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Toxicological Review of Trimethylbenzenes

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Toxicological Review of Trimethylbenzenes EPA/635/R-16/161Fa www.epa.gov/iris Toxicological Review of Trimethylbenzenes [CASRNs 25551-13-7, 95-63-6, 526-73-8, and 108-67-8] September 2016 Integrated Risk Information System National Center for Environmental Assessment Office of Research and Development U.S. Environmental Protection Agency Washington, DC Toxicological Review of Trimethylbenzenes 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. ii Toxicological Review of Trimethylbenzenes CONTENTS TABLES .............................................................................................................................................. v FIGURES ........................................................................................................................................... vi ABBREVIATIONS ..............................................................................................................................vii AUTHORS | CONTRIBUTORS | REVIEWERS ..................................................................................... ix PREFACE .......................................................................................................................................... xii PREAMBLE TO IRIS TOXICOLOGICAL REVIEWS................................................................................ xv EXECUTIVE SUMMARY ................................................................................................................. xxiii LITERATURE SEARCH STRATEGY | STUDY SELECTION AND EVALUATION ................................... xxxi 1. HAZARD IDENTIFICATION ....................................................................................................... 1-1 1.1. OVERVIEW OF THE TOXICOKINETICS OF TMBs ................................................................ 1-2 1.1.1. Toxicokinetics of TMB isomers ............................................................................. 1-2 1.1.2. Description of Toxicokinetic Models .................................................................... 1-4 1.2. SYNTHESIS OF EVIDENCE ................................................................................................. 1-5 1.2.1. Neurological Effects .............................................................................................. 1-5 1.2.2. Respiratory Effects ............................................................................................. 1-34 1.2.3. Reproductive and Developmental Effects .......................................................... 1-40 1.2.4. Hematological and Clinical Chemistry Effects .................................................... 1-46 1.2.5. General Toxicity .................................................................................................. 1-55 1.2.6. Carcinogenicity ................................................................................................... 1-56 1.2.7. Similarities among TMB Isomers Regarding Observed Inhalation and Oral Toxicity ............................................................................................................... 1-58 1.3. SUMMARY AND EVALUATION ....................................................................................... 1-62 1.3.1. Weight of Evidence for Effects Other than Cancer ............................................ 1-62 1.3.2. Weight of Evidence for Carcinogenicity ............................................................. 1-67 1.3.3. Susceptible Populations and Lifestages ............................................................. 1-68 2. DOSE-RESPONSE ANALYSIS .................................................................................................... 2-1 2.1. INHALATION REFERENCE CONCENTRATION FOR EFFECTS OTHER THAN CANCER FOR TMBs ................................................................................................................................ 2-1 2.1.1. Identification of Studies and Effects for Dose-Response Analysis and Derivation of Reference Concentrations for TMBs .................................................................... 2-1 iii Toxicological Review of Trimethylbenzenes 2.1.2. Methods of Analysis for Derivation of Reference Concentrations for TMBs ....... 2-8 2.1.3. Derivation of Candidate Inhalation Values for TMBs ......................................... 2-14 2.1.4. Derivation of Organ/System-Specific Reference Concentrations for TMBs ....... 2-21 2.1.5. Selection of the Overall Reference Concentration for TMBs ............................. 2-22 2.1.6. Uncertainties in the Derivation of the Reference Concentration for TMBs ....... 2-24 2.1.7. Confidence Statement for the Reference Concentration for TMBs ................... 2-26 2.1.8. Calculation of Subchronic Reference Concentrations for TMBs ........................ 2-26 2.2. ORAL REFERENCE DOSE FOR EFFECTS OTHER THAN CANCER FOR TMBs ..................... 2-28 2.2.1. Identification of Studies and Effects for Dose-Response Analysis and Derivation of Reference Doses for TMBs ................................................................................. 2-28 2.2.2. Methods of Analysis for Derivation of Reference Doses for TMBs .................... 2-29 2.2.3. Derivation of the Reference Dose for TMBs....................................................... 2-30 2.2.4. Uncertainties in the Derivation of the Reference Dose for TMBs ...................... 2-35 2.2.5. Confidence Statement for the Reference Dose for TMB ................................... 2-36 2.2.6. Calculation of Subchronic Reference Doses for TMBs ....................................... 2-36 2.3. CANCER RISK ESTIMATES FOR TMBs .............................................................................. 2-37 REFERENCES .................................................................................................................................. R-1 SUPPLEMENTAL INFORMATION ............................................................................................. (see Volume 2) iv Toxicological Review of Trimethylbenzenes TABLES Table P-1. Physical properties and chemical identities of TMB isomers ...................................... xiv Table ES-1. Organ/system-specific chronic RfCs for individual TMB isomers .............................. xxv Table ES-2. Organ/system-specific subchronic RfCs for individual TMB isomers ....................... xxvi Table LS-1. Details of the initial search strategy employed for TMBs ........................................ xxxi Table 1-1. Toxicokinetic similarities between TMB isomers ........................................................ 1-3 Table 1-2. Evidence pertaining to neurological effects of TMBs in animals—inhalation exposures .................................................................................................................. 1-17 Table 1-3. Evidence pertaining to neurological effects of TMBs in animals—oral exposures ... 1-23 Table 1-4. Evidence pertaining to respiratory effects of TMBs in animals—inhalation exposures .................................................................................................................. 1-36 Table 1-5. Evidence pertaining to reproductive and developmental effects of TMBs in animals— inhalation exposures ................................................................................................. 1-43 Table 1-6. Evidence pertaining to hematological and clinical chemistry effects of TMBs in animals—inhalation exposures ................................................................................. 1-49 Table 1-7. Evidence pertaining to hematological and clinical chemistry effects of TMBs in animals—oral exposures ........................................................................................... 1-52 Table 1-8. Similarities between 1,2,3-TMB, 1,2,4-TMB, and 1,3,5-TMB regarding observed inhalation and oral toxicity ....................................................................................... 1-62 Table 2-1. Target and actual exposure concentrations used in BMD modeling of 1,2,4-TMB, 1,2,3-TMB, and 1,3,5-TMB endpoints considered for the derivation of the RfC ........ 2-4 Table 2-2. Endpoints observed in rats in the Korsak studies (Korsak et al., 2000a, b; Korsak et al., 1997; Korsak and Rydzyński, 1996) considered for the derivation of the RfC for TMBs ........................................................................................................................... 2-5 Table 2-3. Endpoints observed in rats in the Saillenfait et al. (2005) study considered for the derivation of the RfC for TMBs ................................................................................... 2-6 Table 2-4. Isomer-specific DAFs using default dosimetric methods .......................................... 2-13 Table 2-5. Summary of derivation of PODs for TMBs ................................................................ 2-14 Table 2-6. Summary of derivation of candidate inhalation values for TMBs............................. 2-19 Table 2-7. Organ/system-specific RfCs and overall RfC for TMBs .............................................. 2-22 Table 2-8. Summary of derivation of subchronic RfC values for TMBs ...................................... 2-27 v Toxicological Review of Trimethylbenzenes FIGURES Figure LS-1. Literature search and study selection strategy for TMBs. .................................... xxxiii
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