if!; United States Environmental Protectioi if % Agency EPA/690/R-16/001F Final 9-28-2016 Provisional Peer-Reviewed Toxicity Values for oAminophenol (CASRN 95-55-6) Superfund Health Risk Technical Support Center National Center for Environmental Assessment Office of Research and Development U.S. Environmental Protection Agency Cincinnati, OH 45268 ------- AUTHORS, CONTRIBUTORS, AND REVIEWERS CHEMICAL MANAGER Q. Jay Zhao, PhD, MPH, DABT National Center for Environmental Assessment, Cincinnati, OH DRAFT DOCUMENT PREPARED BY SRC, Inc. 7502 Round Pond Road North Syracuse, NY 13212 PRIMARY INTERNAL REVIEWERS Scott C. Wesselkamper, PhD National Center for Environmental Assessment, Cincinnati, OH Jeffry L. Dean II, PhD National Center for Environmental Assessment, Cincinnati, OH This document was externally peer reviewed under contract to: Eastern Research Group, Inc. 110 Hartwell Avenue Lexington, MA 02421-3136 Questions regarding the content of this PPRTV assessment should be directed to the EPA Office of Research and Development's National Center for Environmental Assessment, Superfund Health Risk Technical Support Center (513-569-7300). li o-Aminophenol ------- TABLE OF CONTENTS COMMONLY USED ABBREVIATIONS AND ACRONYMS iv BACKGROUND 1 DISCLAIMERS 1 QUESTIONS REGARDING PPRTVs 1 INTRODUCTION 2 REVIEW OF POTENTIALLY RELEVANT DATA (NONCANCER AND CANCER) 5 HUMAN STUDIES 8 ANIMAL STUDIES 8 Oral Exposures 8 Inhalation Exposures 10 OTHER DATA (SHORT-TERM TESTS, OTHER EXAMINATIONS) 10 Genotoxicity 10 Supporting Animal Toxicity Studies 15 Metabolism/Toxicokinetic Studies 17 Mode-of-Action/Mechanistic Studies 17 DERIVATION 01 PROVISIONAL VALUES 18 DERIVATION OF ORAL REFERENCE DOSES 18 DERIVATION OF INHALATION REFERENCE CONCENTRATIONS 19 CANCER WEIGHT-OF-EVIDENCE DESCRIPTOR 19 DERIVATION OF PROVISIONAL CANCER POTENCY VALUES 19 APPENDIX A. SCREENING PROVISIONAL VALUES 20 APPENDIX B. REFERENCES 32 in o-Aminophenol ------- COMMONLY USED ABBREVIATIONS AND ACRONYMS a2u-g alpha 2u-globulin MN micronuclei ACGIH American Conference of Governmental MNPCE micronucleated polychromatic Industrial Hygienists erythrocyte AIC Akaike's information criterion MOA mode of action ALD approximate lethal dosage MTD maximum tolerated dose ALT alanine aminotransferase NAG N-acetyl-P-D-glucosaminidase AST aspartate aminotransferase NCEA National Center for Environmental atm atmosphere Assessment ATSDR Agency for Toxic Substances and NCI National Cancer Institute Disease Registry NOAEL no-observed-adverse-effect level BMD benchmark dose NTP National Toxicology Program BMDL benchmark dose lower confidence limit NZW New Zealand White (rabbit breed) BMDS Benchmark Dose Software OCT ornithine carbamoyl transferase BMR benchmark response ORD Office of Research and Development BUN blood urea nitrogen PBPK physiologically based pharmacokinetic BW body weight PCNA proliferating cell nuclear antigen CA chromosomal aberration PND postnatal day CAS Chemical Abstracts Service POD point of departure CASRN Chemical Abstracts Service Registry PODadj duration-adjusted POD Number QSAR quantitative structure-activity CBI covalent binding index relationship CHO Chinese hamster ovary (cell line cells) RBC red blood cell CL confidence limit RDS replicative DNA synthesis CNS central nervous system RfC inhalation reference concentration CPN chronic progressive nephropathy RfD oral reference dose CYP450 cytochrome P450 RGDR regional gas dose ratio DAF dosimetric adjustment factor RNA ribonucleic acid DEN diethylnitrosamine SAR structure activity relationship DMSO dimethylsulfoxide SCE sister chromatid exchange DNA deoxyribonucleic acid SD standard deviation EPA Environmental Protection Agency SDH sorbitol dehydrogenase FDA Food and Drug Administration SE standard error FEVi forced expiratory volume of 1 second SGOT glutamic oxaloacetic transaminase, also GD gestation day known as AST GDH glutamate dehydrogenase SGPT glutamic pyruvic transaminase, also GGT y-glutamyl transferase known as ALT GSH glutathione SSD systemic scleroderma GST glutathione-S-transferase TCA trichloroacetic acid Hb/g-A animal blood-gas partition coefficient TCE trichloroethylene Hb/g-H human blood-gas partition coefficient TWA time-weighted average HEC human equivalent concentration UF uncertainty factor HED human equivalent dose UFa interspecies uncertainty factor i.p. intraperitoneal UFh intraspecies uncertainty factor IRIS Integrated Risk Information System UFS subchronic-to-chronic uncertainty factor IVF in vitro fertilization UFd database uncertainty factor LC50 median lethal concentration U.S. United States of America LD50 median lethal dose WBC white blood cell LOAEL lowest-observed-adverse-effect level iv o-Aminophenol ------- FINAL 09-28-2016 PROVISIONAL PEER-REVIEWED TOXICITY VALUES FOR £>-AMINOPHENOL (CASRN 95-55-6) BACKGROUND A Provisional Peer-Reviewed Toxicity Value (PPRTV) is defined as a toxicity value derived for use in the Superfund Program. PPRTVs are derived after a review of the relevant scientific literature using established Agency guidance on human health toxicity value derivations. All PPRTV assessments receive internal review by a standing panel of National Center for Environment Assessment (NCEA) scientists and an independent external peer review by three scientific experts. The purpose of this document is to provide support for the hazard and dose-response assessment pertaining to chronic and subchronic exposures to substances of concern, to present the major conclusions reached in the hazard identification and derivation of the PPRTVs, and to characterize the overall confidence in these conclusions and toxicity values. It is not intended to be a comprehensive treatise on the chemical or toxicological nature of this substance. The PPRTV review process provides needed toxicity values in a quick turnaround timeframe while maintaining scientific quality. PPRTV assessments are updated approximately on a 5-year cycle for new data or methodologies that might impact the toxicity values or characterization of potential for adverse human health effects and are revised as appropriate. It is important to utilize the PPRTV database (http://hhpprtv.ornl.gov) to obtain the current information available. When a final Integrated Risk Information System (IRIS) assessment is made publicly available on the Internet (http://www.epa.gov/iris). the respective PPRTVs are removed from the database. DISCLAIMERS The PPRTV document provides toxicity values and information about the adverse effects of the chemical and the evidence on which the value is based, including the strengths and limitations of the data. All users are advised to review the information provided in this document to ensure that the PPRTV used is appropriate for the types of exposures and circumstances at the site in question and the risk management decision that would be supported by the risk assessment. Other U.S. Environmental Protection Agency (EPA) programs or external parties who may choose to use PPRTVs are advised that Superfund resources will not generally be used to respond to challenges, if any, of PPRTVs used in a context outside of the Superfund program. This document has been reviewed in accordance with U.S. EPA policy and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. QUESTIONS REGARDING PPRTVs Questions regarding the content of this PPRTV assessment should be directed to the EPA Office of Research and Development's National Center for Environmental Assessment, Superfund Health Risk Technical Support Center (513-569-7300). 1 o-Aminophenol ------- FINAL 09-28-2016 INTRODUCTION o-Aminophenol, CASRN 95-55-6, also known as 07^/?o-aminophenol, 2-aminophenol, o-hydroxyaniline, 2-hydroxyaniline, 2-amino-l-hydroxybenzene, o-aminohydroxybenzene, or o-hydroxyphenylamine, is a white crystalline solid commonly used in the fur and leather industry (under the name Oxidation Base 17 or C.I. 76520) to convert leather, fur, and hair from shades of gray to yellow-browns (Mitchell and Waring. 2012). o-Aminophenol is also used as a chemical intermediate for a variety of substances including pharmaceuticals (HSDB. 2011). stains and dyes (Mitchell et al.. 2003). and heterocyclic compounds such as oxyquinolines, phenoxamines, and benzoxazoles (Mitchell and Waring. 2012). In addition, o-aminophenol is a strong reducing agent used in photographic developers (Mitchell et al., 2003). It readily undergoes an oxidation/cyclization reaction in the presence of air (oxygen) and light to yield 2-aminophenoxazin-3-one (CASRN 1916-59-2) (Mitchell et al.. 2003). To avoid this undesirable reaction, o-aminophenol is often converted to a salt, such as a hydrochloride (CASRN 51-19-4), an acetate, or a sulfate (CASRN 67845-79-8), to increase its stability (Mitchell et al.. 2003V The empirical formula for o-aminophenol is C6H7NO (see Figure 1). Table 1 summarizes the physicochemical properties of o-aminophenol. Although o-aminophenol can act as both an acid and a base, the basic dissociation constant is larger (Mitchell et al„ 2003). As a result, it is more common to protonate the amine group than it is to remove a proton from the hydroxy group. o-Aminophenol does not exist as a dipolar ion (Mitchell et al.. 2003). NH Figure 1. o-Aminophenol Structure 2 o-Aminophenol ------- FINAL 09-28-2016 Table 1. Physicochemical Properties of o-Aminophenol (CASRN 95-55-6) Property (unit) Value Physical state White crystals that rapidly become yellow-brown when exposed to air and light3 Boiling point (°C) 267b Melting point (°C) 173.5b; sublimes rapidly without decomposition at 153°C at a reduced pressure of 11 mm Hg0-'1 Density (g/cm3) 1.328b Vapor pressure (mm Hg) 0.0031 (extrapolated)6 pH (unitless) NV pKa (at 25°C) pKai [-NH3(+i -NH2 + H(+l] = 4.66a; pKa2 [-OH -O1 1 + H(+l] = 9.7la Solubility in water (g/L) 20f Octanol-water partition constant (log Kow) 0.62g Henry's law constant (atm m3/mol at 25°C) 1.98 x 10"'(estimated)'1 Soil adsorption coefficient Koc (mL/g) 92 (estimated)'1 Atmospheric OH rate constant (cm3/molecule-sec at 25°C) 74.2 x 10 12 (estimated)'1 Atmospheric half-life (lir) 1.7 (estimated)'1 Relative vapor density (air = 1) NV Molecular weight (g/mol) 109.13 aMitchell et al. (2003). bHavnes et al. (2014). cMitchell and Waring (2012). do-Aminophenol is often purified via sublimation under reduced pressure. eThe vapor pressure was extrapolated from the measured boiling point using a regression-derived equation. fO'Neil et al. (2013). gHSDB (2011). hU.S. EPA (2012b). NV = not available. o-Aminophenol's moderate vapor pressure and estimated low Henry's law constant indicate that the compound could volatilize from dry surfaces but is unlikely to volatilize from water or moist surfaces. Its measured moderate water solubility and estimated low soil-adsorption coefficient indicate that o-aminophenol is likely to leach to groundwater or undergo runoff after a rain event. Thus, migration to groundwater is likely to compete with light-induced oxidation/cyclization in the environment depending on local conditions (wet, dry, shade, etc.). A summary of available toxicity values for o-aminophenol from EPA and other agencies/organizations is provided in Table 2. 3 o-Aminophenol ------- FINAL 09-28-2016 Table 2. Summary of Available Toxicity Values for o-Aminophenol (CASRN 95-55-6) Source" Value (applicability) Notes Reference Noncancer IRIS NV NA U.S. EPA (2016) HEAST NV NA U.S. EPA (2011a) DWSHA NV NA U.S. EPA (2012a) ATSDR NV NA ATSDR (2016) IPCS NV NA IPCS (2016); WHO (2016) Cal/EPA NV NA Cal/EPA (2014); Cal/EPA (2016a); Cal/EPA (2016b) OSHA NV NA OSHA (2006); OSHA (2011) NIOSH NV NA NIOSH (2016) ACGIH NV NA ACGIH (2015) Cancer IRIS NV NA U.S. EPA (2016) HEAST NV NA U.S. EPA (2011a) DWSHA NV NA U.S. EPA (2012a) NTP NV NA NTP (2014) IARC NV NA IARC (2015) Cal/EPA NV NA Cal/EPA (2011); Cal/EPA (2016a); Cal/EPA (2016b) ACGIH NV NA ACGIH (2015) aSources: ACGIH = American Conference of Governmental Industrial Hygienists; ATSDR = Agency for Toxic Substances and Disease Registry; Cal/EPA = California Enviromnental Protection Agency; DWSHA = Drinking Water Standards and Health Advisories; HEAST = Health Effects Assessment Summary Tables; IARC = International Agency for Research on Cancer; IPCS = International Programme on Chemical Safety; IRIS = Integrated Risk Information System; NIOSH = National Institute for Occupational Safety and Health; NTP = National Toxicology Program; OSHA = Occupational Safety and Health Administration. NA = not applicable; NV = not available. Non-date-limited literature searches were conducted in June 2015 and May 2016 for studies relevant to the derivation of provisional toxicity values for o-aminophenol (CASRN 95-55-6). Searches were conducted using U.S. EPA's Health and Environmental Research Online (HERO) database of scientific literature. HERO searches the following databases: PubMed, ToxLine (including TSCATS1), and Web of Science. The following databases were searched outside of HERO for health-related values: ACGIH, ATSDR, Cal/EPA, U.S. EPA IRIS, U.S. EPA HEAST, U.S. EPA Office of Water (OW), U.S. EPA TSCATS2/TSCATS8e, NIOSH, NTP, OSHA, and WHO. 4 o-Aminophenol ------- FINAL 09-28-2016 REVIEW OF POTENTIALLY RELEVANT DATA (NONCANCER AND CANCER) Tables 3A and 3B provide an overview of the relevant noncancer and cancer databases, respectively, for o-aminophenol and include all potentially relevant short-term-, subchronic-, and chronic-duration studies. The phrase "statistical significance" and the term "significant(ly)," used throughout the document, indicate ap-walue of < 0.05 unless otherwise noted. 5 o-Aminophenol ------- FINAL 09-28-2016 Table 3A. Summary of Potentially Relevant Noncancer Data for o-Aminophenol (CASRN 95-55-6) Category Number of Male/Female, Strain, Species, Study Type, Study Duration Dosimetry3 Critical Effects NO A EL1 BMDL/ BMCLa LOAEL1 Reference (comments) Notesb Human 1. Oral (mg/kg-d) ND 2. Inhalation (mg/m3) ND Animal 1. Oral (mg/kg-d)a Short-temi 5 M/0 F, rat (unspecified strain), diet, 12 d 0, 83, 586 Targets of toxicity include RBCs and potentially the liver and kidney. NDr NDr NDr Eastman Kodak (1979) (Inadequate reporting precludes independent identification of critical effect and NOAEL/LOAEL.) NPR 2. Inhalation (mg/m3) ND "¦Dosimetry: Values are converted to an ADD (mg/kg-day) for oral noncancer effects and an HEC (mg/m3) for inhalation noncancer effects. All repeated exposure values are converted from a discontinuous to a continuous exposure, with the exception of values from animal developmental studies, which are not adjusted to a continuous exposure. bNotes: NPR = not peer reviewed. ADD = adjusted daily dose; BMCL = benchmark concentration lower confidence limit; BMDL = benchmark dose lower confidence limit; F = female(s); HEC = human equivalent concentration; LOAEL = lowest-observed-adverse-effect level; M = male(s); ND = no data; NDr = not determined; NOAEL = no-observed-adverse-effect level; RBC = red blood cell. 6 o-Aminophenol ------- FINAL 09-28-2016 Table 3B. Summary of Potentially Relevant Cancer Data for o-Aminophenol (CASRN 95-55-6) Number of Male/Female, Strain, Species, Study Type, BMDL/ Category and Duration Dosimetry3 Critical Effects BMCLa Reference (comments) Notesb Human 1. Oral (mg/kg-d) ND 2. Inhalation (mg/m3) ND Animal 1. Oral (mg/kg-d)a Carcinogenicity 25 M/0 F, F344 rat, drinking 152 No evidence of hepatic or renal NDr Kurata et al. (1987) PR water, 52 wk (with or without carcinogenicity or tumor initiation with EHEN 2 wk promotion prior to exposure) Carcinogenicity 6 M/0 F, S-D rat, 9 mo 14.5 No evidence of carcinogenicity NDr Miller and Miller (1948) PR (Study is considered inadequate due to lack of controls, low animal number, short exposure duration limited endpoint evaluation and a single low dose that did not approach the MTD.) 2. Inhalation (mg/m3) ND "¦Dosimetry: The units for oral exposures are expressed as HEDs (mg/kg-day); HEDs are calculated using species-specific DAFs based on the animal:human body-weight scaling to the 1/4 power (i.e., BW14) ratio recommended by U.S. EPA (2011b): rat:human ratio = 0.24. bNotes: PR = peer reviewed. BMCL = benchmark concentration lower confidence limit; BMDL = benchmark dose lower confidence limit; DAF = dosimetric adjustment factor; EHEN = 7V-ethyl-7V-hydroxyethylnitrosamine; F = female(s); HED = human equivalent dose; M = male(s); MTD = maximum tolerated dose; ND = no data; NDr = not determined; S-D = Sprague-Dawley. 7 o-Aminophenol ------- FINAL 09-28-2016 HUMAN STUDIES No data regarding the toxicity of o-aminophenol to humans following chronic or subchronic exposure by any route have been identified. No acute oral or inhalation studies have been located; however, methemoglobinemia was reported in humans following an intravenous injection of o-aminophenol [Kiese and Rachor (1964) as cited by Akazawa et al. (2000)1. The only other available human data are acute patch testing studies reporting positive reactions to o-aminophenol in 8.3-25% of test subjects (Matsunaga et al.. 1989; Matsunaga et al.. 1988; Katoh et al.. 1986; Yasuno. 1985). ANIMAL STUDIES Oral Exposures The only repeated-dose oral studies found in the literature are an unpublished 12-day dietary toxicity study in rats with limited data reporting (Eastman Kodak. 1979). a tumor-promotion drinking water study in rats that evaluated limited systemic endpoints (Kurata et al„ 1987), and a 9-month dietary study in rats that evaluated liver carcinogenicity (Miller and Miller. 1948). Short-Term-Duration Studies Eastman Kodak (1979) Groups of five male rats were fed diets containing 0, 0.1, or 1.0% o-aminophenol in diets containing 1% corn oil for 12 consecutive days. The study authors calculated daily intakes to be 0, 83, or 586 mg/kg-day. Blood was collected for hematology (hemoglobin concentration, hematocrit, red blood cell [RBC] morphology, white blood cell [WBC] count, and differential) and serum chemistry (alanine aminotransferase [ALT], aspartate aminotransferase [AST], alkaline phosphatase [ALP], lactate dehydrogenase [LDH], and glucose). At sacrifice, liver and kidney weights were recorded, and unspecified tissues were examined for histopathological lesions. No quantitative data were included in the study report. No mortalities were reported. Clinical signs of toxicity observed at the 586-mg/kg-day dose included a yellowish cast to the fur and rust-colored urine; no clinical signs of toxicity were reported at the 83-mg/kg-day dose. Rats fed the 586 mg/kg-day diet consumed approximately half of the amount of food as controls and did not gain any weight, while rats in the 83-mg/kg-day dose group consumed slightly less than controls but had comparable body-weight gains. According to the study authors, decreased hemoglobin concentration and hematocrit, as well as RBC morphology, in rats fed 586 mg/kg-day were indicative of a chemical-induced anemia. Anemia was not observed at the 83-mg/kg-day dose. No changes in WBC counts or differential were observed in exposed rats relative to controls. Serum chemistry values were unaffected by treatment. Absolute liver and kidney weights were significantly reduced and relative weights were significantly increased in the 586-mg/kg-day group, compared with controls (percentage of changes were not reported); organ-weight effects were considered secondary to lack of body-weight gain. The only organ-weight change reported in the 83-mg/kg-day group was a significant increase in relative liver weight, compared with control. Histopathological changes attributed to treatment in the 586-mg/kg-day group were mild-to-moderate diffuse hyperkeratosis in the nonglandular portion of the stomach (due to irritation), minimal to moderate hypocellularity and congestion in the spleen, and atrophy of mesenteric fat (secondary to reduced food intake). None of these histopathological changes were observed in the 83-mg/kg-day group (control incidence not reported). The study authors 8 o-Aminophenol ------- FINAL 09-28-2016 concluded that toxicity targets of o-aminophenol included the RBC and potentially the liver and kidney. Data reporting is inadequate for independent analysis; therefore, a no-observed-adverse-effect level/lowest-observed-adverse-effect level (NOAEL/LOAEL) determination was not made for this study. Subchronic-Duration Studies No studies evaluating adverse effects following sub chronic-duration oral exposure to o-aminophenol have been identified. Chronic-Duration/Carcinogenicity Studies Kurataetal. (1987) Seventy-five male Fischer 344 rats were divided into three groups (25/group). Two groups were initiated with 0.1% A-ethyl-A'-hydroxyethylnitrosamine (EHEN) in the drinking water for 2 weeks. Following the 2-week EHEN exposure, one of the groups was fed a diet containing 0.8% o-aminophenol for 50 weeks (EHEN + o-aminophenol); the other group continued to receive the basal diet (EHEN only). The third group was fed the 0.8% o-aminophenol test diet for 50 weeks without EHEN-pretreatment (o-aminophenol only). All rats were sacrificed in Week 52. At sacrifice, body, liver, and kidney weights were recorded. Kidney and liver sections were microscopically evaluated for neoplastic lesions. Additional liver sections were also evaluated for glutathione-»Y-transferase placental type (GST-P) positive foci using immunohistochemistry. Based on terminal animal numbers, it appears that one rat from EHEN + o-aminophenol group, four rats from the EHEN-only group, and three rats from the o-aminophenol-only group died prior to study termination, but mortality details were not provided. Body weights were significantly decreased by 11-19% in the EHEN + o-aminophenol and o-aminophenol-only groups, compared with the EHEN-only group. Absolute liver weights were significantly decreased by 31-41% in the EHEN + o-aminophenol and o-aminophenol-only groups, compared with the EHEN-only group; relative liver weight was also significantly decreased by 35% in the o-aminophenol-only group, compared with the EHEN-only group. Absolute kidney weights were comparable among groups, but relative kidney weights were significantly increased by 20-29% in the EHEN + o-aminophenol and o-aminophenol-only groups, compared with the EHEN-only group. No neoplastic liver or kidney lesions were seen in the rats from the o-aminophenol-only group. The number of hepatocellular carcinomas in the liver of rats from the EHEN + o-aminophenol group (9/24) was significantly decreased compared with the incidence in the EHEN-only group (15/21), suggesting that o-aminophenol inhibited liver tumor development. Additionally, rats receiving EHEN + o-aminophenol showed significant decreases in the incidence of GST-P positive foci and the area of the foci, compared to rats that received EHEN alone. The incidence of neoplastic lesions in the kidney was comparable between the EHEN + o-aminophenol group and the EHEN-only group. Based on these results, o-aminophenol was not a carcinogenic or tumor-promoting agent in the liver and kidneys under the conditions of this study. A NOAEL/LOAEL determination for non-neoplastic effects (body and organ weights) was not made due to lack of an untreated control. Based on reference body weights and water consumption values for male F344 rats in a chronic-duration study (U.S. EPA. 1988). the estimated daily intake of o-aminophenol is 9 o-Aminophenol ------- FINAL 09-28-2016 632 mg/kg-day, which converts to a human equivalent dose (HED) of 152 mg/kg-day using the rat:human dosimetric adjustment factor (DAF) of 0.24 based on the animal :human body-weight scaling to the 1/4 power (i.e., BW1/4) ratio recommended by the U.S. EPA (2011b). Miller and Miller (1948) A group of six male Sprague-Dawley (S-D) rats was fed a diet containing 0.117% o-aminophenol hydrochloride for up to 9 months. A positive control group of 12 male rats was fed a diet containing 0.06% 4-dimethylaminoazobenzene up to 9 months. It is unclear whether a negative control group was used. The rats were sacrificed at 9 months, and the liver was examined for gross evidence of cirrhosis and tumor incidence. No gross evidence of liver cirrhosis or liver tumors was observed in the rats exposed to dietary o-aminophenol hydrochloride. o-Aminophenol was not carcinogenic under the conditions of this assay; however, confidence in this study is low due to lack of appropriate controls, low animal numbers, limited endpoint analysis, and use of a low dose that did not approach the maximum tolerated dose (MTD). Based on reference body weights and food consumption values for male S-D rats in a chronic-duration study (U.S. EPA. 1988). the estimated daily intake of o-aminophenol hydrochloride is 80.7 mg/kg-day. Based on molar-weight ratios (o-aminophenol accounts for 75% of total molecular weight of o-aminophenol hydrochloride), the estimated intake of o-aminophenol is 60.5 mg/kg-day, which converts to an HED of 14.5 mg/kg-day using the rat:human DAF of 0.24 based on the animal:human BW14 ratio recommended by the U.S. EPA (201 lb). Reproductive/Developmental Studies No studies evaluating the reproductive or developmental toxicity of o-aminophenol following oral exposure have been identified. Inhalation Exposures No studies evaluating the toxicity of o-aminophenol following inhalation exposure have been identified. OTHER DATA (SHORT-TERM TESTS, OTHER EXAMINATIONS) Genotoxicity The genotoxicity of o-aminophenol was evaluated in vitro and in a limited number of in vivo studies. Available studies are summarized below in Table 4. In general, the data indicate that o-aminophenol is a weak mutagen that could cause deoxyribonucleic acid (DNA) damage and clastogenic effects. 10 o-Aminophenol ------- FINAL 09-28-2016 Table 4. Summary of o-Aminophenol (CASRN 95-55-6) Genotoxicity, Mutagenicity, and Clastogenicity Endpoint Test System Dose/ Concentration3 Results without Activationb Results with Activationb Comments References (notes) Genotoxicity studies in prokaryotic organisms Mutation Salmonella tvphimurium TA1535, TA1537, TA98, and TA100 0, 10, 33, 100, 166, 333,666, 1,000 ng/plate + (TA100) (TA1535, TA1537, TA98) + (TA100) (TA1535, TA1537, TA98) Preincubation assay: o-Aininophenol induced a 2-3-fold increase in revertant colonies in TA100 with and without S9 activation at >166 pg/plate. Cytotoxicity was noted at >666 pg/plate without activation. Haworth et al. (1983) (Case Western Reserve University) Mutation S. tvphimurium TA1535, TA1537, TA98, and TA100 0, 10,33, 100,333, 400, 666, 750 ng/plate + (TA100) (TA1535, TA1537, TA98) + (TA100) (TA1535, TA1537, TA98) Preincubation assay: o-Aininophenol induced a 2-3-fold increase in revertant colonies in TA100 without activation at >333 ng/plate and a 2-6-fold increase with S9 activation at >100 pg/plate. Cytotoxicity was noted at >666 pg/plate without activation. Haworth et al. (1983) (EG&G Mason Research Institute) Mutation S. tvphimurium TA1535, TA1537, TA98, and TA100 0, 10, 33, 100, 333, 667, 1,000, 3,333, 6,667, 10,000 ng/plate + (TA100) (TA1535, TA1537, TA98) Preincubation assay: o-Aininophenol induced a 2-fold increase in revertant colonies in TA100 with S9 activation at >1,000 ng/plate. Cytotoxicity was noted at >667 ng/plate without activation and >6,667 ng/plate with activation. Haworth et al. (1983) (SRI International) Mutation S. tvphimurium TA98 and TA100 Concentrations not reported + + Mutagenic activity was 2-3 times greater than controls; unclear whether the effect was observed in one or both strains. Nishimura and Osliima (1983) as cited in U.S. EPA (1985) (Japanese study, abstract only) Mutation S. tvphimurium TA98 and TA100 0, 25, 50, 100, 250, 500 ng/plate + (TA100) (TA98) Plate incorporation assay: o-Aininophenol induced a 2-3-fold increase over control in the number of revertant colonies in TA100 with S9 activation at >100 pg/plate. Cytotoxicity in TA100 was noted at >250 ng/plate without S9 activation. Lavoie et al. (1979) 11 o-Aminophenol ------- FINAL 09-28-2016 Table 4. Summary of o-Aminophenol (CASRN 95-55-6) Genotoxicity, Mutagenicity, and Clastogenicity Endpoint Test System Dose/ Concentration3 Results without Activationb Results with Activationb Comments References (notes) Mutation S tvphimurium G46, TA1535, TA100, C3076, TA1537, D3052, TA1538, and TA98 Plate gradient ranges: 0.1-1, 1-10, 10-100, 100-1,000 ng/inL agar + (TA100) (G46, TA1535, C3076, TA1537, D3052, TA1538, TA98) + (TA100) (G46, TA1535, C3076, TA1537, D3052, TA1538, TA98) Modified gradient plate test: o-Aininophenol was mutagenic at 7-100 iig/mL agar; reporting is inadequate to determine whether the compound was mutagenic with metabolic activation, without metabolic activation or under both tested conditions. ThoniDSon et al. (1983) Mutation S. tvphimurium TA1535, TA1537, TA1538, TA98, and TA100 Concentrations not reported Plate incorporation assay. De Flora et al. (1984) Mutation S. tvphimurium TA98 and TA100 0,0.5, 1.0, 2.0 |imol/platc (~0, 50, 100, 200 ng/plate) + Plate incorporation assay. No cytotoxicity was observed. Desawa et al. (1979) Mutation S. tvphimurium TA98 and TA100 15-150 ng/plate Plate incorporation assay. Yoshikawa et al. (1976) as cited in U.S. EPA (1985) (Japanese study) Mutation S. tvphimurium TA98 10-30 ng/plate NA Watanabe et al. (1991) as cited in CCRIS (1993) (Japanese study) Mutation Escherichia coli WP2and WF2«/vr.4- Plate gradient ranges: 0.1-1, 1-10, 10-100, 100-1,000 ng/mL agar Modified gradient plate test. ThoniDSon et al. (1983) DNA repair test E. coli WP2 (wild-type), WP67 (uvrApolA-), andCM871 (uvrA- recA-, lexA-) Eight 2-fold dilutions starting from solubility or toxic concentration + (CM871, WP67) MIC was 20 ng. De Flora et al. (1984) 12 o-Aminophenol ------- FINAL 09-28-2016 Table 4. Summary of o-Aminophenol (CASRN 95-55-6) Genotoxicity, Mutagenicity, and Clastogenicity Endpoint Test System Dose/ Concentration3 Results without Activationb Results with Activationb Comments References (notes) DNA damage (SOS chromotest) E. coli PQ37 Concentration not reported + NV o-Aminophenol was tested after in vitro nitrosation via incubation with sodium nitrate at 37°C for 1 lir prior to conducting the SOS chromotest. The SOSIP of o-aminophenol was 5.9 compared with compounds that were not genotoxic (SOSIP <0.006). Bartsch et al. (1991); Ohshima et al. (1989) Genotoxicity studies in nonmammalian eukaryotic organisms Sex-linked recessive lethal mutations Drosophila melanogaster 0, 200 (feeding); 0, 100 (injection) (feeding, injection) (feeding, injection) NA Yoonetal. (1985) Genotoxicity studies in mammalian cells—in vitro CAs CHO 0.1,0.2, 0.5 mM + NV o-Aminophenol induced a 4-17-fold increase in CAs. Observed CAs were predominantly chromatid exchanges and breaks, with a small percentage of dicentrics and rings. Kanava (1996) SCE Human lymphocytes 0, 1.6, 3.3, 6.6 ng/mL + NV o-Aminophenol induced a 1.2-1.9-fold, dose-dependent increase in SCE frequency over control. Kirchner and Baver (1982) SCE Human fibroblasts 0,0.01,0.03,0.10, 0.3 mM + NV o-Aminophenol induced a 2-fold increase in SCE frequency at 0.10 mM. Cytotoxicity was noted at 0.30 mM. Wilmer et al. (1981) SCE CHO 0.1,0.2, 0.5 mM + NV o-Aminophenol induced a 1.5-2-fold dose-dependent increase in SCE. Kanava (1996) SCE Chinese hamster V79 5-20 nM + NV NA Wild et al. (1981) (abstract) UDS Primary rat hepatocytes 0.5, 1.0,5.0, 10, 50, 100, 500, 1,000 nmol/mL NV NA Thompson et al. (1983) 13 o-Aminophenol ------- FINAL 09-28-2016 Table 4. Summary of o-Aminophenol (CASRN 95-55-6) Genotoxicity, Mutagenicity, and Clastogenicity Endpoint Test System Dose/ Concentration3 Results without Activationb Results with Activationb Comments References (notes) Genotoxicity studies in mammals—in vivo CAs Ehrlich ascites tumor cells in the mouse Concentration not reported o-Aminophenol was "applied" to tumor cells; no further details provided. Boeaiewski and Boeaiewska (1982) (abstract) SCE Chinese hamster bone marrow cells 5 mg/kg i.p. — — Animal sacrificed 4 lir after injection. Kirchner and Baver (1982) Mouse micronucleus test Mouse bone marrow 0.5-2.0 mM/kg i.p. + + NA Wild et al. (1981) (abstract) Genotoxicity studies with extracellular purified DNA DNA cleavage 32P-5 '-end-labeled DNA fragments from human p53 tumor suppressing gene and c-Ha-rav-1 proto-oncogene 0, 5 nM (without Cu[II]); and 0, 1, 2, and 5 |iIVI (with Cu[II]) (without Cu[II]) + (with Cu[II]) (without Cu[II]) + (with Cu[II]) o-Aminophenol incubated in the presence of Cu(II) caused DNA damage, but did not cause damage without Cu(II). Ohkuma and Kawanishi (2001) Oxidative DNA damage (8-oxodG formation) Calf thymus DNA 0, 1, 2, 5 ^M [with or without Cu(II)] (without Cu[II]) + (with Cu[II]) (without Cu[II]) + (with Cu[II]) o-Aminophenol incubated in the presence of Cu(II) significantly increased the formation of 8-oxodG, compared with control. o-Aminophenol alone did not induce oxidative DNA damage. Ohkuma and Kawanishi (2001) DNA strand break Double-stranded /.DNA 250 nM + + Exposure to o-aminophenol produced DNA fragments between 0.6 and 0.000004 daltons. Yamada et al. (1985) aLowest effective dose for positive results, highest dose tested for negative results. b+ = positive; - = negative. 8-oxoG = 8-oxo-7,8-dihydro-29-deoxyguanosine; CA = chromosomal aberration; CHO = Chinese hamster ovary (cell line cells); Cu = copper; DNA = deoxyribonucleic acid; i.p. = intraperitoneal; MIC = minimally inhibitory concentration; NA = not applicable; NV = not available; SCE = sister chromatid exchange; SOSIP = SOS-inducing potency factor; UDS = unscheduled DNA synthesis. 14 o-Aminophenol ------- FINAL 09-28-2016 Available evidence from in vitro studies indicates that o-aminophenol is a weak mutagen. Several studies indicate that o-aminophenol is weakly mutagenic to Salmonella typhimurium strain TA100 with and without metabolic activation. In general, induction of revertant colonies was only two- to threefold greater than controls at noncytotoxic concentrations [Nishimura and Oshima (1983) as cited in U.S. EPA (1985); Haworth et al. (1983); Thompson et al. (1983); Lavoie et al. (1979)1. Other studies evaluating o-aminophenol found no evidence of mutagenicity in S. typhimurium strain TA100 with or without metabolic activation [Yoshikawa et al. (1976) as cited in U.S. EPA (1985); De Flora et al. (1984); Degawa et al. (1979)1. Mutagenicity was not reported in various other S. typhimurium strains or Escherichia coli strains WP2 or WF2//v/:4 [Watanabe et al. (1991) as cited in CCRIS (1993); Yoshikawa et al. (1976) as cited in U.S. EPA (1985); De Flora et al. (1984); Haworth et al. (1983); Nishimura and Oshima (1983); Thompson et al. (1983); Degawa et al. (1979); Lavoie et al. (1979)1. o-Aminophenol did not cause sex-linked recessive lethal mutations in Drosophila melanogaster following exposure via feeding or injection (Yoon et al.. 1985). o-Aminophenol caused clastogenic effects in several in vitro assays without metabolic activation, including chromosomal aberrations (CAs) in Chinese hamster ovary (CHO) cells and sister chromatid exchanges (SCEs) in human lymphocytes, human fibroblasts, CHO cells, and Chinese hamster V79 cells (Kan ay a. 1996; Kirchner and Bayer. 1982; Wild et al.. 1981; Wilmer et al.. 1981). Micronuclei (MN) were induced in mouse bone marrow cells following intraperitoneal (i.p.) injections of o-aminophenol (Wild et al„ 1981). However, in other in vivo assays, o-aminophenol did not induce CA in Ehrlich ascites tumor cells injected into mice (Bogaiewski and Bogaiewska. 1982) or SCE in Chinese hamster bone marrow cells (Kirchner and Bayer. 1982). Available data indicate that o-aminophenol is capable of causing DNA damage in vitro; however, findings are inconsistent among different test systems. o-Aminophenol inhibited DNA repair in E. coli strains CM871 and WP67, but not wild-type WP2 at concentrations >20 |ig/plate (De Flora et al.. 1984). DNA damage was induced in E. coli strain PQ37 incubated with nitrosated o-aminophenol in the SOS chromotest; o-aminophenol was not tested prior to nitrosation (Bartsch et al.. 1991; Ohshima et al.. 1989). Unscheduled DNA synthesis was not induced in primary rat hepatocytes exposed to o-aminophenol (Thompson et al.. 1983). In isolated DNA samples, o-aminophenol induced strand breaks in double-stranded XDNA (Yamada et al.. 1985). o-Aminophenol also caused DNA damage in calf thymus DNA and 32P-5'-end-labeled DNA fragments from humanp53 tumor-suppressing gene and c-Ha-ra.s -1 proto-oncogene in the presence, but not absence, of copper (Cu[II]), suggesting that oxidation of o-aminophenol to the o-aminophenoxyl radical in the presence of Cu(II) underlies the observed DNA damage in isolated DNA fragments (Ohkuma and Kawanishi. 2001). Supporting Animal Toxicity Studies Acute Toxicity Acute studies indicate that o-aminophenol is a strong inducer of methemoglobinemia in rats, but not mice. Methemoglobinemia was reported in rats exposed once to o-aminophenol at an oral dose of 750 mg/kg, with methemoglobin formation of 50% in exposed rats compared with 0.71% in controls 2 hours post-treatment (Eastman Kodak, 1979). In an i.p. injection study, methemoglobin formation increased in a dose-related manner in rats exposed to o-aminophenol at doses of 0.15-1.0 mM/kg (55-110 mg/kg); methemoglobin formation was -10% at the lowest dose and -70% at the highest dose at 1 hour postinjection (data reported graphically, control data 15 o-Aminophenol ------- FINAL 09-28-2016 not reported) (Harrison and Jollow. 1987). In contrast, methemoglobin formation rates were much lower in mice (2-3%) following an i.p. injection of 300 mg/kg (control data not reported); the study authors concluded that o-aminophenol was not a strong inducer of methemoglobin formation in mice (Itoh. 1987). Itoh (1987) also reported low Heinz body formation (<4%) in exposed mice following i.p. injection. There is limited evidence from acute parenteral studies that o-aminophenol may cause mild kidney toxicity. Itoh (1987) reported mild tubular vacuolated degeneration and slight flattening of collecting tubules with dilatation in rat kidneys 1 week following an i.p. dose of 200 mg/kg (but not <150 mg/kg); however, no histological damage was observed in the kidneys of rats 48 hours after a single intravenous injection of 2.8 mM/kg (310 mg/kg) (Calder et al.. 1971). Other parenteral studies reported no changes in kidney weight or serum blood urea nitrogen (BUN) levels (Rankin et al.. 1996; Newton et al.. 1982). although Rankin et al. (1996) reported a transient increase in urinary protein excretion in rats exposed to o-aminophenol. Reported oral median lethal dose (LD50) values include 951 mg/kg in male rats, 1,100 mg/kg in male and female rats, and 800 mg/kg in male mice (Eastman Kodak. 1979; University of Miami, 1975). Animals receiving single doses >940 mg/kg showed clinical signs of neurotoxicity, including tremors, convulsions, and central depression; it is unclear whether or not neurotoxic effects were limited to moribund animals (University of Miami. 1975). In anesthetized mice, the effective i.p. dose that caused 50% of mice (effective dose [ED50]) to have a myoclonic convulsion (jerk) in response to a strong pinch was 3.42 mM/kg (376 mg/kg) (Angel and Rogers. 1972). Carcinogenicity No elevated incidences of squamous metaplasia or carcinoma of the bladder were observed in mice following implantation of cholesterol-based pellets containing o-aminophenol in the urinary bladder, compared with mice implanted with a cholesterol pellet containing no chemicals (Clavson et al.. 1958). In a dermal cancer bioassay, no evidence of carcinogenicity was observed in rats following skin exposure to a hair-dye formulation containing several chemicals, including 0.3% o-aminophenol, for 2 years (Burnett and Goldenthal. 1988). Reproductive/Developmental Effects A two-generation reproduction study conducted by dermal exposure found no adverse reproductive effects in rats following skin exposure to a hair-dye formulation containing several chemicals, including 0.3% o-aminophenol (Burnett and Goldenthal. 1988). Developmental effects of o-aminophenol were studied only by parenteral exposure. Dose-related increases in frequency of litters with one or more malformed fetuses, number of fetuses presenting with one or more malformations, and number of fetal resorptions were observed in Syrian golden hamsters (LKV strain) following maternal exposure to 150-200 mg/kg via i.p. injection on Gestation Day (GD) 8, compared with controls; these effects were not observed at 100 mg/kg (Rutkowski and Ferm. 1982). Induced malformations included neural tube defects (encephalocele, exencephaly, and spina bifida), eye, limb, tail, and rib defects, and umbilical hernia (often involving eventration of the abdominal viscera). 16 o-Aminophenol ------- FINAL 09-28-2016 o-Aminophenol was not toxic to the dams at these doses, suggesting that the fetus may be a sensitive target for o-aminophenol toxicity. Metabolism/Toxicokinetic Studies Oral absorption is very high (-95%) in laboratory animals (U.S. EPA. 1985). No evidence of percutaneous absorption was observed through depilated abdominal skin in guinea pigs during a 24-hour exposure in occluded conditions (Eastman Kodak. 1979). No distribution data were located for o-aminophenol. o-Aminophenol is metabolized primarily via conjugation at the phenolic group with sulfate or glucuronide, and the conjugated metabolites are excreted in the urine (Elder. 1988; U.S. EPA. 1985). A-acetylation can also occur, forming an acetamidophenol metabolite, which may be further conjugated with glucuronide prior to excretion in the urine (see Table 5) (U.S. EPA. 1985). Table 5. Percent Recovery of Administered Dose in the Urine over 24 Hours Following a Single Oral Dose of o-Aminophenol in Rabbits (1,000 mg/Rabbit)a Parent or Metabolite Percent of Total Parent 11 Aminophenylglucuronide 52 Aminophenolsulfate 15 Acetamidophenol 2-4 Acetamidophenylglucuronide 13 Acetamidophenylsulfate 0 aU.S. EPA (1985). Mode-of-Action/Mechanistic Studies Mode-of-action (MOA)/mechanistic data are consistent with the short-term-duration Eastman Kodak (1979) in vivo study regarding toxicity to RBCs, kidney, and liver. Limited evidence from acute human and animal studies suggests that methemoglobinemia may occur following o-aminophenol exposure [Kiese and Rachlor (1964) as cited in Akazawa et al. (2000); Harrison and Jollow (1987); Eastman Kodak (1979)1. o-Aminophenol also induces methemoglobin formation in erythrocyte suspensions in vitro (Akazawa et al.. 2000; Harrison and Jollow. 1987; Eckert and Ever. 1983; Smith et al.. 1967). The kidney (Rankin et al.. 1996; Itoh. 1987; Newton et al.. 1982; Eastman Kodak. 1979; Calder et al.. 1971) and liver (Eastman Kodak. 1979) may be potential targets of o-aminophenol toxicity. In vitro, o-aminophenol was moderately toxic to renal slice cultures from male F344 and S-D rats, as evidenced by significantly reduced glutathione levels and decreased gluconeogenesis in response to stimulation with pyruvate or 1,6-diphosphate at concentrations of >0.1 mM (Valentovic and Ball. 1998; Valentovic et al.. 1996). Significantly increased LDH leakage (indicative of cell death) was observed at 1 mM in slices from F344 rats only (Valentovic and Ball. 1998; Valentovic et al.. 1996). Gluconeogenesis in response to stimulation with pyruvate was also observed in hepatic slices from F344 rats at 2 mM o-aminophenol, without evidence of cytotoxicity (Valentovic et al.. 1996). 17 o-Aminophenol ------- FINAL 09-28-2016 DERIVATION OF PROVISIONAL VALUES Tables 6 and 7 present summaries of noncancer and cancer references values, respectively. Table 6. Summary of Noncancer Reference Values for o-Aminophenol (CASRN 95-55-6) Toxicity Type (units) Species/Sex Critical Effect p-Reference Value* POD Method POD (HED) UFc Principal Study Screening subchronic p-RfD (mg/kg-d)* Rat/M Increased severity of nephrosis 4 x 1(T2 NOAEL 12 (based on surrogate POD) 300 Burnett et al. (1989) as cited in U.S. EPA (2005b) Screening chronic p-RfD (mg/kg-d)* Rat/M Increased severity of nephrosis 4 x 1(T3 NOAEL 12 (based on surrogate POD) 3,000 Burnett et al. (1989) as cited in U.S. EPA (2005b) Subchronic p-RfC (mg/m3) NDr Chronic p-RfC (mg/m3) NDr *See detailed derivation in Appendix A. HED = human equivalent dose; M = rnale(s); NDr = not determined; NOAEL = no-observed-adverse-effect level; POD = point of departure; p-RfC = provisional reference concentration; p-RfD = provisional reference dose; UFC = composite uncertainty factor. Table 7. Summary of Cancer Reference Values for o-Aminophenol (CASRN 95-55-6) Toxicity Type (units) Species/Sex Tumor Type Cancer Value Principal Study p-OSF (mg/kg-d) 1 NDr p-IUR (mg/m3)-1 NDr NDr = not determined; p-IUR = provisional inhalation unit risk; p-OSF = provisional oral slope factor. DERIVATION OF ORAL REFERENCE DOSES No studies were located regarding toxicity of o-aminophenol to humans by oral exposure. Oral studies of o-aminophenol in animals were of inadequate duration and/or scope to support derivation of a subchronic or chronic provisional reference dose (p-RfD). The only repeated-dose study that evaluated non-neoplastic endpoints was conducted by Eastman Kodak (19791 in which five male rats per dose were fed diets with 0, 83, or 586 mg/kg-day o-aminophenol for 12 days. The study is limited by the use of a single sex (male), small animal groups (five/group), and short duration (12 days). As a result of the limitations of the available data for o-aminophenol, subchronic and chronic p-RfDs are not derived. Instead, screening p-RfDs are derived in Appendix A using an alternative surrogate approach. 18 o-Aminophenol ------- FINAL 09-28-2016 DERIVATION OF INHALATION REFERENCE CONCENTRATIONS No subchronic- or chronic-duration inhalation studies of o-aminophenol in humans or animals have been located, precluding derivation of provisional reference concentrations (p-RfCs) for o-aminophenol based on chemical-specific data. An alternative surrogate approach was attempted, but screening p-RfCs could not be derived due to a lack of inhalation toxicity values for potential surrogates (see Appendix A). CANCER WEIGHT-OF-EVIDENCE DESCRIPTOR Table 8 identifies the cancer weight-of-evidence (WOE) descriptor for o-aminophenol. Table 8. Cancer WOE Descriptor for o-Aminophenol (CASRN 95-55-6) Possible WOE Descriptor Designation Route of Entry Comments "Carcinogenic to Humans " NS NA There are no human data to support this. "Likely to Be Carcinogenic to Humans " NS NA Results from available animal studies are not sufficient to support this, and no human data are available. "Suggestive Evidence of Carcinogenic Potential" NS NA Results from available animal studies are not sufficient to support this, and no human data are available. "Inadequate Information to Assess Carcinogenic Potential" Selected Inhalation and oral No carcinogenicity studies are available that evaluated oral and inhalation exposure. "Not Likely to Be Carcinogenic to Humans " NS NA The available data do not support this. NA = not applicable; NS = not selected; WOE = weight of evidence. No data in humans are available to assess the carcinogenic potential of o-aminophenol. o-Aminophenol did not cause liver tumors in rats in a 9-month dietary study by Miller and Miller (1948); however, this bioassay is considered inadequate due to lack of appropriate control group, low animal numbers, short duration, limited endpoint analysis, and use of a low dose that did not approach the MTD. The only other studies evaluating the carcinogenic potential of o-aminophenol included a drinking water tumor promotion assay and a bladder implantation assay; neither of these limited studies indicated that o-aminophenol was a carcinogenic or tumor-promoting agent (Kurata et al.. 1987; Clavson et al.. 1958). Genotoxicity data suggest that o-aminophenol is a weak mutagen and may cause DNA damage and clastogenic effects. Under the U.S. EPA cancer guidelines (U.S. EPA, 2005a), there is inadequate information to assess the carcinogenic potential of o-aminophenol. DERIVATION OF PROVISIONAL CANCER POTENCY VALUES Derivation of quantitative estimates of cancer risk for o-aminophenol is precluded by the absence of adequate carcinogenicity data for this compound. 19 o-Aminophenol ------- FINAL 09-28-2016 APPENDIX A. SCREENING PROVISIONAL VALUES For reasons noted in the main provisional peer-reviewed toxicity values (PPRTV) document, it is inappropriate to derive provisional toxicity values for o-aminophenol. However, information is available for this chemical which, although insufficient to support derivation of a provisional toxicity value under current guidelines, may be of limited use to risk assessors. In such cases, the Superfund Health Risk Technical Support Center summarizes available information in an appendix and develops a "screening value." Appendices receive the same level of internal and external scientific peer review as the PPRTV documents to ensure their appropriateness within the limitations detailed in the document. Users of screening toxicity values in an appendix to a PPRTV assessment should understand that there is considerably more uncertainty associated with the derivation of an appendix screening toxicity value than for a value presented in the main body of the assessment. Questions or concerns about the appropriate use of screening values should be directed to the Superfund Health Risk Technical Support Center. APPLICATION OF AN ALTERNATIVE SURROGATE APPROACH The surrogate approach allows for the use of data from related compounds to calculate screening values when data for the compound of interest are limited or unavailable. Details regarding searches and methods for surrogate analysis are presented in Wang et al. (2012). Three types of potential surrogates (structural, metabolic, and toxicity-like) are identified to facilitate the final surrogate chemical selection. The surrogate approach may or may not be route-specific or applicable to multiple routes of exposure. In this document, it is limited to the oral noncancer effects only, based on the available toxicity data. All information was considered together as part of the final weight-of-evidence (WOE) approach to select the most suitable surrogate both toxicologically and chemically. Structural Surrogates (Structural Analogs) An initial surrogate search focused on the identification of structurally similar chemicals with toxicity values from the Integrated Risk Information System (IRIS), PPRTV, Agency for Toxic Substances and Disease Registry (ATSDR), or California Environmental Protection Agency (Cal/EPA) databases to take advantage of the well-characterized chemical-class information. This was accomplished by searching EPA's DSSTox database (DSSTox. 2016) and the National Library of Medicine's (NLM's) ChemlDplus database (ChemlDplus. 2016). Two structural analogs to o-aminophenol were identified that have oral toxicity values: w-aminophenol (U.S. EPA. 2006) andp-aminophenol (U.S. EPA. 2005b); no structural analogs with inhalation toxicity values were identified. Table A-l summarizes the physicochemical properties and similarity scores of the structural analogs. The DSSTox similarity scores for both analogs were relatively high (>85% similar), while the ChemlDplus similarity scores were low (<50%). Comparison of physicochemical properties of the surrogates to o-aminophenol suggests that they will both behave in a manner analogous to o-aminophenol in the environment. Based on this finding, it may be expected that exposure pathways and bioavailability from environmental media might be comparable for the three compounds. Both m- and /;-aminophenol are considered to be appropriate structural surrogates for o-aminophenol. 20 o-Aminophenol ------- FINAL 09-28-2016 Table A-l. Comparison of Physicochemical Properties for o-Aminophenol (CASRN 95-55-6) and Candidate Analogs3 o-Aminophenol /w-Aminophenol p-Aminophenol Structure nh2 6-°" H2N^—-OH XX rr h2n^^ CASRN 95-55-6 591-27-5 123-30-8 Molecular weight 109.13 109.13 109.13 DSSTox similarity score (%)b 100 86 89 ChemlDplus similarity score (%)° 100 <50 <50 Melting point (°C) 173.5d 123 187.5 Boiling point (°C) 267d 164 (at 11 mmHg) 284 Vapor pressure (mm Hg at 25°C) 0.0031 (extrapolated)6 0.0019 (estimated)0 0.00004 (extrapolated) Henry's law constant (estimated) (atm-m3/mole at 25°C) 2.0 x 10-10 2.0 x 10-10 2.0 x 10-10 Water solubility (mg/L) 20,000f 27,000 16,000 Log Iv 0.62g 0.21 0.04 pKa pKai = 4.66h; pKa2 = 9.71h 4.37 5.48 aData were gathered from the PHYSPROP database for each respective compound unless otherwise specified (U.S. EPA. 2012c). bDSSTox (DSSTox. 2016). °ChemIDplus Advanced, similarity scores (ChemlDplus, 2016). dHavnes et al. (2014). eThe vapor pressure was extrapolated from the measured boiling point using a regression-derived equation. fO'Neil et al. (2013). gHSDB (2011). 'Mitchell et al. (2003). Metabolic Surrogates Oral absorption is high (78-100%) in laboratory animals for o-, m-, andp-aminophenol (U.S. EPA. 1985). In general, metabolism and elimination pathways are the same for the different aminophenol isomers. Each compound is conjugated at the phenolic group with sulfate or glucuronide, and conjugated metabolites are excreted in the urine (Elder. 1988; U.S. EPA. 1985). A'-Acetylation also occurs, resulting in an acetamidophenol metabolite, which may be further conjugated with sulfate or glucuronide prior to excretion in the urine (Elder. 1988; U.S. EPA. 1985). Different rates for these processes lead to differences in the proportions of the resulting urinary metabolites produced, primarily minor, but also including absence of acetamidophenylsulfate following treatment with o-aminophenol and absence of aminophenylsulfate following treatment with w-aminophenol (see Table A-2). 21 o-Aminophenol ------- FINAL 09-28-2016 Table A-2. Percent Recovery in the Urine over 24 Hours Following a Single Oral Dose in Rabbits (1,000 mg/Rabbit)a Parent or Metabolite 0-Aminophenol /w-Aminophenol p-Aminophenol Parent 11 0 2 Aminophenylglucuronide 52 59 45 Aminophenolsulfate 15 0 8 Acetamidophenol 2-4 12-19 13-25 Acetamidophenylglucuronide 13 5 16 Acetamidophenylsulfate 0 15 4 aU.S. EPA (1985). The proximal toxicant(s) of aminophenol isomers' toxicity have not been clearly identified, so it is unclear whether minor differences in the formation and distribution of metabolites observed for aminophenol isomers could result in differences in toxicity. It has been proposed that formation of an electrophilic compound, possibly a benzoquinone imine, is necessary for ^-aminophenol to induce nephrotoxic effects (Elder. 1988). The acetylated metabolite of ^-aminophenol is acetaminophen (A-acetyl-p-aminophenol) (Elder, 1988; U.S. EPA. 1985); however, it is unclear if the toxic metabolite of acetaminophen (iV-acetyl-^-benzoquinone imine [NAPQ1]) is formed following ^-aminophenol exposure. Renal macromolecule binding assays indicate that either ^-aminophenol or a nonconjugated metabolite is involved in renal toxicity, and inhibition or alteration of conjugation processes (such as glucuronide formation) increases the severity of the renal lesions (Elder. 1988). Methemoglobin formation following exposure top- and o-aminophenol is thought to be caused by cyclic oxidation-reduction transformation of ferro- to ferrihemoglobin via an oxidized quinone imine intermediate (Elder. 1988). Due to a lack of significant differences in the absorption, distribution, metabolism, and elimination of the aminophenol isomers, as well as insufficient data to identify any difference in proximal toxicants, both m- and ^-aminophenol are considered appropriate metabolic surrogates for o-aminophenol. Toxicity-Like Surrogates Table A-3 summarizes the available oral and inhalation human health assessment values and acute toxicity data for o-aminophenol and the compounds identified as potential surrogates. Acute lethality studies for o-aminophenol provide oral median lethal dose (LD50) values in rats and mice. The rat LD50 data suggest that ^-aminophenol may be more acutely toxic than o- or w-aminophenol. 22 o-Aminophenol ------- FINAL 09-28-2016 Table A-3. Comparison of Available Human Health Assessment Values and Acute Toxicity Data for o-Aminophenol (CASRN 95-55-6) and Candidate Analogs o-Aminophenol /w-Aminophenol /7-Aminophenol Structure H2N^—-OH u rr h2n^^ CASRN 95-55-6 591-27-5 123-30-8 Repeat-dose toxicity—oral, subchronic POD (mg/kg-d) NA 80 50 POD type NA NOAF.I. NOAF.I. UFC NA 300 300 p-RfD (mg/kg-d) NA 3 x 10-1 2 x 10-1 Critical effects NA Reduced body weight and tremors Increased severity of nephrosis Other effects NA Increased total bilirubin and reticulocyte ratio; thyroid follicular cell hypertrophy Reduced body weight concomitant with reduced food intake, anemia Species NA Rat (neonatal) Rat (males, females) Duration NA 18 d 90 d Route NA Oral (gavage) Oral (diet) Notes NA Newborn rats were more sensitive than older rats examined in 4- and 13-wk studies. Effects noted at higher doses in older rats included hemolytic anemia, potential liver toxicity (elevated ALT), and potential kidney toxicity (increased BUN in females, hyaline droplets in males) Hyperactivity and convulsions, reductions in food consumption and body weight, mild hematological changes, and embryo/fetotoxic effects Source NA U.S. EPA (2006) U.S. EPA (2005b) Repeat-dose toxicity—oral, chronic POD (mg/kg-d) NA 240 50 POD type NA NOAF.I. NOAEL UFC NA 3,000 3,000 p-RfD (mg/kg-d) NA 8 x 10-2 2 x 10-2 Critical effects NA Hemolytic anemia Increased severity of nephrosis Other effects NA Thyroid follicular cell hypertrophy; reduced body weight concomitant with reduced food intake Reduced body weight concomitant with reduced food intake, anemia Species NA Rat (female) Rat (males, females) Duration NA 90 d 90 d 23 o-Aminophenol ------- FINAL 09-28-2016 Table A-3. Comparison of Available Human Health Assessment Values and Acute Toxicity Data for o-Aminophenol (CASRN 95-55-6) and Candidate Analogs o-Aminophenol /w-Aminophenol /7-Aminophenol Route NA Oral (diet) Oral (diet) Notes NA NA NA Source NA U.S. EPA (2006) U.S. EPA (2005b) Acute toxicity Rat oral LD50 (mg/kg) 951 924 375 Toxicity target Tremor, cyanosis Excitement, spastic paralysis Muscle weakness, cyanosis Mouse oral LD50 (mg/kg) 800 401 NA Toxicity target Tremor, cyanosis Excitement, spastic paralysis NA Rat inhalation LC50 (mg/m3) NA 1,162 >5 Toxicity target NA Excitement, spastic paralysis NR Mouse inhalation LC50 (mg/m3) NA NA NA Toxicity target NA NA NA Reference ChemlDolus (2016) ChemlDolus (2016) ChemlDolus (2016) ALT = alanine aminotransferase; BUN = blood urea nitrogen; LC50 = median lethal concentration; LD50 = median lethal dose; NA = not applicable; NOAEL = no-observed-adverse-effect level; NR = not reported; POD = point of departure; p-RfD = provisional reference dose; UFC = composite uncertainty factor. The repeat-dose oral database for o-aminophenol consists of a single unpublished short-term-duration study in rats (Eastman Kodak. 1979); this study is of limited use for risk assessment due to the use of one sex (males), small group sizes (five/group), and short duration (12 days). Based on acute and short-term-duration animal studies, the red blood cells (RBCs) and potentially kidney and liver are targets of o-aminophenol toxicity (Rankin et al.. 1996; Harrison and Jollow. 1987; Itoh. 1987; Eastman Kodak. 1979). The critical effects identified following oral exposure to w-aminophenol included reduced body weight and tremors in neonatal rats exposed via gavage for 18 days (lowest-observed-adverse-effect level [LOAEL] 240 mg/kg-day) and hemolytic anemia in adult female rats exposed via diet for 90 days (LOAEL 900 mg/kg-day). Other effects noted with repeated oral exposure included increased total bilirubin and reticulocyte ratio and thyroid follicular cell hypertrophy, as well as potential liver and kidney toxicity thought to be secondary to hemolytic anemia (modest increases in alanine aminotransferase [ALT], slight increases in blood urea nitrogen [BUN] in females, and hyaline droplets in males) (U.S. EPA. 2006). The subchronic provisional reference dose (p-RfD) of 0.3 mg/kg-day is based on a point of departure (POD) of 80 mg/kg-day for neonatal effects in the 18-day gavage study, and the chronic p-RfD of 8 x 10~2 mg/kg-day is based on a POD of 240 mg/kg-day for hemolytic anemia in adult female rats (U.S. EPA, 2006). 24 o-Aminophenol ------- FINAL 09-28-2016 The critical effect identified following oral exposure to/^-aminophenol was increased severity of nephrosis in male and female rats exposed via diet for 90 days (LOAEL 150 mg/kg-day). Other effects noted at higher exposure levels included anemia and reduced body weight concomitant with reduced food intake (U.S. EPA. 2005b). Both the subchronic p-RfD of 0.2 mg/kg-day and the chronic p-RfD of 2 x 10 2 mg/kg-day are based on a POD of 50 mg/kg-day for nephrotoxic effects (U.S. EPA, 2005b). In a comparison of relative toxicities, the subchronic POD value for /^-aminophenol is fourfold lower than that of w-aminophenol. The lower reference value for /^-aminophenol is based on adverse renal effects that occurred at lower doses than anemia following exposure for 90 days. In animals exposed to w-aminophenol for 90 days in the diet, anemia was observed in the absence of renal toxicity, and in young rats in a 28-day gavage study, doses that caused hemolytic anemia produced evidence of only mild kidney damage. Therefore, /^-aminophenol appears to be a more potent renal toxicant than w-aminophenol. While the potency may differ among aminophenol isomers, evidence for similar toxicity targets (kidney and RBC) suggests that both m- and /^-aminophenol are appropriate toxicity-like surrogates for o-aminophenol for oral exposure. No repeat-exposure inhalation studies were available for o-, m-, or /^-aminophenol and inhalation toxicity values were not derived. Weight-of-Evidence Approach A WOE approach is used to evaluate information from potential candidate surrogates as described by Wang et al. (2012). Commonalities in structural/physicochemical properties, toxicokinetics, metabolism, toxicity, or mode of action between potential surrogates and chemical(s) of concern are identified. Emphasis is given to toxicological and/or toxicokinetic similarity over structural similarity. Surrogate candidates are excluded if they do not have commonality or demonstrate significantly different physicochemical properties and toxicokinetic profiles that set them apart from the pool of potential surrogates and/or chemical(s) of concern. From the remaining potential surrogates, the most appropriate surrogate (most biologically or toxicologically relevant analog chemical) with the highest structural similarity and/or most conservative toxicity value is selected. The structural surrogate analysis indicated that both m- and ^-aminophenols have relatively high similarity scores (>85%) compared to o-aminophenol based on the DSSTox database search. A comparison of physicochemical properties of these surrogates to o-aminophenol suggests that these surrogate chemicals share similar physicochemical properties to o-aminophenol. Metabolic surrogate analysis indicated that, in general, the metabolism and elimination pathways are the same for the different aminophenol isomers. However, there are insufficient data to identify the proximal toxicant of aminophenols to inform a more refined selection of a particular metabolic surrogate. Based on the acute and short-term-duration animal studies with o-aminophenol, the RBC, liver, and kidney are potential toxicity targets. The two surrogate chemicals also share the same toxicity targets (i.e., RBC and kidney), and w-aminophenol also affects the liver; nevertheless, relative potency among the aminophenol isomers might differ in each of these target tissues. Thus, these analyses suggest that both candidate analogs, m- and /^-aminophenol, are acceptable as structural, metabolic, and toxicity-like surrogates. 25 o-Aminophenol ------- FINAL 09-28-2016 For this assessment, />-aminophenol was selected over w-aminophenol as the surrogate for o-aminophenol for both the subchronic and chronic oral toxicity values because the POD based on /;-aminophenol will provide a more conservative/health-protective toxicity value for both subchronic and chronic oral exposure to o-aminophenol. ORAL TOXICITY VALUES Derivation of a Screening Subchronic Provisional Reference Dose Based on the overall WOE presented in this PPRTV assessment, />-aminophenol is selected as the surrogate for o-aminophenol for the screening subchronic p-RfD. The study used for the subchronic p-RfD for /;-aminophenol is a 13-week (90 days) dietary study in male and female weanling Sprague-Dawley (S-D) rats by Burnett et al. (1989) as cited in U.S. EPA (2005b). The PPRTV report for/;-aminophenol (U.S. EPA. 2005b) described this study as follows: In order to investigate the effects of longer-term oral exposure, a combined subchronic feeding, teratology, and dominant lethal study ofp-aminophenol was conducted in rats. Groups of 40 male and 45 female weanling Sprague-Dawley rats were fed diets containing 0, 0.07, 0.20, or 0.70% of p-aminophenol (>98.1% purity) in their diet for 13 weeks (Burnett et al, 1989). At that time, 10 males and 10 females of each group were sacrificedfor toxicity evaluation, and 25 females fi'om each group were removedfi'om the test diets and mated with untreated males. After mating, the pregnant females were returned to their test diets throughout gestation and sacrificed on gestation day 20 for fetal examinations. Males not sacrificed at week 13 were continued on their test diets until week 20, when 20 males fi'om each group were removedfi'om the test diets and mated with untreatedfemales in a dominant lethal assay until their sacrifice on week 2 7. The remaining 10 males and 10 females fi'om each group were maintained on their test diets until sacrifice on week 17. Based on food consumption and body weight data presented graphically in the paper, doses were approximately 0, 50, 150, and 560 mg/kg-day in males and 0, 60, 175, and 620 mg/kg-day in females. Animals were observed daily for general condition and monitored weekly for signs of toxicity, body weight, andfeed consumption (Burnett et al, 1989). At 6 weeks, blood was collectedfi'om 5 males and 5 females fi'om the high dose group (0.70%) for methemoglobin analyses. At week 12, urine was collectedfi'om 10 males and 10 females selected from each group for bacterial mutagenicity testing; and at week 13, the same 10 rats/group were sacrificed and blood collectedfor hematology and clinical chemistry analysis. At necropsy, the major organs were weighed, and a complete histopathological examination was performedfor animals fi'om the control and high dose groups. The liver, kidney, urinary bladder, and gross lesions were also examinedfi'om animals in the low- and mid-dose groups. The same procedures were used to collect blood and autopsy rats sacrificed at end of the 27 week study. Hyperactivity and convulsions were noted in a few of the females consuming the high-dose test diet after 6 weeks on study (Burnett et al, 1989). No treatment-related deaths occurred (one low-dose female died of unknown causes). Food consumption was markedly lower than controls in both males andfemales 26 o-Aminophenol ------- FINAL 09-28-2016 from the high-dose group during the first week of the study, and remained significantly lower than controls for most of the study in both sexes. Body weights of both males and females in this group were significantly lower than controls throughout the study, with deficits of 10-15% in males and 15-20% in females after week 5. Food consumption and body weight were similar to controls in the low and mid-dose groups. Hematology analyses showed statistically significant decreases in red blood cell counts (-10%) and hemoglobin level (-5%) in high-dose females at 13 weeks, but not at 27 weeks. Other hematology and clinical chemistry findings were reportedly unremarkable (data not presented in paper). The assay for methemoglobin in high-dose rats showed no difference from controls. Increased relative weights were observedfor several organs in high-dose males andfemales, secondary to the decrease in body weight at this dose. Statistically significant changes in other organ weights (increased absolute and relative pituitary weight in low- and mid-dose females at 13 weeks, and increased absolute heart weight in low-dose males at 13 weeks) were not considered by the researchers to be treatment-related. No gross lesions were seen at autopsy. Microscopic evaluation revealed nephrosis characterized by cytoplasmic eosinophilic droplets in the tubular epithelial cells of male and female rats of all groups, but with a dose-related increase in incidence and or severity (Table 1). In males, the lesions were similar to glomeridonephropathy typical of aging rats (albeit more severe in the treated groups), while in females the droplets were smaller and intensely brown. Statistical analysis of the data in Table 1 was performedfor this review. The Jonckheere-Terpstra trend test for ordered categorical data showed statistically significant (p< 0.001) increases in severity of nephrosis with increasing dose in both males andfemales, using the 13-week data for all 4 dose groups. Pairwise comparisons using the same test showed significant (p< 0.005) differences from controls in mid- and high-dose males and high-dose females. No other treatment-related histopathological changes were noted. A LOAEL of 150 mg/kg-day (0.2%) andNOAEL of 50 mg/kg-day (0.07%) is identifiedfrom this study, based on increased severity of nephrosis in males. A similar study (Re et al., 1984) with a combined sub chronic-duration feeding and teratology of w-aminophenol reported similar effects, but these effects occurred at a higher dose level. In this study, four groups of 35 S-D female rats were fed diets containing 0, 0.13, 0.25, or 0.98% w-aminophenol. From reported body-weight and food consumption data, average doses are estimated to be about 0, 120, 240, or 900 mg/kg-day. The PPRTV report for w-aminophenol (U.S. EPA. 2006) described findings from this study as follows: This study identified a LOAEL of900 mg/kg-day (0.98% in the diet) based on evidence of hemolytic anemia (increased incidence and or severity of iron-positive pigmentation in the spleen, liver and kidneys, along with reduced red blood cell count and hemoglobin). Body weight was lower than controls in both the mid- and high-dose groups, but the change was minimal in the mid-dose group and was secondary to reduced food intake at both doses (suggesting an organoleptic, rather than toxic, effect). Histological changes in the thyroid consistent with hypertrophy (reducedfollicle size and increasedfollicular 27 o-Aminophenol ------- FINAL 09-28-2016 epithelial cell height) were reported in both the mid- and high-dose groups (incidence reported only as "several" animals in the mid-dose group). Thyroid hormone measurements were not made. However, reported changes in thyroid weight were not consistent with a hyperthyroid effect. There was an increase in relative, but not absolute thyroid weight in the high dose group, apparently secondary to the decrease in body weight at this dose. In the mid-dose group, absolute and relative thyroid weights were actually reduced. Therefore, the thyroid effects are considered to be adaptive rather than adverse. Thus, the 240 mg/kg-day dose (0.25%) is considered a NOAEL for m-aminophenol. Therefore, a POD based on/;-aminophenol will provide a more conservative/health-protective toxicity value for both subchronic and chronic oral exposure to o-aminophenol. The selection of a POD of 50 mg/kg-day is also supported by a 3-month oral toxicity study [Fournier (1981) as cited in SCCS (2010)1 in rats treated with 50 mg/kg-day o-aminophenol. Based on a secondary report from the Scientific Committee on Consumer Safety (SCCS. 2010). clinical observation, body-weight gain, hematological parameters, blood biochemistry, and urine examination revealed no difference between the treated and the control group. Histopathological examination showed broncho-pulmonary injuries, which did not permit to affirm the toxicity of the o-aminophenol. In addition, a developmental toxicity study [Boutemy et al. (1981) as cited in SCCS (2010)1 in rats treated with o-aminophenol identified a NOAEL of 70 mg/kg-day for maternal and developmental toxicity. The SCCS report (SCCS. 2010) also reported two 30-day oral toxicity studies in rats treated with o-aminophenol. One study [Boutemy (1989) as cited in SCCS (2010)1 identified a LOAEL of 20 mg/kg-day (the lowest dose tested) based on increased vacuolization of the urothelium of the bladder in males and females, and observed renal cells in the urine of male rats. The other study [Coleman et al. (1989) as cited in SCCS (2010)1 identified a NOAEL of 5 mg/kg-day and a LOAEL of 15 mg/kg-day due to increased thyroid weight. These findings from 30-day studies were inconsistent with the no toxicity effect found in rats treated with 50 mg/kg-day o-aminophenol for 3 months [Fournier (1981) as cited in SCCS (2010)1, which also included a pathological examination of these target organs/tissues. The toxicity data summarized in the SCCS report are only presented here as supportive evidence because the report has limited information available and makes no final conclusion on the safety of o-aminophenol (SCCS. 2010). Further, the studies cited in the SCCS report were not available for review. Therefore, a POD based on/;-aminophenol is considered appropriate for deriving screening p-RfDs. The critical effect for the subchronic toxicity portion of the study of />-aminophenol was increased severity of nephrosis in male rats; the NOAEL of 50 mg/kg-day for this effect was used as the POD. The subchronic p-RfD for /;-aminophenol was derived using a composite uncertainty factor (UFc) of 300 reflecting 10-fold uncertainty factor values for interspecies extrapolation (UFa), a 10-fold for intraspecies variability (UFh), and a 3-fold for database uncertainties (UFd, reflecting lack of a second species in the study). Wang et al. (2012) indicated that the uncertainty factors applied in deriving a surrogate toxicity value for the chemical of concern should be the same as those applied to the selected analog unless additional information is available. However, the EPA endorses body-weight scaling to the 3/4 power (i.e., BW3/4) as a default to extrapolate toxicologically equivalent doses of orally administered agents from all laboratory animals to humans for the purpose of deriving an RfD from effects 28 o-Aminophenol ------- FINAL 09-28-2016 that are not portal-of-entry (U.S. EPA. 2011b). Therefore the surrogate POD was converted into a human equivalent dose (HED) and the UFa was reduced to a 3 (rather than 10-fold) for the derivation of a screening subchronic p-RfD for o-aminophenol. Additionally, a 10-fold UFd (rather than 3-fold) was applied due to lack of useful repeat-dose toxicity studies for o-aminophenol (Table A-4). Following U.S. EPA (2011b) guidance, the POD for the 13-week study in rats exposed to /;-aminophenol is converted to an HED through the application of a dosimetric adjustment factor (DAF) derived as follows: DAF = (BWa14 - BWh14) where: DAF = dosimetric adjustment factor BWa = animal body weight BWh = human body weight Using a reference BWa of 0.25 kg for rats and a reference BWh of 70 kg for humans (U.S. EPA. 1988). the resulting DAF is 0.24. Applying this DAF to the NOAEL identified in the 13-week rat study yields a NOAEL (HED) as follows: POD (HED) = NOAEL (mg/kg-day) x DAF = 50 mg/kg-day x 0.24 = 12 mg/kg-day Using the surrogate POD (HED), the screening subchronic p-RfD for o-aminophenol is derived as follows: Screening Subchronic p-RfD = Surrogate POD (HED) ^ UFc = 12 mg/kg-day -^300 = 4 x 10"2 mg/kg-day Table A-4 summarizes the uncertainty factors for the screening subchronic p-RfD for o-aminophenol. 29 o-Aminophenol ------- FINAL 09-28-2016 Table A-4. Uncertainty Factors for the Screening Subchronic p-RfD for o-Aminophenol (CASRN 95-55-6) UF Value Justification UFa 3 A UFa of 3 (10°5) is applied to account for uncertainty associated with extrapolating from animals to humans when a cross-species dosimetric adjustment (HED calculation) is performed. UFh 10 A UFh of 10 is applied for interindividual variability to account for human-to-human variability in susceptibility in the absence of quantitative information to assess the toxicokinetics and toxicodynamics of o-aminophenol in humans. UFd 10 A UFd of 10 is applied. The repeat-dose oral database for o-aminophenol consists of a single study that is limited due to use of one sex (males), small group sizes (five/group), and short duration (12 d). Therefore, the POD is based on a surrogate chemical. UFl 1 A UFl of 1 is applied because the POD is a NOAEL. UFs 1 A UFS of 1 is applied because a subchronic-duration study was selected as the principal study. UFC 300 Composite UF = UFA x UFH x UFD x UFL x UFS. HED = human equivalent dose; NOAEL = no-observed-adverse-effect level; POD = point of departure; UF = uncertainty factor. Derivation of a Screening Chronic Provisional Reference Dose Based on the overall surrogate approach presented in this PPRTV assessment, /;-aminophenol is selected as the surrogate for o-aminophenol for the screening chronic p-RfD. The chronic p-RfD for />aminophenol was derived by adding an additional UF of 10 to extrapolate from subchronic to chronic duration (UFs); the UFc was 3,000. Similarly, the screening chronic p-RfD for o-aminophenol is derived by factoring in a UFs of 10 to the screening subchronic p-RfD of 4 x 10 2 mg/kg-day derived above. The screening chronic p-RfD for o-aminophenol is derived as follows: Screening Chronic p-RfD = Surrogate POD (HED) ^ UFc = 12 mg/kg-day ^ 3,000 = 4 x 10"3 mg/kg-day Table A-5 summarizes the uncertainty factors for the screening chronic p-RfD for o-aminophenol. 30 o-Aminophenol ------- FINAL 09-28-2016 Table A-5. Uncertainty Factors for the Screening Chronic p-RfD for o-Aminophenol (CASRN 95-55-6) UF Value Justification UFa 3 A UFa of 3 (10"5) is applied to account for uncertainty associated with extrapolating from animals to humans when cross-species dosimetric adjustment (HED calculation) is performed. UFh 10 A UFh of 10 is applied for interindividual variability to account for human-to-human variability in susceptibility in the absence of quantitative information to assess the toxicokinetics and toxicodynamics of o-aminophenol in humans. UFd 10 A UFd of 10 is applied. The repeat-dose oral database for o-aminophenol consists of a single study that is limited due to use of one sex (males), small group sizes (five/group), and short duration (12 d). Therefore, the POD is based on a surrogate chemical. UFl 1 A UFl of 1 is applied because the POD is a NOAEL. UFS 10 A UFS of 1 is applied because a subclironic-duration study was selected as the principal study. UFC 3,000 Composite UF = UFA x UFH x UFD x UFL x UFS. HED = human equivalent dose; NOAEL = no-observed-adverse-effect level; POD = point of departure; UF = uncertainty factor. Derivation of Screening Provisional Reference Concentrations No subchronic- or chronic-duration inhalation studies examining the effects of candidate analogs for o-aminophenol in humans or animals have been located (U.S. EPA. 2006. 2005b). precluding derivation of provisional reference concentrations (p-RfCs) for o-aminophenol based on an alternative surrogate approach. 31 o-Aminophenol ------- FINAL 09-28-2016 APPENDIX B. 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