Toxicological Review for Cyclohexane

Toxicological Review for Cyclohexane

EPA 635/R-03/008 www.epa.gov/iris TOXICOLOGICAL REVIEW OF CYCLOHEXANE (CAS No. 110-82-7) In Support of Summary Information on the Integrated Risk Information System (IRIS) August 2003 U.S. Environmental Protection Agency Washington, DC DISCLAIMER This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. Note: This document may undergo revisions in the future. The most up-to-date version will be made available electronically via the IRIS Home Page at http://www.epa.gov/iris. ii CONTENTS — TOXICOLOGICAL REVIEW OF CYCLOHEXANE (CAS No. 110-82-7) LIST OF TABLES .............................................................v LIST OF FIGURES ........................................................... vi FOREWORD ............................................................... vii AUTHORS, CONTRIBUTORS, AND REVIEWERS ............................... viii 1. INTRODUCTION ..........................................................1 2. CHEMICAL AND PHYSICAL INFORMATION RELEVANT TO ASSESSMENTS ................................................3 3. TOXICOKINETICS RELEVANT TO ASSESSMENTS ............................5 3.1. ABSORPTION .....................................................5 3.2. DISTRIBUTION ....................................................7 3.3. METABOLISM ....................................................11 3.4. EXCRETION ......................................................13 4. HAZARD IDENTIFICATION ................................................18 4.1. STUDIES IN HUMANS—EPIDEMIOLOGY, CASE REPORTS, CLINICAL CONTROLS ....................................................18 4.2. PRECHRONIC AND CHRONIC STUDIES AND CANCER BIOASSAYS IN ANIMALS—ORAL AND INHALATION .............................20 4.3. REPRODUCTIVE/DEVELOPMENTAL STUDIES—ORAL AND INHALATION ...................................................24 4.4. OTHER STUDIES ..................................................29 4.4.1. Acute Toxicity .............................................29 4.4.2. Neurological Studies .........................................30 4.4.3. Genotoxicity ...............................................32 4.5. SYNTHESIS AND EVALUATION OF MAJOR NONCANCER EFFECTS AND MODE OF ACTION ..............................................33 4.6. WEIGHT-OF-EVIDENCE EVALUATION AND CANCER CHARACTERIZATION ...........................................35 4.7. SUSCEPTIBLE POPULATIONS ......................................36 4.7.1. Possible Childhood Susceptibility ..............................36 4.7.2. Possible Gender Differences ...................................36 5. DOSE-RESPONSE ASSESSMENTS ..........................................38 5.1. ORAL REFERENCE DOSE (RfD) .....................................38 5.2. INHALATION REFERENCE CONCENTRATION (RfC) ..................38 5.2.1. Choice of Principal Study and Critical Effect—with Rationale and Justification ...............................................38 iii 5.2.2. Methods of Analysis—Benchmark Concentration Analysis ..........41 5.2.3. RfC Derivation—Including Application of Uncertainty Factors (UFs) . 44 5.3. CANCER ASSESSMENT ............................................45 6. MAJOR CONCLUSIONS IN THE CHARACTERIZATION OF HAZARD AND DOSE RESPONSE ...........................................46 6.1. HUMAN HAZARD POTENTIAL .....................................46 6.2. DOSE-RESPONSE .................................................47 7. REFERENCES ............................................................49 APPENDIX A: SUMMARY OF EXTERNAL PEER REVIEW COMMENTS AND DISPOSITION APPENDIX B: BENCHMARK DOSE iv LIST OF TABLES Table 3-1. Uptake and disappearance of cyclohexane in mouse blood after inhalation exposure ........................................8 Table 3-2. Tissue, saline, blood, and oil/air partition coefficients for cyclohexane ................9 Table 3-3. Cyclohexane burdens in rat cerebrum and perirenal fat after repeated exposure ..........................................10 Table 3-4. Concentration of cyclohexane in rat tissues after repeated exposure ................10 Table 5-1. Mean pup weights (G)—F1 generation .....................................39 Table 5-2. Mean pup weights (G)–F2 generation ......................................39 Table B-1. Summary of model outcomes, reproductive toxicity/multigenerational study (DuPont HLR, 1997a) ............................B-3 Table B-2. Summary of model fits, reproductive toxicity/multigenerational study (DuPont HLR, 1997a) ..............................................B-4 Tables of Standardized Residuals (Tables B-3a – B-3f) Table B-3a. F1: linear, constant variance model for average d25 pup weight .................B-6 Table B-3b. F1: linear, constant variance model for average pup weight gain d25-d7 ..........B-6 Table B-3c. F1: linear, heterogeneous variance model for average pup weight gain d25-d7 ......B-6 Table B-3d. F1: quadratic, heterogeneous variance model for average pup weight gain d25-d7 ..................................................B-6 Table B-3e. F2: linear, constant variance model for average pup weight gain d25-d7 ..........B-7 Table B-3f. F2: quadratic, constant variance model for average pup weight gain d25-d7 ........B-7 Tables B-4 - B-6 and Figure 2 refer to the results from the rat developmental study (DuPont HLR, 1997b) Table B-4. Summary of model outcomes, developmental study .........................B-11 Table B-5. Summary of model fits, developmental study ...............................B-12 Tables B-6a - B-6c. Standardized Residuals (DuPont HLR, 1997b) Table B-6a. Linear, heterogeneous variance model for average dam weight gain, gd17-gd7 ........................................................B-13 Table B-6b. Linear, constant variance model for average dam weight gain, gd17-gd7 .........B-13 Table B-6c. Linear, constant variance model for average dam body weight, gd17 ............B-13 v LIST OF FIGURES Figure B-1a. F1: linear, constant variance model for average d25 pup weight ............B-8 Figure B-1b. F1: linear, constant variance model for average pup weight gain d25-d7 .....B-8 Figure B-1c. F1: linear, heterogeneous variance model for average pup weight gain d25-d7 ..........................................................B-9 Figure B-1d. F1: quadratic, heterogeneous variance model for average pup weight gain d25-d7 ..........................................................B-9 Figure B-1e. F2: linear, constant variance model for average pup weight gain d25-d7 .....B-10 Figure B-1f. F2: quadratic, constant variance model for average pup weight gain d25-d7 . B-10 Figure B-2a. Linear, heterogeneous variance model for average dam weight gain, gd17-gd7 (DuPont HLR, 1997b) .................................................B-14 Figure B-2b. Linear, constant variance model for average dam weight gain, gd17-gd7 (DuPont HLR, 1997b) .................................................B-14 Figure B-2c. Linear, constant variance model for average dam body weight, gd17 .......B-15 vi FOREWORD The purpose of this Toxicological Review is to provide scientific support and rationale for the hazard and dose-response assessment in IRIS pertaining to chronic exposure to cyclohexane. It is not intended to be a comprehensive treatise on the chemical or toxicological nature of cyclohexane. In Section 6, EPA has characterized its overall confidence in the quantitative and qualitative aspects of hazard and dose response. Matters considered in this characterization include knowledge gaps, uncertainties, quality of data, and scientific controversies. This characterization is presented in an effort to make apparent the limitations of the assessment and to aid and guide the risk assessor in the ensuing steps of the risk assessment process. For other general information about this assessment or other questions relating to IRIS, the reader is referred to EPA’s IRIS Hotline at 301-345-2870. vii AUTHORS, CONTRIBUTORS, AND REVIEWERS CHEMICAL MANAGER Colette S. Hodes, Ph.D. Office of Pollution Prevention and Toxics U.S. Environmental Protection Agency Washington, DC AUTHORS Colette S. Hodes, Ph.D. Andrea Pfahles-Hutchens Office of Pollution Prevention and Toxics Office of Pollution Prevention and Toxics U.S. Environmental Protection Agency U.S. Environmental Protection Agency Washington, DC Washington, DC Elizabeth H. Margosches, Ph.D. Martha G. Price, Ph.D. Office of Pollution Prevention and Toxics Office of Pollution Prevention and Toxics U.S. Environmental Protection Agency U.S. Environmental Protection Agency Washington, DC Washington, DC REVIEWERS This document and summary information on IRIS have received peer review both by EPA scientists and by independent scientists external to EPA. Subsequent to external review and incorporation of comments, this assessment has undergone an Agency-wide review process whereby the IRIS Program Director has achieved a consensus approval among the Office of Research and Development; Office of Air and Radiation; Office of Prevention, Pesticides, and Toxic Substances; Office of Solid Waste and Emergency Response; Office of Water; Office of Policy, Economics, and Innovation; Office of Children’s Health Protection; Office of Environmental Information; and the Regional Offices. viii INTERNAL EPA REVIEWERS Angela Auletta, Ph.D. Susan Rieth, M.P.H. Office of Pollution Prevention and Toxics Office of Research and Development U.S. Environmental Protection Agency

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