United States Environmental Protection 1=1 m m Agency EPA/690/R-13/004F Final 7-25-2013 Provisional Peer-Reviewed Toxicity Values for Dibenzothiophene (CASRN 132-65-0) 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 Carrie R. Fleming, PhD National Center for Environmental Assessment, Cincinnati, OH CONTRIBUTOR Jason C. Lambert, PhD, DABT National Center for Environmental Assessment, Cincinnati, OH DRAFT DOCUMENT PREPARED BY ICF International 9300 Lee Highway Fairfax, VA 22031 PRIMARY INTERNAL REVIEWERS Ghazi Dannan, PhD National Center for Environmental Assessment, Washington, DC Suryanarayana V. Vulimiri, BVSc, PhD, DABT National Center for Environmental Assessment, Washington, DC This document was externally peer reviewed under contract to Eastern Research Group, Inc. 110 Hartwell Avenue Lexington, MA 02421-3136 Questions regarding the contents of this document may be directed to the U.S. EPA Office of Research and Development's National Center for Environmental Assessment, Superfund Health Risk Technical Support Center (513-569-7300). li Dib enzothi ophene ------- CONTENTS COMMONLY USED ABBREVIATIONS iv BACKGROUND 1 DISCLAIMERS 1 QUESTIONS REGARDING PPRTVs 1 INTRODUCTION 2 REVIEW OF POTENTIALLY RELEVANT DATA (CANCER AND NONCANCER) 4 HUMAN STUDIES 7 ANIMAL STUDIES 7 Oral Exposures 7 Inhalation Exposures 8 OTHER DATA (SHORT-TERM TESTS, OTHER EXAMINATIONS) 9 DERIVATION 01 PROVISIONAL VALUES 15 DERIVATION OF ORAL REFERENCE DOSES 15 Derivation of Subchronic p-RfD 15 Derivation of Chronic p-RfD 16 DERIVATION OF INHALATION REFERENCE CONCENTRATIONS 16 CANCER WEIGHT-OF-EVIDENCE (WOE) DESCRIPTOR 16 DERIVATION OF PROVISIONAL CANCER POTENCY VALUES 16 APPENDIX A. PROVISIONAL SCREENING VALUES 17 APPENDIX B. DATA TABLES 20 APPENDIX C. BMD OUTPUTS 21 APPENDIX D. REFERENCES 22 in Dib enzothi ophene ------- COMMONLY USED ABBREVIATIONS BMC benchmark concentration BMCL benchmark concentration lower bound 95% confidence interval BMD benchmark dose BMDL benchmark dose lower confidence limit HEC human equivalent concentration HED human equivalent dose IUR inhalation unit risk LOAEL lowest-observed-adverse-effect level LOAELadj LOAEL adjusted to continuous exposure duration LOAELhec LOAEL adjusted for dosimetric differences across species to a human NOAEL no-ob served-adverse-effect level NOAELadj NOAEL adjusted to continuous exposure duration NOAELhec NOAEL adjusted for dosimetric differences across species to a human NOEL no-ob served-effect level OSF oral slope factor p-IUR provisional inhalation unit risk POD point of departure p-OSF provisional oral slope factor p-RfC provisional inhalation reference concentration p-RfD provisional oral reference dose RfC inhalation reference concentration RfD oral reference dose UF uncertainty factor UFa interspecies uncertainty factor UFC composite uncertainty factor UFd database uncertainty factor UFh intraspecies uncertainty factor UFl LOAEL-to-NOAEL uncertainty factor UFS subchronic-to-chronic uncertainty factor WOE weight of evidence iv Dib enzothi ophene ------- FINAL 7-25-2013 PEER-REVIEWED PROVISIONAL TOXICITY VALUES FOR DIBENZOTHIOPHENE (CASRN 132-65-0) 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 flittp://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 (www.epa.eov/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. QUESTIONS REGARDING PPRTVs Questions regarding the contents and appropriate use 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 Dib enzothi ophene ------- FINAL 7-25-2013 INTRODUCTION Dibenzothiophene, CAS No. 132-65-0, is an organosulfur compound found in crude oil and petroleum. It is used as a chemical intermediate in cosmetics and pharmaceuticals (NLM. 2006). The empirical formula for dibenzothiophene is C^HgS (see Figure 1). A table of physicochemical properties for dibenzothiophene is provided below (see Table 1). Figure 1. Dibenzothiophene Structure Table 1. Physicochemical Properties of Dibenzothiophene (CASRN 132-65-0)a Property (unit) Value Boiling point (°C) 332.5 Melting point (°C) 99.5 Density (g/cm3) ND Vapor pressure (mm Hg at 25°C) 0.000205 pH (unitless) ND Solubility in water (mg/L at 25°C) 1.47 Relative vapor density (air =1) ND Molecular weight (g/mol) 184.26 "NLM (20061. ND = no data. A summary of available relevant health information for dibenzothiophene from U.S. EPA and other agencies/organizations is provided in Table 2. 2 Dib enzothi ophene ------- FINAL 7-25-2013 Table 2. Summary of Available Toxicity Values for Dibenzothiophene (CASRN 132-65-0) Source/Parameter" Value (Applicability) Notes Source Date Accessed Cancer IRIS NV NA U.S. EPA 7-16-2013 HEAST NV NA U.S. EPA (2011M NA IARC NV NA IARC (2013) NA NTP NV NA NTP (2011) NA Cal/EPA NV NA Cal/EPA (2009) NA Noncancer ACGIH NV NA ACGIH 7-16-2013 ATSDR NV NA ATSDR 7-16-2013 Cal/EPA NV NA Cal/EPA (2012. 2009) 7-16-2013 NIOSH NV NA NIOSH (2007) NA OSHA NV NA OSHA (2006) NA IRIS NV NA U.S. EPA 7-16-2013 Drinking water NV NA U.S. EPA (2011a) NA HEAST NV NA U.S. EPA (2011b) NA CARA HEEP NV NA U.S. EPA (1994) NA WHO NV NA WHO (2004) NA aSources: Integrated Risk Information System (IRIS) database; Health Effects Assessment Summary Tables (HEAST); International Agency for Research on Cancer (IARC); National Toxicology Program (NTP); California Environmental Protection Agency (Cal/EPA); American Conference of Governmental Industrial Hygienists (ACGIH); Agency for Toxic Substances and Disease Registry (ATSDR); National Institute for Occupational Safety and Health (NIOSH); Occupational Safety and Health Administration (OSHA); Chemical Assessments and Related Activities (CARA) list; Health and Environmental Effects Profile (HEEP); World Health Organization (WHO). NA = not applicable; NV = not available. Literature searches were conducted on sources published from 1900 through July 2013, for studies relevant to the derivation of provisional toxicity values for dibenzothiophene, CASRN 132-65-0. The following databases were searched by chemical name, synonyms, or CASRN: ACGIH, ANEUPL, ATSDR, BIOSIS, Cal EPA, CCRIS, CDAT, ChemlDplus, CIS, CRISP, DART, EMIC, EPIDEM, ETICBACK, FEDRIP, GENE-TOX, HAPAB, HERO, HMTC, HSDB, IARC, INCHEM IPCS, IP A, ITER, IUCLID, LactMed, NIOSH, NTIS, NTP, OSHA, OPP/RED, PESTAB, PPBIB, PPRTV, PubMed (toxicology subset), RISKLINE, RTECS, TOXLINE, TRI, U.S. EPA IRIS, U.S. EPA HEAST, U.S. EPA HEEP, U.S. EPA OW, and U.S. EPA TSCATS/TSCATS2. The following databases were searched for relevant health information or exposure limits: ACGIH, ATSDR, Cal EPA, U.S. EPA IRIS, U.S. EPA HEAST, U.S. EPA HEEP, U.S. EPA OW, U.S. EPA TSCATS/TSCATS2, NIOSH, NTP, OSHA, and RTECS. 3 Dib enzothi ophene ------- FINAL 7-25-2013 REVIEW OF POTENTIALLY RELEVANT DATA (CANCER AND NONCANCER) Table 3 provides an overview of the relevant database for dibenzothiophene and includes all potentially relevant and repeated short-term, subchronic, and chronic-duration studies. Principal studies are identified in bold and are labeled PS. The phrase "statistical significance" used throughout the document indicates ap-walue of <0.05. 4 Dib enzothi ophene ------- FINAL 7-25-2013 Table 3. Summary of Potentially Relevant Data for Dibenzothiophene (CASRN 132-65-0) Category Number of Male/Female, Strain, Species, Study Type, Study Duration Dosimetry" Critical Effects NOAEL" BMDL/ BMCLa LOAEL' Reference Notesb Human 1. Oral (mg/kg-d)a Acute0 ND Short-termd ND Long-term6 ND Chronicf ND 2. Inhalation (mg/m3)a Acute0 ND Short-termd ND Long-term0 ND Chronicf ND Animal 1. Oral (mg/kg-d)a Subchronic ND Chronic Male (number not specified), albino, rat, diet, 165 d 0 (historical), 13,27,63 (Adjusted) Increased liver weight8 compared with laboratory historical controls 13 DUB 27 Thomas et al. (1942) PS, PR Developmental ND Reproductive ND Carcinogenicity ND 5 Dib enzothi ophene ------- FINAL 7-25-2013 Table 3. Summary of Potentially Relevant Data for Dibenzothiophene (CASRN 132-65-0) Category Number of Male/Female, Strain, Species, Study Type, Study Duration Dosimetry3 Critical Effects NOAEL3 BMDL/ BMCL3 LOAEL3 Reference Notesb 2. Inhalation (mg/m3)a Subchronic ND Chronic ND Developmental ND Reproductive ND Carcinogenicity ND ""Dosimetry: NOAEL, BMDL/BMCL, and LOAEL values are converted to an adjusted daily dose (ADD in mg/kg-d) for oral noncancer effects. ADD = Total Dibenzothiophene Consumption per Animal over Study Duration x (1 Body Weight) x (1 -f- Days Dosed) bNotes: PS = principal study; PR = peer reviewed. cAcute = exposure for <24 hr (U.S. EPA. 2002). ''Short-term = repeated exposure for >24 hr < 30 d (U.S. EPA. 2002). "Long-term = repeated exposure for >30 d < 10% lifespan (based on 70-yr typical human lifespan) (U.S. EPA. 2002). 'Chronic = repeated exposure for >10% lifespan (U.S. EPA. 2002). 8For liver weight evaluation, animals dosed with dibenzothiophene were compared with laboratory historical controls matched according to body weight. Therefore, the differences from the control group approximate a change in organ weight relative to body weight. DUB = data not amenable to BMD modeling; ND = no data. 6 Dib enzothi ophene ------- FINAL 7-25-2013 HUMAN STUDIES No studies were identified. ANIMAL STUDIES Oral Exposures The effects of oral exposure to dibenzothiophene in animals have not been evaluated in subchronic, developmental, or reproductive studies although a chronic-duration study that investigated the effects of dibenzothiophene in rats was identified (Thomas et al.. 1942). Chronic-duration studies Thomas et al. (1942) The study by Thomas et al. (1942) is selected as the principal study for derivation of the screening chronic provisional reference dose (p-RfD). In a published, peer-reviewed study, Thomas et al. (1942) administered dibenzothiophene (purity not reported) in the diet of male albino rats (source and number not reported) aged 25-28 days with an average body weight of 48 g at the beginning of the study. The animals received 0.25, 0.50, or 1.00% dibenzothiophene in the diet for the first 4 days of the dosing period (number of animals per dose group not reported). Because of low food intakes and decreases in body weight, the doses were decreased to 0.025, 0.050, or 0.100% dibenzothiophene for the remainder of the 165-day dosing period. Adjusted daily doses are estimated to be 13, 27, and 63 mg/kg-day, respectively, based on total dibenzothiophene consumption reported by the study authors and time-weighted average body weights obtained by digitizing the growth curves provided by the study authors. Animals were housed five to a cage; other details regarding animal husbandry were not provided. Appearance and behavior were recorded by the study authors "throughout the duration of the study." Food and water were provided ad libitum; animals and food cups were weighed twice a week for the duration of the study. Experimental data for each exposure group were compared with data for age- or body-weight-matched historical control animals; the type of historical control used for each endpoint is listed below with the results for that endpoint. At study termination, animals were sacrificed, and histopathological examinations were performed. The study authors noted that they used an necropsy technique previously described by Wilson et al. (1938): the spleen, liver, adrenal glands, kidneys, testes, ovaries, and heart were weighed under this necropsy protocol. Histopathological sections of the liver, spleen, adrenal gland, heart, bladder, intestine, lung, testis, and stomach were prepared from five animals in each exposure group and stained with hematoxylin and eosin (Thomas et al.. 1942). Frozen sections of the livers from three animals in the high-dose group and all animals in the low-dose group were stained with Sudan IV. Blood was collected on Days 107 and 157 from the tails of five high-dose animals and analyzed for hemoglobin and for erythrocyte, reticulocyte, and total and differential white cell counts. Although the study authors indicated statistical significance of their findings, no information was provided regarding their statistical methods. This study was performed prior to the adoption of good laboratory practice (GLP), and little information regarding the laboratory procedures was provided. The study authors also reported a second experiment examining the presence of dibenzothiophene metabolites in the urine of rabbits, as described in Table 4B. 7 Dib enzothi ophene ------- FINAL 7-25-2013 No deaths or clinical signs of toxicity were reported during the study. Body weights throughout the course of the study were presented graphically, and mean terminal body weights were provided in numerical form for each exposure group (see Table B.l). A dose-dependent decrease in body weight was observed; however, the study authors attributed this to reduced food consumption and did not consider it a direct effect of dibenzothiophene. For the evaluation of organ weights, animals dosed with dibenzothiophene were compared with laboratory historical controls matched according to body weight. As a result, the differences from the control group approximate a change in relative (to body weight) organ weight. The only significant effects on organ weight observed were in the liver and spleen. Although statistical significance for weight changes in both the liver and spleen were noted by the study authors, neither an indication of the dose at which significance occurred nor any levels of significance were reported. Data for these organs are presented in Table B.l. Liver weights increased (7-115%) in a dose-dependent manner, with changes greater than 10% occurring at >27 mg/kg-day. Spleen weights decreased (29-57%) in a dose-dependent manner. The decreased spleen weight may be related to the decreased food consumption as spleen weight has been shown to decrease disproportionately to body weight when food consumption is decreased (Peters and Bovd. 1966). Gross examination revealed that the livers in the mid- and high-dose animals were large and presented a yellowish, fatty appearance. Spleens appeared normal except for a reduction in their sizes upon gross examination. Liver and kidney histopathological lesions were reported by the study authors; however, incidence was not reported, and no control group was examined. Histopathology of livers from the high-dose animals revealed extensive fatty metamorphosis of the hepatic cells, abnormal fat accumulation, and irregular vacuolation of the parenchymal cells extending throughout the lobules. Livers from high-dose animals also had some cells with indistinct borders where it appeared that adjacent cells had fused. Other liver cells had a rim of homogenous, deeply stained cytoplasm surrounding groups of vacuoles. Similar changes, but less severe, were observed in the mid-dose group. The liver effects observed in the low-dose group were described as "still less severe" than those observed at the mid-dose. There was no evidence of fibrosis or necrosis, and the Kupffer cells were unchanged. Kidneys of all exposed animals had slight-to-moderate, light brown, granular pigmentation of the epithelial cells of the proximal convoluted tubules, but there was no evidence of cell destruction. Histopathological abnormalities in other organs, including the spleen, were not observed. Hematological effects were compared to age-matched controls. There were no hematological effects observed based on the blood analyses of the high-dose animals when compared with age-matched laboratory historical controls. In addition, the study authors noted that similar blood counts were seen in previously published hematological data from untreated animals and in animals treated with the closely related compound, diphenylene oxide. Liver effects seen at the low dose as well as decreased spleen weight and granular pigmentation of the renal epithelial cells were not considered adverse effects of dibenzothiophene exposure. Therefore, based on increased liver weight and histopathological changes in the liver, the NOAEL and LOAEL identified for this study are 13 and 27 mg/kg-day, respectively. Inhalation Exposures No studies were identified. 8 Dib enzothi ophene ------- FINAL 7-25-2013 OTHER DATA (SHORT-TERM TESTS, OTHER EXAMINATIONS) Dibenzothiophene is deemed not mutagenic based on the few available studies on its mutagenic potential. Dibenzothiophene was negative for mutagenicity in the Ames test for doses up to 500 jug (Mct'all et al.. 1984; Pelrov et al.. 1983; Dickson and Adams. 1980) and was negative in the Chinese hamster ovary cell (CHO) mutation assay for doses up to 100 |ag/m L (Rasmussen et al.. 1991). These data are further described in Table 4A. Additional studies investigating the metabolism of dibenzothiophene in rats (Jacob et al.. 1991; Vignier et ai, 1985), the elimination of dibenzothiophene in the urine of rabbits (Thomas et al.. 1942). and the acute toxicity of dibenzothiophene in mice (Leighton. 1989) are also available. See Table 4B for the details of these studies. 9 Dib enzothi ophene ------- FINAL 7-25-2013 Table 4A. Summary of Dibenzothiophene Genotoxicity Endpoint Test System Dose Concentration" Resultsb Comments References Without Activation With Activation Genotoxicity studies in prokaryotic organisms Reverse mutation Ames assay using Salmonella typhimurium strain TA98 treated with 10-100 |ig dibenzothiophene per plate dissolved in DMSO and incubated at 37°C for 48 hr with Aroclor 1254-induced rat-liver S9 homogenate activation (S9 concentrations of 4, 10, or 20%) 100 ng ND Not mutagenic at any dose; S9 volume did not affect activity Mcfall et al. (1984) Ames assay using S. typhimurium strains TA98, TA100, TA1535, TA1537, and TA1538 treated with an unreported quantity of dibenzothiophene dissolved in DMSO with Aroclor 1254-induced rat-liver S9 homogenate activation NR ND Not mutagenic; mutagenicity results presented as revertant ratio (number of revertants per plate/number of spontaneous revertants); dibenzothiophene reportedly had "no mutagenic response" with an average revertant ratio <2.0 Dickson and Adams (1980) Ames assay using S. typhimurium strains TA98, TA100, TA1535, and TA1537 treated with 2-500 |ig dibenzothiophene per plate dissolved in DMSO with and without Aroclor 1254-induced rat-liver S9 homogenate activation 500 ng Not mutagenic at any dose Pelrov et al. (1983) SOS repair induction ND Genotoxicity studies in nonmammalian eukaryotic organisms Mutation ND Recombination induction ND Chromosomal aberration ND 10 Dib enzothi ophene ------- FINAL 7-25-2013 Table 4A. Summary of Dibenzothiophene Genotoxicity Endpoint Test System Dose Concentration" Resultsb Comments References Without Activation With Activation Chromosomal malsegregation ND Mitotic arrest ND Genotoxicity studies in mammalian cells—in vitro Mutation Chinese hamster ovary (CHO-K1BH4) cells treated with 1-100 ng/mL dibenzothiophene with Ham's F12 medium, activated with 4% Aroclor-induced rat-liver S9 solution and incubated for 5 hr; control experiments conducted with DMSO as the control and methyl methane sulfonate as a positive control 100 iig/mL ND Not mutagenic at any dose Rasmussen et al. ("19911 Chromosomal aberrations ND Sister chromatid exchange (SCE) ND DNA damage ND DNA adducts ND Genotoxicity studies in mammals—in vivo Chromosomal aberrations ND Sister chromatid exchange (SCE) ND DNA damage ND DNA adducts ND 11 Dib enzothi ophene ------- FINAL 7-25-2013 Table 4A. Summary of Dibenzothiophene Genotoxicity Endpoint Test System Dose Concentration" Resultsb Comments References Without With Activation Activation Mouse biochemical or visible specific locus test ND Dominant lethal ND Genotoxicity studies in subcellular systems DNA binding ND "Low est effective dose for positive results or highest dose tested for negative results. b+ = positive; ± = equivocal or weakly positive; - = negative; ND = no data; NR = not reported; DMSO = dimethyl sulfoxide. 12 Dib enzothi ophene ------- FINAL 7-25-2013 Table 4B. Other Studies Test Materials and Methods Results Conclusions References Short-term studies CD-I mice treated via gavage Pilot range-finding studies: 4 mice/sex/dose, single dose of 0-3,250 mg/kg or 4 consecutive daily doses of 0-325 mg/kg; necropsy performed 24 hr after last dose; blood taken from hearts of mice and examined for hematological effects; liver, kidney, spleen, heart, lungs, thymus, and duodenum examined at necropsy LDsn Experiment 1: 12 male mice/dose. 12 vehicle controls, 8 untreated controls; single doses of 0; 260; 374; 540; 777; 1,118; or 1,609 mg/kg; LD50 determined at 7 d; surviving mice sacrificed on Day 14 and performed histology of liver, lung, heart, and thymus LD™ Experiment 2: 12 mice/treatment aroiiD. 5 preinduced vehicle controls; mixed-function oxidase (MFO) pretreatment (one intraperitoneal [i.p.] injection of 3-methylcholanthrene [80 mg/kg] followed by daily i.p. injections of phenobarbital [50 mg/kg] in sterile saline for 3 d) followed 24 hr later by single doses of 0, 215, 265, 325, 400, 492, 605, or 744 mg/kg Pilot ranee finding studies: No treatment-related hematological changes seen; no treatment-related histological lesions seen in the kidney, duodenum, spleen, or heart; liver lesions included centrilobular or periacinar degeneration and necrosis LD™ experiments: All mortality occurred within 72 hr of treatment and was increased in groups with prior induction of MFO; animals were sluggish; gross lesions in mice found dead included pulmonary congestion and edema, mild to moderate hydrothorax, intestinal hemorrhage, and mottled livers; all MFO-induced mice had mild fibrinous peritonitis; histological lesions included severe centrilobular hepatic necrosis across doses in both experiments, necrosis of lymphocytes in thymic cortices at >540 mg/kg in Exp. 1 and >265 mg/kg in Exp. 2, and degenerative changes in the walls of small arteries in the lung in 5 mice dosed with 265-492 mg/kg (Exp. 2) Without induction: acute LD50 of 470 mg/kg; with prior induction of MFO, acute LD50 of 335 mg/kg; preinduction of MFO potentiated the toxicity of dibenzothiophene Leighton (1989) Metabolism/ toxicokinetic Male Wistar rat (number not specified), treated with daily i.p. injections of 40 mg/kg dibenzothiophene for 3 d, 3-methylcholanthrene for 3 d, 500 mg/kg Aroclor 1254 for 5 d, or twice daily i.p. injections of 40 mg/kg phenobarbital for 4 d, then starved for 24 hr after final injection; liver microsomes isolated; in vitro oxidation assay performed using dibenzothiophene (0.02-0.50 mM) and rat liver microsomal suspension (10 |iL) Dibenzothiophene metabolic pathway determined to be S-oxidation with metabolites of dibenzothiophene-5-oxide (primary) and dibenzothiophene-5 -dioxide (secondary); Aroclor 1254, 3-methylcholanthrene, and phenobarbital increased rate of formation of sulfoxide, but dibenzothiophene pretreatment had no effect; carbon monoxide inhibited sulfoxidation Dibenzothiophene metabolite dibenzothiophene-5-oxide was further oxidized to dibenzothiophene-5 -dioxide; P-450 monooxygenases most likely involved in the metabolism Vignier et al. C1985) 13 Dib enzothi ophene ------- FINAL 7-25-2013 Table 4B. Other Studies Test Materials and Methods Results Conclusions References Metabolism/ toxicokinetic Male Wistar rat (number not specified), treated with i.p. injections of 40 mg 5,6-benzoflavone/kg for 3 d, 200 mg Aroclor/kg once, or 80 mg phenobarbital/kg in 0.9% NaCl over 3 d and sacrificed 24 hr after last dose; microsomes from 4 animals per group were incubated with 50 |imol/L dibenzothiophene for 20 min at 37°C and analyzed; solvent-only controls Metabolic products were sulfoxide (main product) and sulfone; no pretreatments affected sulfoxide formation, but pretreatments with phenobarbital and Aroclor increased sulfone formation Dibenzothiophene metabolites (using rat microsomes) were sulfoxide and sulfone, controlled by different enzymes; only the one responsible for sulfone formation can be induced by P-450 inducers such as phenobarbital Jacob et al. (1991) 1 rabbit (sex and strain not specified) given an emulsion of 2 g dibenzothiophene in water administered via stomach tube; urine collected (time not specified) and analyzed Main excretion product was mono-hydroxy- diphenylene sulfone Dibenzothiophene oxidized to mono-hydro xy-diphenylene sulfone in the rabbit Thomas et al. f1942s) 14 Dib enzothi ophene ------- FINAL 7-25-2013 DERIVATION OF PROVISIONAL VALUES Tables 5 and 6 present summaries of noncancer and cancer reference values, respectively. IRIS data are indicated in the tables, if available. Table 5. Summary of Noncancer Reference Values for Dibenzothiophene (CASRN 132-65-0) Toxicity Type (units) Species/ Sex Critical Effect p-Reference Value POD Method PODhed UFC Principal Study Subchronic p-RfD (mg/kg-d) NDr Screening chronic p-RfD (mg/kg-d) Rat/M Increased liver weight 1 x 1(T2 NOAEL 3.1 300 Thomas et al. f 1942s) Subchronic p-RfC (mg/m3) NDr Chronic p-RfC (mg/m3) NDr NDr = not determinable. Table 6. Summary of Cancer Values for Dibenzothiophene (CASRN 132-65-0) 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 determinable. DERIVATION OF ORAL REFERENCE DOSES Derivation of Subchronic p-RfD No subchronic p-RfD value can be derived because no subchronic oral studies on exposure to dibenzothiophene were identified. The only available chronic oral study is a peer-reviewed, published study by Thomas et al. (1942). in which male albino rats were exposed to dibenzothiophene by oral administration for 165 days. This study relied on historical laboratory control groups instead of a concurrent control group, and information regarding statistical methods was not provided. Due to the shortcomings of this study, a chronic p-RfD cannot be confidently derived here. However, the effects in the liver (increased liver weight and fatty metamorphosis of the liver) reported by Thomas et al. (1942) are pronounced and are supported by liver pathology observed by Leighton (1989) during acute and short-term studies in mice (see Table 4B for details). A "screening-level" value for chronic oral exposure based on these liver effects is provided in Appendix A. This value is thought to be protective of shorter duration exposures as well. 15 Dib enzothi ophene ------- FINAL 7-25-2013 Derivation of Chronic p-RfD As described above, no chronic p-RfD value can be derived because no adequate, well-described studies are available. A "screening-level" value for chronic oral exposure based on these liver effects is provided in Appendix A. DERIVATION OF INHALATION REFERENCE CONCENTRATIONS No subchronic or chronic provisional reference concentration (p-RfC) can be derived because no inhalation studies on exposure to dibenzothiophene were identified. Furthermore, sufficient information on the oral toxicity and metabolism of dibenzothiophene and the potential role of first-pass effects in this toxicity does not exist to support route-to-route extrapolation. CANCER WEIGHT-OF-EVIDENCE (WOE) DESCRIPTOR Table 7 identifies the cancer WOE descriptor for dibenzothiophene. Table 7. Cancer WOE Descriptor for Dibenzothiophene Possible WOE Descriptor Designation Route of Entry (oral, inhalation, or both) Comments "Carcinogenic to Humans " NS NA No human carcinogenicity studies were identified. "Likely to Be Carcinogenic to Humans" NS NA No animal carcinogenicity studies were identified. "Suggestive Evidence of Carcinogenic Potential" NS NA No animal carcinogenicity studies were identified. "Inadequate Information to Assess Carcinogenic Potential" Selected Both Selected due to the lack of any data on carcinogenicity. "Not Likely to Be Carcinogenic to Humans" NS NA There are no data to indicate that dibenzothiophene is not likely to be carcinogenic to humans. NA = not applicable; NS = not selected. DERIVATION OF PROVISIONAL CANCER POTENCY VALUES Although several studies have produced negative results regarding the mutagenicity of dibenzothiophene in bacteria and CHO cells (Rasmussen et al.. 1991; Mcfall et al.. 1984; Pelrov et al.. 1983; Dickson and Adams. 1980). no data were located on the carcinogenicity of dibenzothiophene in whole animals. The lack of data on the carcinogenicity of dibenzothiophene precludes the derivation of quantitative estimates for either oral (p-OSF) or inhalation (p-IUR) exposure. 16 Dib enzothi ophene ------- FINAL 7-25-2013 APPENDIX A. PROVISIONAL SCREENING VALUES For reasons noted in the main PPRTV document, it is inappropriate to derive provisional toxicity values for dibenzothiophene. 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 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. DERIVATION OF SCREENING PROVISIONAL ORAL REFERENCES DOSES Derivation of Screening Chronic p-RfD The published, peer-reviewed study by Thomas et al. (1942) represents the only chronic-duration oral study available for dibenzothiophene and is selected as the principal study for derivation of the screening chronic p-RfD. The critical effect is increased liver weight in male rats. Details of the study are provided in the "Review of Potentially Relevant Data" section of this document and briefly described below. Following dietary dibenzothiophene exposure of rats for 165 days, effects were reported in the liver, kidney, and spleen (Thomas et al.. 1942). Decreased spleen weight was reported; however, this could be explained by the dose-related decrease in food consumption that occurred. According to Peters and Boyd (1966). spleen weight decreases disproportionately to body weight in instances of decreased food consumption. There were neither histopathological changes to the spleen nor any hematological changes that could have indicated functional impairment. In addition, no histopathological changes in the spleen were seen in mice following gavage treatment of 3,250 mg/kg dibenzothiophene (single dose) or 325 mg/kg-day dibenzothiophene for 4 consecutive days (Leighton. 1989). Therefore, the changes in spleen weight are not considered a direct, adverse effect of dibenzothiophene exposure. Renal effects observed in the Thomas et al. (1942) study included only a slight-to-moderate, light brown, granular pigmentation of the epithelial cells of the proximal convoluted tubules with no evidence of cell destruction in all treated animals. These renal changes are also not considered adverse. A dose-dependent, biologically relevant increase in liver weight was observed with changes of >10% (over body weight-matched laboratory historical controls) at the middle dose of 27 mg/kg-day. Histopathological lesions in the liver (fat accumulation, irregular vacuolation of the parenchymal cells [hepatocytes] throughout the lobules, and indications that adjacent cells had fused) were also observed at all doses; however, incidence of lesions was not provided, and severity was described as much less in the low-dose group (13 mg/kg-day) animals. The LOAEL in the study by Thomas et al. (1942) is 27 mg/kg-day based on increased liver weight (relative to body weight-matched laboratory historical controls) and histopathological changes in the liver. There is also support that the liver is a target organ of dibenzothiophene toxicity provided by the reported severe centrilobular hepatic lesions (degeneration and necrosis) in CD-I mice following a single lethal oral dose and during a 4-day range finding study (Leighton, 1989). 17 Dib enzothi ophene ------- FINAL 7-25-2013 Data from the Thomas et al. (1942) study are not amenable to BMD modeling because the required information (i.e., number of animals per dose group) is not available. Therefore, a NOAEL/LOAEL approach is employed to identify the point of departure (POD). The POD is a NOAEL of 13 mg/kg-day based on changes in liver weight and liver histopathology at >27 mg/kg-day. In EPA's Recommended Use of Body Weight3/4 as the Default Method in Derivation of the Oral Reference Dose (U.S. EPA. 201 1c). the Agency endorses a hierarchy of approaches to derive human equivalent oral exposures using data from laboratory animal species, with the preferred approach being physiologically based toxicokinetic modeling. Other approaches might include using some chemical-specific information without a complete physiologically based toxicokinetic model. In lieu of chemical-specific models or data to inform the derivation of human equivalent oral exposures, EPA endorses the use of body-weight scaling to the 3/4 power (i.e., BW3 4) to extrapolate toxicologically equivalent doses of orally administered agents from all laboratory animals to humans for the purpose of deriving an RfD under certain exposure conditions. More specifically, the use of BW3 4 scaling for deriving an RfD is recommended when the observed effects are associated with the parent compound or a stable metabolite, but not for portal-of-entry effects or developmental endpoints. Following U.S. EPA (2011c) guidance, the POD of increased liver weight and liver histopathology in male albino rats is converted to an HED through application of a dosimetric adjustment factor (DAF)1 derived as follows: DAF = BWa1/4 - BWh1/4 Where: DAF = dosimetric adjustment factor BWa = animal body weight BWh = human body weight Using a BWa of 0.25 kg for rats and a BWh of 70 kg for humans (U.S. EPA. 1988). the resulting DAF is 0.24. Applying this DAF to the NOAEL identified for the critical effect in male albino rats yields a NOAELhed as follows: NOAELhed = NOAEL (mg/kg-day) x DAF = 13 mg/kg-day x 0.24 = 3.1 mg/kg-day The screening chronic p-RfD for dibenzothiophene based on a NOAELhed of 3.1 mg/kg-day in male rats is derived as follows: Screening Chronic p-RfD = NOAELhed UFc = 3.1 mg/kg-day -^300 = 1 x 10~2 mg/kg-day :As described in detail in Recommended Use of Body Weight3/4 as the Default Method in Derivation of the Oral Reference Dose (U.S. EPA. 2011c'). rate-related processes scale across species in a manner related to both the direct (BW11) and allometric scaling (BW3'4) aspects such that BW34 BW11 = BW converted to a DAF of BWa1/4 + BWh1/4. 18 Dib enzothi ophene ------- FINAL 7-25-2013 Table A. 1 summarizes the uncertainty factors (UFs) for the screening chronic p-RfD for dib enzothi ophene. Table A.l. UFs for the Screening Chronic p-RfD for Dibenzothiophene UF Value Justification UFa 3 A UFa of 3 (10°5) has been applied to account for uncertainty in characterizing the toxicodynamic differences between rats and humans following oral dibenzothiophene exposure. The toxicokinetic uncertainty has been accounted for by calculation of a human equivalent dose (HED) through application of a dosimetric adjustment factor (DAF) as outlined in the EPA's Recommended Use of Body Weight3'4 as the Default Method in Derivation of the Oral Reference Dose (U.S. EPA. 20 lie). ufd 10 A UFd of 10 has been applied because there are no acceptable two-generation reproductive toxicity or developmental toxicity studies. UFh 10 A UFh of 10 has been applied for inter-individual variability to account for human-to-human variability in susceptibility in the absence of quantitative information to assess the toxicokinetics and toxicodynamics of dibenzothiophene in humans. ufl 1 A UFl of 1 has been applied for LOAEL-to-NOAEL extrapolation because the POD is a NOAEL. UFS 1 A UFS of 1 has been applied because a chronic-duration study was selected as the principal study. UFC 300 19 Dib enzothi ophene ------- FINAL 7-25-2013 APPENDIX B. DATA TABLES Table B.l. Body, Liver, and Spleen Weights of Male Albino Rats After Dietary Exposure to Dibenzothiophene for 165 Daysa'b Parameter Exposure Group, % (ADD, mg/kg-d)d'e 0f 0.025 (13) 0g 0.050 (27) 0h 0.100 (63) Terminal body weight (g) 310 310 273 273 212 212 Absolute liver weight (g)c 10.00 ±0.11 10.70 ±0.29 (107) 9.50 ±0.27 12.80 ±0.48 (135) 8.40 ± 0.22 18.10 ±0.74 (215) Absolute spleen weight (g)c 0.97 ± 0.062 0.69 ±0.015 (71) 0.92 ± 0.072 0.64 ± 0.067 (70) 0.83 ±0.041 0.36 ±0.010 (43) "Thomas et al. (19421. Statistical analysis was not reported and is not conducted because number of animals per group was not reported. 0Weights are expressed as mean ± probable errors (% of laboratory historical control). dAnimals were provided dibenzothiophene in the food at 0.25, 0.50, or 1.00% for the first 4 d. Because of low food intakes and decreases in body weight, doses were then decreased to 0.025, 0.050, or 0.100% dibenzothiophene for the remainder of the 165-d study period. The study authors provided the amount of dibenzothiophene consumed. The following equation was used to convert that information to mg/kg-d: ADD = Total Dibenzothiophene Consumption per Animal over Study Duration x (1 Body Weight) x (1 ^ Days Dosed) eData for each exposure group were compared with data for laboratory historical controls. For the evaluation of organ weights, historical controls were matched according to body weight. fMatched laboratory historical controls for 13-mg/kg-d dose group. 8Matched laboratory historical controls for 27-mg/kg-d dose group. hMatched laboratory historical controls for 63-mg/kg-d dose group. 20 Dib enzothi ophene ------- FINAL 7-25-2013 APPENDIX C. BMD OUTPUTS There are no BMD outputs for dibenzothiophene. 21 Dib enzothi ophene ------- FINAL 7-25-2013 APPENDIX D. 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