantities were released via

underground injection (TRI21 2022). These releases are summarized in Table 5-2.

γ-HCH has historically been released to the soil by direct application of the pesticide to soil, and can be

released by direct or indirect releases during formulation, storage, and/or disposal. Hazardous waste sites

where γ-HCH has been disposed of in the past are sources of γ-HCH in soils. However, the application of

γ-HCH to laboratory refuse columns simulating municipal landfills indicated that γ-HCH did not

volatilize or leach from the refuse surface, and movement through the column was slight, suggesting that

codisposal of γ-HCH with municipal refuse will result in minimal releases (Reinhart and Pohland 1991;

Reinhart et al. 1991).

5.4 ENVIRONMENTAL FATE

5.4.1 Transport and Partitioning

Air. HCH isomers are volatile, relatively persistent substances in the atmosphere and are expected to be

capable of long-range transportation. HCH can exist in the vapor and particulate phases based on the

reported vapor pressures of the isomers (NLM 2021). Volatilization of γ-HCH used as a seed treatment

was confirmed, with 12–30% of the applied pesticide volatilizing within 6 weeks of planting the seed

(Waite et al. 2001, 2007). Correspondingly, atmospheric concentrations of γ-HCH were variable and

increased when pesticide usage occurred; α-HCH concentrations were less variable throughout the year

(Hoff et al. 1992a). During the winter, higher ratios of α-HCH to γ-HCH reflected the movement of air

containing the more persistent α-HCH isomer from the colder Arctic regions to the south, while the lower

ratios in the summer reflected both increased γ-HCH usage in the region and the lack of movement of

Arctic air (Hoff et al. 1992a). γ-HCH was also seen to move with warm air during the summer months

from the lower United States (or areas even further to the south) to the Great Lakes region, although a

similar trajectory could not be identified for the more ubiquitous α-HCH. Levels of α-HCH in air are not

dominated by volatilization or partitioning to surfaces, but are dependent on local temperature changes

(Hoff et al. 1992b). α-HCH appears to have a long residence time in the atmosphere and is controlled

primarily by transport. Long-range transport potentials were estimated for α- and γ-HCH based on North

HEXACHLOROCYCLOHEXANE (HCH) 246

5. POTENTIAL FOR HUMAN EXPOSURE

American monitoring data, and were reported to be 11,151 miles (17,946 km) and 6,047 miles

(9,732 km), respectively (Shen et al. 2004). The potential for widespread global distribution has been

reported in several studies (Hargrave et al. 1988; Knap and Binkley 1991; Tanabe et al. 1982; Wittlinger

and Ballschmiter 1990). α- and γ-HCH have been measured in arctic air as recently as 2018, but

concentrations have been declining due to declining global emissions and limited use of lindane (Wong et

al. 2021).

HCH isomers in the atmosphere are likely to be subject to rain-out and dry deposition, which may result

in the contamination of surface soil and water. Air-sea exchange fluxes of -0.95 and -17 ng/m

/day were

observed over the northwest Pacific Ocean for α- and γ-HCH, respectively, supporting the oceans as an

important sink for atmospheric HCH (Wu et al. 2020). γ-HCH removal rates were 2.5%/week by rainfall

and 3.3%/week by dry deposition, and the estimated residence time of γ-HCH in the atmosphere was

17 weeks (Atkins and Eggleton 1971). The dry deposition flux rate of α-HCH ranged from 0.1 to

5.1 ng/m

/day in deposition samples collected in June–August 1997 near the southern Baltic Sea (Wiberg

et al. 2001). The flux rate of γ-HCH was 0.9–32.6 ng/m

/day over the same time frame. Seasonal

variation resulted in lower dry deposition rates during the winter months. In samples collected between

February and March 1998, the flux rate for α-HCH ranged from 0.25 to 0.54 ng/m

/day, and the dry

deposition flux rate for γ-HCH was 3.4–14.1 ng/m

/day (Wiberg et al. 2001). The dry deposition flux rate

of γ-HCH in south central Saskatchewan in 1998 where it had been used as a seed treatment in a canola

field ranged from <29 to 2,203 ng/m

/day, and the amount in rainfall over the same period ranged from

<10 to 200 ng/L (Waite et al. 2001). Uptake by plants may be another removal pathway, as observed for

α- and γ-HCH under experimental conditions with lettuce, romaine, and garlic leaf (Yang et al. 2007).

Removal was controlled by plant-air equilibration and correlated strongly with the reported log octanol-

air partition coefficients (K

), 7.44 and 7.72 α- and γ-HCH, respectively (Yang et al. 2007).

Water. In surface waters, HCH has a slight tendency to dissolve and remain in the water column based

on the water solubilities and octanol-water partition coefficients (K

) of the isomers (Clayton and

Clayton 1981; Hansch and Leo 1995; Hollifield 1979; Kurihara et al. 1973). Although γ-HCH has a

relatively high vapor pressure and Henry’s law constant compared with many other organochlorine

insecticides, evaporative loss of γ-HCH from water is not considered to be significant. Mackay and

Leinonen (1975) calculated theoretical losses of several pesticides from saturated water solutions and

predicted a volatilization half-life of 191 days for γ-HCH. Evidence of increased flux from the Arctic

Ocean of α-HCH due to increased temperatures and decreased sea ice coverage may suggest this as

pathway of growing significance as global warming continues (Wong et al. 2021).

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5. POTENTIAL FOR HUMAN EXPOSURE

γ-HCH released to water may undergo adsorption/desorption with sediments and other materials in the

water. Adsorption and desorption studies of γ-HCH in natural water-sediment systems performed by

Saleh et al. (1982) indicate that a diversity of the natural water-sediment characteristics may affect the

sorption-desorption behavior of γ-HCH in addition to the organic carbon content of the sediments.

γ-HCH is sorbed to silt solutions with a slow desorption rate, indicating that transport through the

environment is most likely to be particle mediated (Noegrohati and Hammers 1992). Biosorption of

γ-HCH was seen for the fungus Rhizopus arrhizus and activated sludge, with equilibrium being reached

within 1 and 4 hours, respectively. Death of the sludge biomass resulted in rapid desorption with zero-

order kinetics, suggesting that adsorbed γ-HCH can be released back into the environment (Tsezos and

Wang 1991a). The sorption of γ-HCH from water using wood charcoal has been described

(Keerthinarayana and Bandyopadhyay 1998); it was found to be a good sorbent for γ-HCH from water.

Sediment and Soil. HCH present in soil can leach to groundwater, sorb to soil particulates, or

volatilize to the atmosphere. In general, the leaching of organic chemicals through soil is governed by the

water solubility of the chemicals and their propensity to bind to soil. Based on the results of a number of

laboratory soil column leaching studies that used soils of both high and low organic carbon content as

well as municipal refuse, γ-HCH generally has low to moderate mobility in soils, with K

values ranging

from 641 to 3,362; log K

range of 2.810–3.5266 (EPA 1982b; Melancon et al. 1986; Reinhart et al.

1991). Adsorption of γ-HCH to soil particulates is generally a more important partitioning process than

leaching to groundwater. However, groundwater sediments, which have low organic carbon content

(<0.1%), are not sufficient to adsorb γ-HCH to the extent that groundwater contamination is prevented

(Nordmeyer et al. 1992). The presence of black carbon in soils from incomplete combustion may impact

sorption affinity. HCH isomers showed varying preference for partitioning to black carbon (α-HCH >

β-HCH > δ-HCH) in soils with 0.82–2.26% organic carbon and 0.04–0.5% black carbon (Ali et al. 2016).

Sorption was observed to be a limiting factor in bioavailability of γ-HCH in soil to earthworms (Šmídová

et al. 2012).

Using sediment (0.44% organic carbon) obtained from a sugarcane growing region of Australia, the K

of γ-HCH was measured as 2,164 (Just et al. 1990). The K

of γ-HCH in a mineral soil containing 1.26%

organic carbon content was measured as 832 (Chiou et al. 1998). In a sandy soil (0.105% organic carbon)

γ-HCH had a measured K

of 3,362, and a desorption K

of 3.53 (Melancon et al. 1986). The partition

coefficient (K

) of γ-HCH in a laboratory column experiment with municipal solid waste was

853 (Reinhart et al. 1991). In a study involving a laboratory sediment/water system (pH 7.42; 2.18%

HEXACHLOROCYCLOHEXANE (HCH) 248

5. POTENTIAL FOR HUMAN EXPOSURE

organic carbon), α- and γ-HCH isomers were adsorbed on sediments under both aerobic and anaerobic

conditions and few differences were noted in the adsorption behavior of each isomer. Under aerobic and

anaerobic conditions, the K

values of α-HCH were 681 and 617, respectively, while the K

values for

γ-HCH were 641 and 694, respectively (Wu et al. 1997). A mixture of HCH isomers (α-, β-, γ-, and

δ-HCH) sorbed very strongly to a soil from Nagpur, India (pH 7.6, 0.387% organic carbon), with a K

value of 54,000. Some desorption was observed, believed to be due to the water solubility of HCH

(Wadaskar et al. 2006). Desorption experiments with a sandy loam soil slurry showed isomeric

differences in desorption capacity, α- ≥ γ- > δ- > β-HCH (Quintero et al. 2005).

γ-HCH sorbed to the soil can partition to the atmosphere by wind erosion of surface soil particulates

(Stanley et al. 1971) and via volatilization from treated agricultural soils and plant foliage (Lewis and Lee

1976). In tests conducted in a model laboratory system at 10 and 20°C, volatilization half-lives of γ-HCH

from soil and oat plant surfaces of 2.3–24.8 and 0.29–0.73 days, respectively, were reported (Dorfler et al.

1991a); half-lives were greater on dry, sandy soils versus peat soils; however, when moisture was added

to the soils, the half-life was greater for the peat soil, while warmer temperatures decreased the half-life

under all soil and moisture conditions (Dorfler et al. 1991b). In tests performed with a wind tunnel, a

volatilization rate of >20% for γ-HCH from soil surfaces within a 24-hour period was determined (Rüdel

1997). A 6-fold increase in γ-HCH volatilization from soil was seen in laboratory experiments when the

temperature increased from 15 to 45°C; flooding the soil also increased the volatilization (Samuel and

Pillai 1990). A field study conducted in south central Saskatchewan, Canada in 1997–1998 in which

γ-HCH was applied as a seed treatment to canola, determined that between 12 and 30% of the initial

amount applied volatilized to the atmosphere (Waite et al. 2001); a follow-up study determined

volatilization rates of 190 mg/hectare/week at 1 week after application and 420 mg/hectare/week 2 weeks

after application (Waite et al. 2007). The volatilization rate from plant surfaces was 55% for γ-HCH.

Application of γ-HCH to fields of sunflowers and sugarbeets resulted in a 54% evaporative loss of the

pesticide within 24 hours (Neururer and Womastek 1991).

Other Media. γ-HCH has a low to moderate potential to bioaccumulate. A summary of some of the

bioconcentration factors (BCFs) from experimental studies with γ-HCH are provided in Table 5-4.

γ-HCH shows limited uptake from soils and bioconcentration by plants and terrestrial organisms and does

not appear to biomagnify to a great extent.

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5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-4. Results of Experimental Bioaccumulation

Studies with γ-Hexachlorocyclohexane

Species

Exposure route

Bioconcentration factor

Reference

Brine shrimp

Water

183

Matsumura and Benezet 1973

Rainbow trout (fry)

Water

319

Ramamoorthy 1985

Pink shrimp

Water

Schimmel et al. 1977

Pinfish

Water

218

Grass shrimp

Water

Sheepshead minnow

Water

490

Brine shrimp

Sand

Matsumura and Benezet 1973

Northern brook silverside

fish

Sand

1,613

A BCF of 1,273 (lipid basis) in prawns (crustacean) was seen to be 0.58 times the γ-HCH concentration in

the underlying sediment, indicating that aquatic organisms may accumulate γ-HCH from the water

column, and uptake from contaminated sediment alone may not be extensive (Just et al. 1990). BCFs for

the isomers of HCH, using zebra fish under steady-state conditions, were 1,100 for α-HCH, 1,460 for

β-HCH, 850 for γ-HCH, and 1,770 for δ-HCH; BCFs determined by uptake and clearance rate constants

were slightly lower (Butte et al. 1991). Elimination of γ-HCH occurred rapidly in zebra mussels (BCF of

10) and metabolism of γ-HCH was not observed (Berny et al. 2002). BCFs on a wet weight basis for

γ-HCH in different fish species were positively correlated with their lipid content (Geyer et al. 1997).

The bioaccumulation of γ-HCH by tubificide oligochaetes from a static system consisting of sediment and

water has been reported (Egeler et al. 1997). Microalgae Scenedesmus quadricauda and Coccomyxa

subellipsoidea were exposed for 24 hours to mine dump effluent containing α-, β-, γ-, and δ-HCH,

resulting in bioaccumulation factors (BAFs) of 74.6, 60.5, 29.4, and 107.2 for α-, β-, γ-, and δ-HCH,

respectively, in S. quadricauda, and BAFs of 50.8, 47.6, 21.5, and 56.3 for α-, β-, γ-, and δ-HCH,

respectively, in C. subellipsoidea (

Kováčik et al. 2018).

γ-HCH applied to an aquatic mesocosm (i.e., a small, artificial ecosystem) at 61.3 μg/L was reduced by

50% at 24 hours post-application, while at 19 weeks post-application, the concentration in the water was

only 0.2%; no γ-HCH was detected at 21 weeks. The biological half-life was estimated to be 16.7 days.

Movement through the water column was shown by increasing sediment concentrations up to a maximum

of 75.4 μg/kg at 96 hours post-application; however, sediment concentrations decreased to below the

detection limit at 23 weeks to give a half-life in sediment of 48.1 days. Rooted aquatic macrophytes have

a BCF of 56 at a maximum concentration of 1.7 mg/kg at 24 hours post-application; however, at

14 weeks, all residues were below the detection limit for a half-disappearance time of 18 days.

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5. POTENTIAL FOR HUMAN EXPOSURE

Gastropods in the system had a maximum γ-HCH concentration of 7.2 mg/kg at 24 hours post-treatment,

yielding a BCF of 232.4 and a half-disappearance time of 13.7 days with all residues eliminated by

13 weeks (Caquet et al. 1992).

Trophic transfer of γ-HCH may occur in the foodweb. A study assessed the potential of transfer between

zebra mussels and their predators, tufted ducks (Aythia fugigula) at the birds’ wintering grounds in Lake

Geneva, bordering Switzerland and France. γ-HCH concentrations in the mussels ranged from

approximately 5 to 500 ng/g wet weight, while γ-HCH in the liver of the tufted ducks ranged from 8.9 to

175.6 ng/g wet weight (Bemy et al. 2003).

In tests with radiolabeled γ-HCH, grain, maize, and rice plants accumulated 0.95, 0.11, and 0.04%,

respectively, of the amount of bound residues following 14–20 days growth in a sandy loam soil.

Bioconcentration increased by 4–10 times when the plants were grown in test soils containing both bound

and extractable residues of γ-HCH (Verma and Pillai 1991). Plants and grains grown on soil treated with

γ-HCH showed α-HCH as the predominant isomer, although all isomers were found to some extent;

amounts decreased with increasing time after application (Singh et al. 1991). A different trend in isomer

uptake was observed in garlic. Garlic (Allium sativum L.) was planted in pots containing soil treated with

α-, β-, γ-, and δ-HCH isomers. The BCFs of the underground parts were in the range of 0.48–0.90, 1.60–

1.84, 1.40–2.34, and 2.60–3.64 for α-, β-, γ-, and δ-HCH, respectively, and above-ground parts were

1.50–2.26, 4.50–6.79, 5.16–6.81, and 9.30–12.18, respectively (Chen et al. 2013). The phytoavailability

of the isomers was observed to be δ- > γ- ≥ β- > α-HCH, which generally agreed with the isomer’s water

solubility and vapor pressure (Chen et al. 2013). Evidence of plant uptake from air has been reported.

Lettuce, romaine, and garlic leaf were maintained in air chambers that exposed them to air polluted with

α- and γ-HCH for 5 days. Measured accumulation factors of α-HCH in the crops were 77.25, 190.8, and

95.23 for lettuce, romaine, and garlic leaf, respectively, and accumulation factors of γ-HCH were 187.6,

321.9, and 124.5, respectively (Yang et al. 2007).

Uptake of γ-HCH by earthworms from a treated soil has also been reported. Eisenia andrei exposed to

grassland soil spiked with γ-HCH for 24 hours had measured BAFs ranging from 5 to 35 (

Šmídová et al.

2015)

. Following exposure to 5 ppm of the compound for up to 8 weeks, earthworms bioconcentrated

γ-HCH by a factor of 2.5. The earthworms biotransformed more than 50% of the accumulated γ-HCH;

the main degradation product was γ-2,3,4,5,6-pentachlorocyclohex-1-ene (Viswanathan et al. 1988).

HEXACHLOROCYCLOHEXANE (HCH) 251

5. POTENTIAL FOR HUMAN EXPOSURE

γ-HCH and the other isomers of HCH do not appear to undergo biomagnification in terrestrial food chains

to a great extent, although there is a moderate potential for transfer of γ-HCH to animal tissue as a result

of soil ingestion or ingestion of contaminated foliage (Wild and Jones 1992). Clark et al. (1974) found

that γ-HCH levels in the adipose tissue of cattle were 10 times higher than in the feed (0.002 mg/kg).

Szokolay et al. (1977) examined relative accumulation of HCH isomers including γ-HCH and various

components in the food chain in Czechoslovakia. Lower γ-HCH residues were found in tissues of

animals (chickens, sheep, pigeons) feeding entirely on plant material, whereas carnivores had higher

concentrations.

γ-HCH that is adsorbed to sediments may be recycled to the atmosphere as gas bubbles that are formed in

the sediment by the methanogenesis and denitrification processes of bacteria. In one case studied, it was

estimated that 85% of the γ-HCH associated with the sediment gas bubbles would be released to the

atmosphere, with the remaining 15% being dissolved in the water column as the bubble rises toward the

surface (Fendinger et al. 1992).

5.4.2 Transformation and Degradation

Air. HCH is degraded in the atmosphere by reacting with photochemically produced hydroxyl radicals.

The rate of this reaction is not very rapid however, and all of the HCH isomers have rather long

atmospheric lifetimes. The rate constants for the reaction of α- and γ-HCH with hydroxyl radicals were

measured as 1.4x10

-13

and 1.9x10

-13

/molecule-second, respectively (Brubaker and Hites 1998).

Using an average hydroxyl radical concentration of 5x10

molecule/cm

, the corresponding half-lives are

about 115 and 84 days for α- and γ-HCH, respectively. In locations where the atmospheric hydroxyl

radical concentration is very low, the persistence times of these compounds are much longer. Cortes and

Hites (2000) estimated that the average half-life of α- and γ-HCH around the Great Lakes region ranged

from about 3 to 4 years. Calculated half-lives based on artic air measurements ranged from 4.6 to

8.9 years for α-HCH, and from 4.4 to 10 years for γ-HCH; one arctic station reported a half-life

of -28 years for γ-HCH, possibly due to the shorter monitoring period and the lack of change in

concentrations over this period (Wong et al. 2021). Since HCH does not absorb light >290 nm, direct

photolysis in the atmosphere is not expected to be an important environmental fate process. However,

Chen et al. (1984) reported photodegradation half-lives of 91, 152, 104, and 154 hours for thin films of

α-HCH, β-HCH, γ-HCH, and δ-HCH, respectively, when irradiated with light of wavelength 295–

305 nm. No absorption bands were observed in this spectral region, however, for any of the HCH

isomers, and the mechanism of photodegradation and its environmental significance are uncertain. A

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5. POTENTIAL FOR HUMAN EXPOSURE

direct photolysis study of α-HCH showed maximum absorption in the middle ultraviolet (UV) range at

252 nm, with a half-life around 2 hours (pseudo-first-order rate constant of 0.34/hour) (Zhang et al. 2014).

The environmental relevance of this is unclear, since the middle UV range wavelengths are filtered out by

the stratosphere. Similar indirect photolysis studies were conducted at ≥280 nm with α-HCH in the

presence of H

at a molar ratio of 100:1 (H

:α-HCH). The indirect photolysis half-life was around

4.3 hours (pseudo-first-order rate constant 0.16/hour). A proposed final photolysis product is

2,4,6-trichlorophenol (Zhang et al. 2014).

Water. Biodegradation is believed to be the dominant degradative process for γ-HCH in aquatic systems,

although hydrolysis and indirect photolysis may also occur. Sharom et al. (1980) found that <30% of the

applied γ-HCH remained in unsterilized natural waters in capped bottles after 16 weeks. Biodegradation

was concluded to be responsible for these results, although it was unclear to what extent hydrolysis or

adsorption to the glass bottles may have contributed. Zoeteman et al. (1980) estimated river, lake, and

groundwater half-lives for γ-HCH from degradation data in these environments to be 3–30, 30–300, and

>300 days, respectively. In natural lake water with a pH of 9.0 and a hardness of >600 mg calcium

carbonate/L, the half-life of γ-HCH was estimated to be 65 hours (Ferrando et al. 1992). γ-HCH, applied

at concentrations of 50 or 500 μg/L to aerobic batch cultures of microorganisms with sodium acetate as a

carbon source, was initially removed by adsorption and followed by desorption onto the biomass with

subsequent decomposition (McTernan and Pereira 1991). Approximately 56–62% of the γ-HCH was

removed from the water column in 23 days, with 26% removal by adsorption onto the biological solids

produced in these batch reactors. Microbial growth, using γ-HCH in the absence of sodium acetate,

increased as the microorganisms became acclimated; the pesticide still showed toxic properties, as

evidenced by a concurrent increase in microbial death rates. Evidence of biodegradation of HCH isomers

in groundwater has also been reported. In an in situ study of a former pesticide formulating plant, the

biodegradation half-lives of α-, β-, and δ-HCH isomers were determined in groundwater below the site by

compound-specific stable carbon isotope analysis respectively. Half-lives were determined based on

isotopic depletion from samples collected over 3 years at various wells spreading out from the

contaminant source. Half-lives were 223, 62–287, and 120–632 days for α-, β-, and δ-HCH isomers,

respectively (Bashir et al. 2015).

It has been shown that γ-HCH is degraded by nitrogen-fixing blue-green algae. These algae reduce the

toxic effects of γ-HCH following repeated inoculations (Kar and Singh 1979b). The degradation of

γ-HCH became more efficient with time, thus reducing the pesticide's toxicity in cultures of nitrogen-

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5. POTENTIAL FOR HUMAN EXPOSURE

fixing blue-green algae. Dechlorination of γ-HCH to γ-pentachlorocyclohexene was also shown to occur

with fungi in aqueous suspensions (Macholz and Kujawa 1985) and in algal cultures (Sweeney 1969).

Hydrolysis is not considered an important degradation process for HCH in aquatic environments under

neutral pH conditions. However, under alkaline conditions, γ-HCH is hydrolyzed fairly rapidly. Saleh et

al. (1982) tested rates of hydrolysis of γ-HCH in sterilized natural waters at 25°C and found that

hydrolysis of γ-HCH followed first-order kinetics with half-lives of 92 hours at pH 9.3, 648 hours at

pH 7.8, and 771 hours at pH 7.3. EPA (1989b) reported a hydrolysis half-life of 207 days at pH 7 and

25°C using distilled water. Alkaline hydrolysis (pH 9.78) of α-HCH was observed with a calculated half-

life of 1,083 hours (based on pseudo-first-order rate constant of 0.0064/hour), giving

1,3,4,5,6-pentachlorocyclohexane, 1,2,4-trichlorobenzene, and 1,2,3-trichlorobenzene as the major

products (Zhang et al. 2014).

Somewhat conflicting information is available on the rate of photolysis of γ-HCH in water. Since HCH

does not contain chromophores that absorb light >290 nm, direct photolysis is not expected to occur.

However indirect photolysis, whereby a photosensitizing agent may absorb light and then transfer its

excitation energy to HCH, may occur. Humic and fulvic acids are well-known photosensitizing agents

and are practically ubiquitous in natural waters. In the study by Saleh et al. (1982), the authors reported

γ-HCH first-order photolysis half-lives of 169, 1,791, and 1,540 hours in pond water, lake water, and

water from a quarry at pH 9.3, 7.3, and 7.8, respectively, when solutions were exposed to direct sunlight.

However, the rapid rate of degradation at pH 9.3 may have been enhanced by hydrolysis reactions rather

than by photolysis. In another study, α- and γ-HCH were shown to undergo enhanced photolysis when

aqueous solutions were spiked with 5 and 25 ppm of soil fulvic acid, and irradiated with natural sunlight

(Malaiyandi et al. 1982). Hamada et al. (1981) found that γ-HCH underwent photodegradation to form

two isomers of tetrachlorohexene and pentachlorohexene in propanol solution when irradiated with UV

light produced by a low-pressure mercury lamp. Oxidants commonly found in natural waters, such as

peroxy radicals, hydroxyl radicals, and singlet oxygen species, can degrade HCH in water. Mill (1999)

estimated that the indirect photolysis half-life of HCH in natural waters is about 270 days, and the

dominant oxidant for HCH was the hydroxyl radical. Photolysis of γ-HCH in aqueous solution in the

presence of polyoxomethallate, a strong oxidizing agent, has also been demonstrated (Hiskia et al. 1997).

Sediment and Soil. γ-HCH in soil or sediment is degraded primarily by biodegradation, although

hydrolysis may occur in moist soils under alkaline conditions. Tu (1976) reported that 71 of

147 microorganisms isolated from a loamy sand soil were able to utilize a γ-HCH solution as the sole

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5. POTENTIAL FOR HUMAN EXPOSURE

carbon source. White rot fungus degraded radiolabeled γ-HCH in aerobic pure culture laboratory tests.

In a silt loam soil/corncob test matrix, 34.7% of the compound was degraded over a 60-day test period,

whereas 53.5% degradation was observed in liquid cultures over a 30-day test period (Kennedy et al.

1990). The results of this study have been confirmed by more recent studies (Mougin et al. 1996, 1997).

The isolation of γ-HCH-degrading bacteria, classified as Sphingomonas paucimobilis, from contaminated

soils has been reported (Thomas et al. 1996). A Pseudomonas species has also been isolated from

pretreated soil that is able to degrade γ- and α-HCH, but not β-HCH, within 10–20 days under both

flooded (anaerobic) and unflooded (aerobic) conditions; greater degradation rates were observed under

aerobic conditions (Sahu et al. 1993). Under aerobic conditions, actinobacteria strains of Streptomyces

sp. isolated from a polluted site were able to utilize α-HCH as its only carbon source, and some were able

to utilize β-HCH when supplemented to the α-HCH system; no growth was observed in the presence of

δ-HCH. At pH 7 and 30°C, the actinobacteria were able to degrade up to 100% α-HCH and 55% β-HCH

after 7 days (Sineli et al. 2014). The concentrations and persistence of γ-HCH in soil may be dependent

on soil types. An analysis of two soil types, loamy sand (approximately 1–2% organic matter) and muck

(approximately 27–56% organic matter), for γ-HCH residues showed that mean residues in the loamy

sand soil had decreased from 95 ppb dry weight in 1971 to below the detection limit of 10 ppb in 1989;

however, in muck, residues had decreased from 426 ppb in 1971 to 168 ppb in 1989 (Szeto and Price

1991). The presence of crops on the soils also affects the persistence of HCH residues, with half-lives of

58.8 and 83.8 days for cropped and uncropped plots, respectively. β-HCH was the most persistent

isomer, with half-lives of 184 and 100 days, respectively, on cropped and uncropped plots; γ-HCH was

next at 107 and 62.1 days, followed by α-HCH at 54.4 and 56.1 days, and finally, δ-HCH at 33.9 and

23.4 days. Only trace amounts of the isomers were found to leach below 20 cm soil depth (Singh et al.

1991). The β-HCH isomer comprised 80–100% of the total HCH residues found in soil or vegetation on

land surrounding an industrial landfill in Germany 10 years after the final HCH input (Heinisch et al.

1993). Biodegradation was observed to be a limiting factor in uptake of γ-HCH by earthworms (Šmídová

et al. 2012).

Most available information suggests that γ-HCH transformation is favored in biologically rich, anaerobic

environments (EPA 1979; Haider 1979; Kalsch et al. 1998). In bench-scale anaerobic digestion tests

designed to assess the fate of semivolatile organic pollutants in primary and secondary sludges, γ-HCH

was found to undergo 98% degradation at 120 days. Sorption of the compound to the digester solids

accounted for 2% of the initial feed; none of the compound was lost by volatilization. The digesters were

operated at 35°C with a 30-day solids retention time (Govind et al. 1991). Similar results were seen with

live activated sludge where initially reversible biosorption dominates the removal process followed by an

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5. POTENTIAL FOR HUMAN EXPOSURE

increased aerobic biodegradation after approximately 10 hours of acclimation. The biodegradation

process includes hydrolytic dechlorination with subsequent ring cleavage and finally, partial or total

mineralization (Tsezos and Wang 1991b). Adaptation of sewage sludge is slow and may take 1–

2 months; however, once acclimation occurs, 70–80% biodegradation of γ-HCH may occur, with the

percentage of degradation decreasing with increasing sludge age (Nyholm et al. 1992). Co-oxidation and

reductive dechlorination are the probable degradation mechanisms (Jacobsen et al. 1991; Nyholm et al.

1992).

Numerous diverse studies on biological degradation have shown that γ-HCH was transformed to

tetrachlorohexene; tri-, tetra-, and pentachlorinated benzenes; penta- and tetracyclohexanes; other isomers

of HCH; and other related chemicals. The products varied depending on the organisms present, analytical

methods applied, and when the sample was analyzed relative to its collection date (EPA 1979).

Laboratory studies have demonstrated the bioisomerization of γ-HCH to α-, β-, and δ-HCH but

bioisomerization in the environment was considered to be nonsignificant by an investigator who

conducted a field study (Waliszewski 1993). Levels of individual isomers were approximately 0.1–

1.4 and 0.8–4.0% of the γ-HCH concentrations at 3–31 and 34–46 weeks, respectively, following γ-HCH

treatment of soil. The study authors suggested that their inability to simulate all environmental conditions

in the laboratory could explain differences between laboratory and field results.

Abiotic transformation and degradation processes of γ-HCH in soil/sediment are not thought to be

significant pathways. As discussed earlier for water, photolysis or hydrolysis are not considered

important degradation pathways of γ-HCH and other isomers; the exception being hydrolysis under

alkaline conditions.

Other Media. Several Organisation for Economic Cooperation and Development (OECD) and

European Union standardized tests exist to quantify potential for biodegradation in a wastewater

treatment facility. A closed bottle test, conducted according to EC directive 92/69/EEC, was initiated

with 2 mg/L of γ-HCH in a 25 mg/L slurry of activated sludge in mineral nutrient medium, under aerobic

conditions. γ-HCH achieved 100% degradation based on theoretical oxygen uptake after 9 days (Lapertot

and Pulgarin 2006).

HEXACHLOROCYCLOHEXANE (HCH) 256

5. POTENTIAL FOR HUMAN EXPOSURE

5.5 LEVELS IN THE ENVIRONMENT

Reliable evaluation of the potential for human exposure to HCH depends, in part, on the reliability of

supporting analytical data from environmental samples and biological specimens. Concentrations of

HCH in unpolluted atmospheres and in pristine surface waters are often so low as to be near the limits of

current analytical methods. In reviewing data on HCH levels monitored or estimated in the environment,

it should also be noted that the amount of chemical identified analytically is not necessarily equivalent to

the amount that is bioavailable.

Table 5-5 shows the lowest limit of detections that are achieved by analytical analysis in environmental

media. An overview summary of the range of concentrations detected in environmental media, based on

the most recent data available, post-cancellation of γ-HCH as a pesticide, is presented in Table 5-6.

Table 5-5. Lowest Limit of Detection Based on Standards

Media

Detection limit

Reference

Air

0.2 pg/m

– 200 ng/m

(α-, β-, γ-HCH)

EPA 1999d

Drinking water

0.0053 μg/L (α-HCH)

0.0036 μg/L (β-HCH)

0.0060 μg/L (γ-HCH)

0.0020 μg/L (δ-HCH)

EPA 1995

Surface water and groundwater

7 pg/L – 0.0053 μg/L (α-HCH)

6 pg/L – 0.0036 μg/L (β-HCH)

9 pg/L – 0.0060 μg/L (γ-HCH)

5 pg/L – 0.0020 μg/L (δ-HCH)

EPA 1995, 2007

Soil

6 ng/L; 1.3 ng/kg (α-HCH)

7 ng/L; 0.6 ng/kg (β-HCH)

11 ng/L; 0.7 ng/kg (γ-HCH)

5 ng/L; 2.0 ng/kg (δ-HCH)

EPA 2000b, 2007

Sediment

0.500 μg/kg; 6 ng/L (α-HCH)

0.221; 7 ng/L (β-HCH)

0.200 μg/kg; 11 ng/L (γ-HCH)

5 ng/L (δ-HCH)

EPA 2000b; USGS 2003

Whole blood

1 ppb (α-, β-, γ-HCH)

1.3 ng/g lipid (β-HCH)

0.92 ng/g lipid (γ-HCH)

CDC 2019; EPA 1980

Detection limits based on using appropriate preparation and analytics. These limits may not be possible in all

situations.

HEXACHLOROCYCLOHEXANE (HCH) 257

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-6. Summary of Ambient Environmental Levels of HCH

Media

Low

High

Reference

α-HCH

Outdoor air (ng/m

)

0.00016

0.017

WQP 2023

Indoor air

No data

Surface water (ng/L)

0.1

1.7

WQP 2023

Groundwater

Not detected

WQP 2023

Drinking water

No data

Food

Not detected

FDA 2020b

Soil and sediment

Not detected

WQP 2023

β-HCH

Outdoor air (ng/m

)

0.00034

0.064

WQP 2023

Indoor air

No data

Surface water (ng/L)

0.11

1.2

WQP 2023

Groundwater

Not detected

WQP 2023

Drinking water

No data

Food

Not detected

FDA 2020b

Soil and sediment (μg/kg)

0.032

0.39

WQP 2023

γ-HCH

Outdoor air (ng/m

)

<1.7

No data

EPA 2021

Indoor air

No data

Surface water

No data

Groundwater

No data

Drinking water

No data

Food

Not detected

FDA 2020b

Soil and sediment

No data

δ-HCH

Outdoor air

Not detected

WQP 2023

Indoor air

No data

Surface water (ng/L)

0.44

3.7

WQP 2023

Groundwater

Not detected

WQP 2023

Drinking water

No data

Food

Not detected

FDA 2020b

Soil and sediment

Not detected

WQP 2023

HCH, technical grade

Outdoor air

No data

Indoor air

No data

Surface water

No data

Groundwater

No data

Drinking water

No data

HEXACHLOROCYCLOHEXANE (HCH) 258

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-6. Summary of Ambient Environmental Levels of HCH

Media

Low

High

Reference

Food

No data

Soil and sediment (μg/kg)

0.47

1.26

WQP 2023

Detections of HCH in air, water, and soil at NPL sites are summarized in Table 5-7.

Table 5-7. Hexachlorocyclohexanes (HCHs); Levels in Water, Soil, and Air of

National Priorities List (NPL) Sites

Medium

Median

Geometric

mean

Geometric

standard

deviation

Number of

quantitative

measurements

NPL sites

α-HCH

Water (ppb)

0.987

1.08

45.2

Soil (ppb)

3,390

2,970

156

Air (ppbv)

0.0016

0.0010

β-HCH

Water (ppb)

0.68

1.09

18.7

Soil (ppb)

950

911

61.7

Air (ppbv)

0.0017

0.00080

7.1

γ-HCH

Water (ppb)

0.515

0.819

49.2

Soil (ppb)

2,800

2,090

127

Air (ppbv)

0.0044

0.0038

δ-HCH

Water (ppb)

0.57

1.18

34.5

Soil (ppb)

1,100

392

71.9

Air (ppbv)

0.0002

0.00016

1.5

HCH, technical grade

Water (ppb)

0.86

3.0

Soil (ppb)

8,700

2,300

Air (ppbv)

0.000017

Concentrations found in ATSDR site documents from 1981 to 2022 for 1,868 NPL sites (ATSDR 2022). Maximum

concentrations were abstracted for types of environmental media for which exposure is likely. Pathways do not

necessarily involve exposure or levels of concern.

HEXACHLOROCYCLOHEXANE (HCH) 259

5. POTENTIAL FOR HUMAN EXPOSURE

5.5.1 Air

HCH isomers have been detected in ambient air. The highest concentrations were found prior to γ-HCH

agricultural use restrictions; available monitoring data after the restriction and ban of γ-HCH pesticides

showed a gradual decrease and the results of the most recent monitoring studies are below the parts per

billion range. The results of outdoor air monitoring studies are presented in Table 5-8. Precipitation

samples, if available, are included in Table 5-8 because they reflect removal of atmospheric HCH.

One reference to indoor air monitoring was located in the literature search. In a study of preschool

children’s potential exposure to pesticides in North Carolina, indoor air samples from 13 daycare centers

and 129 homes of the preschool children (ages 20–66 months) were collected between 2000 and 2001

(Morgan et al. 2014). γ-HCH was detected in ranges of below the limit of detection (<0.09 ng/m

) to

18.5 ng/m

in the children’s homes and <0.09–8.97 ng/m

in the preschools. Detection frequencies were

13 and 20%, respectively. Seventy-four percent of the homeowners reported applying insecticides at their

homes, and 90% of these had applied an insecticide in the past year before sampling. Among the daycare

centers, 62% reported using insecticides, and 88% of those reported usage within a year of sample

collection (Morgan et al. 2014).

5.5.2 Water

Water monitoring data are presented in Table 5-9. HCH isomers have been detected in surface water,

groundwater, and drinking water. The highest concentrations were found in groundwater below a facility

that processed pesticides and stored wastes in unlined trenches until 1996 (Law et al. 2004). A study of

the same site some years later still detected HCH isomers (Chartrand et al. 2015). Generally, surface

water concentrations are lower than those detected in groundwater. Data from the EPA’s Water Quality

Portal (WQP), a system that maintains water monitoring data from stations across the United States, have

been divided into two categories: prior to γ-HCH pesticide cancellation (years up to and including 2006)

and recent years post-cancellation (WQP 2023). Although recent data are limited, a decrease in surface

and groundwater concentrations of α-, β-, and δ-HCH can be seen in this dataset; data for γ-HCH were not

reported. From other studies, a decrease of γ-HCH in surface water can be observed, possibly due to use

limitations; trends for drinking water and groundwater are not as clear. Most recent monitoring data

report concentrations below the parts per billion range for surface water and groundwater.

HEXACHLOROCYCLOHEXANE (HCH) 260

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-8. Outdoor Air Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic type

Date(s)

Range

Mean

Notes

Reference

α-HCH

Alabama

Not reported

January–October 1996

and May 1997

0.092 ng/m

Jantunen et

al. 2000

Eagle Harbor,

Michigan; Sleeping

Bear Dunes State

Park, Michigan;

Sturgeon Point,

New York

Rural

1990–1997

0.110–

0.140 ng/m

Cortes and

Hites 2000

Chesapeake Bay

Rural and

agricultural

April 2000–September

2003; excluding winter

months

0.002–

0.142 ng/m

0.026 ng/m

Gas phase; average of

averages at three sites;

detection frequency 99–100%

Goel et al.

2010

Chesapeake Bay

Rural and

agricultural

April 2000 –September

2003; excluding winter

months

0.0012 ng/m

Particulate phase; detection

frequency 1%

Goel et al.

2010

Chesapeake Bay

Rural and

agricultural

April 2000–September

2003; excluding winter

months

0.2–11 ng/L

1.7 ng/L

Rainwater; average of

averages at three sites;

detection frequency 3–18%

Goel et al.

2010

Youngstown, Ohio

Urban/suburban

2000–2001

0.051 ng/m

Shen et al.

2004

Solomons, Maryland

Rural

2000–2001

0.091 ng/m

Shen et al.

2004

Wilmington, North

Carolina

Urban/suburban

2000–2001

0.015 ng/m

Shen et al.

2004

Turkey Point,

Florida

Rural

2000–2001

0.029 ng/m

Shen et al.

2004

Muscle Shoals

Suburban/rural

2000–2001

0.056 ng/m

Shen et al.

2004

United States

Ambient air

2015–2019

0.00016–

0.017 ng/m

0.0042 ng/m

Detected in 83% of

481 samples; no data reported

for 2020–2023

WQP 2023

HEXACHLOROCYCLOHEXANE (HCH) 261

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-8. Outdoor Air Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic type

Date(s)

Range

Mean

Notes

Reference

β-HCH

United States

Ambient air

2015–2018

0.00034–

0.064 ng/m

0.005 ng/m

Detected in 28% of

481 samples; no data reported

for 2020–2023

WQP 2023

γ-HCH

College Station,

Texas

Rural

1979–1980

0.01–

1.60 ng/m

0.23 ng/m

Ground level, ambient air

Atlas and

Giam 1988

College Station,

Texas

Rural

1979–1980

0.30–

7.8 ng/L

2.81 ng/L

Rainwater samples

Atlas and

Giam 1988

Adirondack

Mountains, New

York

Not reported

1985

0.509 ng/m

Troposphere samples

Knap and

Binkley 1991

Newport News,

Virginia

Not reported

1988

0.021 ng/m

Troposphere samples

Knap and

Binkley 1991

Alabama

Not reported

January–October 1996

and May 1997

0.050 ng/m

Jantunen et

al. 2000

Eagle Harbor,

Michigan; Sleeping

Bear Dunes State

Park, Michigan;

Sturgeon Point,

New York

Rural

1990–1997

0.024–

0.062 ng/m

Cortes and

Hites 2000

Lake Superior

Not reported

1984; wetfall season

3.0 ng/L

Rainwater samples, annual

loading rate of 2.0 μg/m

/year

Strachan

1988

Portland, Oregon

Urban

1982

0.45–1 ng/L

Rain and snow water

Pankow et al.

1984

Hawaii

Not reported

1970–1971

1–19 ng/L

5 ng/L

Rainwater

Bevenue et

al. 1972

Youngstown, Ohio

Urban/suburban

2000–2001

0.049 ng/m

Shen et al.

2004

Solomons, Maryland

Rural

2000–2001

0.072 ng/m

Shen et al.

2004

HEXACHLOROCYCLOHEXANE (HCH) 262

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-8. Outdoor Air Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic type

Date(s)

Range

Mean

Notes

Reference

Wilmington, North

Carolina

Urban/suburban

2000–2001

0.026 ng/m

Shen et al.

2004

Turkey Point,

Florida

Rural

2000–2001

0.031 ng/m

Shen et al.

2004

Muscle Shoals

Suburban/

agricultural

2000–2001

0.055 ng/m

Shen et al.

2004

North Carolina

Not reported

2000–2001

<0.09–

0.11 ng/m

Air samples collected outside

daycare centers; detection

frequency 8%

Morgan et al.

2014

North Carolina

Not reported

2000–2001

<0.09–

6.15 ng/m

Air samples collected outside

students; homes; detection

frequency 12%

Morgan et al.

2014

Chesapeake Bay

Rural and

agricultural

April 2000–September

2003; excluding winter

months

0.0012–

0.382 ng/m

0.049 ng/m

Gas phase; average of

averages at three sites;

detection frequency 81–100%

Goel et al.

2010

Chesapeake Bay

Rural and

agricultural

April 2000–September

2003; excluding winter

months

0.0013–

0.027 ng/m

0.024 ng/m

Particulate phase; average of

averages at two sites; detection

frequency 2–7%

Goel et al.

2010

Chesapeake Bay

Rural and

agricultural

April 2000–September

2003; excluding winter

months

0–35 ng/L

4.0 ng/L

Rainwater; average of

averages at two sites; detection

frequency 1–61%

Goel et al.

2010

Texas

Various ambient air

monitoring sites

January–December

2007

0.005 ng/m

Detected in 20 samples; below

the limit of detection in

345 samples

EPA 2021

Texas

Various ambient air

monitoring sites

January–December

2008

<1.7 ng/m

Below the limit of detection in

488 samples

EPA 2021

Texas

Various ambient air

monitoring sites

January–June 2009

<1.7 ng/m

Below the limit of detection in

120 samples

EPA 2021

HEXACHLOROCYCLOHEXANE (HCH) 263

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-8. Outdoor Air Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic type

Date(s)

Range

Mean

Notes

Reference

δ-HCH

United States

Ambient air

2015–2019

Not detected in 26 samples; no

data reported for 2020–2023

WQP 2023

Liquid unit conversion: 1 ng/L = 1 ppt = 0.001 ppb; gaseous unit conversion: ppbv = ([concentration ng/m

] x 0.001) / 11.89, assuming standard temperature and

pressure.

As of June 2023.

Data collected by USGS monitoring stations across the United States; mean and ranges do not reflect samples reported as not detected/below detection limit.

ND = not detected; USGS = U.S. Geological Survey

HEXACHLOROCYCLOHEXANE (HCH) 264

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-9. Water Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic type

Date(s)

Range

Mean

Notes

Reference

α-HCH

Lake

Superior

Surface water

Spring 1997

2.8 ng/L

Marvin et al.

2004

Lake Erie

Surface water

Spring 1998

0.41 ng/L

Marvin et al.

2004

Lake Ontario

Surface water

Spring 1998

0.40 ng/L

Marvin et al.

2004

York River

estuary

Surface water

June 1998–

April 1999

~0.025–

0.175 ng/L

Concentrations were lower in freshwater

areas than areas with higher salinity

Padma and

Dickhut 2002

United States

Surface water

1978–2006

2.93x10

-5

–

55,000 ng/L

150 ng/L

Detected in 0.5% of 35,766 samples

WQP 2023

United States

Surface water

2020

Not detected in 775 samples

WQP 2023

United States

Surface water

2021

0.11–

0.976 ng/L

0.54 ng/L

Detected in 0.2% of 902 samples

WQP 2023

United States

Surface water

2022

0.1–1.7 ng/L

0.28 ng/L

Detected in 2% of 945 samples

WQP 2023

United States

Surface water

2023

Not detected in 9 samples

WQP 2023

United States

Surface water at

Portland Harbor

Superfund Site

2003–2006

4.2x10

-5

–

0.002 ng/L

0.026

Detected in 45% of 193 samples

WQP 2023

United States

Groundwater

1981–2006

1.1–5,000

ng/L

153 ng/L

Detected in 0.3% of 16,493 samples

WQP 2023

United States

Groundwater

2020, 2022

Not detected in 125 samples; no data

reported for 2021 or 2023

WQP 2023

United States

Groundwater at

EPA Region 10

Superfund Sites

1987–2002

Not detected in 396 samples

WQP 2023

United States

Groundwater at

Boomsnub

Superfund Site

1995

Not detected in 18 samples

WQP 2023

HEXACHLOROCYCLOHEXANE (HCH) 265

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-9. Water Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic type

Date(s)

Range

Mean

Notes

Reference

Northeastern

Florida

Groundwater below

active pesticide

reformulating and

packaging facility

2000

58–

5.0x10

ng/L

51,000 ng/L

Samples collected from 19 shallow wells;

not detected (<20 ng/L) in 6 wells; mean

and ranges do not reflect samples reported

as not detected/below detection limit

Law et al. 2004

Northeastern

Florida

Groundwater below

active pesticide

reformulating and

packaging facility

2000

30–

4.2x10

ng/L

44,000 ng/L

Samples collected from 15 deep wells; not

detected (<20 ng/L) in 5 wells; mean and

ranges do not reflect samples reported as

not detected/below detection limit

Law et al. 2004

Northeastern

Florida

Surface water near

active pesticide

reformulating and

packaging facility

2000

660–680 ng/L

670 ng/L

Three samples collected from creek

adjacent to the site; not detected

(<20 ng/L) in one sample; mean and

ranges do not reflect samples reported as

not detected/below detection limit

Law et al. 2004

β-HCH

United States

Surface water

1980–2006

0.0385–

80,000 ng/L

1,260 ng/L

Detected in 1% of 7,198 samples

WQP 2023

United States

Surface water

2020

Not detected in 248 samples

WQP 2023

United States

Surface water

2021

0.18–0.84 ng/L

0.49 ng/L

Detected in 4% of 221 samples

WQP 2023

United States

Surface water

2022

0.11–1.2 ng/L

0.42 ng/L

Detected in 8% of 454 samples

WQP 2023

United States

Surface water

2023

Not detected in 5 samples

WQP 2023

United States

Surface water

Portland Harbor

Superfund Site

2004–2006

0.00017–

0.0337

0.0060

Detected in 25% of 190 samples

WQP 2023

United States

Groundwater

1981–2006

10–300

ng/L

48 ng/L

Detected in 1% of 2,478 samples

WQP 2023

United States

Groundwater

2020

Not detected in 3 samples; no data

reported for 2021–2023

WQP 2023

United States

Groundwater at

EPA Region 10

Superfund Sites

1987–2002

Not detected in 395 samples

WQP 2023

United States

Groundwater at

Boomsnub

Superfund Site

1995

Not detected in 18 samples

WQP 2023

HEXACHLOROCYCLOHEXANE (HCH) 266

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-9. Water Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic type

Date(s)

Range

Mean

Notes

Reference

Northeastern

Florida

Groundwater below

active pesticide

reformulating and

packaging facility

2000

30–43,000 ng/L

12,000 ng/L

Samples collected from 19 shallow wells;

not detected (<20 ng/L) in 8 wells; mean

and ranges do not reflect samples reported

as not detected/below detection limit

Law et al. 2004

Northeastern

Florida

Groundwater below

active pesticide

reformulating and

packaging facility

2000

82–820 ng/L

340 ng/L

Samples collected from 15 deep wells; not

detected (<20 ng/L) in 8 wells; mean and

ranges do not reflect samples reported as

not detected/below detection limit

Law et al. 2004

Northeastern

Florida

Surface water near

active pesticide

reformulating and

packaging facility

2000

38–440 ng/L

300 ng/L

Three samples collected from creek

adjacent to the site

Law et al. 2004

γ-HCH

New Jersey

Wells

Not reported

(1981 or

earlier)

NR–900 ng/L

1,076 wells, not detected in around half of

samples

Page 1981

Chesterfield

County,

South

Carolina

Rural drinking

water

Not reported

(1978 or

earlier)

0–93 ng/L

23 ng/L

Sandhu et al.

1978

Hampton,

South

Carolina

Rural drinking

water

Not reported

(1978 or

earlier)

0–319 ng/L

147 ng/L

Sandhu et al.

1978

Cincinnati,

Ohio

Drinking water

Not reported

(1976 or

earlier)

0.01 ng/L

Keith et al. 1976

Oahu, Hawaii

Drinking water

1970–1971

0.2 ng/L

Bevenue et al.

1972

HEXACHLOROCYCLOHEXANE (HCH) 267

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-9. Water Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic type

Date(s)

Range

Mean

Notes

Reference

Ozark

Plateaus

Province of

Arkansas,

Kansas,

Missouri, and

Oklahoma

Groundwater

April–

September

1993

28 and 32 ng/L

Detected in two samples from domestic

wells

Adamski and

Pugh 1996

Connecticut

Drinking water well

Not reported

(1999 or

earlier)

60 ng/L

Eitzer and

Chevalier 1999

United States

Drinking water

1998–2005

1–690 ng/L

62 ng/L

Samples collected from 44 states across

the United States; ranges and averages do

not include samples reported to be below

the method reporting level

EPA 2010

Washington,

D.C. and

Denver,

Colorado

Surface water

Not reported

(1984 or

earlier)

52–100 ng/L

Cole et al. 1984

Niagara

River

Surface water

1980–1981

2.1 ng/L

Mean of 99% samples

Kuntz and Warry

1983

Lake

Michigan

tributary

streams

Surface water

Not reported

(1974 or

earlier)

ND–150 ng/L

EPA 1974

United States

Surface water

Not reported

(1985 or

earlier)

Median: 20 ng/L

Detected in 27% of 4,505 samples

Staples et al.

1985

Lake Ontario

Surface water

1983

0.806–1.85

ng/L

Biberhofer and

Stevens 1987

Patuxent

River

Surface water

1995

1.0 ng/L

Harman-Fetcho

et al. 1999

Lake

Superior

Surface water

Spring 1997

0.38 ng/L

Marvin et al.

2004

HEXACHLOROCYCLOHEXANE (HCH) 268

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-9. Water Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic type

Date(s)

Range

Mean

Notes

Reference

Lake Erie

Surface water

Spring 1998

0.32 ng/L

Marvin et al.

2004

Lake Ontario

Surface water

Spring 1998

0.24 ng/L

Marvin et al.

2004

York River

estuary

Surface water

June 1998–

April 1999

~0.04–

0.21 ng/L

Concentrations were higher in freshwater

areas than areas with higher salinity

Padma and

Dickhut 2002

Northeastern

Florida

Groundwater below

active pesticide

reformulating and

packaging facility

2000

110–

6.6x10

ng/L

99,000 ng/L

Samples collected from 19 shallow wells;

not detected (<20 ng/L) in 11 wells; mean

and ranges do not reflect samples reported

as not detected/below detection limit

Law et al. 2004

Northeastern

Florida

Groundwater below

active pesticide

reformulating and

packaging facility

2000

120–

3.6x10

ng/L

73,000 ng/L

Samples collected from 15 deep wells; not

detected (<20 ng/L) in 10 wells; mean and

ranges do not reflect samples reported as

not detected/below detection limit

Law et al. 2004

Northeastern

Florida

Surface water near

active pesticide

reformulating and

packaging facility

2000

440–470 ng/L

460 ng/L

Three samples collected from creek

adjacent to the site; not detected

(<20 ng/L) in one sample; mean and

ranges do not reflect samples reported as

not detected/below detection limit

Law et al. 2004

δ-HCH

United States

Surface water

1980–2006

0.00339–

75,000 ng/L

1.56 ng/L

Detected in 0.8% of 7,106 samples

WQP 2023

United States

Surface water

2020

Not detected in 248 samples

WQP 2023

United States

Surface water

2021

0.48–1 ng/L

0.72 ng/L

Detected in 3% of 221 samples

WQP 2023

United States

Surface water

2022

0.44–3.7 ng/L

0.97 ng/L

Detected in 5% of 545 samples

WQP 2023

United States

Surface water

2023

Not detected in 5 samples

WQP 2023

United States

Surface water

Portland Harbor

Superfund Site

2004–2006

0.000508–1.67

0.14

Detected in 14% of 190 samples

WQP 2023

United States

Ground water

1980–2006

20–300 ng/L

4.8 ng/L

Detected in 1% of 2,417 samples

WQP 2023

United States

Ground water

2020

Not detected in three samples; no data

reported for 2021–2023

WQP 2023

HEXACHLOROCYCLOHEXANE (HCH) 269

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-9. Water Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic type

Date(s)

Range

Mean

Notes

Reference

United States

Groundwater at

EPA Region

10 Superfund Sites

1987–2002

Not detected in 391 samples

WQP 2023

United States

Groundwater at

Boomsnub

Superfund Site

1995

Not detected in 18 samples

WQP 2023

Northeastern

Florida

Groundwater below

active pesticide

reformulating and

packaging facility

2000

40–

5.7x10

ng/L

74,000 ng/L

Samples collected from 19 shallow wells;

not detected (<20 ng/L) in 8 wells; mean

and ranges do not reflect samples reported

as not detected/below detection limit

Law et al. 2004

Northeastern

Florida

Groundwater below

active pesticide

reformulating and

packaging facility

2000

36–

2.9x10

ng/L

26,000 ng/L

Samples collected from 15 deep wells; not

detected (<20 ng/L) in 3 wells; mean and

ranges do not reflect samples reported as

not detected/below detection limit

Law et al. 2004

Northeastern

Florida

Surface water near

active pesticide

reformulating and

packaging facility

2000

55–970 ng/L

640 ng/L

Three samples collected from creek

adjacent to the site

Law et al. 2004

HCH, mixture

Northeastern

Florida

Groundwater below

contaminated site

Not reported

(2015 or

earlier)

30,000–

4.2x10

ng/L

Range reported for α-, γ-, and δ-HCH

Chartrand et al.

2015

Liquid unit conversion: 1 ng/L = 1 ppt = 0.001 ppb.

Data collected by USGS monitoring stations across the United States; mean and ranges do not reflect samples reported as not detected/below detection limit.

As of June 2023.

ND = not detected; USGS = U.S. Geological Survey

HEXACHLOROCYCLOHEXANE (HCH) 270

5. POTENTIAL FOR HUMAN EXPOSURE

5.5.3 Sediment and Soil

HCH has been detected in soil and sediment as a result of agricultural use. Soil and sediment monitoring

data are presented in Table 5-10. Data from the EPA’s WQP has been divided into two categories to

reflect potential detection decreases as a result of the γ-HCH pesticide cancellation in 2006 (WQP 2021).

A clear trend could not be discerned from the data, possibly due to the large ranges reflecting differences

in land use. Most recent monitoring data report concentrations at the parts per billion range.

5.5.4 Other Media

HCH isomers have been detected in aquatic organisms; the results of these monitoring studies are

summarized in Table 5-11. Data on terrestrial organism monitoring were not located. Schmitt et al.

(1985) reported the results of a monitoring study of fish tissues from 107 freshwater stations in the United

States from 1976 to 1981, which supported a decline in tissue occurrence of detectable α- and γ-HCH

residues in aquatic organisms. α- and β-HCH have been detected in organisms as recently as 2018,

however (WQP 2021). The most recent monitoring studies have detected HCH isomers in aquatic

organisms in the parts per billion range.

Historically, as a result of pesticide use, γ-HCH was detected in meat, vegetables, and other food items,

both imported to and produced in the United States. Due to the discontinued agricultural use of γ-HCH

by the United States and many other countries, residues are typically no longer detected in food products.

γ-HCH was detected in 5 out of 612 imported rice samples at a maximum concentration of 0.03 ppm

during an FDA pesticide monitoring study conducted in 1993–1994 (Roy et al. 1997). A 10-year (1982–

1991) FDA study of ready-to-eat foods commonly consumed in the United States showed that α-, β-, δ-,

and γ-HCH were frequently detected (Rogers et al. 1995). The results of this study reported average

concentrations of 0.0010, 0.0027, 0.0030, and 0.0012 ppm for α-, β-, δ-, and γ-HCH isomers,

respectively, in 243 ready-to-eat foods. HCH isomers were also detected in the following feed types

formulated for infants and toddlers and in adult diet foodstuffs: whole milk and other dairy products;

meat, fish, and poultry; oils and fats; vegetables; and sugars and adjuncts (Gartrell et al. 1986a, 1986b).

γ-HCH residues were detected in fat samples of domestic farm animals collected in Ontario, Canada, in

1986–1988. Mean concentrations in fat from chickens, turkeys, beef, lamb, and pork ranged from

0.012 to 0.032 ppm; the mean concentration in hen eggs was 0.008 ppm (Frank et al. 1990). A pesticide

HEXACHLOROCYCLOHEXANE (HCH) 271

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-10. Soil and Sediment Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic

type

Date(s)

Range

Mean

Notes

Reference

α-HCH

Alabama

Soil

Not

reported

(1999 or

earlier)

0–

0.269 µg/kg

Detected in 26 of 39 soils from

6 regions

Harner et al. 1999

Sequoia National Park, Rocky

Mountain National Park, Mt.

Rainier National Park, Denali

National Park, Noatak

National Preserve, and Gates

of the Arctic National Park

and Preserve

Sediment core

from deepest

point in several

lakes

2003–

2005

<0.8 µg/kg

Not detected

Genualdi et al. 2011

United States

Soil and

sediment

1978–2006

4.0x10

-5

–

879 µg/kg

3.0 µg/kg

Detected in 8% of 9,360 samples

WQP 2023

United States

Soil and

sediment

2020–2021

Not detected in 178 samples; no

data reported for 2022–2023

WQP 2023

United States

Soil and

sediment at

Lower

Duwamish

Waterway

Superfund Site

1991–2006

0.14–

1.8 µg/kg

0.59 µg/kg

Detected in 2% of 335 samples

WQP 2023

United States

Soil/sediment

at Portland

Harbor

Superfund Site

1997–2006

0.00238–

120 µg/kg

1.6 µg/kg

Detected in 15% of 1,772 samples

WQP 2023

United States

Soil at Delta

400 West

Plume

2004

Not detected in 7 samples

WQP 2023

HEXACHLOROCYCLOHEXANE (HCH) 272

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-10. Soil and Sediment Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic

type

Date(s)

Range

Mean

Notes

Reference

β-HCH

United States

Soil and

sediment

1983–2006

4.0x10

-5

–

4,230 µg/kg

18 µg/kg

Detected in 8% of 8,106 samples

WQP 2023

United States

Soil and

sediment

2020

0.032–

0.39 µg/kg

0.17 µg/kg

Detected in 4% of 142 samples

WQP 2023

United States

Soil and

sediment

2021

Not detected in 8 samples; no

data reported for 2022–2023

WQP 2023

United States

Soil and

sediment at

Lower

Duwamish

Waterway

Superfund Site

1991–2006

0.087–

13 µg/kg

4.1 µg/kg

Detected in 1% of 327 samples

WQP 2023

United States

Soil/sediment

at Portland

Harbor

Superfund Site

1997–2006

0.00138–

318 µg/kg

3.9 µg/kg

Detected in 42% of 1,819 samples

WQP 2023

United States

Soil at Delta

400 West

Plume

2004

Not detected in 7 samples

WQP 2023

γ-HCH

Alabama, Arkansas, Georgia,

Illinois, Iowa

Soil

Not

reported

(1974 or

earlier)

10–

150 µg/kg

52 µg/kg

Crockett et al. 1974

Alabama

Soil

Not

reported

(1999 or

earlier)

0–1.07 µg/kg

Detected in 26 of 39 soils from

6 regions

Harner et al. 1999

HEXACHLOROCYCLOHEXANE (HCH) 273

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-10. Soil and Sediment Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic

type

Date(s)

Range

Mean

Notes

Reference

Niagara River

Suspended

sediment

Not

reported

(1983 or

earlier)

2 µg/kg

Detection frequency 33%

Kuntz and Warry 1983

Lake Ontario

Settling

particulates

1982

2.4 µg/kg

Oliver and Charlton

1984

James River, Virginia

Creek

sediments

1976

7.3–

8.5 µg/kg

Saleh et al. 1978

Gulf of Mexico

Sediment

1987

<0.02–

1.74 µg/kg

0.07 µg/kg

Detection frequency 19%

Sericano et al. 1990

Around the Great Lakes

Sediment

May 1989

<0.10–

0.99 µg/kg

wet weight

Verbrugge et al. 1991

Indian River Lagoon, Florida

Sediment from

impoundments

along the river

Not

reported

(1992 or

earlier)

9.4–

34.4 µg/kg

33 sediment samples from

11 impoundment

Wang et al. 1992

δ-HCH

United States

Soil and

sediment

1983–2006

0.0078–

89.8 µg/kg

3.4 µg/kg

Detected in 6% of 5,747 samples

WQP 2023

United States

Soil and

sediment

2020–2021

Not detected in 162 samples; no

data reported for 2022–2023

WQP 2023

United States

Soil and

sediment at

Lower

Duwamish

Waterway

Superfund Site

1991–2006

0.081–

1,100 µg/kg

160 µg/kg

Detected in 3% of 254 samples

WQP 2023

United States

Soil/sediment

at Portland

Harbor

Superfund Site

1997–2006

0.00216–

45.4 µg/kg

1.3 µg/kg

Detected in 9% of 1,797 samples

WQP 2023

HEXACHLOROCYCLOHEXANE (HCH) 274

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-10. Soil and Sediment Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Geographic

type

Date(s)

Range

Mean

Notes

Reference

United States

Soil at Delta

400 West

Plume

2004

Not detected in 7 samples

WQP 2023

HCH, mixture

South Carolina

0–10 cm

surface soils

from cotton

fields

November

1999

0.1–0.54

µg/kg dry

weight

0.27 µg/kg

dry weight

Reported as sum of α-, β-, and

γ-isomers; not detected

(<0.1 µg/kg dry weight) in 10 of

16 samples; mean and ranges do

not reflect samples reported as not

detected/below detection limit

Kannan et al. 2003

Georgia

0–10 cm

surface soils

from cotton

fields

December

1999

0.16–

0.49 µg/kg

dry weight

0.33 µg/kg

dry weight

Reported as sum of α-, β-, and

γ-isomers; not detected

(<0.1 µg/kg dry weight) in 14 of

16 samples; mean and ranges do

not reflect samples reported as not

detected/below detection limit

Kannan et al. 2003

United States

Sediment

2017

0.47–

1.26 µg/kg

0.75 µg/kg

HCH isomer or mixture not

specified; detected in 19% of

42 samples

WQP 2023

Solid unit conversion: 1 µg/kg = 1 ppb.

Data collected by USGS monitoring stations across the United States; mean and ranges do not reflect samples reported as not detected/below detection limit.

As of July 2023.

ND = not detected; USGS = U.S. Geological Survey

HEXACHLOROCYCLOHEXANE (HCH) 275

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-11. Organism Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Species

Date(s)

Range

Mean

Notes

Reference

α-HCH

Southwestern and

Midwestern United

States

Freshwater Fish

1980–

1981

0.03–

0.04 ng/g

Highest concentrations detected

from 107 monitoring stations

across the United States

Schmitt et al.

1985

United States

Freshwater fish

1984

NR–

10 ng/g

<10 ng/g

Schmitt et al.

1990

Louisiana section of

the Mississippi River

Blue crab, cobia, flathead

catfish, freshwater drum, long-

nose gar, red drum, red snapper,

river shrimp, small-mouth

buffalo, spotted gar

1990–

1994

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Bigmouth buffalo

1990–

1994

2.4 ng/g

Average detection in 1 of

3 sampling years; not detected in

other years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Blue catfish

1990–

1994

0.333–

26.3 ng/g

Range of average detections in

3 of 4 sampling years; not

detected in other years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Carp

1990–

1994

31.1 ng/g

Range of average detections in

3 of 4 sampling years; not

detected in other years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Channel catfish

1990–

1994

1.83–

7.23 ng/g

Range of average detections in

2 of 3 sampling years; not

detected in other years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Crawfish

1990–

1994

4.25 ng/g

Average detection in 1 of

1 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Largemouth bass

1990–

1994

1.00 ng/g

Average detection in 1 of

2 sampling years; not detected in

other years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Striped bass

1990–

1994

2.88 ng/g

Average detection in 1 of

2 sampling years; not detected in

other years

Watanabe et

al. 2003

HEXACHLOROCYCLOHEXANE (HCH) 276

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-11. Organism Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Species

Date(s)

Range

Mean

Notes

Reference

Louisiana section of

the Mississippi River

White bass

1990–

1994

1.44 ng/g

Average detection in 1 of

3 sampling years; not detected in

other years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

White crappie

1990–

1994

1.75 ng/g

Average detection in 1 of

3 sampling years; not detected in

other years

Watanabe et

al. 2003

Southwestern

Michigan

Adult green frogs

1998

0.02 ng/g

0.04 ppb detected in juvenile

frogs

Gilliland et al.

2001

Gulf of California

Clams (Chione californiensis)

Not

reported

(2015 or

earlier)

<0.005–

1.77 ng/g

wet weight

Detection frequency 16.7% in 1 of

3 study areas, not detected in

other areas; adipose tissue

samples; surrounding area has

primarily agricultural activity

Vargas-

Gonzalez et

al. 2016

Lake Apopka, Florida

Largemouth bass (Micropterus

salmoides)

March

2013

Limit of quantification 0.1–

0.5 ng/g wet weight

Dang et al.

2016

United States

Freshwater fish

2020–

2022

Not detected in 253 samples; no

data reported for 2023

WQP 2023

β-HCH

Upper Steele Bayou,

Mississippi

Fish

1988

ND–

20 ng/g

wet weight

Ford and Hill

1991

Upper Steele Bayou,

Mississippi

Snakes

1988

Ford and Hill

1991

Southwestern

Michigan

Adult green frogs

1998

0.01 ng/g

Not detected in juvenile frogs

Gilliland et al.

2001

Louisiana section of

the Mississippi River

Cobia, long-nose gar, red drum,

red snapper

1990–

1994

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Bigmouth buffalo

1990–

1994

2.25–

11.2 ng/g

Range of average detection in

3 of 3 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Blue catfish

1990–

1994

3.67–

8.33 ng/g

Range of average detection in

3 of 4 sampling years; not

detected in other year

Watanabe et

al. 2003

HEXACHLOROCYCLOHEXANE (HCH) 277

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-11. Organism Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Species

Date(s)

Range

Mean

Notes

Reference

Louisiana section of

the Mississippi River

Blue crab

1990–

1994

4.00–

11.0 ng/g

Range of average detections in

2 of 2 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Carp

1990–

1994

5.00–

11.3 ng/g

Range of average detections in

2 of 3 sampling years; not

detected in other years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Channel catfish

1990–

1994

0.333–

7.77 ng/g

Range of average detections in

3 of 4 sampling years; not

detected in other years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Crawfish

1990–

1994

27.5 ng/g

Average detection in 1 of

1 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Flathead catfish

1990–

1994

0.500 ng/g

Average detection in 1 of

1 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Freshwater drum

1990–

1994

0.333 ng/g

Average detection in 1 of

1 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Largemouth bass

1990–

1994

2.00 ng/g

Average detection in 1 of

2 sampling years; not detected in

other year

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

River shrimp

1990–

1994

8.67 ng/g

Average detection in 1 of

1 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Small-mouth buffalo

1990–

1994

0.25–

2.00 ng/g

Range of average detection in

3 of 4 sampling years; not

detected in other years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Spotted gar

1990–

1994

39.0 ng/g

Average detection in 1 of

1 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Striped bass

1990–

1994

5.50–

57.9 ng/g

Range of average detection in

2 of 2 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

White bass

1990–

1994

3.11 ng/g

Average detection in 1 of

3 sampling years; not detected in

other years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

White crappie

1990–

1994

1.00–

11.0 ng/g

Range of average detection in

2 of 3 sampling years; not

detected in other years

Watanabe et

al. 2003

HEXACHLOROCYCLOHEXANE (HCH) 278

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-11. Organism Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Species

Date(s)

Range

Mean

Notes

Reference

Gulf of California

Clams (C. californiensis)

Not

reported

(2015 or

earlier)

Limit of detection 0.01 ng/g wet

weight

Adipose tissue samples;

surrounding area has primarily

agricultural activity

Vargas-

Gonzalez et

al. 2016

Lake Apopka, Florida

Largemouth bass (M. salmoides)

March

2013

Limit of quantification 0.1–

0.5 ng/g wet weight

Dang et al.

2016

United States

Freshwater fish

2020

Not detected in 172 samples

WQP 2023

United States

Freshwater fish; Oncorhynchus

kisutch

2022

1.7–

1.8 ng/g

1.9 ng/g

Detected in 11% of 19 samples;

detected only in Oncorhynchus

kisutch (33% of 6 samples); no

data reported for 2021 or 2023

WQP 2023

γ-HCH

Gulf of Mexico

Oyster

1987

<0.25–

9.06 ng/g

1.74 ng/g

Detection frequency 80%

Sericano et al.

1990

United States

Freshwater fish

1980–

1981

0.02–

0.03 ng/g

Whole body concentrations were

>0.01 ng/g at 1 of 107 monitoring

stations

Schmitt et al.

1985

United States

Freshwater fish

1984

NR–

40 ng/g

<10 ng/g

Schmitt et al.

1990

Southwestern

Michigan

Adult green frogs

1998

0.07 ng/g

Not detected in juvenile frogs

Gilliland et al.

2001

Louisiana section of

the Mississippi River

Blue crab, channel catfish,

cobia, crawfish, flathead catfish,

freshwater drum, long-nose gar,

red drum

1990–

1994

Not detected

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Bigmouth buffalo

1990–

1994

1.00–

1.80 ng/g

Range of average detection in

2 of 3 sampling years; not

detected in other year

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Blue catfish

1990–

1994

2.25–

26.5 ng/g

Range of average detection in

3 of 4 sampling years; not

detected in other year

Watanabe et

al. 2003

HEXACHLOROCYCLOHEXANE (HCH) 279

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-11. Organism Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Species

Date(s)

Range

Mean

Notes

Reference

Louisiana section of

the Mississippi River

Carp

1990–

1994

0.714–

5.00 ng/g

Range of average detections in

2 of 3 sampling years; not

detected in other years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Largemouth bass

1990–

1994

1.00 ng/g

Average detection in 1 of

2 sampling years; not detected in

other year

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Red snapper

1990–

1994

0.333 ng/g

Average detection in 1 of

1 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

River shrimp

1990–

1994

1.67 ng/g

Average detection in 1 of

1 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Small-mouth buffalo

1990–

1994

0.250–

7.00 ng/g

Range of average detection in

4 of 4 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Spotted gar

1990–

1994

857 ng/g

Average detection in 1 of

1 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

Striped bass

1990–

1994

0.500–

1.25 ng/g

Range of average detection in

2 of 2 sampling years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

White bass

1990–

1994

7.56 ng/g

Average detection in 1 of

3 sampling years; not detected in

other years

Watanabe et

al. 2003

Louisiana section of

the Mississippi River

White crappie

1990–

1994

0.750–

1.20 ng/g

Range of average detection in

2 of 3 sampling years; not

detected in other years

Watanabe et

al. 2003

Gulf of California

Clams (C. californiensis)

Not

reported

(2015 or

earlier)

Not detected

Limit of detection 0.005 ng/g wet

weight; adipose tissue samples;

surrounding area has primarily

agricultural activity

Vargas-

Gonzalez et

al. 2016

HEXACHLOROCYCLOHEXANE (HCH) 280

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-11. Organism Monitoring Data for Hexachlorocyclohexanes (HCHs)

Locations

Species

Date(s)

Range

Mean

Notes

Reference

Lake Apopka, Florida

Largemouth bass (M. salmoides)

March

2013

0.8 ng/g wet

weight

(gastrointestinal

tract)

1.6 ng/g wet

weight (liver)

2.6 ng/g wet

weight (kidney)

0.8 ng/g wet

weight (spleen)

4.8 ng/g wet

weight (brain)

1.8 ng/g wet

weight (gonad)

1.3 ng/g wet

weight (muscle)

117.8 ng/g lipid (gastrointestinal

tract)

29.4 ng/g lipid (liver)

742.6 ng/g lipid (kidney)

102.0 ng/g lipid (spleen)

144.1 ng/g lipid (brain)

77.6 ng/g lipid (gonad)

125.2 ng/g lipid (muscle)

Dang et al.

2016

δ-HCH

Southwestern

Michigan

Adult green frogs

1998

0.03 ng/g

Not detected in juvenile frogs

Gilliland et al.

2001

Gulf of California

Clams (C. californiensis)

Not

reported

(2015 or

earlier)

<0.01–

1.97 ng/g

wet weight

Detection frequency 16.7% in 1 of

3 study areas, not detected in

other areas; adipose tissue

samples; surrounding area has

primarily agricultural activity

Vargas-

Gonzalez et

al. 2016

Lake Apopka, Florida

Largemouth bass (M. salmoides)

March

2013

Not detected

Limit of quantification 0.1–

0.5 ng/g wet weight

Dang et al.

2016

United States

Freshwater fish

2020

Not detected in 191 samples; no

data reported for 2022–2023

WQP 2023

Organism concentration unit conversion: 1 ng/g = 1 ppb.

As of June 2023.

Data collected by USGS monitoring stations across the United States; mean and ranges do not reflect samples reported as not detected/below detection limit.

Not detected; NR = not reported; USGS = U.S. Geological Survey

HEXACHLOROCYCLOHEXANE (HCH) 281

5. POTENTIAL FOR HUMAN EXPOSURE

residue screening program carried out by the H.E.B. Food Stores of San Antonio between 1989 and 1991

detected γ-HCH in 4 of 429 onion samples (detection limit 0.02 ppm); however, none of the positive

samples exceeded the action level for this commodity (Schattenberg and Hsu 1992). γ-HCH was detected

at levels of ≤10 ppm in 6 out of 5,784 fruit and vegetable commodities analyzed in Canada from 1992 to

1994 (Neidert and Saschenbrecker 1996). α-, β-, and γ-HCH were detected in butter samples from the

United States at mean levels of 0.38, 0.42, and 0.78 ppb, respectively (Kalantzi et al. 2001). HCH

isomers were also detected in butter samples from 20 other countries, with the highest levels being

observed in a single butter sample from India with reported concentrations of 98, 108, and 164 ppb for α-,

β-, and γ-HCH, respectively (Kalantzi et al. 2001).

Based on the most recent pesticide residue monitoring results published by the FDA from 2018, no

γ-HCH residues were detected on food products produced in or imported to the United States (FDA

2020a). The products sampled were broadly encompassing of domestic and imported food and

agricultural commodities, and included fruits, vegetables, grains, beans, nuts, honey, milk, and meat,

amongst many other categories. A recent study, however, detected averages of 0.22 ppb α-HCH and

0.77 ppb γ-HCH in tobacco products (n=20; cigarettes from one pack were pooled for analysis) purchased

in the United States (Quadroni and Bettinetti 2019). It is unclear if these products were domestic or

imported.

Strategies exist to reduce pesticide residues on food products. γ-HCH residues on tomatoes decreased by

23.9% 15 days after application of the pesticide (from 0.1956 to 0.1488 ppm). Processing the tomatoes

(e.g., pureeing, making tomato juice) reduced the residue levels by 100% after the waiting period;

however, washing the tomatoes reduced the residues by up to 55.9% (Bessar et al. 1991). An analysis of

pesticide residues in green coffee and after roasting indicated that technical-grade HCH was found in

green coffee at concentrations ranging from <0.005 to 0.204 ppm. However, storage and roasting reduced

the pesticide residues by 60–67% and up to 98%, respectively, with darker roasting resulting in the

greatest reduction (McCarthy et al. 1992).

5.6 GENERAL POPULATION EXPOSURE

Exposure of the general population to HCH has declined steadily since its use as a pesticide was

discontinued. Human exposure to γ-HCH may result from environmental exposures to contaminated

water or soil, or possible ingestion of small amounts in drinking water. Historically, γ-HCH and its most

persistent metabolite, β-HCH, have been detected in blood, adipose tissue, and breast milk. Based on the

HEXACHLOROCYCLOHEXANE (HCH) 282

5. POTENTIAL FOR HUMAN EXPOSURE

most recent U.S. population survey, γ-HCH is generally no longer detected in blood, but β-HCH still is

(CDC 2019). This is consistent with the decreased general population exposure to γ-HCH as a pesticide.

Medicinal exposure to γ-HCH can occur from prescription scabies and lice treatments. An analysis of

data from 238 families in Missouri between June 1989 and March 1990 indicated that 9.2% of the

families reported using Kwell shampoo (contains γ-HCH) for lice control on children (Davis et al. 1992).

In general, accidental or intentional ingestion of these products would lead to the highest exposures.

Worker exposure constitutes the next highest exposure population, although worker exposure is

decreasing in both the number of workers exposed and the levels of exposure. Lastly, the general

population receives the lowest levels, which occur mainly from ingestion of foods and water with γ-HCH

residues. Living near a waste disposal site contaminated with γ-HCH will also increase the likelihood of

exposure.

Ingestion of food containing pesticide residue, historically a significant route of exposure, is no longer

expected to be a likely route of non-medicinal human exposure to γ-HCH. During studies conducted

between 1982 and 1991, γ-HCH was detected in 4–6% of the foods collected in eight market basket

surveys from different regions of the United States (Gunderson 1988, 1995a, 1995b). The most recent

results of this survey reported no detections (limit of detection 0.4–2.8 ppb) in foods surveyed in 2017 for

α-, β-, γ-, or δ-HCH (FDA 2020b). γ-HCH was also not detected in domestic or imported food products

in the United States by the FDA (FDA 2020a). Foods representative of consumption patterns by eight

infant and adult population groups were prepared for consumption prior to analysis in a revision to FDA's

Total Diet Studies methodology. The estimated mean daily intakes (ng/kg body weight/day) of α-, β-,

and γ-HCH for these groups continuously decreased between all study periods (1982–1984, 1984–1986,

and 1986–1991). From 1986 to 1991 daily intakes ranged from 0.5 to 2.7 ng/kg/day for α-HCH, were all

<1 ng/kg/day for β-HCH, and ranged from 0.6 to 3.2 ng/kg/day for γ-HCH (Gunderson 1988, 1995a,

1995b). An estimated γ-HCH daily dietary intake based on 2003 FDA pesticide residue monitoring data

for fruits and vegetables was determined to be trace only for domestic produce and 0.00754 ng/kg/day for

imported produce (Katz and Winter 2009). While HCH isomers have been previously detected in

freshwater fish, lindane was not detected (<0.25 ng/mL) in the serum of Detroit area anglers who

consumed their catches, in 2013 (Wattigney et al. 2022). Because γ-HCH and its isomers were not

detected in most recently available food monitoring data, current daily intake can be assumed to be

negligible.

A small degree of exposure to γ-HCH from drinking water may be possible. α-, β-, and δ-HCH have

been detected in recent surface water samples, although these may not represent drinking water sources

HEXACHLOROCYCLOHEXANE (HCH) 283

5. POTENTIAL FOR HUMAN EXPOSURE

(WQP 2023). γ-HCH was detected in drinking water samples collected for the 1998 to 2005 EPA 6-year

review of drinking water quality (EPA 2010). Data for HCH were not reported for the most recent

available period, 2006–2011.

Contaminated soils, which have been sampled as recently as 2021, may present another exposure pathway

(WQP 2023). Studies in which soils containing 10 ppm radiolabeled γ-HCH were added to human skin

samples at quantities that exceeded monolayer coverage (5 mg soil/cm

skin) demonstrated mean γ-HCH

absorptions of 1.04% from sandy soils and 1.64% from silt soils (Duff and Kissel 1996). However, data

from soil absorption studies can vary due to factors such as the amount of soil added to skin, exposure

time, and possible evaporation of the contaminant.

The results of biomonitoring studies can be used as indicators of human exposures to HCH. The National

Human Adipose Tissue Survey (NHATS) conducted in 1982 showed that β-HCH (the most prevalent

HCH isomer in fatty tissue) was detected in 87% of 46 composite samples at concentrations <19–

570 ng/g (ppb) (EPA 1986). It was detected most often in postmortem samples collected from individuals

from the southern United States. In another survey conducted in 1970–1975, β-HCH was detected in

>90% of the postmortem human adipose tissue samples at an average level of 300 ppb (Kutz et al. 1979).

In a review of the NHATS data available from 1970 to 1983, EPA (1985c) reported that the estimated

1983 national median level of β-HCH was 80 ppb, in comparison to the historic level of 140 ppb. The

median level had decreased over time, but the compound continued to be detected in nearly 100% of the

population surveyed. Median levels were highest in the South census region and tended to increase with

age but had not been found to differ across the sexes or racial groups. A further analysis of the NHATS

data indicated that average β-HCH concentrations in fat had decreased from 0.45 ppm in 1970 to

approximately 0.16 ppm since 1981 (Kutz et al. 1991). In a similar study in Japan, levels of HCHs in the

adipose tissue of Japanese males increased from the late 1940s to 1966, coinciding with an increased

annual production of HCH, and began dropping when HCHs were banned in 1971, with only the only the

more persistent β-HCH isomer detected after 1974 (Loganathan et al. 1993). Recent adipose tissue

concentrations in the United States were not located, but the trend towards lower concentrations may have

continued following the discontinued use of γ-HCH as a pesticide.

A comparison of the levels of α- and β-HCH in the whole blood and biopsy fat of 25 patients showed

median levels of <0.04 ng/g (maximum, <0.04 ng/g [LOD]) and 0.13 ng/g (maximum, 2.60 ng/g) for the

blood and 1.1 ng/g (maximum, 9.6 ng/g) and 18.0 ng/g (maximum, 748.6 ng/g) for the fat tissue,

respectively (Mes 1992). A further comparison of β-HCH levels in breast milk and adipose tissue

HEXACHLOROCYCLOHEXANE (HCH) 284

5. POTENTIAL FOR HUMAN EXPOSURE

samples was made for populations living near the Great Lakes (Canada only) and in other Canadian

regions. Mean β-HCH levels in breast milk (0.6 ng/g, n=70 samples) and adipose tissue (23.4 ng/g,

n=16 samples) were lower near the Great Lakes than in other parts of Canada (0.8 [n=305 samples] and

30.8 ng/g [n=90 samples], respectively) (Mes and Malcolm 1992). In addition, studies indicate that

γ-HCH can also be present in breast milk at a previously reported average level of 0.006 ppm in Alberta,

Canada (Currie et al. 1979). In a study of 50 donors of breast milk in Oahu, Hawaii, Takahashi et al.

(1981) demonstrated HCH in 82% of the samples at a mean level of 81 ppb within a range of 0–480 ppb,

expressed in terms of extractable lipid.

γ-HCH was one of the most frequently detected pesticides in the blood of Virginia residents, although the

number of individuals sampled was not identified (Griffith and Blanke 1975). γ-HCH blood

concentrations were the highest in residents of the middle age group (41–60 years). Some of the

frequency of γ-HCH occurrence in the state was attributed to its common use in commercial vaporizers

and its presence in cigarette smoke (Griffith and Blanke 1975). NHANES analyzed blood and urine

specimens for the presence of HCH isomers. β-HCH was detected in approximately 13.9% of the

U.S. population (12–74 years) in the Northeast, Midwest, and South. The median level for the 91%

quantifiable positive results was 1.7 ppb (Murphy and Harvey 1985).

In a more recent study (1999–2000) of pesticide serum concentrations in pregnant Latina women living in

an agricultural community in California, median serum levels were 36.9 ng/g lipid for β-HCH and

1.1 ng/g lipid for γ-HCH (Bradman et al. 2007). The median serum concentration of β-HCH was 5.9 ng/g

lipid in 48 mothers enrolled in the California Childhood Leukemia Study in 2006–2007 (Whitehead et al.

2015). Maternal and blood cord samples were collected predominantly from Latina women, who were in

their second or third trimester of pregnancy, as part of a study from October 2010 to June 2011 in San

Francisco, California. Sixty-seven percent of maternal blood samples were above the method detection

limit for β-HCH (5 ng/L wet weight or 0.005 ng/g wet weight). The lipid adjusted median cord:maternal

serum ratio was 1.0, suggesting equivalent exposures for the fetus and the mother. (Morello-Frosch et al.

2016). In another study of 10 whole blood samples obtained from a blood donation center in Palo Alto,

California, α-HCH was detected in all samples, β- and δ-HCH were detected in 60% of samples, and

γ-HCH was detected in 80% of samples. Whole blood concentrations were 0.291–0.828, 0.544–1.15,

0.250–0.694, and 0.550–1.26 ng/g for α-, β-, γ-, and δ-HCH, respectively (Hao et al. 2020). Because

HCH is persistent and can be transported long distances, its isomers have been detected in peoples living

near the Arctic Circle. In 2019, β-HCH was detected in 59% of plasma samples (n = 54) from people in

Old Crow, Canada, which is predominantly Vuntut Gwitchin First Nation people (Drysdale et al. 2021).

HEXACHLOROCYCLOHEXANE (HCH) 285

5. POTENTIAL FOR HUMAN EXPOSURE

The geometric mean was below the detection limit (0.01 ng/L or 9.8x10

-6

ng/g) with a 95

percentile of

8.3x10

-5

ng/g (0.085 ng/L; 13,000 ng/g lipid adjusted). γ-HCH was not detected (Drysdale et al. 2021).

The Centers for Disease Control and Prevention (CDC) completed its Fourth National Report on Human

Exposure to Environmental Chemicals that was derived from data obtained from NHANES (CDC 2019).

The first report on 27 chemicals was issued in March 2001. This fourth report, released in January 2019,

presents blood and urine levels of environmental chemicals from a sample of people who represent the

noninstitutionalized, civilian U.S. population during 2-year study periods over 1999–2016. Lipid serum

levels of β- and γ-HCH from the most recent available study periods, 2015–2016 and 2011–2012,

respectively, are summarized in Table 5-12. Serum monitoring was not conducted in the following

NHANES study periods.

Table 5-12. Geometric Mean of the Serum Concentration (ng/g) of β-Hexachloro-

cyclohexane (β-HCH) (2015–2016) and γ-Hexachlorocyclohexane (γ-HCH) (2011–

2012) in the U.S. Population

Population group (sex, age)

Geometric mean

Unadjusted standard error

Sample size (pools)

β-HCH

Non-Hispanic white

Male, 12–19 years

Male, 20–39 years

Male, 40–59 years

0.012

0.001

Male, ≥60 years

0.03

0.004

Female, 12–19 years

Female, 20–39 years

Female, 40–59 years

0.015

0.002

Female, ≥60 years

0.095

0.026

Non-Hispanic black

Male, 12–19 years

Male, 20–39 years

Male, 40–59 years

0.013

0.002

Male, ≥60 years

0.017

0.001

Female, 12–19 years

Female, 20–39 years

Female, 40–59 years

0.018

0.002

Female, ≥60 years

0.095

0.014

HEXACHLOROCYCLOHEXANE (HCH) 286

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-12. Geometric Mean of the Serum Concentration (ng/g) of β-Hexachloro-

cyclohexane (β-HCH) (2015–2016) and γ-Hexachlorocyclohexane (γ-HCH) (2011–

2012) in the U.S. Population

Population group (sex, age)

Geometric mean

Unadjusted standard error

Sample size (pools)

Mexican American

Male, 12–19 years

Male, 20–39 years

0.011

0.002

Male, 40-59 years

0.027

0.005

Male, ≥60 years

0.058

0.01

Female, 12–19 years

Female, 20–39 years

0.016

0.003

Female, 40–59 years

0.055

0.006

Female, ≥60 years

0.16

0.037

All Hispanic

Male, 12–19 years

Male, 20–39 years

8.86

1.79

Male, 40–59 years

17.6

3.9

Male, ≥60 years

81.2

Female, 12–19 years

Female, 20–39 years

11.9

Female, 40–59 years

52.5

5.3

Female, ≥60 years

135

Asian

Male, 12–19 years

0.058

0.015

Male, 20–39 years

0.391

0.127

Male, 40–59 years

0.488

0.114

Male, ≥60 years

0.805

0.108

Female, 12–19 years

0.056

0.007

Female, 20–39 years

0.496

0.225

Female, 40–59 years

0.166

0.078

Female, ≥60 years

1.2

0.11

γ-HCH

Non-Hispanic white

Male, 12–19 years

Male, 20–39 years

Male, 40–59 years

Male, ≥60 years

Female, 12–19 years

Female, 20–39 years

Female, 40–59 years

Female, ≥60 years

HEXACHLOROCYCLOHEXANE (HCH) 287

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-12. Geometric Mean of the Serum Concentration (ng/g) of β-Hexachloro-

cyclohexane (β-HCH) (2015–2016) and γ-Hexachlorocyclohexane (γ-HCH) (2011–

2012) in the U.S. Population

Population group (sex, age)

Geometric mean

Unadjusted standard error

Sample size (pools)

Non-Hispanic black

Male, 12–19 years

Male, 20–39 years

Male, 40–59 years

Male, ≥60 years

Female, 12–19 years

Female, 20–39 years

Female, 40–59 years

Female, ≥60 years

Mexican American

Male, 12–19 years

Male, 20–39 years

Male, 40–59 years

Male, ≥60 years

Female, 12–19 years

Female, 20–39 years

Female, 40–59 years

Female, ≥60 years

All Hispanic

Male, 12–19 years

Male, 20–39 years

Male, 40–59 years

Male, ≥60 years

Female, 12–19 years

Female, 20–39 years

Female, 40–59 years

Female, ≥60 years

Asian

Male, 12–19 years

Male, 20–39 years

Male, 40–59 years

Male, ≥60 years

Female, 12–19 years

Female, 20–39 years

HEXACHLOROCYCLOHEXANE (HCH) 288

5. POTENTIAL FOR HUMAN EXPOSURE

Table 5-12. Geometric Mean of the Serum Concentration (ng/g) of β-Hexachloro-

cyclohexane (β-HCH) (2015–2016) and γ-Hexachlorocyclohexane (γ-HCH) (2011–

2012) in the U.S. Population

Population group (sex, age)

Geometric mean

Unadjusted standard error

Sample size (pools)

Female, 40–59 years

Female, ≥60 years

Each pool contained serum from eight people.

NA = not available; proportion of results below limit of detection (1.3 ng/g lipid for β-HCH and 0.92 ng/g lipid for

γ-HCH) was too high to provide a valid result.

Standard error of the mean is >30%.

Source: CDC 2019

Factors such as age, dietary habits, and residence can influence the body burden of γ-HCH in exposed

individuals. In one study, it was shown that women between the ages of 26 and 34 years who lived in a

rural area of India and were nonvegetarians tended to show higher body levels of γ-HCH than other

Indian women who lived in an urban area or who were vegetarians (Saxena et al. 1981a). The higher

levels of γ-HCH in women at an older child-bearing age suggest that a longer life span may cause a

greater accumulation of pesticide in the body. Higher pesticide levels were found in mutton, eggs, and

chicken, which are common in nonvegetarian meals; therefore, there tended to be a higher level of γ-HCH

in the bodies of nonvegetarians. In another study, when corrected for age and BMI, vegans had an almost

statistically significantly lower (p=0.076) mean β-HCH plasma concentration, not adjusted for lipids, than

omnivores. Mean β-HCH plasma concentrations were 6.151 ng/g lipid for vegans and 5.720 ng/g lipid

for omnivores (Arguin et al. 2010). In a study of hair samples, 460 ng/g γ-HCH was detected in samples

from people who worked as pesticide applicators and 40 ng/g γ-HCH was detected in samples from

people who lived close to farms in Atlanta, Georgia. Hair collected from people in Houston, Texas,

representing urban environmental exposure, had 1,500 ng/g γ-HCH detected (Smith-Baker and Saleh

2011). The study authors did not suggest an explanation for the higher levels in the samples from

environmentally exposed persons in Houston, Texas compared with levels in pesticide applicators in

Atlanta, Georgia; however, the sample sizes were very small (eight applicators and eight each

environmentally exposed persons in Atlanta and Houston). In addition, the ages of the volunteers from

whom hair samples were collected were not reported, and hair from older individuals could have higher

accumulation of γ-HCH. Further, there was no information on whether any volunteers had previous

exposure to γ-HCH applied to the scalp for treatment of lice.

HEXACHLOROCYCLOHEXANE (HCH) 289

5. POTENTIAL FOR HUMAN EXPOSURE

A study conducted in Colorado indicated, in general, that no quantitative relationships were demonstrated

between pesticide levels in household dust and pesticide levels in blood. However, γ-HCH levels in

blood sera in a pesticide formulator (16.8 ng/g) and his wife (5 ng/g) were found to be elevated in a

household in which dust levels measured 5.85 ng/g (Starr et al. 1974). It is possible that the γ-HCH found

in the wife's blood and in the household came from the clothes and person of the pesticide formulator.

The Nonoccupational Pesticide Exposure Study (NOPES) conducted by EPA was based on the Total

Exposure Assessment Methodology (TEAM) approach to exposure estimation. NOPES was designed to

provide estimates of nonoccupational exposure to 32 household pesticides in the United States. Samples

were collected at two locations: (1) Jacksonville, Florida, an area representative of high pesticide usage;

and (2) Springfield/Chicopee, Massachusetts, an area of low-to-moderate pesticide usage. Detectable

levels of γ-HCH were found in the personal air samples of 32–70% of the Jacksonville sample population;

the range of mean concentrations in the air samples was 7–22 ng/m

. For the Springfield population,

detectable levels of γ-HCH were found in personal air samples collected from 8–10% of the population,

with mean concentrations of 0.7–5 ng/m

(EPA 1990).

5.7 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES

The populations with the most potential for chronic-duration exposure to HCH are workers who work at

facilities that produce, process, or use γ-HCH. Exposure of the general population to γ-HCH tends to be

low because federal regulations limiting its use have taken effect. However, γ-HCH is available in some

prescription medications (e.g., shampoos, lotions), and the possibility of exposure may arise from use of

these products. Individuals living near hazardous waste sites contaminated with HCH may also be

exposed.

Historically, the largest occupational exposures came from people who work with pesticides. A study on

occupational pesticide exposure of commercial seed-treating applicators was conducted in Montana (Grey

et al. 1983). No exposure was detectable on the chest and arm pads, but γ-HCH was detected on the

hands and on the respirator pads. Workers involved with γ-HCH application complained of nasal

irritation if they did not wear a respirator or mask. The α-, β-, γ-, and δ-isomers of HCH have been

detected in the blood serum and adipose tissue of individuals occupationally exposed to HCH in pesticide

formulation. Serum levels of <0.5 ppb–1 ppm α-HCH, <0.9 ppb–0.72 ppm β-HCH, <0.7 ppb–0.17 ppm

γ-HCH, and 0.002–0.16 ppm δ-HCH have been detected in exposed workers (Baumann et al. 1980;

Kashyap 1986; Morgan and Lin 1978; Nigam et al. 1986). Mean adipose tissue levels of 5.8 mg

HEXACHLOROCYCLOHEXANE (HCH) 290

5. POTENTIAL FOR HUMAN EXPOSURE

α-HCH/kg, 45.6 mg β-HCH/kg, and 3.1 mg γ-HCH/kg have also been reported in exposed workers

(Baumann et al. 1980).

A number of case reports (e.g., Bhalla and Thami 2004; Daud et al. 2010; Juan et al. 2004; Paul et al.

2013; Shah et al. 2013; Ramabhatta et al. 2014; Wiles et al. 2015; Yu et al. 2015) have documented toxic

effects in humans overexposed to γ-HCH through excessive dermal application or accidental or

intentional ingestion of products used to treat scabies and head lice; effects observed in these studies are

described in Chapter 2.

HEXACHLOROCYCLOHEXANE (HCH) 291

CHAPTER 6. ADEQUACY OF THE DATABASE

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with the

Administrator of EPA and agencies and programs of the Public Health Service) to assess whether

adequate information on the health effects of HCH is available. Where adequate information is not

available, ATSDR, in conjunction with NTP, is required to assure the initiation of a program of research

designed to determine the adverse health effects (and techniques for developing methods to determine

such health effects) of HCH.

Data needs are defined as substance-specific informational needs that, if met, would reduce the

uncertainties of human health risk assessment. This definition should not be interpreted to mean that all

data needs discussed in this section must be filled. In the future, the identified data needs will be

evaluated and prioritized, and a substance-specific research agenda will be proposed.

6.1 EXISTING INFORMATION ON HEALTH EFFECTS

Studies evaluating the health effects of inhalation, oral, and dermal exposure of humans and animals to

HCH that are discussed in Chapter 2 are summarized in Figures 6-1, 6-2, 6-3, and 6-4. The purpose of

these figures is to illustrate the information concerning the health effects of HCH. The number of human

and animal studies examining each endpoint is indicated regardless of whether an effect was found and

the quality of the study or studies.

6.2 IDENTIFICATION OF DATA NEEDS

Missing information in Figures 6-1, 6-2, 6-3, and 6-4 should not be interpreted as a “data need.” A data

need, as defined in ATSDR’s Decision Guide for Identifying Substance-Specific Data Needs Related to

Toxicological Profiles (ATSDR 1989), is substance-specific information necessary to conduct

comprehensive public health assessments. Generally, ATSDR defines a data gap more broadly as any

substance-specific information missing from the scientific literature.

HEXACHLOROCYCLOHEXANE (HCH) 292

6. ADEQUACY OF THE DATABASE

Figure 6-1. Summary of Existing Health Effects Studies on

α-Hexachlorocyclohexane by Route and Endpoint*

Potential body weight, liver, and cancer effects were the most studied endpoints

The majority of the studies examined oral exposure in animals (versus humans)

Cancer

Other Noncancer

Developmental

Reproductive

Neurological

Immunological

Endocrine

Ocular

Dermal

Renal

Hepatic

Musculoskeletal

Hematological

Gastrointestinal

Cardiovascular

Respiratory

Body weight

Death

Oral Studies

Acute

12%

Intermediate

47%

Chronic

41%

Oral Route Duration

*Includes studies discussed in Chapter 2; the number of studies include those finding no effect. Most

studies examined multiple endpoints. No inhalation or dermal studies in humans or animals were located.

Human studies of unknown route and/or duration were classified as chronic oral studies for the purpose of

this figure.

HEXACHLOROCYCLOHEXANE (HCH) 293

6. ADEQUACY OF THE DATABASE

Figure 6-2. Summary of Existing Health Effects Studies on

β-Hexachlorocyclohexane by Route and Endpoint*

Potential developmental, other noncancer, and cancer effects were the most studied endpoints

The majority of the studies examined exposure in humans (versus animals)

Cancer

Other Noncancer

Developmental

Reproductive

Neurological

Immunological

Endocrine

Ocular

Dermal

Renal

Hepatic

Musculoskeletal

Hematological

Gastrointestinal

Cardiovascular

Respiratory

Body weight

Death

Oral Studies

Acute

15%

Intermediate

23%

Chronic

63%

Oral Route Duration

*Includes studies discussed in Chapter 2; the number of studies include those finding no effect. Most

studies examined multiple endpoints. No inhalation or dermal studies in humans or animals were located.

Human studies of unknown route and/or duration were classified as chronic oral studies for the purpose of

this figure.

HEXACHLOROCYCLOHEXANE (HCH) 294

6. ADEQUACY OF THE DATABASE

Figure 6-3. Summary of Existing Health Effects Studies on γ-Hexachlorocyclohexane by Route and Endpoint*

Potential body weight, liver, and neurological effects were the most studied endpoints

The majority of the studies examined oral exposure in animals (versus humans)

Cancer

Other Noncancer

Developmental

Reproductive

Neurological

Immunological

Endocrine

Ocular

Dermal

Renal

Hepatic

Musculoskeletal

Hematological

Gastrointestinal

Cardiovascular

Respiratory

Body weight

Death

Inhalation Studies

Oral Studies

Dermal Studies

Acute

43%

Intermediate

29%

Chronic

29%

Inhalation Route Duration

Acute

23%

Intermediate

35%

Chronic

42%

Oral Route Duration

Acute

83%

Intermediate

17%

Chroni

Dermal Route Duration

*Includes studies discussed in Chapter 2; the number of studies include those finding no effect. Most studies

examined multiple endpoints. Human studies of unknown route and/or duration were classified as chronic oral

studies for the purpose of this figure.

HEXACHLOROCYCLOHEXANE (HCH) 295

6. ADEQUACY OF THE DATABASE

Figure 6-4. Summary of Existing Health Effects Studies on

δ-Hexachlorocyclohexane and Unspecified

Hexachlorocyclohexanes by Route and Endpoint*

Potential hepatic and cancer effects were the most studied endpoints

The majority of the studies examined exposure in animals (versus humans)

Cancer

Other Noncancer

Developmental

Reproductive

Neurological

Immunological

Endocrine

Ocular

Dermal

Renal

Hepatic

Musculoskeletal

Hematological

Gastrointestinal

Cardiovascular

Respiratory

Body weight

Death

Oral Studies

Dermal Studies

Intermediate

20%

Chronic

80%

Oral Route Duration

Intermediate

100%

Dermal Route Duration

*Includes studies discussed in Chapter 2; the number of studies include those finding no effect.

Most studies examined multiple endpoints. No inhalation or dermal studies in humans or

inhalation studies in animals were located. Human studies of unknown route and/or duration

were classified as chronic oral studies for the purpose of this figure.

HEXACHLOROCYCLOHEXANE (HCH) 296

6. ADEQUACY OF THE DATABASE

Acute-Duration MRLs. The inhalation database is inadequate to derive acute-duration inhalation

MRLs for any HCH isomer. The oral database is adequate to derive acute-duration oral MRLs for β- and

γ-HCH, but not for α- or δ-HCH. Acute oral studies providing data on effects of α- and δ-HCH at low

doses are needed.

Intermediate-Duration MRLs. The inhalation database is inadequate to derive intermediate-duration

inhalation MRLs for any HCH isomer. The oral database is adequate to derive intermediate-duration oral

MRLs for α-, β-, and γ-HCH, but not for δ-HCH. Intermediate oral studies providing data on effects of

δ-HCH at low doses are needed.

Chronic-Duration MRLs. The inhalation database is inadequate to derive chronic-duration inhalation

MRLs for any HCH isomer. The oral database is adequate to derive a chronic-duration oral MRL for

α-HCH, but not for β-, γ-, or δ-HCH. Chronic-duration oral studies providing data on effects of β-, γ-,

and δ-HCH at low doses are needed.

Health Effects.

Hepatic. Available animal studies provide abundant evidence for hepatic effects after oral

exposure to α- and β-HCH for intermediate and chronic durations, and to γ-HCH for all exposure

durations. Very limited data are available for liver effects in animals exposed chronically to

δ-HCH by oral administration. Additional studies examining sensitive liver endpoints after acute-

duration oral exposure to α- and β-HCH, all durations of oral exposure to δ-HCH, and inhalation

exposure of all durations to all HCH isomers would complete the database for this health effect.

Neurotoxicity. Studies examining sensitive neurological and neurobehavioral effects in animals

exposed to α-, β-, and δ-HCH by oral and inhalation exposure are needed, as studies of γ-HCH

have shown neurotoxicity after inhalation, oral, and dermal exposure of animals and case-reports

have demonstrated severe neurological effects in exposed humans. For γ-HCH, specialized

neurotoxicity studies of inhalation exposure (all durations) are needed.

Developmental. There are no data on the developmental effects of α- or δ-HCH and very

limited data on the developmental effects of β-HCH. One epidemiological study in children

under 4 years of age suggested that β-HCH in serum may be associated with deficits in cochlear

function, but the findings varied by age at blood sampling; further assessment of the potential

HEXACHLOROCYCLOHEXANE (HCH) 297

6. ADEQUACY OF THE DATABASE

ototoxicity of β-HCH in humans or animals is needed to enable conclusions regarding this health

effect. Data in animals exposed via oral administration of γ-HCH demonstrate a wide variety of

serious effects on the developing organism, including effects on birth outcomes, reproductive

tract development, and the development of the central nervous system and heart. Therefore, the

lack of information on potential developmental toxicity of the other isomers represents a

significant data gap. In addition, there are no studies of these endpoints in animals exposed to

any HCH isomer by inhalation; availability of such information is needed to provide adequate

data for derivation of inhalation MRLs.

Immunotoxicity. There are no data on the effects of α- or δ-HCH on the immune system of

animals exposed by any route, and very limited data on the effects of β-HCH after oral exposure.

Data in animals exposed via oral administration of γ-HCH demonstrate immune suppression in a

variety of species after acute- and intermediate-durations. Specialized studies examining the

functioning of the immune system in animals exposed orally to α-, β-, and δ-HCH are needed, as

are studies of immunotoxicity in animals exposed by inhalation to the HCH isomers.

For the key health outcomes, especially those shown above, data on the mechanisms by which HCH

isomers induce toxicity are limited. Additional mechanistic studies may improve the understanding of the

human relevance of toxic effects observed in animals.

Epidemiology and Human Dosimetry Studies. In the United States, γ-HCH and technical HCH

are no longer used for agricultural purposes, and HCH is not produced in the United States. Currently

authorized uses are limited to prescription shampoos or lotions containing 1% γ-HCH for treatment of lice

and scabies. As a result of the limited current exposures to HCH isomers, additional follow-up of

occupational cohorts established previously may be the most useful approach to obtaining additional

human data. Other epidemiological studies have used blood or tissue levels of HCH isomers in the

general population to evaluate past exposure, an approach that is viable for the more persistent β-HCH

isomer, but not for the isomers with shorter half-lives.

Biomarkers of Exposure and Effect. Methods exist for the analysis of HCH isomers in blood

(normalized by lipid content) and hair and for HCH metabolites in urine. Serum measurements of γ-HCH

represent short-term exposure because γ-HCH is metabolized and excreted rapidly. Due to its high lipid

solubility and persistence, β-HCH levels represent longer-term exposures. However, reported blood

levels of HCH have not been quantitatively correlated with ambient HCH levels or past exposure.

HEXACHLOROCYCLOHEXANE (HCH) 298

6. ADEQUACY OF THE DATABASE

Methods that measure the levels of HCH metabolites in urine are not specific enough to detect exposure

to HCH alone. More information could be provided by studies designed to correlate biomarkers of

exposure with exposure levels. No biomarkers of effect, specific for HCH isomers, have been identified

in the literature. Several studies have demonstrated increases in lipid peroxidation and depletion of

antioxidants in the central nervous system, liver, male reproductive tract, and maternal or fetal tissues in

animals exposed to γ-HCH; however, these are nonspecific effects induced by a wide range of

compounds. Additional studies designed to assess mechanisms of action and/or adverse outcome

pathways may serve to identify specific biomarkers of effect for health outcomes of concern for HCH

isomers (e.g., liver, neurological, developmental, and immune system effects).

Absorption, Distribution, Metabolism, and Excretion. Information is available to evaluate the

toxicokinetics of HCH isomers following oral and dermal exposure in animals and humans. Studies

evaluating toxicokinetic properties following inhalation exposure would be helpful. Limited information

suggests differences in the metabolism of the HCH isomers. Additional data on metabolism of the α-, β-,

and δ-HCH isomers would be beneficial, especially if such information was linked to differences in

specific health outcomes. In vitro studies using rat liver microsomes have demonstrated the formation of

a reactive epoxide metabolite; however, investigations have not been conducted to examine the epoxide

formation in vivo or its role in inducing mutagenic and carcinogenic effects. Further information on the

possible role of epoxide formation in carcinogenesis in vivo, as well as its rate of formation under various

conditions, would be useful.

Comparative Toxicokinetics. The development and validation of additional PBPK models that

compare predictions against observations in humans could provide valuable information in extrapolating

animal toxicity data to humans.

Children’s Susceptibility. Data needs relating to both prenatal and childhood exposures, and

developmental effects are discussed in detail in the Developmental Toxicity subsection above. Limited

data are available on the toxicokinetics or health effects of α- and β-HCH isomers on exposed children.

Further, additional animal studies evaluating potential early life susceptibility to neurotoxicity and/or

cancer after exposure to γ-HCH would be useful.

Physical and Chemical Properties. Sufficient information is available on the physical and chemical

properties of γ-HCH and the other HCH isomers (see Chapter 4) to permit an assessment of the

environmental fate of these compounds. No additional studies are warranted at this time.

HEXACHLOROCYCLOHEXANE (HCH) 299

6. ADEQUACY OF THE DATABASE

Production, Import/Export, Use, Release, and Disposal. Production methods for HCH are well

described in the literature (IARC 1979). γ-HCH is used as an insecticide and as a therapeutic scabicide

and pediculicide for treatment of ectoparasites in humans and animals (Budavari et al. 1989). The

production and use of γ-HCH as a pesticide has been restricted in the United States, and the use of γ-HCH

was voluntarily canceled in 2006 (EPA 2006b). Recent data suggest that the uses and import/export

volumes of γ-HCH are decreasing (EPA 2012, 2016; Hauzenberger et al. 2002). Release of γ-HCH to

environmental media has been primarily from its use as a pesticide. Wastes containing γ-HCH must be

contained, incinerated, and disposed of in landfills (EPA 1975). Carbon absorption or flocculation are

useful treatment methods for the removal of HCH from aqueous effluent streams, except when methanol

is also contained in the effluents (NLM 2021). Disposal methods are currently subject to revision under

EPA guidance.

Environmental Fate. HCH released to the environment partitions to the atmosphere, soils, and

sediments (Atkins and Eggleton 1971; Lewis and Lee 1976; Melancon et al. 1986; Saleh et al. 1982;

Stanley et al. 1971). HCH is transported in the atmosphere, surface water, and groundwater (Mackay and

Leinonen 1975; Nordmeyer et al. 1992; Stanley et al. 1971). HCH is transformed via biodegradation in

soils and surface waters (Govind et al. 1991; Kar and Singh 1979b; Kennedy et al. 1990; Macholz and

Kujawa 1985; Sharom et al. 1980; Tu 1976). Wet and dry deposition are significant removal processes

for HCH in the atmosphere (Atkins and Eggleton 1971; Hamada et al. 1981; Wiberg et al. 2001).

Additional information on the transport, transformation, and persistence of the individual isomers in soils

and groundwater, particularly at hazardous waste sites, are needed to identify the most important routes of

human exposure to HCH. There is information regarding the half-lives for γ-HCH in water (3–30, 30–

300, and >300 days for river, lake, and groundwater, respectively) (Zoeteman et al. 1980). Reported half-

lives determined in groundwater of a contaminated site were 223, 62–287, and 120–632 days for α-, β-,

and δ-HCH isomers, respectively (Bashir et al. 2015). Hydrolysis occurs slowly under most

environmental conditions, but the rate is much more rapid under alkaline conditions. At 25°C, hydrolysis

half-lives of 92, 648, and 771 hours were observed for γ-HCH at pH 9.3, 7.8, and 7.3, respectively (Saleh

et al. 1982). The alkaline hydrolysis (pH 9.78) half-life of α-HCH was calculated at 1,083 hours (Zhang

et al. 2014). The degradation of HCH in the atmosphere occurs through the reaction with

photochemically generated hydroxyl radicals, and half-lives of γ- and α-HCH are around 100 days, but

can be much longer based upon environmental conditions (Brubaker and Hites 1998).

HEXACHLOROCYCLOHEXANE (HCH) 300

6. ADEQUACY OF THE DATABASE

Bioavailability from Environmental Media. Evidence of absorption following inhalation and

dermal exposure is available for workers involved in the formulation of pesticide products containing

HCH isomers and in the use of γ-HCH (Baumann et al. 1980; Grey et al. 1983). Dietary intake is not a

major route of exposure for the general population (FDA 2020a, 2020b). Additional information on the

absorption of γ-HCH, following ingestion of or contact with media containing residues of the compound,

would be helpful. As mentioned in Section 6.3.1, Duff and Kissel (1996) showed that bioavailability of

γ-HCH via dermal exposure depended upon levels of soil loading. Dermal absorption ranged from

0.45 to 2.35%. For populations living in the vicinity of hazardous waste sites, additional information on

absorption following dermal contact with, or ingestion of, contaminated soil is needed, given the expected

strong sorption of the compound to soil particulates. Because of the potential of HCH to contaminate air,

drinking water, and soil, further information on the bioavailability of the HCH isomers from these

environmental media are needed for assessing possible health concerns for humans.

Food Chain Bioaccumulation. γ-HCH in surface waters and soils is taken up and bioconcentrated by

terrestrial and aquatic organisms (Just et al. 1990; Matsumura and Benezet 1973; Ramamoorthy 1985;

Schimmel et al. 1977; Verma and Pillai 1991; Viswanathan et al. 1988). Uptake from soils and

bioconcentration by plants and terrestrial organisms appears to be limited (Chen et al. 2013; Šmídová et

al. 2015; Verma and Pillai 1991; Wild and Jones 1992). Plant uptake from air may be greater (Yang et al.

2007). Limited information suggests that the compound is not biomagnified in terrestrial food chains

because of its metabolism by terrestrial organisms (Schmitt et al. 1985). Trophic level transfer of γ-HCH

has been observed (Bemy et al. 2003). Bioconcentration values in zebra fish for α- and β-HCH have been

reported (Butte et al. 1991). Among the HCH isomers, β-HCH accumulates the most in the food chain

(Szokolay et al. 1977). Additional information on the potential bioaccumulation of α-, β-, and δ-HCH

isomers in terrestrial and aquatic food chains is needed.

Exposure Levels in Environmental Media. γ-HCH has been detected in air, surface water and

groundwater, sediment, soil, and food. A gradual decrease of α- and γ-HCH air has been seen across the

decades (Atlas and Giam 1988; Cortes and Hites 2000; WQP 2021), and there is evidence of decreases of

α- and β-HCH in surface water and groundwater although the data have a large range (WQP 2021).

Trends for soil, reflecting varying land uses, are not as clear for the isomers. Although the use of γ-HCH

as a pesticide was voluntarily canceled in 2006 (EPA 2006b), it is uncertain whether new environmental

measurements will show considerably lower levels of HCH since there are remaining impacts from

importing and processing HCH, and evidence of persistency of the isomers. For example, a study of a

pesticide reformulating and packaging facility reported groundwater contamination at the site (Chartrand

HEXACHLOROCYCLOHEXANE (HCH) 301

6. ADEQUACY OF THE DATABASE

et al. 2015). Therefore, additional information on the levels of γ-, α-, β-, and δ-HCH isomers would be

beneficial to determine current potential human exposure to the chemicals from environmental media,

particularly near hazardous waste sites.

Exposure Levels in Humans. HCH can be detected in the blood (Baumann et al. 1980; Bradman et

al. 2007; Griffith and Blanke 1975; Hao et al. 2020; Murphy and Harvey 1985; Whitehead et al. 2015),

urine (Murphy and Harvey 1985), adipose tissue (Baumann et al. 1980; EPA 1986), breast milk

(Takahashi et al. 1981), hair (Smith-Baker and Saleh 2011), and semen (Stachel et al. 1989) of exposed

individuals. Most of the data on the body burden of HCH in adipose tissue and breast milk are prior to

the 2006 voluntary cancellation of γ-HCH for agricultural use. Additional information after this time

point would be helpful to assess current population body burdens. Additionally, most of the data on the

body burden of HCH are from adipose tissue and blood serum analyses conducted postmortem or on

occupationally exposed individuals. The disadvantage of using postmortem blood is that the HCH

concentration may change after death. The occupational studies often do not report environmental levels;

therefore, it is not possible to correlate body HCH levels with environmental levels. The results of the

NHATS conducted in 1982 showed that β-HCH, the most prevalent isomer in fatty tissue, was detected

most often in postmortem samples collected from individuals from the southern United States. Samples

of human milk that were collected over the years in certain populations and used to monitor other

contaminants (e.g., polychlorinated biphenyls) could be tested for HCHs content. Additional information

is needed on exposure to γ-, α-, β-, and δ-HCH isomers in populations living in the vicinity of hazardous

waste sites.

This information is necessary for assessing the need to conduct health studies on these populations.

Exposures of Children. Prenatal exposure of children to HCH has been demonstrated; it is well

documented that placental transfer of HCH occurs, and HCH levels have been measured in placenta and

cord blood in humans (Morello-Frosch et al. 2016; Nair et al. 1996; Saxena et al. 1981b) and in amniotic

fluid and fetal tissues in mice (Srivastava and Raizada 1993). Infants have previously also been exposed

via ingestion of breast milk and cow’s milk. Exposure may also occur via ingestion of water containing

HCH and possibly through incidental ingestion of household dust; exposure is less likely from food and

animal products. It has been demonstrated that household dust can be an important source of

environmental HCH (Starr et al. 1974). This occurs especially if the parents work in facilities that

process or use HCH and can bring home residues of HCH via their work clothes, skin, hair, tools, or other

objects removed from the workplace. A take-home exposure study on pesticide applicators might be

HEXACHLOROCYCLOHEXANE (HCH) 302

6. ADEQUACY OF THE DATABASE

useful if such occupational exposure settings occur. Limited studies conducted on exposure of infants and

children to γ-HCH from application of 1% γ-HCH lotion as scabicide indicated dermal absorption

occurred (Ginsburg et al. 1977). Adipose tissue is a major storage depot for HCH. Although data from a

national human adipose tissue survey exist (EPA 1986), no quantitative data are currently available on the

body burden of HCH in children. These studies are needed because unique exposure pathways for

children exist, and children may be different from adults in their weight-adjusted intake of HCH because

of their higher surface area to volume ratio and higher ingestion rate of household dust.

6.3 ONGOING STUDIES

No ongoing studies were identified in the National Institutes of Health (NIH) RePORTER (2023)

database, which tracks projects funded by NIH.

HEXACHLOROCYCLOHEXANE (HCH) 303

CHAPTER 7. REGULATIONS AND GUIDELINES

Pertinent international and national regulations, advisories, and guidelines regarding HCH in air, water,

and other media are summarized in Table 7-1. This table is not an exhaustive list, and current regulations

should be verified by the appropriate regulatory agency.

ATSDR develops MRLs, which are substance-specific guidelines intended to serve as screening levels by

ATSDR health assessors and other responders to identify contaminants and potential health effects that

may be of concern at hazardous waste sites. See Section 1.3 and Appendix A for detailed information on

the MRLs for HCH.

Table 7-1. Regulations and Guidelines Applicable to Hexachlorocyclohexane

(HCH)

Agency

Description

Information

Reference

Air

EPA

RfC

Not evaluated

IRIS 1987a, IRIS

1987b, IRIS

1987c, IRIS

1987d, IRIS

1987f

WHO

Air quality guidelines

No data

WHO 2010

Water & Food

EPA

Drinking water standards and health

advisories

EPA 2018a

γ-HCH

1-Day health advisory (10-kg child)

1 mg/L

10-Day health advisory (10-kg child)

1 mg/L

DWEL

0.2 mg/L

National primary drinking water regulations

EPA 2009

γ-HCH

MCL and MCLG

0.0002 mg/L

RfD

β-HCH

0.00006 mg/kg/day

EPA 2006c

γ-HCH

3x10

-4

mg/kg/day

IRIS 1987c

WHO

Drinking water quality guidelines

WHO 2022

γ-HCH

Guideline value

0.002 mg/L

ADI

0–0.005 mg/kg body weight

FDA

Substances added to food

Not listed

FDA 2023

Allowable level in bottled water

FDA 2017

γ-HCH

0.0002 mg/L

HEXACHLOROCYCLOHEXANE (HCH) 304

7. REGULATIONS AND GUIDELINES

Table 7-1. Regulations and Guidelines Applicable to Hexachlorocyclohexane

(HCH)

Agency

Description

Information

Reference

Cancer

HHS

Carcinogenicity classification

NTP 2021

γ-HCH, technical HCH and other HCH

isomers

Reasonably anticipated to be

human carcinogens

EPA

Carcinogenicity classification

α-HCH

Group B2

IRIS 1987a

β-HCH

Group C

IRIS 1987b

γ-HCH

Suggestive evidence of

carcinogenicity, but not

sufficient to assess human

carcinogenic potential

EPA 2002

δ-HCH

Group D

IRIS 1987d

Technical HCH

Group B2

IRIS 1987f

Inhalation unit risk

α-HCH

1.8x10

-3

per µg/m

IRIS 1987a

β-HCH

5.3x10

-4

per µg/m

IRIS 1987b

Technical HCH

5.1x10

-4

per µg/m

IRIS 1987f

Oral slope factor

α-HCH

6.3 per mg/kg/day

IRIS 1987a

β-HCH

1.8 per mg/kg/day

IRIS 1987b

Technical HCH

1.8 per mg/kg/day

IRIS 1987f

IARC

Carcinogenicity classification

γ-HCH

Group 1

IARC 2018

HCH

Group 2B

IARC 1987

Occupational

OSHA

PEL (8-hour TWA) for general industry,

shipyards, and construction

OSHA 2021a,

OSHA 2021b,

OSHA 2021c

γ-HCH

0.5 mg/m

NIOSH

REL (up to 10-hour TWA)

NIOSH 2019

γ-HCH

0.5 mg/m

IDLH

NIOSH 1994

γ-HCH

50 mg/m

Emergency Criteria

EPA

AEGLs-air

No data

EPA 2018b

HEXACHLOROCYCLOHEXANE (HCH) 305

7. REGULATIONS AND GUIDELINES

Table 7-1. Regulations and Guidelines Applicable to Hexachlorocyclohexane

(HCH)

Agency

Description

Information

Reference

DOE

PACs-air

DOE 2016

γ-HCH

TEEL-1

9.1 mg/m

TEEL-2

100 mg/m

TEEL-3

1,000 mg/m

The Substances Added to Food inventory replaces EAFUS and contains the following types of ingredients: food and

color additives listed in FDA regulations, flavoring substances evaluated by FEMA or JECFA, GRAS substances

listed in FDA regulations, substances approved for specific uses in food prior to September 6, 1958, substances that

are listed in FDA regulations as prohibited from use in food, delisted color additives, and some substances "no

longer FEMA GRAS."

Group B2: probable human carcinogen.

Group C: possible human carcinogen.

Group D: not classifiable as to human carcinogenicity.

Group 1: carcinogenic to humans.

Group 2B: possibly carcinogenic to humans.

Skin notation.

Definitions of PAC terminology are available from DOE (2022).

ADI = acceptable daily intake; AEGL = acute exposure guideline levels; DOE = Department of Energy;

DWEL = drinking water equivalent level; EAFUS = Everything Added to Food in the United States;

EPA = Environmental Protection Agency; FAO = Food and Agriculture Organization; FDA = Food and Drug

Administration; FEMA = Flavor and Extract Manufacturers Association of the United States; GRAS = generally

recognized as safe; HHS = Department of Health and Human Services; IARC = International Agency for Research

on Cancer; IDLH = immediately dangerous to life or health; IRIS = Integrated Risk Information System;

JECFA = Joint FAO/WHO Expert Committee on Food Additives; MCL = maximum contaminant level;

MCLG = maximum contaminant level goal; NIOSH = National Institute for Occupational Safety and Health;

NTP = National Toxicology Program; OSHA = Occupational Safety and Health Administration; PAC = protective

action criteria; PEL = permissible exposure limit; REL = recommended exposure limit; RfC = inhalation reference

concentration; RfD = oral reference dose; TEEL = temporary emergency exposure limit; TWA = time-weighted

average; WHO = World Health Organization

HEXACHLOROCYCLOHEXANE (HCH) 306

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Yu Y, Wang B, Wang X, et al. 2013. Hexachlorocyclohexanes (HCHs) in placenta and umbilical cord

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HEXACHLOROCYCLOHEXANE (HCH) A-1

APPENDIX A. ATSDR MINIMAL RISK LEVEL WORKSHEETS

MRLs are derived when reliable and sufficient data exist to identify the target organ(s) of effect or the

most sensitive health effect(s) for a specific duration for a given route of exposure. An MRL is an

estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk

of adverse noncancer health effects over a specified route and duration of exposure. MRLs are based on

noncancer health effects only; cancer effects are not considered. These substance-specific estimates,

which are intended to serve as screening levels, are used by ATSDR health assessors to identify

contaminants and potential health effects that may be of concern at hazardous waste sites. It is important

to note that MRLs are not intended to define clean-up or action levels.

MRLs are derived for hazardous substances using the NOAEL/uncertainty factor approach. They are

below levels that might cause adverse health effects in the people most sensitive to such chemical-

induced effects. MRLs are derived for acute (1–14 days), intermediate (15–364 days), and chronic

(≥365 days) durations and for the oral and inhalation routes of exposure. Currently, MRLs for the dermal

route of exposure are not derived because ATSDR has not yet identified a method suitable for this route

of exposure. MRLs are generally based on the most sensitive substance-induced endpoint considered to

be of relevance to humans. LOAELs for serious health effects (such as irreparable damage to the liver or

kidneys, or serious birth defects) are not used as a basis for establishing MRLs. Exposure to a level above

the MRL does not mean that adverse health effects will occur.

MRLs are intended only to serve as a screening tool to help public health professionals decide where to

look more closely. They may also be viewed as a mechanism to identify those hazardous waste sites that

are not expected to cause adverse health effects. Most MRLs contain a degree of uncertainty because of

the lack of precise toxicological information on the people who might be most sensitive (e.g., infants,

elderly, nutritionally or immunologically compromised) to the effects of hazardous substances. ATSDR

uses a conservative (i.e., protective) approach to address this uncertainty consistent with the public health

principle of prevention. Although human data are preferred, MRLs often must be based on animal studies

because relevant human studies are lacking. In the absence of evidence to the contrary, ATSDR assumes

that humans are more sensitive to the effects of hazardous substances than animals and that certain

persons may be particularly sensitive. Thus, the resulting MRL may be as much as 100-fold below levels

that have been shown to be nontoxic in laboratory animals.

HEXACHLOROCYCLOHEXANE (HCH) A-2

APPENDIX A

Proposed MRLs undergo a rigorous review process: Health Effects/MRL Workgroup reviews within the

Office of Innovation and Analytics, Toxicology Section, expert panel peer reviews, and agency-wide

MRL Workgroup reviews, with participation from other federal agencies and comments from the public.

They are subject to change as new information becomes available concomitant with updating the

toxicological profiles. Thus, MRLs in the most recent toxicological profiles supersede previously

published MRLs. For additional information regarding MRLs, please contact the Office of Innovation

and Analytics, Toxicology Section, Agency for Toxic Substances and Disease Registry, 1600 Clifton

Road NE, Mailstop S106-5, Atlanta, Georgia 30329-4027.

HCH is a mixture of eight isomers, four of which are of commercial significance: α-HCH (CAS Registry

Number 319-84-6), β-HCH (CAS Registry Number 319-85-7), γ-HCH (CAS Registry Number 58-89-9),

and δ-HCH (CAS Registry Number 319-86-8). Technical HCH, which is used as an insecticide, is made

up of the various isomers at different concentrations. The wide variations in isomer composition of

technical HCH preclude the possibility of MRL derivation. MRL derivation was considered for the

isomers included in this toxicological profile: α-, β-, γ-, and δ-HCH.

HEXACHLOROCYCLOHEXANE (HCH) A-3

APPENDIX A

MINIMAL RISK LEVEL (MRL) WORKSHEET

Chemical Name: α-HCH

CAS Number: 319-84-6

Date: March 2024

Profile Status: Final

Route: Inhalation

Duration: Acute

MRL Summary: There are insufficient data for derivation of an acute-duration inhalation MRL for

α-HCH.

Rationale for Not Deriving an MRL: No acute-duration inhalation studies of α-HCH in humans or

animals were located, precluding derivation of an acute-duration inhalation MRL.

Agency Contacts (Chemical Managers): Malcolm Williams

HEXACHLOROCYCLOHEXANE (HCH) A-4

APPENDIX A

MINIMAL RISK LEVEL (MRL) WORKSHEET

Chemical Name: α-HCH

CAS Number: 319-84-6

Date: March 2024

Profile Status: Final

Route: Inhalation

Duration: Intermediate

MRL Summary: There are insufficient data for derivation of an intermediate-duration inhalation MRL

for α-HCH.

Rationale for Not Deriving an MRL: No intermediate-duration inhalation studies of α-HCH in humans

or animals were located, precluding derivation of an intermediate-duration inhalation MRL.

Agency Contacts (Chemical Managers): Malcolm Williams

HEXACHLOROCYCLOHEXANE (HCH) A-5

APPENDIX A

MINIMAL RISK LEVEL (MRL) WORKSHEET

Chemical Name: α-HCH

CAS Number: 319-84-6

Date: March 2024

Profile Status: Final

Route: Inhalation

Duration: Chronic

MRL Summary: There are insufficient data for derivation of a chronic-duration inhalation MRL for

α-HCH.

Rationale for Not Deriving an MRL: No chronic-duration inhalation studies of α-HCH in humans or

animals were located, precluding derivation of a chronic-duration inhalation MRL.

Agency Contacts (Chemical Managers): Malcolm Williams

HEXACHLOROCYCLOHEXANE (HCH) A-6

APPENDIX A

MINIMAL RISK LEVEL (MRL) WORKSHEET

Chemical Name: α-HCH

CAS Number: 319-84-6

Date: March 2024

Profile Status: Final

Route: Oral

Duration: Acute

MRL Summary: There are insufficient data for derivation of an acute-duration oral MRL for α-HCH.

Rationale for Not Deriving an MRL: No adequate exposure-response data were available for humans.

Data on effects in laboratory animals exposed orally to α-HCH for acute durations are limited to a

freestanding NOAEL of 20 mg/kg/day for body weight changes during the first 14 days of a 28-day study

comparing gene expression profiles for α- and γ-HCH (Sumida et al. 2007). Increased relative liver

weight (24%) and decreased serum ALP (19%) were seen at this dose after 14 days, but histopathology

was not evaluated at this time, so reliable hepatic effect levels could not be determined for this study.

Thus, this study did not provide an adequate basis for MRL derivation.

Agency Contacts (Chemical Managers): Malcolm Williams

HEXACHLOROCYCLOHEXANE (HCH) A-7

APPENDIX A

MINIMAL RISK LEVEL (MRL) WORKSHEET

Chemical Name: α-HCH

CAS Number: 319-84-6

Date: March 2024

Profile Status: Final

Route: Oral

Duration: Intermediate

MRL: 0.002 mg/kg/day (2 µg/kg/day)

Critical Effect: Increased liver weight and liver histopathology changes

Reference: Sumida et al. 2007

Point of Departure: 2 mg/kg/day (NOAEL)

Uncertainty Factor: 100

Modifying Factor: 10

LSE Graph Key: 6

Species: Rat

MRL Summary: An intermediate-duration oral MRL of 0.002 mg/kg/day (2 µg/kg/day) was derived

based on a NOAEL of 2 mg/kg/day for liver effects in a 28-day study in rats (Sumida et al. 2007). The

NOAEL was divided by a total uncertainty factor of 100 (10 for human variability and 10 for animal to

human extrapolation) and a modifying factor of 10 (for lack of studies examining developmental and

immunological effects and limitations in available data on neurotoxicity).

Selection of the Critical Effect: No dose-response data are available for humans. In animal studies,

hepatic effects (including cancers) occurred at lower doses than effects on body weight or kidneys. A

single study found no effects on motor nerve conduction velocity in rats exposed to 106.2 mg/kg/day for

30 days (Muller et al. 1981). The α-hexachlorocyclohexane database only contains studies with body

weight, renal, hepatic, neurological, and cancer endpoints; no other effects were evaluated in the available

studies. Table A-1 summarizes the hepatic effects from intermediate-duration oral studies in laboratory

animals exposed to doses up to 70 mg/kg/day.

Table A-1. Summary of NOAELs and LOAELs from Candidate Intermediate-

Duration Studies in Laboratory Animals Orally Exposed to

α-Hexachlorocyclohexane

Species

Exposure

scenario

NOAEL

(mg/kg/day)

LOAEL

(mg/kg/day)

Effect

Reference

Hepatic effects

Mouse (dd)

20–40 M

24 weeks

(F)

33% relative liver weight

increase; hepatocellular

hypertrophy

Ito et al.

1973

Rat

(Fischer-344)

4 M

28 days

(GO)

Increased relative liver weight

(25%); centrilobular

hepatocellular hypertrophy

Sumida et al.

2007

Rat (W strain)

18–24 M

48 weeks

(F)

Hepatocellular hypertrophy

Ito et al.

1975

Rat (Wistar)

8 M

24 weeks

(F)

Mild liver cell hypertrophy;

2-fold increase in liver weight

Nagasaki et

al. 1975

HEXACHLOROCYCLOHEXANE (HCH) A-8

APPENDIX A

Table A-1. Summary of NOAELs and LOAELs from Candidate Intermediate-

Duration Studies in Laboratory Animals Orally Exposed to

α-Hexachlorocyclohexane

Species

Exposure

scenario

NOAEL

(mg/kg/day)

LOAEL

(mg/kg/day)

Effect

Reference

Hamster

(Golden Syrian)

6–10 M

24 weeks

(F)

20–38% increase in liver

weight; liver cell hypertrophy

Nagasaki et

al. 1975

Rat (Wistar)

10 F, 10 M

6–9

months (F)

60 M

70 F

(serious

LOAEL for

decreased

survival)

Decreased survival;

moderate histopathology

changes (focal necrosis, fatty

degeneration); >2-fold

increase in liver weight

Fitzhugh et

al. 1950

Principal study for the MRL.

(F) = feed; F = female(s); (GO) = gavage in oil vehicle; LOAEL = lowest-observed-adverse-effect level; M = male(s);

ND = not determined; NOAEL = no-observed-adverse-effect level

Selection of the Principal Study: As Table A-1 shows, the lowest effect level (18 mg/kg/day) was

associated with a relative liver weight increase of 33% and hepatocellular hypertrophy in mice exposed

via diet for 24 weeks (Ito et al. 1973). A NOAEL was not identified for this study. In a study of rats

exposed by gavage for only 28 days (Sumida et al. 2007), a slightly higher LOAEL of 20 mg/kg/day was

identified for similar hepatic effects; the NOAEL in that study was 2 mg/kg/day. All of the other studies

identified hepatic effects at the lowest doses tested (no other NOAEL was identified). The study by

Sumida et al. (2007) was selected as the principal study for MRL derivation because the NOAEL

identified in the study was lower than the LOAELs identified in all other studies and because a NOAEL

was not identified in the study by Ito et al. (1973). Although the LOAEL (18 mg/kg/day) from Ito et al.

(1973) is slightly lower than the LOAEL (20 mg/kg/day) identified by Sumida et al. (2007), use of the

LOAEL from Ito et al. (1973) as the point of departure (POD) would necessitate the use of an uncertainty

factor of 10, while use of the NOAEL (2 mg/kg/day) from Sumida et al. (2007) does not. In addition, if

the LOAEL from Ito et al. (1973) were used as the POD, it would be equivalent to the value derived

based on the NOAEL from Sumida et al. (2007) (18 mg/kg/day divided by an uncertainty factor of 10 for

use of a LOAEL yields 1.8 mg/kg/day, which rounds to 2 mg/kg/day).

Summary of the Principal Study:

Sumida K, Siato K, Oeda K, et al. 2007. A comparative study of gene expression profiles in rat liver

after administration of α-hexachlorocyclohexane and lindane. J Toxicol Sci 32(3):261-288.

Groups of four male F344 rats were administered α-HCH (99% purity, in corn oil) by gavage at doses of

0 (corn oil control), 2, or 20 mg/kg/day for 28 consecutive days. The following parameters were

evaluated: body weight, serum clinical chemistry (AST, ALT, ALP, and total bilirubin in blood collected

at necropsy), liver weight, hepatic histopathology, and gene expression in the liver. There were no effects

on body weight at any dose. After 28 days of exposure, small but statistically significant increases in

AST and ALT were seen at 2 mg/kg/day, but not at 20 mg/kg/day. At the high dose, ALP was decreased

by 19% at the end of 28 days. At 20 mg/kg/day, liver weights were increased by 20% (absolute) and 25%

(relative) compared to controls. At 2 mg/kg/day, relative liver weight was increased by a small, but

HEXACHLOROCYCLOHEXANE (HCH) A-9

APPENDIX A

statistically significant margin of 6%. Hepatocellular hypertrophy was observed in 4/4 animals at

20 mg/kg/day compared to 0/4 in control and 2 mg/kg/day groups. Based on the increase in liver weight

and histological changes at 20 mg/kg/day, this dose is a LOAEL. No exposure-related changes occurred

at the 2 mg/kg/day, indicating that this dose is a NOAEL.

Selection of the Point of Departure for the MRL: The NOAEL of 2 mg/kg/day was selected as the POD

for derivation of the intermediate-duration oral MRL for α-HCH. Although quantitative data on

histopathology findings in the liver were reported, the incidence data increased from 0/4 at 2 mg/kg/day

to 4/4 at 20 mg/kg/day, so the data were not amenable to benchmark dose (BMD) modeling. BMD

modeling of relative liver weight data was undertaken, but that dataset was also not amenable to BMD

modeling, as neither the constant nor nonconstant variance models provide an adequate fit to the variance

data. Thus, the NOAEL was selected as the POD.

Adjustment for Intermittent Exposure: Not applicable.

Uncertainty and Modifying Factor: The NOAEL of 2 mg/kg/day was divided by a total uncertainty

factor (UF) of 100 and a modifying factor (MF) of 10:

• 10 for extrapolation from animals to humans

• 10 for human variability

A modifying factor of 10 was applied to the NOAEL to account for lack of data on developmental

toxicity and immunotoxicity and limitations in available data on neurotoxicity. These are sensitive

endpoints for other HCH isomers.

MRL = NOAEL ÷ (UF x MF)

2 mg/kg/day ÷ ((10 x 10) x 10) = 0.002 mg/kg/day

Other Additional Studies or Pertinent Information that Lend Support to this MRL: Hepatic effects

have been observed in rats, mice, and hamsters after intermediate- and chronic-duration oral exposures to

α-HCH. Observed effects include increases in absolute and relative liver weight, hepatocellular

hypertrophy and/or hyperplasia, focal necrosis, fatty degeneration, hepatomegaly, bile duct proliferation,

oval cells, nodular hyperplasia, and megalocytosis (Fitzhugh et al. 1950; Ito et al. 1973, 1975, 1976;

Nagasaki et al. 1975; Sumida et al. 2007; Tryphonas and Iverson 1983). Both rats and mice have also

developed liver tumors at higher doses of α-HCH (Hanada et al. 1973; Ito et al. 1973, 1975, 1976;

Nagasaki et al. 1975; Tryphonas and Iverson 1983; Tsukada et al. 1979).

There are no studies on the effects of α-HCH on the developing organism or on the immune system.

Studies of β- and γ-HCH have shown developmental effects (e.g., Di Consiglio et al. 2009; Hassoun and

Stohs 1996a; La Sala et al. 2009; Rivera et al. 1998; Sauviat et al. 2005; Srinivasan et al. 1991), and for

γ-HCH, these are the effects occurring at the lowest doses in animal studies. γ-HCH, and to a lesser

extent β-HCH, have been demonstrated to induce suppression of the immune system in several species

(e.g., Banerjee et al. 1996; Cornacoff et al. 1988; Desi et al. 1978; Dewan et al. 1980; Hong and Boorman

1993; Khurana et al. 1999; Koner et al. 1998; Mediratta et al. 2008; Meera et al. 1992; Van Velsen et al.

1986). Animal studies of γ-HCH indicate that these effects occur at lower doses than hepatic effects.

Thus, the lack of developmental and immunotoxicity data for α-HCH is a significant limitation of the

existing database for this isomer.

Data on the neurotoxicity of α-HCH are limited to a single study showing no change in motor nerve

conduction velocity after 30 days of exposure (Muller et al. 1981). Both β- and γ-HCH have induced

neurotoxic effects in laboratory rodents (e.g., Cornacoff et al. 1988; EPA 1999a; Gilbert and Mack 1995;

HEXACHLOROCYCLOHEXANE (HCH) A-10

APPENDIX A

Parmar et al. 2003; Van Velsen et al. 1986), and γ-HCH has been shown to induce neurotoxicity in

humans exposed orally (e.g., Davies et al. 1983; Harris et al. 1969; Munk and Nantel 1977; Nordt and

Chew 2000; Powell 1980; Starr and Clifford 1972; Storen 1955).

Agency Contacts (Chemical Managers): Malcolm Williams

HEXACHLOROCYCLOHEXANE (HCH) A-11

APPENDIX A

MINIMAL RISK LEVEL (MRL) WORKSHEET

Chemical Name: α-HCH

CAS Number: 319-84-6

Date: March 2024

Profile Status: Final

Route: Oral

Duration: Chronic

MRL: 0.0009 mg/kg/day (0.9 µg/kg/day)

Critical Effect: Increased liver weight and liver histopathology changes

Reference: Fitzhugh et al. 1950

Point of Departure: 0.9 mg/kg/day (NOAEL)

Uncertainty Factor: 100

Modifying Factor: 10

LSE Graph Key: 14

Species: Rat

MRL Summary: A chronic-duration oral MRL of 0.0009 mg/kg/day (0.9 µg/kg/day) was derived for

α-HCH based on a NOAEL of 0.9 mg/kg/day and a LOAEL of 4 mg/kg/day for increased liver weight

and liver histopathology changes in rats exposed to α-HCH in the diet for 107 weeks (Fitzhugh et al.

1950). A total uncertainty factor of 100 (10 for extrapolation from animals to humans and 10 for human

variability) and a modifying factor of 10 (for lack of immunotoxicity data and limitations in data on

potential neurotoxicity) were applied to the NOAEL to derive the MRL.

Selection of the Critical Effect: Two chronic-duration oral studies of α-HCH were located: Fitzhugh et

al. (1950) and Ito et al. (1975). While Ito et al. (1975) examined only cancer endpoints, Fitzhugh et al.

(1950) evaluated histopathology in a large number of organs and identified the liver as the most sensitive

target of chronic-duration oral exposure.

Selection of the Principal Study: Only Fitzhugh et al. (1950) evaluated endpoints other than cancer, so

this study was selected for use in derivation of the chronic-duration oral MRL.

Summary of the Principal Study:

Fitzhugh OG, Nelson AA, Frawley JP. 1950. The chronic toxicities of technical benzene hexachloride

and its α, β, and γ isomers. J Pharmacol Exp Ther 100:59-66.

Groups of 10 male and 10 female Wistar rats were treated with 0, 10, 50, 100, or 800 ppm α-HCH in food

for life. ATSDR calculated doses corresponding to these concentrations using default food intake and

body weight values for male and female Wistar rats in chronic studies as reported in EPA (1988b).

Estimated doses were 0, 0.7, 4, 7, or 60 mg/kg/day in males and 0, 0.9, 4, 9, or 70 mg/kg/day in females.

The lifetime of the animals sacrificed at the end of the experiment was taken as 107 weeks. Endpoints

included clinical signs, body weight, food consumption, organ weights (liver, kidney, and spleen), gross

pathology, and histopathology (lung, heart, liver, spleen, pancreas, stomach, small intestine, colon,

kidney, adrenal, thyroid, leg muscles and bones, bone marrow, and testis or uterus and ovary). The

numbers of animals per group evaluated for histopathology were 10, 8, 14, and 10 in the control through

100 ppm groups.

Survival was significantly reduced at the high dose (mean survival 35.9 weeks at 800 ppm [60–

70 mg/kg/day] versus 58.3 weeks in controls), so effects in this group are considered to reflect

intermediate-duration exposure. The mean age at death in the remaining groups did not differ from

HEXACHLOROCYCLOHEXANE (HCH) A-12

APPENDIX A

controls (58.3, 54.6, 54.9, and 56.2 weeks for control through 100 ppm groups, respectively). Body

weight gain through the first 6 months on study was tabulated for the 100 ppm (7–9 mg/kg/day) and

800 ppm (60–70 mg/kg/day) groups, but not for the 10 or 50 ppm groups. However, the text of the

publication indicated that “lower experimental dosage levels had no effect on growth.” Additionally,

there was no significant difference in body weight gain in the 100 ppm (7–9 mg/kg/day) group, and no

effect on food consumption in any group.

Histopathology findings were reported for the kidney, testes, and liver. Kidney pathological effects were

not observed in groups receiving 10, 50, or 100 ppm, with the exception of slight brown pigmentation of

the convoluted tubular epithelium at 100 ppm (7–9 mg/kg/day). The 800 ppm (60–70 mg/kg/day) group

had slight to moderate kidney damage primarily consisting of tubular dilatation and/or atrophy,

glomerular fibrosis and/or atrophy, and interstitial cell infiltration. The study authors reported a

“questionable” increase in the degree of testicular atrophy in the group exposed to 800 ppm (60–

70 mg/kg/day) α-HCH, but no further information was provided.

Significant increases in relative liver weight (both sexes grouped for analysis) were seen at 50 ppm (32%)

and 100 ppm (44%). Gross and microscopic pathology findings were limited to the liver in the groups

exposed for the full duration; there were no microscopic changes in the controls. Liver histopathology

findings in treated animals were described qualitatively as very slight histological changes at 50 ppm

(4 mg/kg/day) and slight histological changes at 100 ppm (7–9 mg/kg/day). The lesions were described

as “characteristic of certain chlorinated cyclic compounds” with citation to earlier studies of dichloro-

diphenyltrichloroethane (DDT). The earlier studies (e.g., Fitzhugh and Nelson 1947; Laug et al. 1950)

characterized the histological changes as primarily centrilobular hepatocellular hypertrophy with

increased cytoplasmic “oxyphilia” of these cells along with basophilia and margination of cytoplasmic

granules and hyalinization of cytoplasm. There was evidence of increased severity in the group exposed

to 800 ppm and surviving less than a year; these animals exhibited moderate histological damage

including hepatic cell enlargement or atrophy, fatty degeneration, and focal necrosis.

Based on the increase in liver weight and histological changes at 50 ppm, this dose (4 mg/kg/day) is a

LOAEL. No exposure-related changes occurred at the low dose in either sex, indicating that the NOAEL

is 10 ppm (0.7–0.9 mg/kg/day).

Selection of the Point of Departure for the MRL: The NOAEL of 0.9 mg/kg/day (for females) was

selected as the POD for MRL derivation (ATSDR policy is to select the highest NOAEL associated with

the lowest LOAEL for the POD). BMD modeling of the liver weight data was not possible because the

study did not report the numbers of animals per group evaluated for liver weights. Liver histology

findings were reported qualitatively and without incidences, so BMD modeling was not feasible for these

effects.

Adjustment for Intermittent Exposure: Not applicable.

Uncertainty and Modifying Factor: The NOAEL of 0.9 mg/kg/day was divided by a total uncertainty

factor (UF) of 100:

• 10 for extrapolation from animals to humans

• 10 for human variability

A modifying factor of 10 was applied to the NOAEL to account for the limitations (no immune studies,

one neurotoxicity study) in the toxicological database for α-HCH. Immune and nervous system effects

are sensitive endpoints for other HCH isomers.

HEXACHLOROCYCLOHEXANE (HCH) A-13

APPENDIX A

MRL = NOAEL ÷ (UF x MF)

0.9 mg/kg/day ÷ ((10 x 10) x 10) = 0.0009 mg/kg/day