Document e1vnM18RpjaMy23LwOJGG050G

To: Yamada, Richard (Yujiro)[yamada.richard@epa.gov]; Beck, Nancy[Beck.Nancy@epa.gov]; Jackson, Ryan[jackson.ryan@epa.gov] Cc: Segal, Scott[scott.segal@bracewell.com]; Lee,John[john.Iee@bracewell.com] From: Krenik, Edward Sent: Mon 6/26/2017 9:58:57 PM Subject: DPE Letter to Pruitt Letter to ERA 20170626.pdf RE Chloroprene Report June2017.pdf Good afternoon, Look forward to seeing you this week. Attached is a letter that was sent to the Administrator today as well as our environment assessment/report. The Request for Correction will be filed today or tomorrow. I wanted to get this to you before our meeting so that if you have any questions we can get additional information ready for our meeting this week. See you on the 28th. I know our CEO is looking forward to working with EPA to resolve this issue. Thanks again, Ed EDWARD KRENIK Partner edward.krenik@policyres.com T:+1.202.828.5877 | F:+1.800.404.3970 POLICY RESOLUTION GROUP | BRACEWELL LLP 2001 M Street NW, Suite 900 | Washington, D.C. | 20036-3310 policyres.com | profile | download v-card 17cv1906 Sierra Club v. EPA ED_001523_00004235-00001 CONFIDENTIALITY STATEMENT This message is sent by a law firm and may contain information that is privileged or confidential. If you received this transmission in error, please notify the sender by reply e-mail and delete the message and any attachments. 17cv1906 Sierra Club v. EPA ED_001523_00004235-00002 Denka Performance Elastomer LLC 560 Highway 44 LaPlace, LA 70068 June 26,2017 The Honorable Scott Pruitt Administrator U.S. Environmental Protection- Agency Headquarters William Jefferson Clinton Building 1200 Pennsylvania Avenue, N.W. Mail Code: 1101A Washington, D.C. 20460 Re: Request to Withdraw and Correct the 2010 IRIS Review of Chloroprene Dear Administrator Pruitt: I write on behalf of Denka Performance Elastomer LLC (DPE) in support of the request that the U.S. Environmental Protection Agency (EPA) withdraw and correct its Integrated Risk Information System (IRIS) Toxicological Review of Chloroprene (EPA/635/R-09/010F, 2010) (the 2010 IRIS Review). The errors in the 2010 IRIS Review threaten the very survival ofDPE's Neoprene production facility in LaPlace, Louisiana (Facility). In particular, based on those errors and EPA's subsequent flawed determinations concerning the risks caused by Facility emissions, EPA is making stringent air pollution control demands concerning the Facility that are technologically impossible to achieve. EPA must expeditiously apply good science in this matter in order to alleviate the public's undue concerns about the risks associated with this Facility and to prevent further significant damage to DPE's business. Key conclusions of the 2010 IRIS Review are not based on the best available science or sound scientific practices. First, the -2010 IRIS 'Review rejected -the findings of the strongest available epidemiological study, which concluded that there is no increased risk of cancer in workers exposed to chloroprene (some of the study cohorts actually exhibited a lower risk of cancer than the control population). Rather than accepting the overall study conclusions, the 2010 IRIS Review relied on select statistically non-significant comparisons of cancer incidence rates among subgroups of the larger epidemiology study to bolster its classification of chloroprene as "likely to be carcinogenic to humans." Second, the 2010 IRIS Review is flawed because it relied on laboratory animal studies, and then used the results for the most sensitive laboratory animal - female mice - as the basis for a series of overly conservative calculations to develop the human inhalation unit risk (1UR). Contrary to sound scientific practice, the 2010 IRIS Review ignored the known differences between humans and a select strain of female laboratory mice, and relied on results in those female mice to estimate an IUR for humans. Third, -the 2010 IRIS Review gives chloroprene, which EPA designates only as a "likely" and not a "known" human carcinogen, the fifth highest IUR estimate of any similar chemical, including known human carcinogens, in the IRIS database. DuPont, the former Facility owner, provided similar information and analysis to EPA in comments on the draft IRIS Review, which comments were rejected in 2010. DPE's Request for Correction and the Ramboll Environ report provide new information and weight-of-evidence review not available in 2010. 17cv1906 Sierra Club v. EPA Page 1 ED_001523_00004236-00001 Denka Performance Blastomer LLC 560 Highway 44 LaPlace, LA 70068 After EPA published the 2010 IRIS Review, the National Academies of Sciences' National Research Council (NRG) recommended major reforms in the IRIS process. Congress has repeatedly instructed EPA to implement the NRC's recommendations, and EPA has advised Congress that it is doing so. The 2010 IRIS Review is plagued with flaws similar to those that gave rise to these reform initiatives, and it is extremely important that the 2010 IRIS Review now be corrected in light of its scientific and procedural ^deficiencies. These issues are more fully explained in DPE's Request for Correction and in the supporting toxicological and epidemiological expert review prepared by prominent scientists with the consulting firm of Ramboll Environ: Drs. Kenneth Mundt, Robinan Gentry, and Sonja Sax. Their report is entitled Basis for Requesting Correction of the U.S. EPA Toxicological Review of Chloroprene, dated June 2017 ("the Ramboll Environ Report," and attached hereto). The Ramboll Environ Report identifies multiple substantive errors in the 2010 IRIS Review and demonstrates that if chloroprene is to be treated as a possible human carcinogen, the 2010 IRIS Review establishes an IUR that is 156 times too high. By way of background, DPE acquired the Neoprene Facility from DuPont on November 1, 2015. Neoprene is a synthetic rubber utilized in a wide variety of applications, including laptop sleeves, orthopedic braces, electrical insulation, and automotive fan belts. DPE is the only manufacturer ofNeoprene in tlie United States. The Facility is a commercial mainstay of LaPlace, Louisiana. With an annual payroll of $33 million, DPE directly employs 200-250 people in manufacturingjobs and regularly employs between 125 and 150 contractors. DPE also has created 16 new corporate jobs. Additionally, DPE is investing and upgrading the Facility, including taking new measures to reduce its environmental footprint and improve its productivity and competitiveness. The base feedstock for Neoprene is chloroprene. The Facility's air permits authorize it to emit chloroprene, and the Facility operates in compliance with those permit limits. However, shortly after DPE's acquisition of the Facility, on December 17, 2015, EPA publicly released its 2011 National Air Toxics Assessment (NATA), which identified the Facility as creating the greatest offsite risk of cancer of any manufacturing facility in the United States. The NATA findings concerning the Facility are based on the scientifically unwarranted and outdated 2010 IRIS Review and the emission profile of the Facility. Following the public release of the NATA, EPA and the Lou isiana Department of Environmental Quality (LDEQ) pressed DPE to reduce emissions to achieve an extraordinarily miniscule ambient air target concentration of 0.2 pg/m3 for chloroprene on an annual average basis (which is intended to reflect a 100 in 1,000,000 rate of potential excess cancers in a population exposed to such concentrations continuously for 70 years). The 0.2 pg/m3 target is based on a risk assessment that applied the erroneous and scientifically unsubstantiated IUR fam the 2010 IRIS Review, and the target reflects more than a four thousand-fold reduction in the applicable Louisiana 8-hour ambient standard for chloroprene. Ramboll Environ's expert scientific opinion is that the appropriate risk-based ambient target should be 156 times larger or 31.2 pg/m3. There is no agency rule or even proposed rule requiring the attainment ofthe 0.2 pg/m3 target, yet EPA has advised DPE, LDEQ, and the public that 0.2 pgta3 is the appropriate target. As a result of the flawed science embodied in the 2010 IRIS-Review, and as a result of the NATA findings and the Facility's emission profile, DPE has suffered extraordinary hardship in a n umber of ways. Page 2 17cv1906 Sierra Club v. EPA ED_001523_00004236-00002 Denka Performance Elastomer LLC 560 Highway 44 LaPlace, LA 70068 First, despite DPE's concerns about the science behind the 2010 IRIS Review, DPE is currently spending more than $18 million on new pollution controls. On January 6, 2017, DPE entered into an Administrative Cider on Consent with LDEQ to reduce chloroprene emissions by approximately 85% below the level of the Facility's 2014 emissions. DPE estimates that the capital cost of these emission reduction devices is approximately $18 million, and the devices will cost hundreds of thous of dollars per year to operate. Even though DPE is installing the most advanced air pollution controls available, it will still not be able to meet the stringent 0.2 pg/m3 target. Second, because the 2010 IRIS Review is flawed, EPA's very public announcements arising out of that Review and the NATA have created unnecessary public alarm. For example, after issuing the NATA, EPA created a public webpage specifically addressing DPE's chloroprene emissions.1 Moreover, environmental activists and plaintiffs' lawyers have had numerous meetings in the community about DPE, all based on the faulty assumption that 0.2 gg/m3 is the ``safe" level for chloroprene. Further, a local citizen's group has formed and has been handing out misleading flyers and protesting near DPE's Facility. The erroneous IUR in the 2010 IRIS Review and the resulting NATA findings have caused DPE enormous reputational damage. Third, as a result of the NATA findings, EPA Region 6 asked the 'National Environmental Investigations Center (NEIC) to investigate the regulatory compliance status of the Facility. NEIC sent a team of inspectors to the Facility from June 6-10, 2016, approximately seven months after DPE's acquisition. To be clear, DPE fully respects the important function of the EPA in enforcing environmental requirements. It is simply a fact, however, that as a result of the erroneous IUR and the NATA findings, EPA has initiated an enforcement'proceeding against'DPE and has devoted an extraordinary amount Of resources from the Department ofJustice, EPA-headquarters, EPA Region 6, and NEIC to developing and pursuing the issues in the NEIC report. Finally, since acquiring the Facility in November of 2015, DPE's relatively small management team has been buffeted by continuous environmental regulatory demands resulting ftom the erroneous IUR and the NATA findings, hi addition to Facility operation, DPE staff has been in non-stop meetings and negotiations with EPA arid LDEQ. DPE's legal and consulting expenses have been' enormous, in the millions of dollars. Underlying all of these expenses and burdens on DPE is the erroneous IUR in the 2010 IRIS Review, as applied in the NATA risk assessment. DPE needs EPA's assistance in the expeditious application of good science to this matter. In meetings with EPA in 2016 concerning the need to correct the 2010 IRIS Review, EPA officials advised DPE that EPA's ``queue is full". DPE respectfully requests that BPA review the science underlying the 2010 IRIS Review, withdraw the erroneous IUR, and develop a more accurate toxicological review of chloroprene. We are confident that the Ramboll Environ Report will lead you to these conclusions. Without See https://www.epa.gov/la/laplace-louisiana-background-information. 17cv1906 Sierra Club v. EPA Page 3 ED_001523_00004236-00003 Denka Denka Performance Elastomer LLC 560 Highway 44 LaPlace, LA 70068 this relief, it is uncertain whether DPE will be able to reduce emissions sufficiently to satisfy agency demands, or even continue operation . Sincerely, Koki Tabuchi President and Chief Executive Officer Denka Performance Elastomer LLC 17cv1906 Sierra Club v. EPA Page 4 ED_001523_00004236-00004 Intended for Denka Performance Elastomer,LLC 560 Highway 44 LaPlace, LA 70068 Document type Final Date June 2017 BASIS FOR REQUESTING CORRECTION OF THE US EPA TOXICOLOGICAL REVIEW OF CHLOROPRENE Prepared by: Dr. Robinan Gentry Ramboll Environ 3107 Armand Street Monroe, LA 71201 Drs. Kenneth Mundt and Sonja Sax Ramboll Environ 29 Amity Street Suite 2A Amherst, MA 01002 17cv1906 Sierra Club v. EPA ED_001523_00004237-00001 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page ii CONTENTS 1 2 2.1 2.2 2.3 3 3.1 3.2 3.3 4 4.1 4.2 4.2.1 4.2.2 4.2.3 4.2.4 4.3 4.4 5 5.1 5.2 5.3 6 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7 Introduction 1 The IRIS Process: Challenges, Recent Changes, and NRC Recommendationsfor Improvement 4 Purpose of the IRIS program 4 Chai lenges in the IRIS process 4 Recommendations for improvement of the IRIS process in updating the 2010 Review 5 Toxicological Weight of Evidence: Animal Studies 7 Guidelines for evaluating toxicological studies 7 Animal studies show important pharmacokinetic differences across species 7 Conclusions 8 Mechanistic Evidence: ChloropreneMode of Action 9 Guidelines for evaluating mechanistic studies 9 Mechanisticevidence for cancer effects from chloroprene donot support a mutagenic MOA 9 The chloroprene mutagenic profile is distinct from that of1,3-butadiene 10 Evidence does not support the formation of DNA adducts by chloroprene metabolism to an epoxide intermediate in vitro 11 Evidence does not support mutagenicity of chloroprene in vitro 11 Evidence does not support mutagenicity of chloroprene in vivo 13 Evidence supports an alternative MOA for chloroprene based on cytotoxicity 13 Conclusions 14 Epidemiological Evidence: Occupational Studies 15 Evaluation of the epidemiological studies 15 Important limitations of the epidemiology literature 18 The Marsh et al. (2007a, b) studies do not show a causal link between occupational exposure to chloroprene and increased cancer risks 20 Cancer Classification for Chloroprene 24 US EPA Derivationof the ChloroprenelUR 26 USEPA's dose-responsemodelingappliedoverly conservative methodology 26 Extrapolation from animals to humans should have included use of a PBPK model 27 Deriving a composite IUR based on multiple tumors is not scientifically supported 27 IUR adjustment for early life susceptibility is not appropriate 29 Summary of US EPA's derivation of the chloroprene IUR 29 Replication of US EPA's dose-response modeling 30 Conclusions 34 17cv1906 Sierra Club v. EPA ED_001523_00004237-00002 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page Hi 8 The Chloroprene IUR Compared to Known Chemical Carcinogens 35 9 A PBPKModel for Chloroprene 39 9.1 PBPK modeling should be used to quantify the pharmacokinetic differences between species 39 9.2 US EPA calculation of the human equivalent concentration for chloroprene in the 2010 Review 41 9.3 The Allen etal. (2014) study shows that a validated PBPK model should be used to updatethe 2010 chloroprenelUR 42 10 Calculation of an Updated Chloroprene IUR 44 11 Cancer Risk Assessment: Validation of the Chloroprene IUR 51 12 The ChloropreneRfC 53 13 Conclusions 55 References 57 TABLES Table 4.1: Table 4.2: Table 5.1: Table 5.2: Table 5.3: Table 5.4: Table 5.5: Table 7.1: Table 7.2: Table 8.1. Table 9.1: Table 10.1 Table 10.2 Table 10.3 Table 10.4 Table 11.1 Comparison of the Mutagenic Profiles of Chloroprene and 1,3-Butadiene Ames Test Results for Chloroprene withTA1535 and/or TA100 Quality Rankings for Cohort Studies Evaluating Cancer Risks from Occupational Chloroprene Exposure Relative Size of Marsh et al. (2007a,b) Study Compared with Other Available Studies Comparison of Key Study Criteria across Epidemiological Studies Reported Observed Liver Cancer Cases, Expected Counts, and Standardized Mortality Estimates for the Marsh et al. 2007a Study Exposure -Response Analysis for Chloroprene and Liver Cancers, Based on Internal (Relative Risks) and External (Standardized Mortality Ratio) Estimates, Louisville Plant Conservative Assumptions in the Calculation of the Chloroprene IUR Comparison of Dose-Response Modelingfor Female Mice at a Benchmark Response of 0.01 Summary of Potential! y Carcinogenic Compounds by IUR Listed in IRIS Exposure-Dose-Response for Rodent Lung Tumors Internal and External Doses from Yang et al. (2012) NTP (1998) Study - Female B6C3F i Mice Lung Alveolar/bronchiolar adenoma or carcinoma Multistage-Weibull Time-to-Tumor Modeling Results for a Benchmark Risk of 1% Calculation oflURs using Human Equivalent Concentrations Cancer Risk Estimates Based on US EPA and Allen et al. (2014) IURs for Chloroprene Compared with Excess Cancers Observed in the Louisville Plant FIGURES Figure 5.1: Figure 7.1: Liver Cancer RRs and SMRs by Cumulative Chloroprene Exposure, Louisville Illustration of How US EPA's Approach of Summing Individual Tumor Potencies OverestimatesTotalTumor Potency in Female Mice by Assuming In dependence 17cv1906 Sierra Club v. EPA ED_001523_00004237-00003 Basisfor Correctionof US EPA's2010 ToxioologicaReviewof Chloroprene Page iv Al X Appendix A: Appendix B: Toxicological Summary of Carcinogenic Compounds Summary of the Epidemiological Evidence of Known or Likely Carcinogenic Compounds Classified by US EPA Appendix C: Appendix D: Appendix E: Multistage Weibull Modeling Output About Ramboll Environ Expert Biographies 17cv1906 Sierra Club v. EPA ED_001523_00004237-00004 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page v ACRONYMS ADAF AIC BCME BMD BMD10 BMDL BMDL10 DAF DPE EDB: Fl I ARC IRIS IUR LOAEL pg/m3 MOA NATA NDMA NOAEL NRC NTP PBPK POD PPm Ramboll Environ RR SIR SMR US EPA VCM WHO WOE age-dependent adjustment factor Akaike Information Criterion bis(chloromethyl)ether benchmark dose benchmarkdose atthe 10% extra risk level lower 95% confidence limit of the benchmark dose lower95% confidence limitof the benchmark dose atthe 10% extra risk level dosimetry adjustment factor Denka PerformanceElastomer,LLC ethylene dibromide first generation International Agency for Research on Cancer Integrated Risk Information System inhalation unit risk lowest-observed-adverse -effect level microgram(s) per cubic meter mode of action National Air Toxics Assessment nitrosodimethylamine no-observed-adverse-effect level National Research Council National Toxicology Program physiologically based pharmacokinetic (model) point of departure parts per million Ramboll Environ US Corporation relative risk standardized incidence ratio standardized mortality ratio United States Environmental Protection Agency vinyl chloride monomer World Health Organization weightof evidence 17cv1906 Sierra Club v. EPA ED_001523_00004237-00005 BasisforCorrectionof US EPA's 2010ToxioologicaReviewofChloroprene Page ES-1 EXECUTIVE SUMMARY Background In 2010, the United States EnvironmentalProtection Agency (US EPA) Integrated Risk Information System (IRIS) program published a review of the epidemiology and toxicologyliteratureon chloropreneto provide scientific support and rationale for hazard and dose-responseassessmentinIRIS, including deriving an inhalation unit risk (IUR) and other values for chronic exposure (www.epa.gov/iris ). In the "Toxicological Review of Chloroprene" (hereafter referred to as the "2010 Review") (US EPA 2010a), US EPA concluded that chloroprene was "likely to be carcinogenic to humans" based on (1) statistically significant and dose-related informationfroman National Toxicology Program (NTP 1998) chronic inhalation bioassay demonstrating the early appearance of tumors, development of malignant tumors, and the occurrenceof multipletumors withinand across animalspecies; (2) evidence of an association between liver cancer risk and occupational exposure to chloroprene; (3) suggestive evidence of an association between lung cancer risk and occupationalexposure; (4)the proposed mutagenicmode of action (MOA); and (5) structural similarities between chloropren e and known human carcinogens butadiene and vinyl chloride (US EPA 2010a). The 2010 Reviewderived an IUR for lifetime exposure to chloroprene of 5 x 10'4 per microgram per cubic meter (pg/m3). This is the 5th highest IURgenerated by US EPA to date for any chemical(not includingcarcinogenicmetals or coke oven emissions) classified by US EPA or the International Agency for Research on Cancer (IARC)as a known or likely/probablehuman carcinogen. As outlined in detail below, we have determined that US EPA's classification relied on questionable , non transparent evaluation and interpretationof the toxicological and epidemiological evidence. Therefore, the IUR for chloroprene was not based on the best standard methods US EPA has used for other carcinogens. The IRIS Process: Challenges, Recent Changes, and Recommendations for Improvement The US EPA IRIS process has been subject to high-level constructive criticism. Most noteworthy,subsequent to the 2010 Review, the National Research Council (NRC) of the National Academies of Science(NAS) published a series of reports recommend ing important changes to improve the IRIS process (NRC 2011, 2014). The recommendations were well received by US EPA, but have not yet been fully implemented, and have not been applied to previously published reviews. In particular, NRC (2011, 2014) emphasized the importance of transparency and rigor in the review methods. NRC (2011) provided guidanceon development of inclusion and exclusion criteria for studies , and on methods for evaluatingand taking into account various forms of bias and other methodologiccharacteristicsthat could impactstudy findings. While the 2010 Review meets some of these NRC recommendations , it does not meet other key standards such as the evaluation a nd synthesis of the epidemiological and mechanistic data, and would benefit from their consideration and application. A transparent evaluation and integration of the published 17cv1906 Sierra Club v. EPA ED_001523_00004237-00006 BasisforCorrectionof US EPA's 2010ToxioologicaReviewofChloroprene Page ES-2 epidemiological and toxicological evidence on chloroprene carcinogenicity highlights the need to reconsider US EPA's classification of chloroprene as "likely to be carcinogenicto humans"to be in line with the weight of evidence and the InternationalAgency for Research on Cancer's (IARC 1999) classification of chloroprene as "possibly carcinogenic ." Toxicological Evidence US EPA should evaluatethe animal toxicological data that form the basis of the estimated chloroprene inhalation unit risk (IUR) in accordance with the NRC recommendations and US EPA standard risk evaluation methodologies. US EPA relied on the animal studies conducted by the NTP that showed very little consistencvacrossspeciesintumorincidenceand sites. These results indicated substantial species differences and demonstrated a unique sensitivity in the female mouse, with lung tumors being the most sensitiveendpoint. Thus, US EPA used the female mouse data to derivethe IUR, but without fully accounting for important pharmacokinetic differences between the mouse and humans. In addition to revisiting the reliance on the animaldataset forthe estimationof the IUR, US EPA should critically re-evaluate and integrate thecytotoxicand genotoxic evidence for chloroprene. The evidence from these studies indicates that chloroprene acts through a different mode of action (MOA) than the structurally similar and known human carcinogen 1,3-butadiene. Based on an evaluation consistent with the NRC (2011, 2014) recommendations, chloroprene's genotoxicity profile lacks several attributes necessary to conclude that there is a mutagenic MOA. Instead, the evidence supports site-specific cytotoxicity as a more likely MOA, as opposed to US EPA's conclusion that chloroprene acts via a mutagenic MOA. Epidemiological Evidence It is also necessay to critically evaluate the available epidemiological evidence on occupational chloroprene exposure. US EPA evaluated the epidemiological evidence of chloroprenecarcinogenicit\based on severaloccupationalcohorts fromaround the world. This evaluation, however, would have benefited from more transparency and rigorwith regard to how individualstudy qualitywas assessed and weightedin the overall weight -of-the-evidence assessment. In particular, US EPA did not assign more weight to the most recent epidemiological study by Marsh et al. (2007a, b),whichalso is the largestand most robust study to date. This study has been rated by other scientists as the best quality study available in part because it has the most comprehensive characterization of chloroprene exposure (Bukowski et al. 2009). Instead, US EPA equallyweighted this study with poorer qualityRussian, Armenian, and Chinese studies. Marsh et al. (2007a, b) reported no excess occurrence of lung or liver cancers among chloroprene exposed workers. In fact, overall and for all sub -cohorts defined by specific plant(s), standardized morality ratios (SMRs) based on local reference rates were all below 1.0, providing no indication of any excess of these cancers among chloroprene exposed workers. US EPA, however, discounted this primary finding, and instead interpreted a correlation between exposure leveland risk relativeto a comparison subgroup wherethe comparison group exhibited 17cv1906 Sierra Club v. EPA ED_001523_00004237-00007 BasisforCorrectionof US EPA's 2010ToxioologicaReviewofChloroprene Page ES-3 anomalously fewer cancers than expected, creating the appearance of an increased risk in the higher exposure groups. Furthermore, US EPA overlooked that there were as few as two liver cancer deaths in the comparison subgroup, likely reflecting a random deficitamong this group. The US EPA summary of this study indicates incomplete evaluation and misinterpretation of the published results. Properly interpreted, the evidence does not demonstrate an association between occupationalchloropreneexposure and humancancer incidence. US EPA's Derivationof the Chloroprene IUR US EPA derived the current chloroprene IURbased on a number of assumptions that are not substantiated by the scientific evidence, contributing to overestimation of an already conservative risk estimate (i.e., one based on the most sensitive species, gender, and endpoint). Specifically, US EPA based the chloroprene IUR on a composite estimate of risk based on multiple tumors observed primarily in mice, not just the lung tumors for which the data were more conclusive. US EPA then assumed that the female mouse-based IUR was representative of continuous human exposure, and that lung tumors weresystemic rather than portal-of-entry effects; US EPA also rounded up at various stages of adjustment. Finally, US EPA applied an age-dependent adjustment factor (ADAF) based on insufficientdata to supporta mutagenic MOA. A PBPKModel for Chloroprene In calculating the IUR, US EPA should have used theavailiile pharmacokinetic modelfor chloroprene.Himmelstein et al. (2004 a,b) developed a physiologically based pharmacokinetic (PBPK) model for chloroprene to help explain the divergent resultsobservedacrossanimalspecies. The model demonstrates whythe mouseis the most sensitive species and why humans are likely to be comparatively much less sensitive to the effects of chloroprene exposure. The hypothesis that differences in pharmacokinetics are determinants of the observed species differences has been demonstrated for other chemicals, including vinyl chloride. Thus, it is scientifically appropriate that US EPA employ PBPK models , which use the best available science to adjust for these differences, to derive IURs for all chemicals , such as chloroprene, for which data are available. US EPA did not use the PBPK model developed by Himmelstein etal. (2004 a,b) to inform the chloroprene IUR because US EPA noted that the data required to validate the model had not been published. However, all of the quantitative data necessary to refine and verify the critical metabolic parameters for the existing peer-reviewed PBPK model for chloroprene were available at the time of the 2010 Reviewand could have been used. Since then, additional data have been published, and the findings validate the model (Thomas etal. 2013, Yang etal. 2012, Allen etal. 2014). In particular, Allen etal. (2014)derivedan IUR based on PBPKresults and the incidence of respiratory cancer that was 100 times lower than US EPA's value, using a method which integrates both the animaland human evidence. Importantly,the IUR reported by Allen etal. (2014) is consistentwith IURs for similar compounds such as vinyl chloride and 1,3-butadiene, which have stronger and more consistent epidemiologicalevidence of human carcinogenicitythan chloroprene. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00008 BasisforCorrectionof US EPA's 2010ToxioologicaReviewofChloroprene Page ES-4 Calculation of an Up dated Chloroprene IUR We conducted an updated analysisby applyingthe results from validatedPBPK models to arriveat an IUR that includes an understanding of interspecies pharmacokinetics. We applied standard US EPA methodologyand conservative assumptionsto estimate of the potential cancer effects of chloroprene. Our estimated IUR is l.lx 10'2 per ppm or 3.2 x 10'6 perpg/m3, whichis of the same order of magnitude as the IURderived by Allen etal. (2014), and which better reflects the scientificunderstanding of potential chloroprene cancereffects in humans. These results are also consistentwiththe resultsfromvalidatedPBPK models and comparisons with other structurally relevant compounds such as vinyl chloride and 1,3-butadiene, both recognized as known human carcinogens. There is little scientific support for each of US EPA's conservative assumptions and subsequent adjustments. Combining a fullerunderstanding of interspecies pharmacokinetic differences and validated PBPK models with the results from the strongest epidemiological data provides the scientificgrounds for updating the 2010 IUR and calls into question the strength of the evidence to support a"likely to be carcinogenic to humans" classification . Similar adjustments should also be considered in estimating the chloroprene inhalation reference concentrations (RfC), as species - and strain-specific differences are noted . This will assure that policies and decisions resting on these toxicity values meet the test of sound science, transparent methods, and reproduciblefindings. Conclusions The IUR published in the 2010 Review requires correction . An updated lURshould be based on the best available methodology as well as a valid interpretation of the body of published evidence. Correction is critical given that the IUR published in the 2010 Review is being used by US EPA for enforcement actions. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00009 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 1 1 INTRODUC.riON In December, 2015, the United States Environmental Protection Agency (US EPA) published the 2011 National Air Toxics Assessment (NATA), indicating a high off site air pollution cancer risk from emissions of chloroprene from the Neoprene production facility in LaPlace, Louisiana. The previous month, on November 1, 2015, Denka Performance Elastomer, LLC (DPE), had acquired the LaPlace Neoprene production facility . The underlying NATA risk calculations combin ed estimated ambient chloroprene concentrations from air modeling analyses with the cancer inhalation unit risk (IUR) value derived by the US EPA Integrated Risk Information System (IRIS) and documented in the Toxicological Review of Chloroprene (hereafter referred to as the "2010 Review") (US EPA 2010a). On behalfof DPE, Ramboll Environ USCorporation(RambollEnviron) preparedthis summary review of the US EPA toxicity assessment for chloroprene, focusing on a detailed review of US EPA's derivation of the cancer IUR reported in the 2010 Review(US EPA 2010a). US EPA's chloropreneriskassessmentcalculationsre based on and directly proportional to USEPA's lURfor lifetime exposure to chloropreneof 5 x 10'4 per micrograms per cubic meter (pg/m3). The chloroprene IUR is the 5th highest IUR generated to date for any substance classified by US EPA or the International Agency for Researchon Cancer (IARC) as a known or likely/probable human carcinogen (not including carcinogenic metals or coke oven emissions) The chloroprene lURis orders of magnitude higher than IURs derived by US EPA for substances, such as vinyl chloride, 1,3-butadiene, and benzene, that have been classified by US EPA as known human carcinogens.1 In contrast, chloroprene has been classified as "likelyto be carcinogenicto humans" based on a weight -of-evidence (WOE) assessment that includedan animal inhalation study conducted by the NationalToxicologyProgram(NTP1998) and four (of nine) epidemiological studies reportedly indicating increased risks for liver cancer (US EPA 2010a). It was noted thatthese data were insufficient to classify chloroprene as a known human carcinogen. On the other hand, IARC classified chloroprene as "possibly carcinogenicto humans," based on the same evidence from experimental animal studies and similar epidemiological evidence concluded that the human evidence was inadequate (IARC 1999). Since the 2010 Review (US EPA 2010a), the National Academies of Sciences National Research Council (NRC 2011, 2014) has recommended substantive improvements to the IRIS evaluation process, calling for greater transparency including improved methods for and documentation of scientificstudy selection, critical review of study qualityand limitations,and the synthesis of findings across studies. This has provided much of the impetus for changes to the IRIS process. Improvements in the critical evaluation of epidemiological stud y quality and bias were noted as especially important , as statistical associations in epidemiological studies are only meaningful if supported by rigorous study designand data quality control. In addition, NRC noted the need for improved approaches to integrating evidence across diverse lines of investigation --including evidence from animal 1 https://www.epa .gov/fera/dos-eesponse-assessment-assessinq - health-risks-associated -exposure - hazardous -air pollutants 17cv1906 Sierra Club v. EPA ED_001523_00004237-00010 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 2 experiments, mechanistic investigations and epidemiological studies --in drawing conclusions regarding carcinogenicity and in deriving unit risk factors for cancer. NRC recommended better evidence integration that consider s and weighs the entire body of scientific evidence, and that does not rely on select and unrepresentative findings (NRC 2011, 2014). Similarly, using formaldehyde as an example, NRC recommended improved use of evidence in riskassessments NRC (2011) recommended using physiologically based pharmacokinetic (PBPK) modelsto quantify demonstrated differences in pharmacokinetics acrossspecies,and further recognize d PBPK models as a tool to support extrapolations between species, thereby reducing the uncertainty in quantitative1skassessments(NRC2014). These NRC recommendations remain highly relevant to the evaluation of chloroprene. In Section 2, we highlight key recommendations made by the NRC for improvements to the IRIS process that potentially impact the chloroprene evaluation . Consistent with the NRC recommendations to improve the scientific quality and validity of the 2010 Review, US EPA needs to address significant uncertainties associatedwiththe derivationof the IUR. These uncertainties pertain to the human relevance of the animal evidence, and whether or not various cancer types observed in animal experiments should be combined in estimating potential cancer riskto humans. Studies available both at the timeof the 2010 Review, and published since, demonstrate clear and significant pharmacokinetic differences between humans and animals(Himmelstein et al. 2004a, b; Yang etal. 2012; Thomas etal. 2013; Allen etal. 2014). These differences must be considered in order to derive a scientifically valid human cancer unit risk for chloroprene based on animal studies. In Section 3, we discuss the uncertaintiesassociated with toxicological evidence ; and in Section 4 we propose that the available mechanistic evidencesupports a cytotoxic, ratherthan mutagenic, MOA for chloroprene. In Section 5, we discuss US EPA's evaluation of the epidemiological data . US EPA did not fully or accurately summarize the findings from the Marsh et al. (2007a, b) study, which represents the largest and most comprehensive epidemiological study of chloropreneto date. Marsh etal. (2007a, b) reported no evidence of increased risks of liver and lung cancer with occupational chloroprene exposure; however, US EPA drew contrary conclusions fromsmallsubsets of the Marsh et al. (2007a, b) data. In Section 6, we discuss the uncertainty associated with the evidence presented by US EPA to support a classification of "likely to be carcinogenic to humans,"noting that the weight of evidence narrative is incomplete and the evidence is weaker than US EPA reports, and is more consistent with a "suggestive" classification. In Section 7, we summarize the uncertainties associated with the US EPA derivation of the IUR, and in Section 8, we compare the IUR for chloroprene to other chemicalsthat have been classified by US EPA and IARC as known or probably human carcinogens. This comparison shows that the IUR for chloroprene is substantially out of line with the US EPA risk evaluation of chemicals that are known carcinogens. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00011 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 3 In Section 9, we summarize new evidence that indicates that a PBPK model is the most valid and appropriate means of quantifying the large differences between animaland human responses to chloroprene exposure and in Section 10, we use PBPK results and standard US EPA methods endorsed by NRC to calculate an IUR for chloroprene. In Section 11, we use exposure data from the Marsh et al. (2007a, b) study to calculate the expected incidence of cancer among workers using the 2010 US EPA IURand using PBPK-adjustedlURsas a "reality check" to demonstra tethatthePBPK-adjustedlUR, but not the US EPA-derived IUR, is consistent with the epidemiological findings. In Section 12 we discuss the need to apply pharmacokineticmodeling in the derivation of the RfC, which also suffers from application of default methodology that does not properly account for the known pharmacokinetic differences across species, and species - and strain-specific differences in response . Lastly in Section 13 , we conclude that an updated and corrected IRIS assessment, and especially an updated IUR, are warranted and urgently needed. The new assessment should combinethe most up-to-date scientific evidence regarding chloroprene toxicity and carcinogenicitywith improved and more transparent methodsforconductingtoxicologicaland epidemiological reviews, in accordance with the NRC recommendations and guidance (NRC 2011, 2014). We are confident that the substantive and procedural reasons for updating the IRIS assessment for chloroprene, as detailed in this report, will result in a valid and scientifically appropriatelURfor chloroprene that is also consistentwiththeassessmentsfor other substancesincluding several known human carcinogens. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00012 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 4 2 .1'HE IRIS PROCESS: CHAI..LENGES, RECENT CHANGES, AND NRC RECOMMENDATIONS FOR IMPROVEMENT 2.1 Purpose of the IRIS program The IRIS programwasdevelopedto be the primarysource of toxicological information for federal, state,and international regulatory agencies for setting risk based regulatory standards . Itwas intended to provideconsistency among toxicological assessments within US EPA. IRISassessmentscontainhazard evaluations (determinations of whether substances are capable of causing disease) and dose-response assessments (determination s of the levels at which such effects occur) for various chemicals,including cancer and non-cancer outcomes. 2.2 Challenges in the IRIS process While most of the IRIS assessments have been straightforward and well documented, others have proved to be more complex and challenging, sometimes lacking transparency of methods. These problems have led to sign ificant variability and uncertainty regarding the calculated estimates of hazard or risk of health effects in humans. As a consequence, the NRC has been called on multiple times to review some of the more challenging or ambiguous assessments, includingthose for formaldehyde, dioxin, and tetrachloroethylene. In perhaps the most critical evaluation,the NRC (2011) reviewed the draft "Toxicological Review of Formaldehyde - Inhalation Assessment" (US EPA 2010c) and outlined several general recommendations for the IRISprocess,as wellas some specific aspects needing improvement. Subsequently, Congress held several hearings regardingthe IRIS program. A House Report (112-151) that accompanied the Consolidated Appropriations Act of 2012 (Public Law 112 -74)2 specified that as part of the IRIS process, US EPA had to incorporatethe recommendationsof NRC in its IRIS "Toxicological Review of Formaldehyde" whereappropriate, based on chemical-specific information and biological effects. Congress requested that NRC oversee this process to ensure US EPA implemented the changes. CongressaIso directed that NRC should make additional recommendations as needed to further improve the program. In 2014, NRC released a report on the IRIS process, which largely describedthe findings in its 2011 formaldehyde review as they relate more broadly to the IRIS process (NRC 2014). The final Toxicological Review of Formaldehyde has not yet been released. Subsequently, US EPA published a report entitled"Integrated Risk Information System (IRIS) Program: Progress Report and Report to Congress" (US EPA 2015) in which US EPA assured Congress that progress toward improvingthe IRIS process and addressing the NRC recommendations was continuing. NRC (2011, 2014) also emphasized the importance of a detailed protocol, including making the methods and the process of the review transparent . Increased transparency provides not onlythe opportunityfor meaningful peer review, but also 2 Pub. No. 112-74, ConsolidatedAppropriationsAct, 2012 availableat https://www.qpo.gov/fdsys/pkq/PLA-W 112publ74/pdf/PLAW -112publ74.pdf 17cv1906 Sierra Club v. EPA ED_001523_00004237-00013 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 5 for other investigators to verify the methods and replicate findings. The protocol should specify how studies will be evaluated and weighted according to quality rather than on the basis of findings; explicitly state the inclusion and exclusion criteria for studies ; describe how study quality will be evaluated ; and outline methods for evaluatingand taking into account various forms of bias and other methodologiccharacteristicsDf the studies that could impacttheir respective conclusions. The 2010 Review did not followsuch a protocol. Another keycriticismthat the NRC (2011) made specific to the IRIS assessmentof formaldehyde and more generally to the IRIS program as a whole, was that the IRIS process lacked an appropriate framework for systematic review and integration of all applicable lines of evidence. NRC (2011) cited the systematic reviewstandards adopted by the Institute of Medicine(2011) as being appropriate for such an analysis. 2.3 Recommendations for improvement of the IRIS process in updating the 2010 Review Because the 2010 Review predates the NRC critique , it would benefit from application of many of their recommendations. For example, clearer descriptions of how the epidemiological evidence was evaluated would provide greater transpare ncy. Similarly, epidemiological evidence should be evaluated for study quality and assessed for potential bias, as some of the strongest epidemiological evidence was misinterpreted (/.e., from the Marsh etal., 2007a, b studies)and results from some weaker studies (from Russia, Armenia,and China) were given equal weight. US EPA's Guidelinesfor Carcinogen Risk Assessment (US EPA 2005) established study quality criteria for the WOE evaluation and for identifying and justifying the use of specific epidemiological studies in assessing evidence of carcinogenicity, as follows : Clear objectives Properselectionand characterization^ comparisongroups (cohortand reference) Adequate characterization of exposure Sufficient duration of follow-up Valid ascertainment of causes of cancer morbidity and mortality Proper consideration of bias and confounding Adequate sample size to detect an effect Clear, well-documented and appropriate methods for data collectionand analysis Adequate response (minimal loss to follow-up) Complete and clear documentation of results These points were similarly outlined in the NRC critique of the IRIS process (NRC 2014). 17cv1906 Sierra Club v. EPA ED_001523_00004237-00014 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 6 Based on a critical review of the animal toxicology evidence, important differences in chloroprene toxicity have been demonstrated acrossspeciesthat are explained by differences in pharmacokinetics . In such circumstances PBPK models are required to adjust for these differences and have been applied by US EPA for other chemicals . Although a chloroprene-specific PBPK model was available at the time of the 2010 Review, US EPA did not use it. Since the release of the 2010 Review, additional data and a fully validated PBPK model have been peer-reviewed and published . By incorporating the highest quality epidemiological studies and the most recentlypublished data on the pharmacokinetics of chloroprenemetabolism, deriving a scientifically sound IURfor chloroprene is straightforward. As demonstrated below, an IUR derived using methods applied by US EPA and the scientifically highest quality data publically available will produce an lURthat is over 150 times lower than the IUR published in the 2010 Review. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00015 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 7 3 .rOXICOLOGICAL WEIGH.I" OF EVIDENCE: ANIMAL STUDIES 3.1 Guidelines for evaluating toxicological studies US EPA set forth criteria for the evaluation of toxicological data in the "Guidelines for CarcinogenRiskAssessment"(US EPA 2005). These guidelines are largely consistent with the NRC recommendationsfor IRIS (NRC 2014). However, US EPA did not apply these risk assessment guidelines in the 2010 Review in its evaluation and determination of the weight of evidence (WOE) available from the animal, mechanistic, and epidemiological studies of chloroprene. In this section , wed iscuss the toxicological evidence available to evaluate whether it supports carcinogenicity of chloroprene in humans. 3.2 Animal studies show important pharmacokinetic differences across species US EPA based the 2010 IRIS IUR estimate for chloroprene primarily on the findings of a two-year inhalationstudy conducted by the NTP (1998). The NTP (1998) study found statistically significant increases in tumor incidence at multiple sites in the B6C3F1 mice, including: all organs (hemangiomas and hemangiosarcomas), lung (bronchiolar/alveolar adenomas and carcinomas), forestomach, Harderian gland (adenomas and carcinomas), kidney (adenomas), skin, liver, and mammary glands. With increasing exposures, the tumors generally appeared earlier, and statistically significant pair-wise comparisons were reported with increasing exposure level. F344/N rats were less sensitive to chloroprene exposures than B6C3F1 mice. US EPA also considered results from another largestudy conducted by Trochimowicz et al. (1998) in Wistar rats and Syrian hamsters that showed a large variability in the tumor incidence and sites acrossspecies. Trochimowicz etal. (1998)found that although tumors appeared across multiplesites inboth ratsand hamsters, there were no statistically significant increases at any particular site, no significanttrends observed with increasing concentration, and tumor incidencein Iessthan20%of hamsters. These results showed that the Wistar ratand the hamster are less sensitive to the toxicity of chloroprene than B6C3F1 mice or F344/N rats. The results of the NTP (1998) and Trochimowiczet al. (1998) studies indicatedthat the mouse is the most sensitive species to chloroprene among the species tested, based on the concentrations at which statistica lly significant increases in tumor incidence were observed, as well as the number of tumor sites. In the NTP (1998) study, the incidence of lung tumors was observed to be statistically significantly elevated at the lowest exposure tested (12.8 parts per million [ppm]) in both female and male mice. Statistically significantly increased lung tumor incidence was not observed in any other animalspecies that was evaluated, including male and femalerats administeredchloroprene at concentrations up to 80 ppm. For other tumor sites, there were some statistically significantly elevated results in B6C3F1 mice and F344/N rats, but primarily limited to the highest exposure levels (80 ppm). For example, the incidence of liver tumors in mice were only statistically significantly increased in female mice at the highest exposure concentration tested 17cv1906 Sierra Club v. EPA ED_001523_00004237-00016 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 8 (80 ppm). For these reasons, the 2010 Review noted that the differences in response observed between the NTP (1998) and Trochimowicz et al. (1998) studies may be due to species and/or strain differences. Thus, across all tested species, the data demonstrated that mice are the species most sensitiveto chloroprene exposure and that the incidenceof lung tumors is the most sensitive endpoint in mice. The findings therefore are specific to mice and not generalizable across animal species. Given the differences in response in the mouse as comparedto other laboratoryspeciesfollowingchloropreneexposure, it is particularly important to evaluate the potential for difference s in pharmacokinetics to better characterize and explain the cross -species differences, particularly in developing an IUR intended to be predictive of human risk. 3.3 Conclusions US EPA derived a chloroprene human IUR based not only on the highest IUR, which corresponded with the lung tumors (the most sensitiveendpoint) and femalemice (the most sensitive species and gender), but also, as discussedbelow,US EPAthen calculated a human composite IUR that was based on multiple tumor sites in the female mouse. Rats were considerably less sensitive to the carcinogenic effects of chloropreneand thus were not considered further in the dose-response analysis; however, the observed lower incidence of tumors in rats than mice indicates significant species differenc es that cannot be disregarded in the human carcinogenicity evaluation. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00017 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 9 4 MECHANISTIC EVIDENCE: CHLOROPRENE MODE OF AC.riON 4.1 Guidelines for evaluating mechanistic studies As with the evaluation of animal data, US EPA did not apply the guidelinesfor evaluation of mechanistic weight of evidence set forth in the "Guidelines for CarcinogenRiskAssessment"(US EPA 2005) and the NRC recommendations for IRIS (NRC 2014). In this section, we discuss the mechanistic evidence available to evaluate whether it supports a mutagenicmodeof action(MOA) for chloroprene. 4.2 Mechanistic evidence for cancer effects from chloroprene do not support a mutagenic MOA A key determinant of understanding whetheran agent is carcinogenicis to establish an MOA. In the 2010 Review, US EPA hypothesized that chloroprene"acts via a mutagenic MOA involving reactive epoxide metabolites formed at target sites or distributedsystemicallythroughout the body." US EPA noted that"this hypothesized MOA is presumed to applyto alltumor types" (US EPA 2010a), suggesting some non-independent events would be needed for the development of all of the tumors observed. In formulating this hypothesis of a mutagenic MOA, the 2010 Review did not present a description of whether or how the available evide nee was critically evaluated, weighted and integrated. This is inconsistent with US EPA (2005) guidelines which indicated that the purpose of the hazard assessment is to "construct a total analysis examining what the biological data reveal as a whole about carcinogeniceffects and MOA of the agent, and their implicationsfor human hazard and dose-response evaluation." These 2005 guidelines are also consistent with the new NRC (2014) recommendations for the need for integ ration of the evidence to support scientific conclusions. In providing supporting evidencefor a mutagenic MOA, the 2010 Reviewfocused on in vitro studies (using different exposure systems) in bacteria, with less weight placed on the results from in vitro studies in mammalian cells and in vivo studies.3 In particular, in assessing whether chloroprene has a mutagenic MOA, the 2010 Review gave little weight to the studies conducted by the NTP and others (Tice 1988, Tice et al. 1988, NTP 1998, Shelby 1990, Shelbyand Witt 1995). This also is contrary to the recommendations of NRC (2014) regarding evidence integration . The NTP (1998) study that served as the basis of the US EPA IUR for chloroprene states, "chloroprene was not mutagenic in any of the tests performed by the NTP." Furthermore, the majority of the conventional genetic toxicology studies relied on in the 2010 Review did not report positive results following administration of chloroprene. In drawingconclusions concerningthe chloroprene MOA, US EPA should have acknowledged the flaws and methodological limitations in the studies on which it relied . When these studies and their limitationsare considered, along with the predominantly negative in vitro and in vivo genotoxicitytests, there is little evidencefor concluding that chloroprene is mutagenicor genotoxic (NTP 1998, Pagan 2007). Therefore, this evidence should not be used to support a 3 In vitro mammalian and in vivo studies are generally considered to be more relevant to effects that might be observed in humans (e.g., Wetmore eta/. 2013). 17cv1906 Sierra Club v. EPA ED_001523_00004237-00018 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 10 classification of chloroprene as a "likely" human carcinogen and should not influencethe derivation of the chloroprene IUR. In summary, the hypothesized MOA was based on four major assumptions by US EPA (2010a): 1 . There are si milarities i n the MOA for the known human carcinogen 1,3butadiene, which involves metabolism to a reactive epoxide intermediate 2 . Chloroprene forms DNA adducts via its epoxide metabolite 3 . Chloroprene is a point mutagen in vitro 4 . Chloroprene is a point mutagen in vivo However, the integration of the currently available evidence for chloroprene support none of theseassumptions. A discussion of why the available science is inconsistent with these assumptions is provided in the following sections. 4 .2.1 The chloroprene mutagenic profile is distinct from that of 1,3 butadiene US EPA assumed that chloroprene has a similar MOA to that of 1,3-butadiene, which is metabolized to epoxide intermediates and is a rodent carcinogen. While both compounds maybe carcinogenicin rodents, evidenceis available that shows that the mutagenicand clastogenic profiles of 1,3-butadiene are considerably different from the profile of chloroprene (Tice 1988, Tice et al. 1988). Unlike 1,3butadiene, chloroprene does not induce effects when tested in standard in vivo genotoxicity screening studies in mammals (Table 4.1). Although the reactive metabolite of chloroprene (l-chloroethenyl)oxiranedoes induce mutations in vitro in bacterial strains (Himmelstein etal. 2001a), neither the administration of chloroprene nor the reactive epoxide metabolite was genotoxic or mutagenic in in vitro mammalian cells, including Chinese hamster V79 cells (Himmelstein et al. 2001a, Drevon and Kuroki 1979). Also, unlike 1,3-butadiene, chloroprenewas not genotoxic when tested in vivo (Tice 1988, Tice et al. 1988, NTP1998, Shelby 1990, Shelby and Witt 1995). Table 4.1. Comparison of the Mutagenic Profiles of Chloroprene and 1,3-Butadiene Chemical 1,3-Butadiene In Vitro Ames + In Vivo (B6C3F1 mouse)a CA SCE Micronuclei + + + Chloroprene +/- - - - a Exposure was 10-12 days (6 hr/day) inhalation (Tice 1988) These findings indicate that the reactive metabolites formed from chloroprene are effectively detoxified in vivo in the concentration ranges studied. This is an important difference between chloroprene and 1,3-butadiene. In addition, 1,3butadiene appears to be an effective somatic cell genotoxin in mice (Tice 1988), whereaschloroprenewas not genotoxic in in vivo assays (Ticel988, Tice et al. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00019 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 11 1988, Shelby 1990, Shelbyand Witt 1995, NTP 1998). The only published chloroprene-related study showing positive chromosomal aberrations in vivo was a study cited by Sanotskii (1976); but as acknowledged in the 2010 Review,this study wastechnicallydeficient and conflicted with stronger and more recent studies conducted by NTP in mice (Shelby 1990, NTP 1998). Two other major differences between these chemicals are evident from the experimental data. First, the ras profile in lung tumors in treated animals is considerably different for chloroprene and 1,3-butadiene (Sills et al. 1999). Secondly, the toxic effects and histopathology observed in chloroprene-treated F344 rats and B6C3F1 miceare substantially different from those seen in 1,3 butadiene exposed animals (Melnick etal. 1996). These differences in toxic effects and histopathology suggestthat the carcinogenicMOA for 1,3-butadiene also is different from that of chloroprene. Furthermore, even if we disregard the assumption that chloropreneacts via a similar MOA as 1,3-butadiene,the chloroprenelURis morethan an order of magnitudegreaterthan that of 1,3-butadiene. This is inconsistent with the assumption that these compounds havea similarMOA, and is also inconsistent with US EPA's underlyingassumptions regardingthe carcinogenicityand the potency of chloroprene relative to 1,3-butadiene. 4 .2.2 Evidence does not support the formation of DNA adducts by chloroprene metabolism to an epoxide intermediate in vitro The 2010 Review assumed that the chloroprene epoxide metabolite (1chloroethenyl)oxiraneforms DNAadducts. There is little evidence that this occurs in vivo. Although in vitro studies suggest an interaction between this metabolite and DNA adducts, this effect has not been confirmed in vivo. In addition, the lack of any observed genotoxicity/n vivo as described above (Tice 1988, Tice etal. 1988, NTP 1998, Shelby 1990, Shelbyand Witt 1995) does not support an interaction between chloroprene and DNA in vivo. 4 .2.3 Evidence does not support mutagenicityof chloroprene in vitro The 2010 Review also assumed that chloroprene is a point mutagen in vitro. However, the results of the bacterial mutagenicity studies are equivocal, at best, and the findings from the Amestests questiontheclassificationif chloroprene as a mutagen (NTP 1998, Pagan 2007). The resultsfromtwo studies indicatedthat chloroprene was mutagenic in Salmonella typhimurlumTM.00 and/or TA1535, particularly with the additio n of S9 mix, which incorporates the metabolism of chloroprene (Bartsch et al. 1979, Willems 1980). Twootherstudiesfailedto show any increase in TA1535 or TA100 revertants, as shown in Table 4.2. Chloroprene was not mutagenicin S. typhimurium strains TA98orTA1537 (Zeiger et al. 1987). Because toxicity to the Salmonella cells was reported for all of the studies, one can assume there was adequate exposure to chloroprene and its metabolites or oxidativedegradation products, although concentrationsand composition verification were not performed. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00020 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 12 Table 4.2. Ames Test Results for Chloroprene with TA1535 and/or TA100 Study Method Exposure Response With S9 mix Without S9 mix Bartsch etal. 1979 Desiccatora 4 hours ++ + Westphal etal. 1994 Pre -incb 2 hours - - NTP1998 Pre -incb 20 minutes - - Willems 1980 Desiccatora 24-48 hours ++ + a Plates sealed in desiccator at 37 C with tops removed. b Chemical added to sealed tubes and mixed at 37 C. Toxicity results further appear to be dependent on the exposure methods and the form of chloroprene tested (e.g., newly distilled or aged). Westphal eta/. (1994) confirmed the importance of both vehicleand decomposition products in assessing the mutagen city of chloroprene. For example, they showed that freshly distilled chloroprene was not mutagenic, but chloroprene aged for as little as two to three days at room temperature was mutagenic in S. typhimuriumTM.00. The mutagenicity increased linearly with the ageof thedistillate,probablydueto the presence of decomposition products such as cyclic dimers (Westphal etal. 1994). Therefore, it is not possible to conclude from published data that chloroprene is a point mutagen in bacteria. Chloroprene also does not appear to be mutagenic in mammalian cells. Drevon and Kuroki (1979) were not ableto induce point mutations when chloroprene was tested in Chinese hamster V79 cells. The results for mammalian cells should carry more weight than those in bacterial cells, because mammalian cells are more relevantfor understanding any potential effects in humans. Himmelstein et al. (2001a) tested the primary metabolite of chloroprene, (l-chloroethenyl)oxirane, and found it to be mutagenic in the absence of S9, suggestingthatthis metabolite may be the reactive agent in the Ames test; however, this epoxide metabolite was not genotoxic in mammalian cells in vitro (Chinese hamster V79 cells) (Himmelstein etal. 2001a). Therefore, the results from the Ames test may not bean accurate predictor of carcinogenicityof chloroprene, because glutathione and other detoxification pathways that would mitigate or eliminate the production of potentially active metabolites are not present in S9 microsome preparations at levels present in intact cells. Westphal et al. (1994) also found that addition of glutathione to the chloroprene/metabolite Ames tests significantly diminished the reportedmutagenicactivity. The absence of genotoxicity in intact mammalian cells systemsand in vivo studiessuggeststhatthebacterialmutagenicitydata have limited relevance to the genotoxicity of chloroprene in humans. Critically, and as discussed below,in vitro systems do not have the normal levels of detoxifying 17cv1906 Sierra Club v. EPA ED_001523_00004237-00021 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 13 pathwaysfound in intact mammalian cells to further metabolize/detoxify this primary metabolite. 4 .2.4 Evidence does not support mutagenicityof chloroprene in vivo The 2010 Review assumed that chloroprene is a point mutagen in vivo (in carcinogenicity bioassays with mutations identified in proto -oncogenes). Investigatorsstudy mutationsin tumors at target sites to identify" mutagen fingerprints" for specific chemicals. As such, Sills et al. (1999, 2001) produced a proto-oncogene mutation profilefor some target tumors inthe mouse. A comparisonof chloropreneand 1,3-butadiene indicated that the profile for chloroprene differed from that of 1,3-butadiene. In fact, the mutation rates in chloroprene-exposed animals were similar to mutation rates in control animals. Specific mutations were associated with chloroprene exposures across several different tumor types, but showed nodose-dependency. In contrast, the incidence of lung tumors increased with dose. This indicates that thelung tumors likely are independent of and unrelated to the mutations. These findingssuggest thatthe underlying MOA is not the suspected K-ras mutation4 but rather a secondary MOA at target sites; for example, an MOA that follows a dose -dependent tumor response that is not associated with a corresponding dose-dependentincreasein mutations, such as cytotoxicity- induced bronchiolar hyperplasia. If mutagenicity is the MOA, then mutation rates also should be dose-dependent. This is not the case for chloroprene, where mutations are not shown to be dose-dependent. Therefore, a different MOA is likely. 4.3 Evidence supports an alternative MOA for chloroprene based on cytotoxicity Despite the inconsistencies in and questionable nature of the evidence for a mutagenic MOA, the 2010 Review never considered alternative MOAs for chloroprene. Considering alternative MOAs is recommended in US EPA's (2005) "Guidelines for Carcinogen Risk Assessmenfandisconsistentwith recommendations by NRC (2011, 2014) for evidenceintegration and WOE analyses as specified in the Human Relevance Framework (Cohen et al. 2003, Meek et al. 2003, Cohen 2004, IPCS 2005, Boobis et al. 2006). US EPA (2005) guidelines noted that"where alternative approaches have significant biological support, and no scientificonsensusfavorsa singleapproach,an assessmentmaypresentresults using alternative approaches." The likely alternative MOA for chloroprene is cytotoxicity, for which there are supportive experimental findings. At very high concentrations, chloroprene is toxic to animals, but does not demonstrate any genotoxicity (Shelby 1990), supporting an MOA based on target-sitecytotoxicity. In mice, histopat hology evaluations of chloroprene in target tissues are consistent with a non-genotoxic MOA. For example, the incidence of chloroprene-induced bronchiolarhyperplasiain the respiratory system follows the increased incidence of lung tumors, whereas the incidence of lung K-ras mutations (a precursor of many cancers) does not. Also, Melnick et al. (1996)reportedthatthetoxicityand histopathologyobservedin 4 Mutations of the k-ras gene are considered an essential step in the development of many cancers (e.g., Jancik et a!., 2010). 17cv1906 Sierra Club v. EPA ED_001523_00004237-00022 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 14 chloroprene-treated F344 rats and B6C3F1 mice were substantially different from those seen in 1,3-butadiene exposed animals, suggesting an alternative MOA. In this case, a cytotoxicity-driven hyperplasiacould be the cause, which can result from cel I injury or death and subsequent tissue regeneration. Buzard etal. (1996) hypothesized that hyperplastic processes lead to selection of pre-existing oncogene and tumor suppressor gene mutations. Extrapolation from a target -sitecytotoxic MOA involving cell proliferation and tumor promotion to other tumor sites is consistent with the attributesof chloroprene. It is importantto note that the toxicity of chloroprene is observed at very high concentrations in mice and to a lesser extent in rats; however, it has been confirmed using a validated PBPK model that both species would be expected to be more sensi tive to chloroprene exposure than humans. The differences in pharmacokinetics between mice, rats and humans helps to explain the lack of clear evidence of carcinogenicity in humans from epidemiology studies. 4.4 Conclusion s A critical evaluation of the cytotoxic and genotoxic profiles indicated that chloroprene acts through a MOA different from that of l,3-butadiene,a known human carcinogen. Importantly, chloroprene's genotoxicity profile lacks several attributes necessaryto concludea mutagenicMOA: * Standard in vivo tests for genotoxicity are negative and unlike known carcinogenssuch as 1,3 -butadiene: Chloroprene, unlikel,3 butadiene, is not genotoxic to somatic cells in vivo. The study results indicate that the epoxide metabolite of chloroprene is effectively detoxified under in vivo exposure conditions. * Consistent data are lacking for point mutation induction in vitro and in vivo \ Theevidencethat chloroprene is able to produce point mutations in vitro (specifically in bacteria) is equivocal, and chloroprene did not induce mutations in cultured mammalian cells. There is a clear discordance between findings of in vitro point mutation, DNA adduct induction, and in vivo ras mutationsintarget sitetumors, whichindicatethat the observation of these point mutations may not be relevant to the MOA for chloroprene induced tumors. Overall,unlike known carcinogenssuch as 1,3-butadiene, the evidence does not support a mutagenicMOA for chloroprene. Instead, the WOE supportsan alternativeMOA attributedto site-specific cytotoxicity. Thus, it is neither necessary nor appropriate to adjust the cancer unit risk based on a hypothesized mutagenic MOA, and deriving a new IUR. based on an alternative MOA that can be scientifically substantiated is warranted. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00023 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 15 5 EPIDEMIOLOGICAL EVIDENCE: OCCUPATIONAL STUDIES 5.1 Evaluation of the epidemiological studies The 2010 Report classified chloroprene as "likely to be carcinogenic to humans" in part based on USEPA's interpretation of "an association between liver cancer risk and occupational exposure to chloroprene"and "suggestive evidenceof an association between lung cancer risk and occupational exposure." As with the evaluation of the toxicological data, US EPA set forth criteria in the "Guidelines for CarcinogenRiskAssessment"(US EPA 2005) for the evaluation of epidemiological evidence, largely consistent with NRC recommendations (NRC 2014). While US EPA applied some of these criteria in the 2010 Review, US EPAdidnot presentquality assessment and weighting of epidemiological evidence. Our application of these criteria led to largely opposite conclusions: appropriateweighingand synthesis of the epidemiological evidence demonstrated that chloroprene exposure is unlikely to cause lung or livercancer at the occupational exposure levelsencountered in the underlying studies. Furthermore, in contrast with US EPA's interpretation, the lack of any clear cancer risk is consistent with the results from the animals tudies demonstrating significant differences across species in the carcinogenic potential of chloroprene, and the mechanisticevidence that humans are far less sensitive to chloroprene. Using an approach consistent with US EPA (2005) and NRC (2014), Bukowski (2009) evaluated the quality of eight mortality studies of seven chloroprene exposed cohorts from six countries (Table 5.1). Studies were assigned to categories of high, medium or low quality for each of ten quality criteria and a WOE assessmentwas performed The four-cohort Marsh et al. (2007a, b) pooled study isthe most methodologicallyrigorous epidemiologystudy conducted to date. This study has the largest overall cohort size and the most rigorousfollow-up. Based on the large cohort size, the Marsh study has the highest statistical power (see Table 5.2). Finally,the Marsh study has the most comprehensiveexposure assessment, including assessment of exposure to potentially confounding agents such as vinyl chloride. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00024 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 16 Table 5.1. Quality Rankings for Cohort Studies of Cancer Risks from Occupational Chloroprene Exposure USEPA Criteria Marsh et al. (2007 a,b) Study Kentucky1 North Ireland 1 Louisiana1 France Mort*1 Armenia 2 Other Studies FranceIncid "3 Russia4 China5 Clear objectives H* H H H Comparison groups H H-M H-M M Exposure H H H H H H-M H M M M M - L L M M L L Follow-up H H-M H H-M M - L M - L M - L M - L Case ascertainment H H-M H-M H-M M M M H-M Controlof bias H-M H-M H-M M M - L M M M - L Sample size H H M L M - L L H-M M - L Data collection and evaluation H H H H M M M - L M - L Adequate response H H H H M M M H-M Documentation of results H H H H M - L M M L Overall rank (l=best) 1 2 3 4 5 5 5 6 Source: Bukowski2009 * Mort=Mortality ** Incid=Incidence * Subjective estimate of study quality for each specific criterion H = high, M = medium,L=low; 1 - Marsh etal. 2007; 2 -Bulbulyan etal. 1999; 3 - Colonna and Laydevant 2001; 4 - Bulbulyaneta/. 1998; 5 - Li etal. 1989 Table 5.2. Relative Size of Marsh etal. (2007a, b) Study Compared with Other Available Studies Study Bulbulyan et al. 1998 Bulbulyan et al. 1999 Colonnaand Laydevant 2001 Leet and Selevan 1982 Li et al. 1989 Total Other Studies Marsh et al. 2007a (L) Marsh et al. 2007a (M) Marsh et al. 2007a (P) Marsh et al. 2007a (G) Total Marsh etal. (2007a, b) Combined Studies Marsh et al. (2007a,b) / Combined Studies Subjects (Person-years) Lung Cancer Deaths Liver Cancer Deaths 5185 (70,328) 31 10 2314 (21,107) 3 3 717 (17,057) 9 1 Should not be included in the 2010 Review 1258 (20,105)d' 2 6 9474 (128,597) 45 20 5507 (197,010) 266 17 4849 (127,036) 48 1 1357 (30,660) 12 0 717 (17,057) 10 1 12,430 (372,672) 336 19 21,904 (501,269) 381 39 57% (74%) 88% 49% Previously, Rice and Boffetta (2001) reviewed the published epidemiological studies of chloropreneexposed cohorts. Their review included cohorts in the US (Pell 1978), China (Li et al. 1989), Russia (Bulbulyan et al. 1998), and Armenia 17cv1906 Sierra Club v. EPA ED_001523_00004237-00025 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 17 (Bulbulyan et al. 1999) and noted significant methodological limitations in these studies, includingunclear documentation for cohort enumeration,inadequate reference rates for standardized ratios, a lack of detailed histopathology of liver cancer cases, and limited or no information on potential co-exposures. They also remarked that the occupational chloroprene exposure assessment was poor for all published studies, and the statistical power of the available studies was low due to the small number of observed cancers of interest. Notably,one of the co-authors ofthecriticalreview(Boffetta) wasalsoa contributingauthorof the cohort studies in Russia and Armenia (Bulbulyan et al. 1998 and Bulbulyan et al. 1999, respectively). To date, the identified limitations of the studies of Chinese, Russian, and Armenian cohorts remainunaddressed, and most have not been updated. Only the original studies of the US cohort from Louisville, Kentucky (Pell 1978, Leet and Selevan 1982) have been updated and improved. Substantial improvements included detaileddescriptionsof the cohorts, appropriatecomparisonsto localcancer rates, an improved exposure assessment both for chloroprene and associated co exposures (such as vinylchloride), appropriate follow-up times to capture all potential cancers, appropriate and valid determination of cancer cases, and welldocumented methods and results (Marsh et al. 2007a, b). A comparisonof the study limitations for key quality criteria across the differ ent cohortsissummarized in Table 5.3, and discussed in detail in the next section . Table 5.3. Comparison of Key Study Criteria across Epidemiological Studies Key Criteria US and Europe (Marsh etal. 2007a,b) Armenia (Bulbulyan et al. 1999) Russia (Bulbulyan et al. 1998) China (Li et al. 1989) Sample Size Follow-up Exposure Assessment French, Irish and US 12,430 (Kentucky~200,000 person -years ) 1949-2000 Exposure modeling 7 categories 2,314 5,185 1979-1993 1979-1993 Index (none, low, high)- before/after 1980 Index (none, med, high)- IH (inadequate) + job 1,258 1969-1983 High vs. low based on recall Baseline rates National, local plant area counties 1960-1994 Armenian rates 1980-1989 Used local rate comparisons; Confounding Low prevalenceof other liver cancer risk factors IH: Industrialhygiene VCM: vinyl chloridemonomer Alcohol use (high cirrhosis rates) and smoking prevalent Moscowrates From "local area" 1973-1975 1979-1993 or expected lung cancers: 0.4 1992-1993 (liver) Alcohol use (high cirrhosis rates) and smoking; Hepatitis B and aflatoxin; Co-exposure to VCM Co-exposures to VCM 17cv1906 Sierra Club v. EPA ED_001523_00004237-00026 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 18 5.2 Important limitations of the epidemiology literature The 2010 Review considered lung and liver cancer mortality reported in studies of occupationalcohorts from several countries published over 30 years: Pell (1978), Leet and Selevan (1982), Li etal. (1989), Bulbulyan et al. (1998,1999), Colonna and Laydevant (2001), and Marsh etal. (2007a,b). Cohort studies comprisea set of data distributed over time to address a hypothesized exposure-disease association (Checkoway et al. 2004). In synthesizinyesultsof severalcohort studies- or when conducting meta-analyses of such results - it is importantto verifythat eachstudy cohortisan independent sample and that analyticresults are independent,/.e., there should be no overlap (e.g., Greenlandand O'Rourke 2008). Especially for outcomes with long latency periodsand high case-fatality,such as lung and liver cancers, only the most recent and most complete (and non-overlapping) results from cohorts with multiple follow up periods should be used. Updated results always have more observed person years at risk and almost always include larger numbers of the health outcome of interest, increasing statistical stability and reducing the probability of chance findings. The epidemiological literature on chloroprene consists of seven published reports based on ninedistinct cohorts. In the 2010 Review, however, each published epidemiological study was included as if it were independent, including early results from overlappingor updated cohorts. Specifically, the early results from the Pell (1978) and Leet and Selevan (1982) were included in the most recent update (Marsh etal. 2007a, b). Therefore, the Pell (1978) and Leet and Selevan (1982) studies should not have been considered as independent evidence, since all of their cancer deaths were included in the Marsh (2007 a, b) update. Additionally, the Chinese, Russian, and Armenian studies have serious limitations, as documented by several authors includingRice and Boffetta (2001), Acquavella and Leonard (2001), and Bukowski (2009). As noted above, these studies have not been updated and the noted limitationsremain unaddressed. These studies therefore should be given less weight in the synthesis of evidence. The study of Chinese workers (Li et al. 1989) suffered from small numbers of workers, inadequate reference population mortality rates for statistical comparisons, and a lack of adjustment for known causes of lung and liver cancers. The researchers ascertained mortality among 1,213 workers for a 14-year period from 1969 through 1983 and reported 6 deaths due to livercancer and 2 deaths due to lung cancer. However, they used local mo rtality rates for only a three-year period (1973 to 1975) to estimate expected numbers of specific cancers. For rare events such as any specific cancer, estimates based on small numbers will be inherently imprecise. Li et al. (1989) reported 2.5 and 0.4 expected liverand lung cancer deaths, respectively, among all cohort members followed between 1969 and 1983. The limitednumber of observed liverand lung cancerdeaths dividedby the very small expected numbers produced highly imprecise standardized mortality ratios (SMRs) with very large confidence limits. Furthermore, estimates for liver and lung cancer incidenceare higher among Chinese men (in 2002, livercancer mortalitywas 38 per 100,000 persons peryear,and lung cancer mortality was 42 per 100,000 persons per year) and women (livercancer, 14 per 100,000 persons 17cv1906 Sierra Club v. EPA ED_001523_00004237-00027 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 19 per year, and lung cancer, 19 per 100,000 persons per year) (Parkin etal. 2005) compared to the rest of the world. In the most high-risk areas of China, 1 in 10 people died of liver cancer (Hsing etal. 1991). The major causes of liver cancer in China are chronic infection with hepatitis B virus and aflatoxin Bl, in addition to the rising prevalenceof alcohol consumption and tobacco smoking (Chen et al. 2003, Stuverand Trichopoulos 2008, Lee etal. 2009). In contrast, inthe US in the years 2009-2013, there were an estimated 9 liver cancer deaths per 100,000 men and 4 liver cancer deaths per 100,000 women per year (SEER 2017). Therefore, observational studies of liver cancer mortality within this Chinese population should control for known causes of these cancers as potential confounding factors. However, the authors of the Chinese study did not control for these confounding factors, and US EPA did not consider the lack of control for confounders when evaluating the qualityand weight of the evidence from this study. Similar to the Li etal. (1989) study, Bulbulyanand colleagues(1998) calculated expected numbers of livercancers using mortalityand incidence rates for Moscow for only two years (1992 to 1993), resulting in imprecise reference rates and unstable results. Cancer mortality data from 36 European countries, includingthe Russian Federation, showed that liver cancer mortality rates among women increased from 1960, peaked during the late 1970s, and declined to their lowest levels during the early 1990s, the period chosen for the study's reference mortality rates (Levi et al. 2004). In addition, the Armenian cancer registry is incomplete and may have misclassified the histopathology of reported liver cancers for the general population. Using a reference population with incomplete numbers and mortality rates representative of only a small time period would underestimate the expected incidence and mortality of liver cancer, resulting in over-estimates of the riskestimates. In light of the small numbers and the likelihoodthat chance may be an explanation for these estimates, the imprecise numbers reported in Bulbulyan et al. (1999) and repeated in Zaridze etal. (2001) should be viewed skeptically and given little, if any, weight. The Russian and Armenian cohorts also suffered from inadequate consideration of other major causes of liver cancer. In the populations represented in these cohorts, there is a high incidence of alcoholic cirrhosis, a well- known precursor for liver cancer (London and McGlynn 2006). There were 11 deaths from cirrhosis of the liver (3 in males and 8 in females) recorded for the Russian cohort. In the Armenian cohort, 32 cases of cirrhosis of the liver were reported (27 in males and 5 in females). Alcohol consumption and smoking are well known risks factors for liver cancer,and these factors werenot adjusted for inthe eastern European cohort studies (Kellerl977, Makimotoand Higuchil999, Lee etal. 2009). Areport bythe World Health Organization (WHO 2009) reported a prevalenceof 70% and 27% for current tobacco use among Russian men and women, respectively, and noted high levels of alcohol con sumption for the general population. The prevalence of current tobacco use among Armenian men is also very high at 55% (WHO 2009). Proper control for these causes was not possible, increasingthe likelihood of confounding and thus renderingthe results unreliable. Previous reviews have critiqued the Chinese, Russian, and Armenian studies for inadequate descriptions of the source population rates used to calculateSMRs and standardized incidence ratios (SIRs) (Rice and Boffetta 2001). Another important 17cv1906 Sierra Club v. EPA ED_001523_00004237-00028 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 20 methodologicalconcernfor the interpretationof SMRand SIR estimatesis that when they are based on very small expected values (/.e., less than two), they indicate small population size and/or short follow-up, contributing to unstable estimates (Checkoway, 2004). As such,findingsfrom these studies arenot reliable and should carry little if any weight in evaluating cancer causation. Taken together, the epidemiological studies evaluated in the 2010 Review do not establish a clear causal connection between occupational chloroprene exposure and liverand lung cancers. Consequently,the US EPA's interpretationof the epidemiological evidence as justifying a classification of chloroprene as "likely to be carcinogenicto humans"is questionable. In particular, US EPA's giving the same weightto the large a nd more robust Marsh et al. (2007a, b) epidemiological studies as it gave to the lower quality, lower power studies is inappropriate. Although the Marsh et al. (2007a, b) studies have limitations typical of all historical cohort studies, they a re the largeststudiesof potentialcanceroutcomes withthe most complete documentation of exposure. These studies also were designed and conducted specifically to address the limitations previously noted, making the evidence from the Marsh et al. (2007a, b) studies far more valid and informative than that from the other studies evaluated by US EPA. The review by Bukowski (2009) (represented in Table 5.1) ranked the study by Marsh etal. (2007a, b) as having the highest relative strength based on the same criteria for evaluation listed in the US EPA's 'Guidelinesfor Carcinogen Risk Assessment" (US EPA 2005) and consistent withNRC recommendations (NRC 2011, 2014), and it therefore should be given the greatest weight. 5.3 The Marsh et al. (2007a, b) studies do not show a causal link between occupational exposure to chloroprene and increased cancer risks The Marsh et al. (2007 a, b) studies, the most robust epidemiological studies of occupationalchloroprene exposure, found no excess of lung or livercancers (Marsh et al. 2007a, b). The 2010 Review, however, stated, "The study involving four plants (including the Louisville Works plant included in the Leet and Selevan (1982) study by Marsh et al. (2007a, 2007b), which had the largest samplesize and most extensive exposure assessment, also observed increased relative risk estimates for livercancer in relation to cumulativeexposure inthe plant withthe highest exposure levels (trend p value = 0.09, relative risks [RRs] 1.0,1.90, 5.10, and 3.33 across quartiles of exposure)." However, the interpretation of these relative risksis morecomplexthan US EPAstated, as the rate of livercancer deaths among workers was not different from that in the general population. As shown inTable 5.4, Marsh et al. (2007a) computed standardized mortality ratios (SMRs) using nationaland regionalstandard populations for the overallcohorts, for selected demographics (males, females, blue-collarworkers), and for work histories and exposure factors. The authors concluded that occupational exposures to chloroprene at the levels encountered by each of the cohorts did not show evidence of elevated risk of cancer, including liver cancer. In a separate publication, Marsh etal. (2007b) reported exposure-response data for chloroprene exposure and cancer. In Table 5.5 and Figure 5.1, results for the Louisville plant are shown, including both the internal analyses (relative risks or RRs) and external analyses (SMRs) which are based on comparisons with county 17cv1906 Sierra Club v. EPA ED_001523_00004237-00029 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 21 populations. The RRs are the values that US EPA focuses on in their assessment of potential liver cancer risks. However, as noted by Marsh et al., "The elevated RRs result mainly from the exceedingly low death rates associated with the baseline categories of each measure, as reflected by the correspondingly lowSMRs (/.e., the RR for a given non-baseline category is roughly related to the ratio of the corresponding SMRfor that category to the SMR for the baseline category) ." Table 5.4. Reported Observed Liver Cancer Cases, Expected Counts, and StandardizedMortalityEstimatesforthe Marsh et a/. 2007a Study Study Cohort Louisville Maydown Pontchartrain Grenoble Observed Expected* 17 16.35 1 4.17 0 -- 1 1.79 SMR or SIR 1.04 0.24 -0.56 95% Confidence Limits Lower 0.61 0.01 -0.01 Upper -- p-value -- Louisville Subcohorts (local reference) Full Cohort 17 White race 16 Non -White race 1 Males 16 Females 1 Blue collar 17 Short-term worker 4 Long-term worker 13 Duration of employment < 5years 4 5-19 years 6 20+ years 7 Time since 1st employment < 20 years 1 20-29 years 3 30 + years 13 CD exposure status Exposed 17 From Marsh etal. 2007a 18.89 15.69 3.13 17.98 0.94 18.28 8.16 10.74 8.16 3.57 7.14 1.79 3.3 13.68 18.89 0.9 1.02 0.32 0.89 1.06 0.93 0.49 1.21 0.49 1.68 0.98 0.56 0.91 0.95 0.9 0.53 0.58 0.01 0.51 0.03 0.54 0.13 0.64 0.13 0.62 0.4 0.01 0.19 0.5 0.53 1.44 1.65 1.77 1.45 5.93 1.49 1.26 2.07 1.25 3.66 2.03 3.11 2.66 1.62 1.44 0.78 0.99 0.36 0.75 0.99 0.89 0.18 0.57 0.18 0.30 0.99 0.93 0.99 0.99 0.78 17cv1906 Sierra Club v. EPA ED_001523_00004237-00030 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 22 Table 5.5. Exposure-Response Analysis for Chloroprene and Liver Cancers, Based on Internal (Relative Risks) and External (Standardized Mortality Ratio) Estimates, Louisville Plant Liver cancer Deaths Internal Analysis # cases Exposure Duration (years ) <10 6 1500 10-19 4 216 20 + 7 965 Average Intensity of Exposure (ppm) <3.62 3 714 3.62 - 8.12 7 568 8.12-15.99 3 388 16.0 + 4 1011 Cumulative exposure (ppm -years) <4.75 2 744 4.75-55.19 3 725 55.91-164.0 7 653 164.0 + 5 559 From Marsh et al. 2007b; Table 4 CI: confidence interval ppm : parts per million RR (95% CI) 1.00 3.85 (0.75-17.09) 1.75 (0.49-6.44) 1.00 3.81 (0.77-25.76) 1.84 (0.22-15.74) 1.31 (0.20-10.07) 1.00 1.9 (0.21-23.81) 5.1 (0.88-54.64) 3.33 (0.48-39.26) p-value External Analysis Person - years SMR (95% CI) Global=0.24 Trend=0.36 131276 30404 36239 0.61 (0.22-1.32) 2.08 (0.57-5.33) 0.99 (0.40-2.04) Global=0.22 Trend=0.84 69274 27933 28689 72023 0.62 (0.13-1.80) 1.73 (0.70-3.56) 0.94 (0.19-2.74) 0.59 (0.16-1.52) Global=0.17 Trend=0.09 68918 56737 39840 32424 0.43 (0.05-1.55) 0.59 (0.12-1.74) 1.62 (0.65-3.33) 1.00 (0.33-2.34) Liver Cancer RRs and SMRs by Cumulative CD Exposure. Louisville A - J- ' 4 .WM t .h,' = Ct Figure 5.1 Liver Cancer RRs and SMRs by Cumulative Chloroprene Exposure, Louisville 17cv1906 Sierra Club v. EPA ED_001523_00004237-00031 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 23 US EPA noted that 3of the 15 subgroups inTable 5.5 had SMRs greaterthan 1.00, and inferred from these a likely causal relationship between chloroprene exposure and cancer. However, none of these three SMRs reached statistical significance (i.e., the findings may have been due to chance). In fact, the 95% confidence intervals in Table 5.5 show up to a 10-fold marginof error around the estimated SMRs, underscoring the statistical instability and uncertainty of the risk estimates for these subgroups. In addition, as noted by Marsh et al. (2007b), the risk estimates were derived comparing risk from higher exposure groups to risk in the group with the lowest exposure, which had only two livercancer deaths. The occurrence of only two liver cancer deaths in the lowest exposure group represented a clear deficit in the expected rate of livercancer, as demonstrated by the SMR (Table 5.5). Comparison to a group with a deficit (most likely due to chance given the small numbers) led to the spurious appearanceof an increased risk among the more highlyexposed groups. Overall, the chloroprene exposed workers had only about 90% of the expected mortalityrate (17 observed withabout 19 expected), based on a non -exposed population reference rate (Table 5.4). Taken as a whole, the epidemiological evidence on chloroprene and cancer is insufficient to concludethat chloroprene is a human carcinogen. The study by Marsh etal. (2007a, b) is the largest and methodologically the strongest and, therefore, should carry the greatest weight in integrating the epidemiological evidence for chloroprene. This epidemiological evidence is consistent with the toxicological hypothesis that humans are less sensitive than animals to the possible carcinogenic effects of chloroprene, and also supports the conclusion by Allen et al. (2014) that a modified cancer unit risk that accounts for animal-to-human extrapolations is needed. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00032 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 24 6 CANCER CLASSIFICA.riON FOR CHLOROPRENE The 2010 Review determined that chloroprene was "likely to be carcinogenic to humans" based on EPA's conclusions of (1) statistically significant and dose-related information from the NTP (1998) chronic inhalation bioassay data demonstrating the earlyappearance of tumors, developmentof malignanttumors, and the occurrence of multipletumors withinand across animalspecies; (2) evidenceof an association between liver cancer risk and occupational exposure to chloroprene; (3) suggestive evidenceof an association between lung cancer risk and occupational exposure; (4) a proposed mutagenic mode of action (MOA); and (5) structural similaritiesbetween chloroprene and known human carcinogens, 1,3-butadieneand vinyl chloride. As has been demonstrated in this report, three of the five EPA conclusions are not supported by the weightof evidence, and the fourth--structural similarities --has been shown not to be informative,as the chemicalsdemonstrate different modes of action. Based on the limited evidence remaining to support the potential carcinogenicity of chloroprene, we conclude that a more appropriate classification of chloroprene is "suggestive evidence of carcinogenic potential." To classify a chemical as "likely to be carcinogenic to humans,"US EPA notes that "this descriptor is appropriate when the weight of the evidence is adequate to demonstrate carcinogenicpotential to humans but does not reach the weightof evidence for the descriptor "carcinogenicto humans (US EPA, 2005)." Adequate evidenceconsistent withthis descriptorcoversa broad spectrumand as noted by US EPA (2005), "choosing a descriptor is a matter of judgment and cannot be reduced to a formula. Each descriptor maybe applicableto a wide variety of potential data sets and weights of evidence." Strong evidence for carcinogenicity in humans is not needed; however, the weight of evidence is still required to support the classification descriptor. In the 2010 Review, the weight of evidence narrative provided for chloropreneto support the descriptor of "likely to be carcinogenic to humans" was limited to a check-list provided above (US EPA, 2010a, pg. 96 and Table4-39). However, in reviewing the underlying data for the evidence presented in this checklist, we note that only two of the five can be substantiated: (1) statistically significant and doserelated information from the NTP (1998) chronic inhalation bioassay data, and (5) structural similaritiesbetween chloroprene and known human carcinogens, 1,3butadieneand vinyl chloride. We have demonstrated considerable misinterpretation in the 2010 Review of the available science to support other items on the checklist. For example, the epidemiologicalevidence, based on an appropriate weightof evidenceapproach, failsto demonstrateclearlyincreased risks among exposed occupationalgroups and the general population, and a weak difference between exposed and unexposed workers reflecting a deficit among the least exposed (see Section 5). The claim that chloroprene is mutagenic is not supported by the overall evidence from the available data, as discussed in Section 4. Although there are structural similarities of chloroprene and 1,3-butadiene and vinyl chloride, the toxicological evidence including possible modes of action (MOAs) demonstrate substantial differences between chloroprene, vinyl chloride, and 1,3-butadiene. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00033 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 25 Most importantly, the narrative does not include discussion of critical uncertainties in relying on the mouse data from NTP (1998) to predictthe potential for carcinogenic risk in the humans, given ample evidence of important pharmacokinetic differences between mice and other species. In fact, the NTP study and other animalstudies show that there is little evidence of consistent tumorgenicity across species other than the mouse and in particular the hamster (see Section 3). This difference can clearly be explained by evidence of differences in the pharmacokineticsof chloroprene across species. In addition, consideration of the lack of evidence of the carcinogenicityof chloroprene from human studies and the risks that would be predicted relying on the results from human studies (see Section 11) further indicate that a classification of "likely" carcinogen is inappropriate. The weight of evidence supports a reclassification. According to US EPA (2015) the updated classification narrative should address the following: The weight of the evidence should be presented as a narrative laying out the complexity of information that is essential to understanding the hazard and its dependenceon the quality,quantity, and type(s) of data available, as well as the circumstances of exposure or the traits of an exposed population that maybe required for expression of cancer. In borderline cases, the narrative explains the case for choosing one descriptor and discusses the arguments for considering but not choosing another. The descriptors can be used as an introduction to the weight of evidence narrative. The complete weight of evidence narrative, rather than the descriptor alone, provides the conclusions and the basis for them. A complete and accurate narrative also should captureand interpretalldocumented major uncertainties in the evidence as it relates to the classification of chloroprene. Transpare nt documentation of methods, data and assumptions, coupled with an accurate and informative classification of the weight of evidence is needed. Considering the misinterpretation of some data and the uncertainty in relying on responses in the mouse to be predictive of the potential for carcinogenicity in humans, the current classification of "likelyto be carcinogenicto humans" unduly raises public health concerns. We conclude that a descriptor of "suggestive to be carcinogenicto humans" is more represen tativeof the weight of evidence and uncertainties associated with relying significantly on results from a species for which there is evidence of differences that explain the observed sensitivity compared to the human. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00034 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 26 7 OS EPA DERIVATION OF.I'HE CHLOROPRENE IOR As described in Section 3, US EPA relied primarily on the findings of a two -year inhalationstudy conducted by the NTP (1998) in B6C3F1 miceand F344/N rats. Trochimowicz et al. (1998) also conducted studies in Wistar rats and Syrian hamsters. The results of the NTP (1998) and Trochimowicz et al. (1998) studies showed that the mouse is the most sensitive species to chloroprene among the species tested. US EPA selected the results from the female mouse to be the basis for deriving the chloroprene IUR. However, given the differences in response in the mouse compared to other laboratory species, US EPA should have considered the potential for differences in pharmacokinetics to better characterize and explain the cross-species differences. Although this source of bias is likely the largest and most significant, US EPA applied a number of additional assumptions in deriving the chloroprene IUR.that leadto conservative bias and unsupported uncertaintyinthe IUR. The following sections highlight these key sources of uncertainty. 7.1 US EPA's dose-response modeling applied overly conservative methodology US EPA determined the point of departure (POD)5 using dose-response modeling to derive the IUR. Specifically, US EPA estimated the effective dose at a specified level of response (a benchmark dose concentration associated with a 10% risk level [BMDio]) and its lower-bound based on the Iower95% confidenceintervalof the BMDio (BMDLio)foreachchloroprene-inducedtumortypeinthe mouse. Having determined that chloroprene was more potent in inducing tumors in mice than in rats, US EPA did not consider the rat data further in developing the IUR. US EPA further noted that the observed differences may be due to species differences in metabolism. US EPA modeled each mouse tumor endpoint reported in NTP (1998) separately using the US EPA multistage Weibull time-to-tumor model. The multistage Weibull model has the following form: P(d,t) = 1 - exp[-(bo + bid + b2 d2 + ... + bkdk) x (t - to)c] where P(d,t) represents the lifetime risk (probability) of cancer at dose d (the human equivalent exposure inthis case) at time t (a human lifetime in this case); parameters bi > 0, for 1=0, 1, ..., k; t is the time at which the animal's tumor status, eitherno tumor, tumor, or unknown (missingor autolyzed) was observed;to is the latency of response ; and c is a parameter which characterizes the change in response with age. For the analysis performed in the 2010 Review, the latency (to) wasset to zeroforallmodels. The power term parameter c is normally a parameterthat is estimated by the BMDsoftware Forsometumors,themodel software was unable to calculate this parameter and US EPA had to estimatethis value (e.g.,forforestomachtumors). In the modeling, US EPA conservatively considered all tumor types, both benign and malignant. US EPA also assumed that the dose-response was linear in the low 5 A POD is defined as the point on a dose-response curve that marks the beginning of a low-dose extrapolation. This point is ty pica I ly a lower bound, expressed in human-equivalent terms, nearthe lower end of the observed range. This POD is used to extrapolate to lower exposures to the extent necessary. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00035 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 27 dose range, based on the assumption that chloroprene has a mutagenic MOA. This approach is not justified by the available scientific evidence; therefore, the assumption of linearity inappropriately adds another level of uncertainty to the IUR. 7.2 Extrapolation from animalsto humans should have included use of a PBPK model In the 2010 Review, US EPA did not use a PBPK modelfor chloropreneto adjustfor differences across species, even though a model was available. Atthetime, US EPA stated that it did not have sufficient data to validate the model. However, all of the quantitative data necessary to refine and verify the critical metabolic parameters for the existing peer-reviewed model for chloroprene (/.e., Himmelstein et al. 2004b) were available and could have been appliedto adjust the IUR Further, since the release of the 2010 Review, additional peer-reviewed studies have been published, demonstrating consistent results and validatingthe use of the modelfor dose-response modeling and determination of an appropriate human equivalentconcentration for the human IUR (Yang et al. 2012, Thomas et al. 2013, Allen etal. 2014). Instead of using a PBPK model to account for differences between humans and animals, US EPA used a default approach that entails applying a dosimetry adjustment factor (DAF) that accounts for some differences in the blood: air partitioning in animals compared to humans. US EPA used a DAF of 1.0 (essentially assuming equivalence) based on the unsubstantiated assumption that all the lung tumors observed were the result of systemic effects from chloroprene exposures . US EPA provided no evidenceto support the assumption that tumors inthe lungs of mice are the result of systemic effects, rather than the more plausibleportal-ofentry effects that would result from direct contact of chloroprene with lung tissue.6 As noted by US EPA (2010a), "treating lung tumors as systemic effects returns the highest composite unit risk (approximately 60% greater than if lung tumors are treated as portal-of-entry effects)." 7.3 Deriving a composite IUR based on multiple tumors is not scientifically supported Another source of overly-conservative bias in the derivation of the IUR is the use of a composite valueof multipletumor types insteadof the standard approachof using the most sensitive species, gender, and endpoint(s). The use of the compositevaluefor chloroprene is not valid. While US EPA assumed statistical independence of different tumor types based on a hypothesized MOA for chloroprene involving the production of epoxide metabolites, the underlying data do notdemonstratemechanistic or biological independence. The mechanismof action in multiple tissues could also be due to dependent events; for example, a liver tumor could be dependent on the generation of the same metabolite as that needed for the developmentof a lung tumor. Figure 7.1 illustrates how US EPA's assumption of adding risk across multiple tumor sites overestima tes the potential overall cancer risk. Figure 7.1 alsoshows the considerable non-random distribution 6 A portal -of-entry effect is a localized effect that occurs at the point at which a substance enters the body (e.g., via inhalation there would be effects on the respiratory system). Systemic effects, on the other hand, are effects that occur in other organs of the body distant from the portal-of-entry {e.g., effectson the liverfollowing inhalation of the substance). 17cv1906 Sierra Club v. EPA ED_001523_00004237-00036 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 28 of tumors in the animals bearing multiple tumors . Therefore, when US EPA assumed independence based on an unknown MOA, this inflated the effective number of animalsdeveloping tumors and overstated the carcinogenicity of chloroprene. US EPA recognized that the assumption of independencecould not be verified, and that if this assumption did not hold, it indeed would overestimate risk (US EPA 2010a), in this case by another 50%. In calculatingthe compositeestimatedlUR, US EPA a Iso assumed that the IURs were normally distributed around the mean with a 95% upper confidence limit that represents the composite estimate. However, there is no evidence to support a normality assumption eitherin the benchmarkdose (BMD) or the IUR, which adds to the uncertaintyin the riskestimate Based on the US EPA approach of summing IURs for individualtumor types, the estimated composite inhalation IUR for female mice (which were more sensitive to chloroprenethan malemice) was increased by approximately50%, from 1.8 x 10'4 for the most sensitiveendpoint (lungtumors infemalemice) to 2.7 x 10'4 per pg/m3 for all tumors combined. US EPA rounded this to a single significant figure, resulting in an even more conservative IURfor continuous lifetimeexposures to adult humans of 3 x IO'4 per pg/rri3. NTP Data Exposure Level: Controls 12.8 ppm 32 ppm 80 ppm Effective number of tumor bearing animals USEPA Approach Effective number of tumorbearing animals , ' 4 - Lung / 4 \ \ Liver / 12/SO Figure 7.1. Illustration of How US EPA's Approach of Summing IndividualTumor Potencies Overestimates Total Tumor Potency in Female Mice by Assuming Independence. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00037 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 29 7.4 IUR adjustment for early life susceptibility is not appropriate In the finalstep, US EPAappliedan age-dependent adjustmentfactor(ADAF)to account for early-life susceptibility, because of a hypothesized mutagenicMOA. This yielded a final adjusted unit cancer risk of 5 x IO'4 per pg/rrf. This adjustment reflects the use of several sensitivity adjustments for different life-stages, which are applied for presumed mutageniccompounds as specifiedin US EPA's "Supplemental Guidance for Assessing Susceptibility From Early-Life Exposure to Carcinogens " (US EPA 2005). Specifically, as described in the US EPA (2005 b) guidance, US EPA applied the default ADAFs and theirage groupings of 10 for <2 years, 3 for 2 to <16 years, and 1 for 16 years and above. The calculationsare shown below. Risk for birth through <2 yr = 3 x 10-p4 er p3 g/m x 10 x 2 yr/70 yr = 8.6 x 10-p5 er p3 g/m Risk for ages 2 through <16 = 3 x 10 -4per pg/m 3 x 3 x 14 yr/70 yr = 1.8 x 10 -4 per pg/m 3 Risk for ages 16 until 70 = 3 x 10 -4per pg/m 3 x 1 x 54 yr/70 yr = 2.3 x 10 -4 per pg/m 3 The individual risk estimates were then summed to obtain the final lifetime (70 years) IUR for chloroprene: Risk = 8.6 x IO'5 + 1.8 x 10'4 + 2.3 x 10'4 = 5.0 x 10'4 per pg/m3 As with the calculation of a composite IUR (which was increased by 67% based on the combinationof tumors), US EPA's assumption of a mutagenic MOA increased the calculated IUR by another 67%. Taken together, these assumption s increased the IUR calculation to 178% of the IUR calculated based on the most sensitive species at the mostsensitivesite. As discussed in detail in Section 4, the ADAF adjustment is not applicable to chloroprene because there is insufficient evidence of a mutagenic MOA for chloroprene. 7.5 Summary of US EPA's derivation of the chloroprene IUR The chloroprene IUR derived in the 2010 Review was based on the following assumptions, some of which are not scientifically substantiated: 1. US EPA selected the most sensitive species, female B6C3F1 mice,based on the results from the NTP(1998) study; 2. US EPA assumed lung tumors in mice to be a systemic lesion and not a portal-of-entry effect, resulting in a minimal dosimetric adjustment for extrapolating from animals to humans (i.e., application of a DAF =1); 3. US EPA calculated a composite risk estimate based on multipb tumor sites, although multi-tumor data were inconsistent and relatively weak for most tumorsites; 4. US EPA rounded the IUR prior to applyingthe ADAF, increasingthe IUR further; and 5. US EPA applied an ADAF based on the assumption of a mutagenic MOA. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00038 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 30 Table 7.1. Conservative^ssumptiors in the Calculationof the Chloroprene IUR Step Most sensitive endpoint/species (portal -of-entry DAF=1.7) Most sensitive endpoint/species (systemic lesion DAF=1) Multiple tumor adjustment Rounding Application of ADAF Application of ADAF IUR per pg/m3 Basis Amount of overestimate Cumulative overestimate Lung tumors in female mice 1.06 x IO'4 as a portal-of-entryeffect Lung tumors in female mice 1.8 x 10'4 1.7 as a systemic effect 2.7 x 10'4 Multiple tumors 1.5 3 x 10'4 Rounding 1.1 2.8 Adjustment (without 4.5 xlO'4 1.5 4.2 rounding) Adjustment (with 5 x IO"4 1.7 4.8 rounding) Combined,theseassumptionscontributeto a riskestimatethat is over-estimated by about a factor of 5 (Table 7.1). However,these assumptions contribute only to a small overestimate compared to consideration of the documented differences acrossspecies,which was reported by Allen etal. (2014) and confirmed by our own calculations of an updated IUR. Considerationof pharmacokinetic differences acrossspeciesindicate that the chloroprene IUR is likely overestimated by two orders of magnitude. 7.6 Replication of USEPA's dose-response modeling The 2010 Review used the results from the NTP (1998) study in mice to calculate multiple PODs for derivationof the compositelUR (see previous section). USEPA focused specifically on the female mouseasthis wasthe most sensitivespecies and gender, but assumedthatthis animal model was directly applicable to humans. Further, US EPA assumed a default linear dose-responseand appliedthe multistage Weibull model, which accounts for the influenceof competing risks (such as early death) and for the occurrence of multiple tumors, some of which are incidental (benignor not fatal), and others whichare carcinogenic(/.e., fatal). RambollEnvironattemptedto re-create the dose-response modeling for the female mouse endpoints using the same time-to-tumor model provided in the current version of the US EPA BMD software . However, we could not completely replicate US EPA numbers. In attempting to do so, we identified several inconsistencies in the US EPA method and other issues that prevented full replication of US EPA's estimates Furthermore, we were unable to identify adequate documentation supporting US EPA's calculations . The need for transparency highlighted by the NRC (2014), and as underscored by our inability to replicate the 2010 IUR, demonstratethe need to reviewand revise the IUR for chloroprene. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00039 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 31 Examples of the inconsistenciesencountered inour independentmodelingof the NTP (1998) data included the following: 1. We were unable to confirm which version of the US EPA Benchmark Dose Modeling Software was used to conduct the modeling presented in the 2010 Review. This is significant because it appears that US EPA used a version of the model(from 2009) that mayhave containedimportanterrorsthatwere later corrected (personal communication with John Fox, US EPA, June 16, 2016). This could also explain some of the discrepancies inour results compared to those presented in the 2010 Review. 2. US EPA did not provide the complete input files for the model, but only a summary; therefore, we could not verify the data needed for conducting the time-to-tumor model (timeof death of the animals, tumor status: censored (C) for no tumor, incidental(I) or fatal (F) tumors, or unknown (U) when there is no tissue or tissue was unusable). The lack of transparency made it difficult to verify whether US EPA conducted the modeling appropriately . 3. For the analysis of the incidenceof forestomach tumors, US EPA calculateda power parameter (c), as described above, outside of the modeling program and entered it as a specific variable in the analysis. This parameter necessarily was calculated outside of the program because the program was unable to calculate it. It was unclear how US EPA calculated this parameter and whetherthis valueis larger or smallerthan what would be predicted by the program. This could impactthe results and introduced additional uncertainty. 4. US EPA did not applya consistent methodologyacross a lithe endpoints and time points that were examined. For example, in some cases animals that had no tumors or evidence that tumors were naturally "digested" by the animal (autolyzed tumors) were simply removed from the analysis (e.g. ,for the forestomach analysis) and in other cases these were treated as "unknown"tumors (e.g., in the mammary analysis). This approach would result in an overestimate of risk and there was no clear reason why US EPA tookthisapproach. 5. There were also inconsistencies in the number of animals that were reported in each endpoint and time-point group. For example, the number of animals considered in Table C-lof the 2010 Review (data from NTP 1998) did not match the numbers in Table 5-4 (US EPA 2010a). The major differences were identified in the total number of animalsexamined for tumors of the skin, mammary gland, forestomach, Harderian gland, and Zymbal's gland, and for the dose levelsup to 32 ppm, dependingon the endpoint. US EPA reportedthattissuefrom 50 animalswas examined, whereas NTP (1998) reported that tissue from only 49 animals was examined. Althou gh this may not have impact ed the results significantly, it indicated that US EPA allowed errors in their reporting of the results and possibly made errors inputting the results into the model, some of which might be consequential. Without frill transparen cy and availability of model inputs , this could not be verified. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00040 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 32 Ramboll Environ analyzed each endpoint independently, as was done by US EPA, but did not combinethe estimatesto obtaina compositelUR We did not agree that US EPA'sapproach was standard or scientifically justified given that independence could not be confirmed and the MOA across tumor types was unknown. In addition, we corrected the issues associated with the appropriate counts and, following US EPA guidance, removed any unknowns when using an inciden ce-only analysis (assuming all tumors observed were incidental and were not fatal to the animals). A comparison of our independent results and those generated by US EPA is presented in Table 7.2. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00041 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 33 Table 7.2. Comparisonof Dose-Response Modeling for FemaleMiceat a Benchmark Response of 0.01 Site Stage US EPA Results from Tables C-3 and C-4 LL X2 AIC Model Selection BMD PPm Lung One-stage model 1 -83.02 -- 172.0 0.11 Hem angiomas,heman 3 gio-sarcomas, (fatal) (highestdose group 2 -135.85 5.34 279.7 X2, lowest AIC 3.12 dropped) 1 -138.52 -- 283.0 Hemangiomas,heman 3 gio-sarcomas, (all incidental) (highest 2 dose groupdropped) 1 -65.81 2.28 139.6 Lowest AIC -66.95 -- 139.9 4.61 3 -58.26 0.02 126.5 Harderiangland 2 -8.27 0 124.5 1 -58.27 -- 122.5 Lowest AIC 2.58 Mammary gland carcinomas, adenoacanthomas 3 2 1 -87.96 One-stage model -- 181.9 1.95 BMDL PPm 0.09 0.64 2.02 1.20 1.34 Stage 3 2 1 3 2 1 3 2 1 3 2 1 3 2 1 Ramboll Environ Results LL X2 P" value AIC Model Selection -83.0 -0.11 -82.96 0.00 0.74 1.00 176.04 173.93 -82.96 FAILED 171.93 Lowest AIC 279.74 -135.87 5.34 0.02 279.74 Lowest AIC -138.54 FAILED -65.74 2.22 -66.85 -58.22 0.02 -58.23 0.00 -58.23 -84.21 0.00 -84.21 0.00 -84.21 283.08 0.14 0.89 0.98 1.00 0.99 139.48 139.70 126.45 124.47 122.47 178.42 176.42 174.42 Lowest AIC Lowest AIC Lowest AIC BMD PPm 0.11 3.04 4.60 2.50 2.03 3 -19.17 0.84 48.35 3 -19.18 0.84 0.36 46.36 Forestomach 2 19.60 2.35 45.19 Lowest AIC 20.94 5.69 2 -19.60 2.35 0.13 45.20 1 -20.77 -- 45.54 1 -20.78 45.55 Hepatocellular adenomas, carcinomas Skin 3 One-stage 2 model 1 -119.2 -- 245 0.40 0.23 3 2 One-stage model 1 -87.463 -- 180.9 0.91 0.67 3 -119.94 0.00 1.00 249.87 2 -119.94 0.00 1.00 247.87 1 -119.94 245.87 3 -87.395 0.00 1.00 184.79 2 -87.395 0.00 0.99 182.79 1 -87.395 180.79 3 -11.402 0.65 32.8 3 -11.406 0.66 0.42 32.81 Zymbal's gland 2 -11.726 1.77 31.45 2 -11.734 1.76 0.19 31.47 1 -12.611 -- 31.22 Lowest AIC 15.78 5.76 1 -12.612 31.22 AIC: Akaike Information Criterion; BMD: benchmark dose; BMDL: lower 95% confidence limit of the benchmark dose; LL: log likelihood Lowest AIC Lowest AIC Lowest AIC Lowest AIC 20.5 4 0.39 0.89 29.9 BMDL PPm 0.08 0.47 1.92 1.14 1.38 5.48 0.23 0.67 8.23 17cv1906 Sierra Club v. EPA ED_001523_00004237-00042 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 34 7.7 Conclusion s US EPA applied a number of scientifically unsupported conservativeassumptions in deriving the IUR for chloroprenethat result ed in substantial overestimat ion of the IUR and added uncertainty to the toxicityestimate Consistent with the majority of available IRIS profiles on other chemicals,the IUR should be based on the most sensitive endpoint in the most sensitive species, as this will be protective for other effects. Not assuming a systemic lesion for lung cancers yields an initial IUR of 1.06 x 10 '4 based on the female mouse as the most sensitive species. In recommendinga final IUR based on the mouse data, US EPA should have considered the significant pharmacokinetic differences between species and applied the PBPK model for extrapolating from animals to humans (Himmelstein et al. 2004), as demonstrated in Section 10. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00043 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 35 8 .1'HE CHLOROPRENE IUR COMPARED.I'O KNOWN CHEMICALCARCINOGENS The chloroprene IUR reported in the 2010 Review is much higher than those of similar chemicals, including known carcinogens. We compared (and summarize below) the IURs for all compounds classified by IARC as Group 1 (carcinogenic) or 2A (probably carcinogenic), which generally correspond with US EPA's classification for known or likely/probablehuman carcinogens. We used IARC classifications because IARC generally applied consistent methods and criteria for evaluating human carcinogens. We also obtained the US EPA WOE classification and basis of the IUR for carcinogens for which US EPA has calculatedand reported an IUR. These compounds aresummarizedin a table developed and updated by US EPA to be used in dose-responseassessments of hazardous air pollutants.7 In the US EPA table, all hazardous air pollutants are listed with available toxicity values based on source. We excluded metallic compounds, which tend to be associated with particulate exposures, and mixtures, such as coke oven emissions. We sorted the remaining compounds by the IUR calculated by US EPA, from highest to lowest (Table 8.1). In addition, the table shows the WOE conclusions by IARC, the dates of each evaluation, and the relative strength of the epidemiological evidence. More detailed information on the toxicity evaluations and epidemiological evidence can be found in AppendicesA and B, respectively. 7 See Table 1 available at https://www.epa.gov/fera/prioritizatioftjata-sources" chronic -exposure 17cv1906 Sierra Club v. EPA ED_001523_00004237-00044 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 36 Table 8.1. Summary of Potential ly Carcinogenic Compounds by IUR Listed in IRIS Chemical Name US EPA WOE Year IARC J Year WOE IUR per pg/m3 Basis of Strength of | MOA IUR/ Epidemiology | Endpoint Evidence Benzidine A 1987 1 J 2012 0.067 M* Human/ bladder Moderate | Bis(chloromethyl) Ether (BCME) A 1988 1 1 2012 0.062 Rat/lung Moderate | Nitrosodimethyl amine (NDMA) B2 1987 2A 1987 0.014 M* Rat/liver Limited j Ethylene dibromide LH 2004 2A 1999 0.0006 Mouse/ nasal Limited j Chloroprene LH 2010 2B 1999 0.0005 M* Mouse/ multiple Limited 1 Acrylamide LH 2010 2A 1994 0.0001 M* Rat/ thyroid Limited j Polychlorinated biphenyls B2 1996 2A I 2013 0.0001 Rat/liver Very limited ) 1,3-Butadiene CH 2002 1 2012 0.00003 Human/ leukemia Strong (high exposures) Formal dehyde Bl 1 0.000013 Human/nas al Moderate (high exposures) Vinyl chloride CH 2010 Draft 1 j 2012 0.0000088 Rat/liver Moderate (high : exposures) > Benzene CH 2003 1 2012 0.0000022 to ... 0.0000078 Human/ Strong (high leukemia ___ exposures) i Trichloroethylene CH 2011 2A 1 2014 0.0000041 M* Human/ kidney Moderate 1 Epichl orohydrin B2 1988 2A 1999 0.0000012 Rat/ kidney Very limited | Tetrachloroethene LH 2012 2A j 2014 0.00000026 Mouse/ liver Limited for > bladder/NHL/ f MM i US EPA WOE (2005 Guidelines) = CH - carcinogenic to humans; LH - likely to be carcinogenic; US EPA WOE (1986 Guidelines): A - humancarcinogen;Bl - probable carcinogen, limited human evidence; B2 - probable carcinogen, sufficient evidence in animals; IARC WOE for carcinogenicity in humans (1 - carcinogenic; 2A - probably carcinogenic; 2B - possibly carcinogenic).; US EPA MOA (2005 Guidelines) M* - mutagenic and early life data lacking. NHL-non-Hodgkin lymphoma; MM - multiple myeloma Despite being classified by lARCas a 2B carcinogen, chloroprene has the 5th highest IUR (see Table 8.1), which is orders of magnitude greater than the IURs for the known carcinogens vinylchloride, 1,3-butadiene, and benzene. Three of the compounds with IURs higherthan chloroprene (benzidine, bis(chloromethyl)ether [BCME], and N-Nitrosodimethylamine [NDMA]) have IURs that are based on reviews from the 1980s, performed before new methods were developed for integration of evidence, and likely would be different using current methods. Although there may be more recent data available to update the estimates for these compounds, two of these compounds are no longer of concern for human exposures: benzidineis no longer produced inthe US (US EPA 1987a); additionally, there is very limited production of BCME, and what is produced or used is highly regulated (Bruske-Hohfeld2009). The only other compound with a higher IUR than chloroprene is ethylene dibromide (EDB)(US EPA 2004). US EPA (2004) described a single epidemiological study of occupational exposures to EDB, which was determined to be inadequate due to lack of exposure information and potential co-exposures to other carcinogens. Therefore, the IUR for ethylene dibromide was based on animal study results. Like 17cv1906 Sierra Club v. EPA ED_001523_00004237-00045 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 37 chloroprene, however, there were several important areas of uncertainty, including theextrapolationto lowdoses fromhighdoses inrats, theapplicationof thedose for respiratorytumors,portalof entry vs. systemiceffects,and the need to account for metabolic differences between mice and humans. At the time of the assessment, a pharmacokinetic model was available (Hissink et al. 2000, Ploemen et al. 1995) but, as in the case of chloroprene, it was not deemed adequate for use by US EPA due to limited validation of the model. Therefore, updating the IUR for EDB also may be warranted.8 In contrast, there are several examples of carcinogenic compounds that have IURs that are 1 to 2 orders of magnitude /owerthan chloroprene and for which US EPA has based the WOE evaluationand IURdevelopment on much stronger positive human epidemiological evidence (1,3-butadieneand benzene) or for which US EPA appropriatelyused PBPK modelingto extrapolate results from animalsto humans (vinyl chloride). In fact, one of the reasons US EPA classified chloroprene as a likely human carcinogen was structural similarities with 1,3-butadieneand vinyl chloride (US EPA 2010a), and it is particularly relevant to recognize how much higher the 2010 chloroprene lURis compared to vinylchloride and 1,3-butadiene. Both of these compounds were classified as known human carcinogens based on both stronger epidemiologicabvidenceand supporting animalevidence than that available for cholorprene. Vinyl chloride presents a relevant comparison to chloroprene based on its structural similarity to chloroprene and has been classified by IARC (2012) and US EPA (2000) as a known human carcinogen. Unlike chloroprene, however, the epidemiological evidence linking vinyl chloride with angiosarcomas of the liver, as well as primary hepatocellularcancers, isclearand consistent (Mundtet al. 2000, Boffetta etal. 2003, Mundtetal. 2017). US EPA appropriately applied a PBPK model for vinyl chloride to account for differences between animalsand humans, resulting in a cancer IUR that is approximately 57 times lower than the IUR for chloroprene. When accounting for metabolicdifferences between animalsand humans using a PBPK model, the cancer IUR for vinyl chloride was found to be consistent with risk estimates based on human epidemiological data and were lower than those based on external dose concentrations by a factor of 80 (Clewell etal. 2001). 1,3-butadiene has an extensive literature that describes its pharmacokinetics (US EPA 2002). Like chloroprene ,the carcinogenetic mode of action of 1,3-butadiene is proposed to be related to its reactive metabolites , and results from PBPK models have demonstrated that there are important species differences in the rates of formationand detoxificationof these reactive metabolites. In fact, the model results showed that, like chloroprene , pharmacokinetics can explain why mice are considerably more sensitive to the carcinogenic effects of 1,3-butadienethan other species, includinghumans. In comparing chloroprene with 1,3-butadiene, USEPA should have considered the differences observed across species that were also related to pharmacokinetics of 1,3-butadiene in deriving a chloroprene IUR, as similar differences across species have been observed for 1,3-butadiene. 8 This is presented as a comparison for chloroprene, and is outside of the scope of our analysis. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00046 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 38 There are other examples of recent assessments, such as that for trichloroethylene, for which US EPA appropriatelyapplieda PBPKmodelto developthe IUR and for which epidemiological evidence is more robust than for chloroprene. In summary, the comparison of the chloroprene lURwith the IURs of similar chemicals suggests that the chloroprene IUR from the 2010 Review is high even by IRIS standards, and that the chloroprene IUR should be reviewed and corrected . 17cv1906 Sierra Club v. EPA ED_001523_00004237-00047 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 39 PBPK MODEL FOR CHLOROPRENE 9.1 PBPK modelingshould be used to quantify the pharmacokinetic differences between species PBPK modeling is used to predictthe absorption, distribution,metabolismand excretion of chemicalsubstances in humans and other animalspecies . These models are based on the integration of the available science for a specific compound. PBPK modeling is particularly important for use in extrapolating results from animal studies to develop toxicity values for humans, especially when there are significant differences across species. The "Guidelines for Carcinogenic Risk Assessment (US EPA 2005) and the NRC review of the IRIS process (NRC2014) recommend that if sufficient and relevant quantitative information is available (such as blood/tissue partition coefficients and pertinent physiological parameters for the species of interest), PBPK models should be constructed to assistinthe determination of tissue dosimetry, species-to-species extrapolation of dose, and route-to-route extrapolation. In the 2010 Review, US EPA acknowledged the shortcomings intheirderivation of the chloroprene IUR, noting that: "Ideally,a PBPK model for the internal dose(s) of the reactive metabolite(s) would decrease some of the quantitative uncertainty in interspecies extrapolation; however, current PBPK models are inadequate for this purpose" (US EPA, 2010a). Although the PBPK models have been validated since the release of the 2010 Review, a PBPK model for chloroprene was available at the time US EPA prepared the 2010 Review. Despite uncertainties in the application of this model at the time of the development of the IUR, the results from these PBPK models would have explained the large observed inconsistencies in the data between mice,rats and humans. Additionally, there was substantial evidence at that timeshowing that external exposure concentrations from mouse chamber experiments were not representative of human health risks. The 2010 Review noted that pharmacokinetic information on the absorption, distribution, and in vivo metabolismand excretionof chloropreneand/orits metabolites was available primarily for animals, but not humans. Several in vitro studies focused on chloroprenemetabolismin lung and livertissue fractions from rat, mouse, hamster, and humans (Cottrell et al. 2001; Himmelstein eta/. 2001a, b; Himmelstein etal. 2004a, b; Hurst and Ali2007; Munter eta/. 2003; Munter et al. 2007; Summerand Greiml980). These studies indicated that chloroprene is metabolizedvia the CYP450 enzymesystem to activemetabolitesthat arethought to be associated with the carcinogenic MOA for chloroprene. As noted in the 2010 Review, although the metabolic profile for chloroprene is qualitatively similar across species, in vitro kineticstudies using tissues from rodents and humans suggest significant interspeciesand tissue-specific differences that, if operative in vivo, could account for the species, strain, and sex differences observed in chloroprene induced in vivo effects. The available in vitro informationon the metabolismof chloroprene(Cottrelleta/. 2001, Himmelstein etal. 2001b, Himmelstein et al. 2004a) demonstrates significant quantitative differences across species in the production of the major metabolites of chloroprene, and in particular, in the production of the epoxide likely to be the 17cv1906 Sierra Club v. EPA ED_001523_00004237-00048 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 40 carcinogenic constituent. The results from the in vitro studies indicate that greater amounts of these metabolites are produced in mice, followed by rats, and lastly in hamstersand humans. The 2010 Review discussed these differences, but did not incorporate this information when calculatingthe human equivalentdose for dose response modeling. Himmelstein etal. (2004a) also noted species differences in the detoxification of epoxide metabolites, most notably the epoxide hydrolase, which serves to eliminate any epoxide formed. For example, the cross-species ranking of intrinsic clearance in the liver for enzymatic hydrolysis of the chloroprene metabolite was human ~ hamster > rat > mouse. In the lung, the order was human ~ hamster > rat ~ mouse. Therefore, the mouse not only had the highest capability for the generation of epoxide metabolites, but also the slowest capacity for clearance. Overall, the balance of reactive metabolite formation and detoxification across species indicate s that the mouse would be the most sensitive species, based on higher rates of epoxide formation, slower hydrolysis, and more enzyme activity. The mouse-specific pharmacokinetics all contribute to potentially increased formation and sustained concentrations of potentially toxic metabolites at lower exposures to chloroprene, explaining the increased sensitivity of this species . The 2010 Review relied on the animalchamber air concentrations for the mouse exposure data to calculatethe human IUR. Himmelstein etal. (2004b) demonstratedthattherewas no dose-response relationshipwhen air concentrations from animal chambers (the administered dose) were used, whereas when the internal dose 9 was used (obtainedfrom the PBPK model)a dose-response was clearly observed with relation to lung tumors . This is shown in Table 9.1, where the lung tumor incidencerisk is assessed based on the internaldose. This table not only illustrates the dose-response based on internaldose, but clearlyhighlights the d ifferencesacross species,showingthatthe mouse is the most sensitivespecies. When evaluatinginternal dose, whichaccounts for metabolicdifferences between mice, rats and hamsters, the differences in the lung tumor response across these species can be explained. 9 In an experimental setting the administered dose is the concentration of the chemical that is given to the animal (measured in air, water, etc.), whereas the internal dose is the concentration of the chemical that is actually absorbed by the animal (measured inside the animal's body) and delivered to the target tissue. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00049 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 41 Table 9.1. Exposure-Dose-Response for Rodent Lung Tumors Exposure concentration (ppm) PBPK Lung tumor internal dose a incidence Number of animals Extra risk (%)b 0 Hamster 10 0 0 100 0 0.18 0 97 0 50 0.88 0 97 0 0 Wistar rat 10 0 0 97 0 0.18 0 13 0 50 0.89 0 100 0 Fischer rat 0 12.8 0 3 0.22 3 50 0 50 0.3 32 0.55 6 49 7.7 80 1.37 9 50 14.0 B6C3F1 moused 0 12.8 0 15 3.46 32 50 0 50 48.3 32 5.30 40 50 70.4 80 7.18 46 50 89.9 (a) Internal dose- average daily mg Chloroprene metabolized/g lung tissue (AMPLU). (b) The incidence data were corrected for extra risk equal to (Pi - Po)/(1-Po), where P is the probability of tumor incidence in "i" exposed and "o" control animals (Himmelstein etal. 2004b). (c) Male Syrian hamster and Wistar rat data from Trochimowicz etal. (1998). (d) Male Fischer rat and B6C3F1 mouse data from Melnick etal. (199 6). 9.2 US EPA calculationof the human equivalent concentration for chloroprene in the 2010 Review All of the quantitative data necessary to refine and verify the critical metabolic parameters for the existing peer-reviewed PBPK model for chloroprene (Himmelstein et al. 2004b) were available at the time the 2010 Review was published and could have been appliedto adjust the cancer unit risk to account for species-specific target -tissue dosimetry. Instead, the 2010 Review used the default approach and limited default assumptions described in the US EPA (1994) "Methods for Derivation of Inhalation Referenceconcentrations and Applicationof Inhalation Dosimetry. " The 2010 Review assumptions included the following: 1. Lung tumors result primarily from systemic distribution, and 2. Chloroprene is a Category 3 gas accordingto US EPA (1994) guidelines. Based on these assumptions, US EPA calculated the human equivalent concentration for chloroprene using the default DAF for Category 3 gases. As described by US EPA (1994), DAFs are ratios of animal to human physiologic parameters, and are based on the nature of the contaminant (particle or gas) and thetargetsite(e.g., respiratory tract) (US EPA 1994). For Category 3 gases with 17cv1906 Sierra Club v. EPA ED_001523_00004237-00050 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 42 systemic effects, the DAF is expressed as the ratio between the animal and human blood:air partition coefficients: DAF = (Hb/g)A/(Hb/g)H where: (Hb/g)A = the animal blood:air partition coefficient (Hb/g)H = the human blood:air partition coefficient DAF = 7.8/4.5 DAF = 1.7 Furthermore, following US EPA guidelines (1994), US EPA used a default DAF of 1 because, as US EPA noted, "In cases where the animal blood:air partition coefficient is higher than the human value, resulting in a DAF>1, a default value of 1 is substituted (US EPA, 1994)." This was a conservative assumption, as it is noted in the guidelines that the available data for rats indicated that (Hb/g)Ais greaterthan (Hb/g)Hfor most chemicals. This restricted the evaluation to equivalence between the mouse and the human and did not address the important pharmacokinetic differences in chloroprene metabolism inthe mouse compared to the human. 9. 3 The Allen et al. (2014) study shows that a validated PBPK model should be used to update the 2010 chloroprene IUR Allen et al. (2014) combined the results from the most recent PBPK models for chloroprene (Yang et al. 2012) with a statistical maximum likelihood approach to testcommonalityjf low-doseriskacrossspecies. Using this method, Allen etal. (2014) evaluatedthe difference between risk estimates obtained using external (chamberair concentrations) and internaldose (calculatedwith the PBPK model) metrics. The PBPK model for chloroprene incorporates data regarding species differences in metabolism of chloroprene, and allows species -specific estimation of internal exposure metrics, specifically the amount of chloroprene metabolized per gram of lung tissue. By using this model, IURs can then be compared across species based on equivalent internal exposure metrics rather than external air concentrations measured outside of the body. This is an important consideration when the toxicity of a compound is related to how the compound is metabolized in animalsvs. humans. Allen etal. (2014) found that for chloroprene, external concentration-based estimates were not appropriate for calculating and comparing cancer risks across species. As discussedinSection5, epidemiological studies related to occupational exposuresto chloroprenemust also be considered in evaluating the unit risk estimate. These epidemiological studies provide little or no scientific support for the hypothesis that human and animal low -dose risks were equivalent when expressed as a function of air concentrations. In contrast, by accounting for the dailyamount of chloroprenethat is metabolizedpergramof tissueatthe targetsite for different species, the PBPK results provided a substantially betterfitof the modelsto the data. Importantly the differences in internaldose acrossspecies explained the greater sensitivity in mice (Himmelstein et al. 2004b), as well as the lower sensitivity of humans . 17cv1906 Sierra Club v. EPA ED_001523_00004237-00051 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 43 Allen et al. (2014) derived cancer unit risks for respiratory system cancer using the PBPK model results from both animaland human data that ranged from 2.9 x IO-5 to 1.4 x 10'2 per ppm (8.1 x 10'9 to 3.9 x 10'6 per pg/m3), with a maximum likelihood estimate of 6.7 x 10'3 per ppm (1.86 x 10'6 per pg/m3). This estimate is about 100 times lower than the 2010 Review estimate of 6.5 x 10'1 perppm (1.81 x 10'4 per pg/m3) based on the incidenceof lung tumors infemalemice. It is also importantto note that the Allen et al. (2014) assessment is highly conservative in that it does not accountfor species-to-species differences in detoxification and pharmacodynamics, which is justified and would lead to an even lower IUR. It is difficult to apply the method used by US EPA for multi-tumor adjustment using the data provided in the Allen et al. (2014) publication, because the Allen etal. data were limited to lung tumors . However, this method likely would generate an estimatethat is 100 timeslowerthan the US EPA estimate A similar rationale can be used for the application of the ADAF, yielding an IUR of approximately 5 x 10' 6 per pg/m3. However, because there is limited evidence for mutagenicity, we concluded that the 2010 IUR should be closer to the estimate calculated by Allen et al. (2014) of 1.86 x IO'6 per pg, and that this value is appropriately protective. Overall, the evidence indicates that humans are far less sensitive to chloroprene exposures than mice, which is also consistent with the lack of clearor consistent epidemiological evidence of carcinogenicity as discussedin Section 5. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00052 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 44 10 CALCULATION OF AN UPDATED CHLOROPRENE IUR Ramboll Environ recalculatedthe lURfor chloroprene using the same standard methodologies that US EPA has employed in IRIS assessments for several known carcinogens, but did not employ in the 2010 Review of chloroprene. Ramboll Environ employed this methodologyto reducethe significant uncertainty associated with extrapolating results from animalexperiments to humans (and from one route of exposureto another),and in considerationof the substantial body of evidence demonstrating large differences in sensitivity to chloroprene across species. These differences reflect underlying pharmacokinetic differences that, if not taken into account, result in a highly inflated IUR value such as that derived in the 2010 Review. The Allen et al. (2014) analysisprovided a rigorous approachfor integratingthe available epidemiological and toxicological evidence to estimate a chloroprene IUR. However, it incorporated a maximum likelihood statistical method different from the traditional PBPK models used by US EPA in estimating IURs and other toxicity values, such as reference concentration s (RfC) or reference dose s (RfD). In deriving an IUR, US EPA typically applies a PBPK mode I to estimate an internal dose at the targetorganof interest(e.g., the lung), based on the mode of action. As discussedabove, it is hypothesized thatchloroprene itself does not exert a carcinogenic effect, but rather a metabolite of chloroprene exerts the effect. Therefore, carcinogenicity depends on the internal concentration of the metabolite, and not the internal (or external) concentration of chloroprene. The internal concentration of the metabolite is determined by how rapidly it is produced and eliminated from the body, and metabolite production and elimination rates vary considerabl^acrossspecies. Therefore, accounting for species-specific pharmacokinetic differences using PBPK modeling is critical. The US EPA (2005) Guidelines for Carcinogen Risk Assessment states that PBPK models "...generally describe the relationship between exposure and measures of internal dose over time. More complex models can reflect sources of intrinsic variation, such as polymorphisms in metabolism and clearance rates. When a robust model is not available, or when the purpose of the assessment does not warrant developing a model, simpler approaches may be used." The preferred approach to PBPK modelling has been documented in the US EPA (2005) "Guidelines for CarcinogenRiskAssessment? Furthermore, US EPA has applied these PBPK models in estimating toxicity values for several compounds ; for example, dichloromethane, vinyl chloride, tetrachloroethylene, carbon tetrachloride, and acrylamide, specifically to red uce uncertainty associated with animal-to-human extrapolationorroute-to-route extrapolation. Although there maybe no "perfect" model, toxicity values derived from models that best reduce uncertainty are more scientifically supportable and therefore preferred to those obtained using default adjustment factors (DeWoskin eta/. 2007). When an IUR is based on animal data, an animal PBPK model is required to estimate the internal dose corresponding to each of the administered 17cv1906 Sierra Club v. EPA ED_001523_00004237-00053 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 45 concentrations (/.e., ppm in the chamber air), following the same pattern of exposure of the animalsin the study (e.g., days/week). This internal dose estimate is then used (instead of the air concentration) for dose-response modeling and estimatinga Point of Departure(POD). This POD corresponds to the internal dose in the animal. The human PBPK modelthen isappliedto account for known physiological and metabolic differences between the animaland human. This is accomplished by estimating the equivalentexternal concentration that results in the internal dose equal to the POD derived from the animal data. The IUR is estimated by dividing the risk level (benchmark risk or BMR associated with the POD) by the POD. The IUR is interpreted as the risk per unit (ppm or pg/m3) intake. Chloroprene PBPK modeling results for mice,rats, and humans are reported inYang etal. (2012). Specifically, the internal dose estimates associated with the concentrations administeredto both miceand rats in the NTP(1998) study are provided, including gender-specifidnternatissues doses,/.e., the average amount of chloroprenemetabolizedper day per gram of lung (AMPLU) based on the PBPK model. These internal doses represent the concentration of the toxic moiety (/.e., the chloroprene metabolite) identified by US EPA as the key carcinogenic metabolite (US EPA, 2010a). The Yang et al. (2012) analysis showed that micehad the greatest amount of chloroprenemetabolizedper gram of lung, followed by rats and then humans. The human and rat showed linear dose-responses over the range of NTP bioassay concentrations of 12.8, 32 and 80 ppm. Based on this, the following was established as the relationship between the internal dose and the external exposure (ppm) in the human: 1 ppm of constant external exposure inthe human results in 0.008 pmoleof chloroprene metabolized per gram of lung tissue per day. We relied on the internal dose results from the PBPK modeling conducted and reported by Yang et al. (2012), consistent with the PBPK modeling approach that US EPAhas usedinotherIRISassessments(dichloromethane, vinyl chloride, tetrachloroethylene, carbon tetrachloride). In addition, also consistent with the conclusions inthe US EPA (2010) chloroprene review regarding the most sensitive endpoint inthe most sensitive species, we estimated the chloroprene IUR using the results for the combined incidence of alveolar/bronchiolaradenomas and carcinomas(the most sensitiveendpoint) in female mice (the most sensitive species and gender). Using the internal doses for female mice as provided in Table 5 of Yang et al. (2012) (see Table 10.1), time-to-tumor modeling of the lung alveolar/bronchiolar adenomas and carcinomas was performed using the Multistage -Weibull model provided with the US EPA BMDS software (February25, 2010 version). Time-totumordose-response modeling is preferred and was used inthe US EPA (2010) chloroprene assessment to model the incidence of tumors from the NTP (1998) bioassay. This type of dose-response model was necessary, as the survival of the female mice exposed to chloroprene was "significantly less than that of the chamber control" (NTP 1998). Time-to-tumor models adjust for early death of the animal, and thus the probability that the animal, if it had lived longer, may have developed the tumor of interest. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00054 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 46 The female mouse data that we used in our analyses are presented in Table 10.2, with each animal'stime of death and the observation of C, I, F or U to indicate: C=censored or the animaldid not havethe tumor of interest; I = incidentalor the animalhad the tumor of interest but it was not indicatedas the cause of death; F=fatal or the animal had the tumor of interest and it was indicated as the cause of death; or U=unknown or the presence of the tumor could not be determined as the organ was autolyzed or missing in the animal. The alveolar/bronchiolar adenomas or carcinomas were all considered to be incident tumors, consistent with the timeto-tumor dose-response modelsand approaches used in US EPA (2010). One tumor was classifiedas unknown none animalin the 12.8 ppm group, so modeling was conducted both includingand excluding that animalto determineif there was any major impacton the outcome of the dose-response modeling. Consistent with the US EPA (2010) approach, we selected a benchmark risk (BMR) of 1% (see Table 10.3 and Appendix C for the completeMultistage-Weibull modeling results). Note that models including or excluding the animal with the unknown tumor (Animal# 320)10 generated the same estimated IUR. We calculated the external human dose (in ppm) by dividing the POD or lower bound on the benchmarkdose (BMDL) by the factor of 0.008 to obtain the external concentration for continuous exposure inthe human in ppm associated with the internal POD. We then calculated t he IUR by dividingthe BMR by the human equivalent POD/BMDL in either ppm or pg/m3: l! = I \ The final results are presented inTablelO.4. Using the standard methods applied inotherlRISassessmentbyUS EPA and publically available publish ed data, the recalculated IUR for chloroprene was l.lx 10'2 per ppm or 3.2 x 10'6 per pg/m3. This result, which incorporates appropriate PBPK models and adjustments necessary to extrapolate the findings from animalstudies to relevant human exposure considering the differences in pharmacokinetics , is consistent with methodsusedinotherIRISassessmentsbyUSEPA. However, the IUR value is very different from that recommended in the 2010 Review and underscores the scientific importance of correcting and updating it. 10 When it cannot be determined if an animal had the tumor of interest due to the organ being missing or deteriorated too much to examine, the animal will get an observation of "unknown". This data can be used in a time -to-tumor model (e.g. Multistage Weibull)as a timeof death is available for that animal. In this case, including the animal with an observation of unknown or excluding the animal from the modeling did not result in a detectable difference in the results. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00055 Basisfor Correctionof US EPA's2010 ToxioologicaReviewof Chloroprene Page 47 Table 10.1. Internal and External Doses from Yang et al. (2012) External Dose (PPm) 12.8 32 80 PBPK Internal Dose Metric11 (pimole CD metabolized /gram lung tissue/day) Mouse 0.74 1.19 1.58 Human 0.1 0.25 0.64 Linear Relationship between ppm and PBPK metric in humans 0.008 0.008 0.008 11 Data fromYangeta/. (2012)Table5. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00056 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 48 Table 10.2. NTP (1998) Study - Female B6C3F1 Mice Lung Alveolar/bronchiolar adenoma or carcinoma Control = 0 ppm 0 pmole/g tissue/day Dose = 12.8 ppm 0.74 pmole/g tissue/day Dose=32 ppm Dose = 80 ppm 1.19 pmole/g tissue/day 1.58 pmole/g tissue/day Animal # 141 110 138 107 130 135 126 105 146 124 133 103 127 132 101 102 104 106 108 109 111 112 113 114 115 116 117 118 119 120 Time (wks) 5 69 70 71 76 78 88 91 91 95 97 98 101 101 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 Obs.12 C C C C C C C C C C C C C I C C C c c c c c c c c c c c c c Animal # 318 330 350 311 321 342 303 327 344 315 316 328 301 324 347 304 325 343 349 313 314 329 310 308 319 323 332 340 345 306 Time (wks) 41 46 46 63 64 69 75 76 78 79 79 79 87 89 89 90 91 91 91 97 97 97 98 99 99 99 99 99 100 101 Obs. C C U C I C I C C C C C C I I C I I C C I I I C I I I I C I Animal # 505 532 545 535 540 530 502 548 510 529 521 506 512 524 523 531 547 518 519 503 504 511 528 546 533 520 522 536 507 525 Time (wks) 31 50 54 56 57 61 63 65 67 68 70 72 72 73 74 75 75 76 76 77 77 78 79 79 82 84 84 86 87 87 Obs. C I C C C C I I C C C I I C I I C I I C I C I I I I C I I C Animal # 738 711 725 734 729 721 705 741 701 716 735 709 717 722 749 715 726 745 740 710 702 704 746 714 730 703 713 728 712 737 Time (wks) 1 36 47 48 55 64 65 66 67 67 70 75 75 75 75 76 76 77 79 81 83 83 83 84 86 87 88 88 90 90 Obs. C C I C C C I I C I I I I I I I I C I I I I I I I C I I I I 12 Observation s are coded as C=censored, the animal did not have the tumor of interest I = Incidental, the animal had the tumor of interest but it did not cause death F = fatal, the animal had the tumor of interest and it was the cause of death (none in this dataset) U = Unknown,itis notknowniftheanimalhad the tumoror not due to organ being a utolyzedor missing 17cv1906 Sierra Club v. EPA ED_001523_00004237-00057 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 49 Control = 0 ppm 0 pmole/g tissue/day Animal # 121 122 123 125 128 129 131 134 136 137 139 140 142 143 144 145 147 148 149 150 Time (wks) 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 Obs.12 C C I C C C I I C C C C C C C C C C C c Dose = 12.8 ppm 0.74 pmole/g tissue/day Animal # 334 346 331 341 302 305 307 309 312 317 320 322 326 333 335 336 337 338 339 348 Time (wks) 102 102 103 103 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 Obs. I I C I I I I C C I I I C C I I I C I I Dose=32 ppm Dose = 80 ppm 1.19 pmole/g tissue/day 1.58 pmole/g tissue/day Animal # 526 527 539 541 542 544 501 509 516 537 508 517 538 550 534 549 513 515 543 514 Time (wks) 87 89 89 90 90 90 91 91 91 92 93 94 94 94 96 96 97 99 103 105 Obs. I I I I I I I I I I I I I I I C I C I I Animal # 718 727 732 733 736 747 750 724 742 748 707 708 739 744 723 731 743 706 719 720 Time (wks) 91 91 91 91 91 91 91 92 93 93 94 95 95 96 97 97 98 105 105 105 Obs. I I I I I I I I I I I I I I I I I I I I 17cv1906 Sierra Club v. EPA ED_001523_00004237-00058 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 50 Table 10.3. Multistage -Weibull Time-to-Tumor Modeling Results for a Benchmark Risk of 1% Site Female Mouse Lung - incidental. Animal with unknown status excluded Female Mouse Lung - incidental. Animal with unknown status included Stages 3 2 1 3 2 1 Log Likelihood AIC -82.607 175. 21 -82.669 173. 34 -85.722 177. 44 -82.674 175. 35 -82.739 173. 48 -85.882 177. 77 Model Selection Lowest AIC Lowest AIC BMD (pmole/ gram lung tissue/ day) 0.0098 0.0677 0.0049 0.0099 0.0676 0.0048 BMDL (pmole/ gram lung tissue/ day) 0.0052 0.0069 0.0039 0.0053 0.0070 0.0037 BMDU (pmole/ gram lung tissue/ day) 0.0783 0.0770 0.0060 0.0791 0.0768 0.0060 Table 10.4. Calculation of IURs using Human Equivalent Concentrations Results from 2-stage Multistage Weibull Timeto-tumor model BMDL (pmole/gram lung tissue/day) External Concentration (PPm) 13 BMR = 0.01 IUR (Per PPm) External Concentration (pg/m3) IUR (per pg/m3) Female Mouse Lung incidental. Animal with unknown status excluded Female Mouse Lung incidental. Animal with unknown status included 0.0069 0.0070 0.863 0.875 0.012 0.011 3122 3168 3.2E-06 3.2E-06 13 Human doses in ppm are obtained by dividing the BMDL by the conversion factor derived from Yang et al. (2012) Table 5 of 1 ppm = 0.008 pmole/gram lung tissue/day 17cv1906 Sierra Club v. EPA ED_001523_00004237-00059 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 51 11 CANCER RISK ASSESSMENT: VALIDATION OF.I'HE CHLOROPRENE IUR As a validity check, we calculated the excess cancers that would be expected based on application of the US EPA IUR at the chloroprene exposure concentrations reported by Marsh etal. (2007b). Marsh etal. (2007b) modeled the chloroprene exposures for all unique job title classe s usingsixexposureclassesforeachplant over the entire period of chloroprene production in each plant. Job title classes and time-specific chloroprene exposure estimates were linked to each worker's job historyto constructa profile. These subject-specific profiles were then used to compute the statistical estimates of worker exposures used in the risk calculations presented in Table 11.1. As shown in Table 11.1, we calculated risk estimates (excess cancers) for each of the unitriskestimatesthat US EPA derived for chloroprene in the 2010 Review. These includedan IUR based on lung tumors, anIURbased on multipletumors, and an IUR adjusted for lifetime exposures (with application of the ADAF). In addition, we calculated cancer risk estimates based on the IUR derived by Allen et al. (2014), as well as the IUR provided in this report, both of which account for pharmacokineticdifferences between animalsand humans. We derived risk estimates using exposure estimates from the Louisville plant (Marsh 2007a, b), as these exposures were much higher (at least an order of magnitude or more) than the exposures at other plants. In Table 11.1, we compared calculated excess cancer risk estimates with the excess liver cancers observed at the Louisville plant (observed cases minus expected cases, based on both US and local county rates). The risk assessmentsummarizednTablell.l illustratesthat cancerrisk estimates calculated based on the IUR in the 2010 Review overestimated actual liver cancer risks. Marsh et al. (2007a) reported less than one excess livercancer death when compared to US rates, and a deficit of about two livercancer deaths when compared to the more appropriate local country rates. In contrast, using the 2010 Review IUR and mean reported chloroprene exposures, approximately 15 excess livercancer deaths should have been observed. Repeating this exercise using the risk estimate derived by Allen etal. (2014),as well as the Ramboll Environ estimatedlURin this report, we showed that the estimated excess cancer risk estimates were consistent with the observed cases reported by Marsh et al. (2007a). 17cv1906 Sierra Club v. EPA ED_001523_00004237-00060 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 52 Table 11.1. Cancer Risk Estimates Based on US EPA and Allen et al. (2014) IURs for Chloroprene Compared with Excess Cancers Observed in the Louisville Plant Source Unit risk (per PPm) Exposure (ppm)a Excess Cancers (Risk Estimate)3 Excess Liver Cancers (ObservedExpected)0 Comparison Group Median Mean Max Median Mean Max US USEPA (2010) lung tumor 0.65 5.23 8.42 71 3.40 5.5 46 multi tumor 1.08 5.23 8.42 71 5.65 9.1 77 w/ADAF 1.80 5.23 8.42 71 9.41 15.2 128 0.65 Allen et al. (2014) lung tumor 0.0067 5.23 8.42 71 0.04 0.1 0.5 Ramboll Environ lung tumor 0.011 5.23 8.42 71 0.06 0.1 0.8 a Data from Marsh et al. 2007b (Table 3) b Excess cancer risk calculated by multiplyingthe unit risk (perppm) by the exposure level (in ppm) c Data obtained from Marsh etal. 2007a (Table 3). Expected cancers = Observed/SMR Local County -1.89 This analysis demonstratesthatthe2010ReviewIUR overestimates risk, and that a PBPKadjustmentprovidesa betterfitto the best availabldiuman data. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00061 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 53 12.. .1'HE CHLOROPRENE RFC A reference concentration (RfC) is a health risk value that is intended to be protectiveof non-cancer risks from inhalation in humans. The RfC reported in the 2010 Review for chloroprene is 2 x 10'2 mg/m3. The RfC is an estimate of the daily exposure to human populations, includingsusceptible groups such as children and the elderly, which is considered to be without an appreciable risk for non-cancer health effects over a lifetime. The value is calculated by first determining the point of departure, traditionally using a no-observed-adverse-effect level or lowest observed -adverse-effect level (NOAEL or LOAEL, respectively) and more recently using dose-response modeling. Like the calculationof the cancer IUR, US EPA relied upon the results from the 2year chronic inhalation study conducted in rats and mice by the NationalToxicology Prog ram (NTP1998) as the basis for the RfC, but focusing on the non-cancer effects. US EPA also considered a second study conducted in a different strain of rats and in hamsters (Trochimowicz etal.r 1998), but did not rely on this study because it reported a high mortality rate in animals in the lowest exposure group due to failure in the exposure chamber. However, though significant histopathologicallesions were reported inthe NTP (1998) study inthe lungsand spleen inthe lowest exposure group (12.8ppm) in B6C3F1 mice, comparatively few histopathological lesions were observed even in the highest exposure groups in Wistar rats and Syrian hamsters (Trochimowicz etal.r 1998). From the NTP (1998) study, US EPA selected all the non-cancerendpoints that were statistically significantly increased in mice and rats at the low and mid-exposure levels(12.8 and 32 ppm) compared with controls. These endpoints included both portalof entry and systematiclesions observed inthe nose, lung,kidney, forestomach,and spleen in mice and in the nose, lung and kidney of the rats (see Table 5-1 in US EPA 2010a). US EPA used theirown benchmarkdose modeling software (BMDS)to estimatea Point of Departure(POD). As withthe cancer endpoints,theseresultssuggestedsignificant cross -speciesand strain differences in the toxicological response to inhaled chloroprene. In addition,forsomeof the endpoints, no modelprovided an adequate fit to thedata, suggesting external concentrationsmay not correspondto the observed incidences. These results also underscore the importanceof understanding the differencein pharmacokinetics across species to derive the most biologically relevant human equivalent RfC. PBPK methods have been used to derive appropriate RfCs for othe r relevant chemicals, including vinyl chloride (Clewell2001, US EPA 2000). The last source of uncertainty that US EPA should have considered in the derivation of the RfC is the applicationof uncertaintyfactors to the POD. US EPAapplieda total uncertainty factor of 100 to the POD of 2 mg/m3. A standard uncertainty factor of 10 was applied to account for variation in the susceptibility among members of the human population. An uncertainty of 3 was applied to account for extrapolation of animals to humans; however, this uncertainty can be removed if a validated PBPK model is used to derive a human equivalent exposure to chloropienethat accounts for pharmacokineticdifferences between animals and humans. Lastly, an uncertainty factor of 3 was applied to account for database 17cv1906 Sierra Club v. EPA ED_001523_00004237-00062 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 54 deficiencies related to reproductive toxicity. This adjustment is also not needed based on several lines of evidence. First, chloroprene is not expected to accumulatein tissues such that in a multigenerationalstudy, exposures to the second generation (F2) would be greater than experienced by the first generation (Fl). Second, the results of a single generation reproductive toxicity study fora structurally similar chemical, 2,3-dichloro-1,3-butadiene (Mylchreest etal. 2006) indicatethat effectsat the point of contact (nasal effects) in parental animals are more sensitive than reproductive/developmental effects. Specifically, this study reported a NOAEL of 10 ppm for nasal effects in rats, and a NOAEL of 50 ppm for reproductive toxicity (changes in maternal and fetal body weights). Similarly, an unpublished one-generation reproductivetoxicity study of chloroprene in rats reported a NOAEL of 100 ppm for reproductivetoxicity (Appelmanand Dreef van der Meulan 1979). All of these NOAELs are considerably higher than any other non cancereffect and suggest that the application of an uncertainty factor for database deficiencies for the lack of a two-generation reproductivestudy is not necessary. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00063 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 55 13 CONCLUSIONS The IUR derived in the 2010 Report did not address the large recognized differences in cancer susceptibility across animal species , and especially between female mice and humans. Failure to apply well-accepted a nd now specificallyvalidated methods for accounting for these differences led to an invalid (and implausible) IUR for chloroprene. Our critical review and synthesis of the available evidence from toxicological, mechanistic , and epidemiological studies, as well as an integration of the evidence across these lines of scientific inquiry, determined that the approach US EPA used to derive an IUR for chloroprene relied on several unsubstantiated assumptionsand failedto take into accountthe large inter-species cancer susceptibilities. We demonstrated that an IUR derived today would be considerably different from the one recommended inthe 2010 Review. Our approach comported with US EPA methods and guidance, as well as the recommendations made by multiple NRC Committees evaluating the US EPA IRIS evaluation methods. Although animal studies provide d a positive response for carcinogenicity, the current science for chloroprene demonstrates major differences in species-specific cancer response to chloroprene exposure. Quantitative differences in pharmacokinetics across species, specifically related to differences in metabolism and detoxification of potentially active metabolites , can and should be incorporated into a corrected IUR or other risk number. In the 2010 Review, the available chloroprene pharmacokinetic findings were not incorporatedto quantitatively account for differences between the mouse, rat, and human. When genotoxicity/genomics, MOA, and pharmacokinetic data are considered in an appropriatelyintegrated manner, the data strongly suggest that the cancer responses from chloroprene are largely confined to--and possibly uniqueto--the female mouse. Because of these strong interspecies differences, use of the female mouse data for risk evaluation, in the absence of affirmative epidemiologic al data that can be used quantitatively, must incorporate tissue-specific dosimetry and metabolic differences. Additionally, because the available evidence does not support a mutagenicMOA for chloroprene, the cancer unit risk should not be adjusted to account for potential risks from early-life exposures with the application oftheADAF. While appropriate PBPK models were available to US EPA at the time of the 2010 Review, US EPA stated that published data were unavailable to validate the model. Data have now been published, have validated the PBPK model, and should be used to correct the IUR. Our critical review and synthesis of all epidemiological studies of chloroprene exposed workers, using standard methods that consider study qualityand potential sourcesof bias, indicated no clear or consistent association between occupational chloroprene exposure and mortalityfrom lung or livercancers. The strongest study, in fact, demonstrated small deficits in lung and liver cancer mortality among chloroprene-exposed workers (Marsh 2007a, b). Nevertheless, inthe 2010 Review, this study is cited as providing support for a causal association, directly contradicting our conclusions as well as the study authors'own conclusions. In fact, the epidemiology was consistent with the application of a PBPK model to 17cv1906 Sierra Club v. EPA ED_001523_00004237-00064 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 56 adjust the animal experimental evidence and account for the large differences in inter species cancer susceptibilities. There is a substantial body of evidence supporting the conclusion that humans are far lesssusceptibldto the potential carcinogenicity of chloroprene than mice primarily because the way humans metabolize chloroprene does not leadto the production of significant concentrations of the carcinogenic metabolite. The epidemiological studyresultsalsosupportthis conclusion. Using standard methods consistent with the NRC recommendationsand EPA Guidelines, and the most current scientific evidence, we derived an IUR for chloroprenethat is 156 times lower than that derived by US EPA. Following methods used in other IRIS assessments, we derived an IUR of 3.2 x 10'6 per pg/m3. We request that US EPA re-evaluate and correct the IUR, which is based on the most sensitive species and endpoint (lung tumors in female mice) and apply a PBPK model to more appropriately account for the large differences between mice and humans. We recommend no further adjustmentfor multipletumor sites, and no adjustment for a mutagenic MOA. Similarly, the chloroprene RfC will need to be updated to incorporate the same pharmacokinetic differences across species. Based on a comprehensive evaluation and integration of the published epidemiological, toxicological and mechanistic evidence, we consider the US EPA 2010 Review of chloroprene to be outdated and invalid . Accordingly, US EPA should also revisit the cancer classification for chloroprene and provide a transparent and accurate narrative that reflects a weight of evidence approach . Most importantly, however, the IUR derived in the 2010 Report is not scientifically defensible and needs to be corrected. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00065 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 57 REFERENCES Acquavella JF and Leonard RC. (2001). A review of the epidemiology of 1,3butadieneand chloroprene. 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U.S. Environmental Protection Agency; National Center for Environmental Assessment.....:.^ -t ris/iris documents/documents/subst/O US EPA (EnvironmentalProtection Agency). (1987b). N-Nitrosodimethylamine; CASRN62-75-9. Integrated Risk Information System (IRIS): Chemical Assessment Summary. U.S. Environmental Protection Agency; National Center for EnvironmentalAssessment. Avaialble online at: https://cfpub.epa.gov/ncea/iris/iris documents/documents/subst/0045 sum mary.pdf. US EPA (Environmental Protection Agency). (1986). Guidelines for Carcinogen Risk Assessment (1986). U.S. Environmental Protection Agency: https://cfpub.epa.gov/ncea/risk/recordisplay.CTm -Meid ' >> Valentine R and HimmelsteinM. (2001). Overviewof the acute, subchronic, reproductive, developmental and genetic toxicology of g-chloroprene. Chemico Biological Interactions 135-136:81-100. Ward E, Boffetta P, Andersen A, Colin D, Comba P, Deddens JA, De Santis M, Engholm G, Hagmar L, Langard S, Lundberg I, McElvenny D, Pirastu R, Sali D, 17cv1906 Sierra Club v. EPA ED_001523_00004237-00074 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page 66 and Simonato L. (2001). Updateof the follow-up of mortality and cancer incidenceamong European workers employed in the vinyl chloride industry. Epidemiology 12(6):710-718. Westphal GA, Blaszkewicz M, Leutbecher M, Muller A, Hallier E, and Bolt HM. (1994). Bacterial mutagenicity of 2-chloro-1,3-butadiene (chloroprene) caused by decomposition products. ArchivesofToxicology68(2y.79-84. Wetmore, B, Wambaugh, JF, Ferguson, S, Li L, Clewell HJ, Judson, RS, Freeman K, Bao W, SochaskiMA, Chu T-M, Black MB, Healy E, Allen B, Andersen ME, WolfingerRD and Thomas RS. (2013). Relative impact of incorporating pharmacokinetics on predicting in vivo hazard and mode of action from highthroughput in vitro toxicity assays. Toxicological Science 132(2):327-346 doi: 10.1093/toxsci/kft012 WHO (World Health Organization). (2009) . World Health Statistics 2009. Geneva, Switzerland. World Health Organization. Willems MI. (1980). Evaluation of -chloropreneandfourchloroprenedimmersin the Ames test by atmospheric exposure of the tester strains. Final report No. R6392 by Central Institute for Nutrition and Food research for the Joint Industry Committee on Chloroprene. Yang Y, Himmelstein MW, and Clewell HJ. (2012). Kinetic modeling of bchloroprene metabolism: Probabilistic in vitro-in vivo extrapolation of metabolism in the lung, liverand kidneys of mice, rats and humans. Toxicology in Vitro 26:1047-1055. Zani C, Toninelli G, Filisetti B, and Donato F. (2013). Polychlorinated biphenyls and cancer: an epidemiological assessment. Journal of Environmental Science Health C Environmental Carcinog in Ecotoxicol Review 31(2):99-144. Zaridze D, Bulbulyan M, Changuina O, Margaryan A, and Boffetta P. (2001). Cohort studies of chloroprene-exposed workers in Russia. Chemico -Biological Interactions 135-136:487-503. ZeigerE, Anderson B, Haworths, LawlorT, MortelmansK, and SpeckW. (1987). Salmonella mutagenicit\tests: III. Results from the testing of 255 chemicals. Environmental Mutagen 9:1-109 (Publishederratum: Environmental Mutagen (1988) 11:158). 17cv1906 Sierra Club v. EPA ED_001523_00004237-00075 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene APPENDIX A .rOXICOLOGICAL SMMARYOF CARCINOGENIC 17cv1906 Sierra Club v. EPA ED_001523_00004237-00076 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page A-1 ToxicologicalSummaryof CarcinogenicCompounds Chemical IUR (Per pg/m3 ) US EPA Human WOE/Year Data Animal Data Geno toxicity Benzidine** 0.067 A/1987 Sufficient Limited via inhalation Yes Bis(chloromethyl)et her (BCME) ** 0.062 N N itrosod i m ethyla m i ne (NDMA **) 0.014 A/1988 B2/1987 Sufficient Sufficient Yes Limited Limited due to exposure evidence via Yes to mixtures inhalation Ethylene Dibromide 0.0006 B2/2004 Inadequate Sufficient Yes Chloroprene 0.0005 Bl/2010 -- Clear evidence Yes Metabolites Acrylamide 0.000147 B2/2010 Inadequate Sufficient Yes Extrapolation Method Species One-hit with time factor, extra risk Linearized multistage, extra risk Human Occupational (Inhalation) Rat Weibull, extra risk Rat Multistage Rat Linear low-dose extrapolation Mice Route -to-route extrapolation of Rat the oral POD Endpoint Model Used PBPK Model Bladder tumors -- No Respirator y tract -- No tumors Liver tumors -- No Nasal cavity tumors All tumor sites reported Thyroid tumors Multistage -Weibull time -to- No tumor Multistage -Weibull time -to- No tumor Multistage -Weibull Time -to- No tumor Polychlorinated biphenyls (under reassessment)# 1,3-Butadiene 0.0001 B2/1996 0.00003 A/2002 Inadequate Sufficient -- Linear extrapolation Rat below LEDlOs Sufficient Sufficient Yes Metabolites Linear extrapolation Human Liver tumors -- No Relative Leukemia Rate No Model 17cv1906 Sierra Club v. EPA ED_001523_00004237-00077 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page A-2 Chemical IUR (Per pg/m3 ) US EPA Human WOE/Year Data Animal Data Geno toxicity Extrapolation Method Species Formaldehyde 0.00066 Supports carcino genicity/ 2010 (Draft) Supportive, but alone not sufficient Strong support Data suggests genotoxicity Linear extrapolation from the POD Human Vinyl Chloride Benzene 0.0000088 A/2000 0.000002 0.0000078 A/2003 Sufficient Strong evidence Sufficient Limited evidence Yes Metabolites Suggestive but not conclusive Linearized multistage method Low-dose linear; maximum likelihood Rat Human Trichloroethylene (TCE) 0.0000041 CH/2011 Modest Clear evidence Data suggests potential for genotoxicity Linear low dose extrapolation Human Linearized Epichlorohydrin 0.0000012 B2/1988 Inadequate Sufficient Suggestive multistage procedure, Rat extra risk Endpoint Model Used PBPK Model Nas o- pharynge al cancer, Hodgkin -- Yes lymphoma and leukemia Liver tumors Linearized Multistage Yes Model Leukemia -- No Kidney cancer; Weighted Non - linear Hodgkin's regression No lymphoma model ; Liver cancer Kidney lesions -- No Tetrachloroethene 0.0000002 6 LH/2012 Evidenceof association Evidenceof association Insufficient Linear extrapolation Mouse Liver tumors Multistage model Yes US EPA WOE (2005 Guidelines) = CH - carcinogenic to humans; LH - likelyto be carcinogenic;US EPA WOE (1986 Guidelines): A - human carcinogen; Bl - probable carcinogen, limited human evidence; B2 - probable carcinogen, sufficient evidence in animals * Draft version available - currently under public comment ** Only an IRIS Summarywas available,not a full ToxProfile # The draft reassessment is currently in the scoping and problem formulation portion. Therefore, no updated assessment has been performed. PBPK: physiologically based pharmacokinetic (model) IUR: inhalation unit risk 17cv1906 Sierra Club v. EPA ED_001523_00004237-00078 Basisfor Correction of USEPA's2010 ToxicologicaReviewof Chloroprene APPENDIX B SUMMARY OF EPIDEMIOLOGICAL EVIDENCE OF KNOWN OR LIKELYCARCINOGENICCOMPOUNDSCLASSIFIEDBY US EPA 17cv1906 Sierra Club v. EPA ED_001523_00004237-00079 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page B-1 Summary of the Epidemiological Evidence of Chemical Carcin ogensClassifiecbs Known or Likely Human Carcinogens by IARC and/or US EPA Compound Benzidine Bis (chloromethyl) ether(BCME) Nitrosodimethylamine (also NNitrosodimethylamine) Sources US EPA 1987a; Meigs et al. 1986; Tomioka et al. 2016; Golka et al. 2004; IARC 2012 US EPA 1988a; IARC 2012; Bruske -Hohfeld 2009 US EPA 1987b; ATSDR 1989; IARC 1978 Outcomes with strong evidence Bladderand lung cancer Lung cancer Types of studies Several occupational epidemiology studies from the 1980sto 2000sfor bladder cancer; 23 retrospective cohort studies from 1970s-2010s for lung cancer Quantification (if possible) SIR (bladdercancer) = 3.43,95% CI: 1.48-6.76; (Meigs et al. 1986, cited in US EPA) Pooled risk estimate(lung cancer) = 2.33, 95% CI 1.31-4.14 (Tomioka et al. 2016) based on meta -analysis of 23 cohort studies of highly exposed workers 30-fold to 75-fold higher risk of bladder cancer based on occupational cohort studies in China 1980s-2000s (Golka et al. 2004) Occupational epidemiology "Among heavily exposed workers, studies from the 1970s - the RRs are tenfold or more." 1990s (Bruske -Hohfeld 2009) Conclusion US EPA: Category A; IARC 2012: Groupl, "Benzidine causes cancer of the urinary bladder." Risk of lung cancer is statistically significantly elevated; but confounding by co-exposure with beta naphthylamine cannot be ruled out. (Tomioka etal. 2016) "Toxicologically, benzidine has been the most important carcinogenic aromatic amine directed towards the human bladder." (Golka et al. 2004) US EPA: Category A; IARC: Group 1 None specified in humans Numerous multisite tumors in various animal species (inhalation and oral exposures) Animal studies of oral exposure from 1970s1980s; twostudiesof inhalation exposure in animals from 1967 No studies of inhalation and cancerin humans; confounding by co exposure cannot be ruled out No risk estimates in humans available US EPA - Category B2; IARC - Group 2A 17cv1906 Sierra Club v. EPA ED_001523_00004237-00080 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page B-2 Compound Ethylene dibromide (also 1,2Dibromoethane) Sources US EPA2004; IARC 1999 Outcomes with strong evidence Types of studies None in humans. In animals, inhalation (long term) is associated multi -site tumors Three occupational epidemiological studies evaluated by US EPA deemed to be inadequate Quantification (if possible) No risk estimates in humans available Conclusion US EPA - Category LH ; IARC - Categor y 2A "inadequate evidence in humans"but "sufficient evidence"in experimental animals Acrylamide Polychlorinated biphenyls(PCBs) 1,3-Butadiene US EPA 2010b; Pelucchi et al. 2011; IARC 1994 US EPA 1996; ATSDR 2000; Zani et al. 2013; IARC 2016 US EPA2002; IARC 2008 Little evidence in humans In animals, oral exposure associated with multi -site tumors Melanoma Inconsistent findingsfornonHodgkin lymphoma, breast cancer Lymphaticand hematopoietic cancers 5 retrospective and prospective cohort studies of occupational exposure (inhalation/dermalfrom the 1980sto the2000sno strong associations. Meta -analysis of occupational (inhalation/dermal) exposure found positive, but no statistically significant associations (Pelucchi et al. 2011) Many occupational cohort studies of PCB exposure, 1980s-2010s; limitations include smallsamplesizes, confounding exposures, and short follow-up. Select SMRs (95% CI) of meta analysis (Pelucchi et al. 2011): Pancreas, high exposure: 1.67 (0.83-2.99) Kidney, high expos ure:2.2 2 (0.81-4.84) Occupational exposures SMR for melanoma = 2.4, 95% CI: 1.1-4.6 (Ruder 2006, as repo rtedbyZaniet al. 2013) RR = 4.8, 95% CI: 1.5-15.1 for high exposures (Loomis etal. 1997) Many occupational cohort studies; stronger evidence of leukemia; suggestive link with non -Hodgkin lymphoma. US EPA: 43% to 336%increasein leukemia in styrene-butadiene rubber workers, adjusting for styrene and benzene. IARC: Most recent update of the styrene -butadiene rubber worker cohort showno significant risk (IARC 2008). US EPA: Group B2; IARC: Group 2A (Inadequate evidence in humans; sufficient evidence in animals). US EPA - Category B2 IARC - Groupl Sufficient evidence for melanoma. For occupational exposures, "weak evidence of a major role of PCBs as human carcinogens" (Zani et al. 2013) US EPA: Group A; IARC: Group 1 17cv1906 Sierra Club v. EPA ED_001523_00004237-00081 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page B-3 Compound Formaldehyde Vinyl chloride Benzene Trichloroethylene Sources Outcomes with strong evidence US EPA2010c; DRAFT IARC 2012; Checkoway et al. 2015 NasalcanceLeukemia US EPA2000; IARC 2012; Ward et al. 2001; Mundt et al. 2000 Liver cancer US EPA 2003; IARC 2012; Khalade et al. 2010 Leukemia US EPA2011; IARC 2014 Kidney cancer Types of studies Numerous cohort studies of occupationally exposed formaldehyde workers. At least 14 cohort studies from the 1970s to 1990s of liver cancer in occupational workers, including 2 multicenter cohort studies (US and Europe) Numerous occupational benzene -exposed workers in the chemicalindustry, shoemaking, and oil refineries. Consistent excess risk of leukemia across studies Numerouscohortand case -controlstudieswith consistent evidence. Quantification (if possible) Nasopharyngeal cancer: RR =4.14 forhighestexposure (Hauptmann et al. 2004, as reported by US EPA 2010) All leukemia: RR=2.49,95% CI: 1.13-5.49 for highest exposure) Chronic myeloid leukemia: RR=3.81,95% CI :0.36-40.44 for highest exposure (Checkoway et al. 2015) RR=28.3,95%CI: 12.8-62.3 for very high exposures (Ward et al. 2001) HR = 6.0, 95%CI: 2.5-14.4 for exposures > 20 years of exposure (Mundt et al. 2000) Pooled estimate (leukemia) 2.62 (95%CI, 1.57-4.39) for high exposures based on meta-analysis (Kha ladeet a 1.2010) Conclusion US EPA - Category Bl (DRAFT); IARC - Group 1 "Formaldehyde causes cancerofthe nasopharynx and leukemia." US EPA: Category A ; IARC: Group 1 Mundt: "deaths from liver cancers have occurred in excess, due to the well documented association betweenVCMa nd angiosarcoma of the liver." Ward: "A strong relation is observedbetween cumulativeVC exposureand occurrence of liver cancer. " US EPA - Category A; IARC Group 1 "sufficient evidence" in humans for leukemia. Pooled estimate (RR) = 1.58, 95% CI: 1.28, 1.96 based on meta analysis of highest exposure group (US EPA2011) US EPA - CategoryCH; IARC - Group 2A 17cv1906 Sierra Club v. EPA ED_001523_00004237-00082 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page B-4 Compound Epichlorohydrin Tetrachloroethene (Also tetrachloroethylene) Sources Outcomes with strong evidence US EPA 1988b; IARC 1999 US EPA2012; IARC 2014 Pesch et al. 2000 Radican et al. 2008 Seidler et al. 2007 Inadequate data in humans. In animals, stomach and oral cavity cancers via oral and nasaltumors via inhalation exposure Bladder cancer, non-Hodgkin lymphoma, multiple myeloma CI: confidence interval HR: hazard ratio I ARC: International Agency for Research on Cancer NHL: Non-Hodgkin lymphoma RR: relative risk SIR: standardized incidence ratio SMR: standardized mortality ratio US EPA: United States Environmental Protection agency VC: vinyl chloride VCM: vinyl chloridemonomer Types of studies Quantification (if possible) 4 cohort studies (including 3 nested case-control studies)foundweakand inconsistent associations withlung cancerand central nervous system tumors withno dose response (IARC 1999) No risk estimates in humans available Bladder cancer: 10-14% increased risk Five of the six occupational high quality studies(dry cleaner or laundry workers) Non-Hodgkin lymphoma: Five cohort high quality occupational studies Multiple myeloma: Little evidence from lower quality but larger cohort studies Some evidence with higher qualitycohort and case control studies Bladder cancer: RR = 1.8, 95% CI: 1.2,2.7 high exposure (Pesch et al. 2000) NHL: RR = 3.4, 95% CI: 0.7, 17.3for the highest exposure (Seidler et al. 2007) Multiple myeloma: Aircraft maintenance workers cohort RR men: 1.71, 95% CI: 0.42, 6.91 RR women:7.84, 95% CI: 1.43, 43.1 (Radicanetal.2008) Conclusion US EPA - Category B2, IARC Group 2A, "probably carcinogenic to humans," based on animal studies, the "known chemical reactivity of epichlorohydrin and its direct activity in a wide range of genetic tests." US EPA - Category LH, IARC - Category 2A 17cv1906 Sierra Club v. EPA ED_001523_00004237-00083 Basis for CorrectionofUSEPA's2010ToxioologicaReviewof Chloroprene APPENDIX C ML.HS.TAGE WEIBULL MODELING OTPT 17cv1906 Sierra Club v. EPA ED_001523_00004237-00084 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page C-1 MultistageWeibullModel. (Version: 1.6.1; Date: 11/24/2009) Solutions are obtained using donlp2 -intv, (c) by P. Spellucci Input Data File: FMLAdlln.(d) Tue May 02 10:15:41 2017 Female Mouse Lung C+ I Grouped Incidental Risk 1-stage MSW model The form of the probabilityfunction is: Pfresponse] = l-EXP{-(t - t_0)Ac * (beta_0+beta_l*doseAl)} The parameter betas are restricted to be positive Dependent variable = CLASS Independent variables = DOSE, TIME Total number of observations = 199 Total number of records with missing values = 0 Total number of parameters in model = 4 Total number of specified parameters = 1 Degree of polynomial= 1 User specifies the following parameters : t_0 = 0 Maximum number of iterations = 16 Relative FunctionConvergencehas been set to: le-008 Parameter Convergence has been set to: le- 008 Default Initial Parameter Values c = 2.65306 t_0 = 0 Specified beta_0 = 3.87553e-007 beta_l = 8.74531e-006 AsymptoticCorrelationMatrix of Parameter Estimates ( *** The model parameter(s) -t_0 have been estimated at a boundary point, or have been specified by the user, and do not appear in the correlationmatrix ) c beta_0 beta_l c 1 -0. 99 -1 beta_0 -0.99 1 0.98 beta_l -1 0. 98 1 Parameter Estimates 95.0% Wald Confidence Interval Variable c Estimate 2.7855 Std. Err. 0.871309 Lower Conf. Limit Upper Conf. Limit i.enn 4.49324 beta_0 2.09796e-007 8.59988e -007 -1.47575e -006 1.89534e -006 beta_l 4.84999e-006 1.88357e -005 -3.20673e -005 4.17673e -005 Log(likelihood) # Param AIC Fitted Model -85.7218 3 177 .444 17cv1906 Sierra Club v. EPA ED_001523_00004237-00085 Basisfor Correctionof US EPA's2010 ToxioologicaReviewof Chloroprene Data Summary CLASS C F I U Total DOSE 0 46 0 4 0 50 0.74 21 0 28 0 49 1.2 16 0 34 0 50 1.6 8 0 42 0 50 Benchmark Dose Computation Risk Response = Incidental Risk Type = Extra Specified effect = 0.01 Confidence level = 0.9 Time = 105 BMD = 0.00485752 BMDL = 0.00394674 BMDU = 0.00604099 Page C-2 17cv1906 Sierra Club v. EPA ED_001523_00004237-00086 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page C-3 MultistageWeibullModel. (Version: 1.6.1; Date: 11/24/2009) Solutions are obtained using donlp2 -intv, (c) by P. Spellicci Input Data File: FMLAdllo.(d) Tue May 02 09:56:18 2017 Female Mouse LungC + I+U Grouped Incidental Risk 1-stage MSW model The form of the probabilityfunction is : Pfresponse] = l-EXP{-(t - t_0)Ac * (beta_0+beta_l*doseAl)} The parameter betas are restricted to be positive Dependent variable = CLASS Independent variables = DOSE, TIME Total number of observations = 200 Total number of records with missing values = 0 Total number of parameters in model = 4 Total number of specified parameters = 1 Degree of polynomial= 1 User specifies the following parameters : t_0 = 0 Maximum number of iterations= 16 Relative FunctionConvergencehas been set to: le-008 Parameter Convergence has been set to: le- 008 Default Initial Parameter Values c = 2.70833 t_0 = 0 Specified beta_0 = 2.99752e-007 beta_l = 6.82409e-006 AsymptoticCorrelationMatrix of Parameter Estimates ( *** The model parameter(s) -t_0 have been estimated at a boundary point, or have been specified by the user, and do not appear in the correlationmatrix ) c beta_0 beta_l c 1 -0.98 -1 beta_0 -0.98 1 0.98 beta_l -1 0.98 1 Parameter Estimates 95.0% Wald Confidence Interval Variable Estimate Std. Err. Lower Conf. Limit Upper Conf. Limit c 2.82393 0.86564 1.12731 4.52055 beta_0 1.75446e-007 7.14572e -007 -1.22509e -006 1.57598e -006 beta_l 4.07913^006 1.57386e -005 -2.6768e -005 3.49262e -005 Log(likelihood) # Param AIC Fitted Model -85.8823 3 177.765 17cv1906 Sierra Club v. EPA ED_001523_00004237-00087 Basisfor Correctionof US EPA's2010 ToxioologicaReviewof Chloroprene Data Summary CLASS C F I U Total DOSE 0 46 0 4 0 50 0.74 21 0 28 1 50 1.2 16 0 34 0 50 1.6 8 0 42 0 50 Benchmark Dose Computation Risk Response = Incidental Risk Type = Extra Specified effect = 0.01 Confidence level = 0.9 Time = 105 BMD = 0.00482968 BMDL = 0.00372838 BMDU = 0.00600798 Page C-4 17cv1906 Sierra Club v. EPA ED_001523_00004237-00088 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page C-5 Multistage Weibull Model. (Version: 1.6.1; Date: 11/24/2009) Solutions are obtained using donlp2 -intv, (c) by P. Spellucci Input Data File: FMLAd2In.(d) Tue May 02 09:56:302017 Female Mouse Lung C+I Grouped Incidental Risk 2-stage MSW model The form of the probabilityfunction is : Pfresponse] = l-EXP{-(t - t_0)Ac * (beta_0+beta_l*d oseAl+beta_2*doseA2)} The parameter betas are restricted to be positive Dependent variable = CLASS Independent variables = DOSE, TIME Total number of observations= 199 Total number of records with missing values = 0 Total number of parameters in model = 5 Total number of specified parameters = 1 Degree of polynomial= 2 User specifies the following parameters : t_0 = 0 Maximum number of iterations= 16 Relative FunctionConvergencehas been set to: le-008 Parameter Convergencehas been set to: le-008 Default Initial Parameter Values c = 3.71429 t_0 = 0 Specified beta_0 = 2.99856e-009 beta_l = 0 beta_2 = 7.10296e-008 AsymptoticCorrelationMatrix of Parameter Estimates ( *** The model parameter(s) -t_0 -beta_l have been estimated at a boundary point, or have been specified by the user, and do not appear in the correlationmatrix ) c beta_0 beta_2 c 1 -0.99 -1 beta_0 -0.99 1 0.99 beta_2 -1 0.99 1 Parameter Estimates 95.0% Wald Confidence Interval Variable Estimate Std. Err. Lower Conf. Limit Upper Conf. Limit c 3.51729 0.955751 1.64405 5.39052 beta_0 7.51777fr009 3.39426e -008 -5.90086e -008 7.40441e -008 beta_l 0 NA beta 2 1.70594e-007 7.25361e -007 -1.25109e -006 1.59228e -006 17cv1906 Sierra Club v. EPA ED_001523_00004237-00089 Basisfor Correctionof US EPA's2010 ToxioologicaReviewof Chloroprene NA - Indicates that this parameter has hit a bound implied by some inequality constraint and thus has n o standard error. Log(likelihood) # Param Fitted Model -82.6686 4 Data Summary CLASS C F I U Total DOSE 0 46 0 4 0 50 0.74 21 0 28 0 49 1.2 16 0 34 0 50 1.6 8 0 42 0 50 AIC 173.337 Benchmark Dose Computation Risk Response = Incidental Risk Type = Extra Specified effect = 0.01 Confidence level = 0.9 Time = 105 BMD = BMDL = - BMDU 0.0676952 0.00685005 0.0770164 Page C-6 17cv1906 Sierra Club v. EPA ED_001523_00004237-00090 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene MultistageWeibullModel. (Version: 1.6.1; Date: 11/24/2009) Solutions are obtained using donlp2 -intv, (c) by P. Spellucci Input Data File: FMLAd2Io.(d) Tue May 02 09:56:48 2017 Female Mouse LungC + I+U Grouped Incidental Risk 2-stage MSW model The form of the probability function is: Pfresponse] = l-EXP{-(t - t_0)Ac * (beta_0+beta_l*dos eAl+beta_2 *doseA2)} The parameter betas are restricted to be positive Dependent variable = CLASS Independent variables = DOSE, TIME Total number of observations = 200 Total number of records with missing values = 0 Total number of parameters in model = 5 Total number of specified parameters = 1 Degree of polynomial= 2 User specifies the following parameters : t_0 = 0 Maximum number of iterations = 16 Relative FunctionConvergencehas been set to: le-008 Parameter Convergence has been set to: le- 008 Default Initial Parameter Values c = 3.33333 t_0 = 0 Specified beta_0 = 1.77269e-008 beta_l = 0 beta 2 = 3.85864e-007 AsymptoticCorrelationMatrix of Parameter Estimates ( *** The model parameter(s) -t_0 -beta_l Page C-7 17cv1906 Sierra Club v. EPA ED_001523_00004237-00091 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page C-8 c beta_0 beta_2 have been estimated at a boundary point, or have been specified by the user, and do not appear in the correlationmatrix ) c beta_ 0 beta_2 1 -0.99 -1 -0.99 1 0.99 -1 0.99 1 Variable c beta_0 beta_l beta_2 Parameter Estimates Estimate 3.53767 6.83164e-009 0 1.55674e-007 Std. Err. 0.951903 3.07193e -008 NA 6.59259e -007 95.0% Wald Confidence Interval Lower Conf. Limit Upper Conf. Limit 1.67197 5.40336 -5.33771e -008 6.70404e -008 -1.13645e -006 1.4478e-006 NA - Indicates that this parameter has hit a bound implied by some inequality constraint and thus has no standard error. Log(likelihood) # Param Fitted Model - 82.7393 4 Data Summary CLASS C F I U Total DOSE 0 46 0 4 0 50 0.74 21 0 28 1 50 1.2 16 0 34 0 50 1.6 8 0 42 0 50 Benchmark Dose Computation Risk Response = Incidental Risk Type = Extra Specified effect = 0.01 Confidence level = 0.9 Time = 105 BMD = 0.0675827 BMDL = e1.00695368 BMDU = 0.0767564 AIC 173.479 17cv1906 Sierra Club v. EPA ED_001523_00004237-00092 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene MultistageWeibullModel. (Version:1.6.1; Date: 11/24/2009) Solutions are obtained using donlp2-intv, (c) byP. Spellucci Input Data File: FMLAd3In.(d) Tue May 02 09:57:042017 Female Mouse Lung C+I Grouped Incidental Risk 3-stage MSW model The form of the probability function is: Pfresponse] = l-EXP{-(t - t_0)Ac * (beta_0+beta_l*doseAl+beta_2*doseA2+beta_3*doseA3)} The parameter betas are restrictedto be positive Dependent variable = CLASS Independent variables = DOSE, TIME Total number of observations = 199 Total number of records with missing values = 0 Total number of parameters in model = 6 Total number of specified paramete rs = 1 Degree of polynomial= 3 User specifies the following parameters : t_0 = 0 Maximum number of iterations= 16 Relative FunctionConvergencehas been set to: le-008 Parameter Convergence has been set to: le- 008 Default Initial Parameter Values c = 3.51351 t_0 = 0 Specified beta_0 = 7.69524e-009 beta_l = 8.17936e-008 beta_2 = 0 beta 3 = 8.3075e-008 Page C-9 17cv1906 Sierra Club v. EPA ED_001523_00004237-00093 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page C-10 AsymptoticCorrelationMatrix of Parameter Estimates ( *** The model parameter(s) -t_0 -beta_2 have been estimated at a boundary point, or have been specified by the user. and do not appear in the correlationmatrix ) c beta_0 beta_l beta_3 c 1 -0.99 -0.99 -0.99 beta_0 -0.99 1 0.98 0.98 beta_l -0.99 0.98 1 0.97 beta_3 -0.99 0.98 0.97 1 Parameter Estimates 95.0% Wald Confidence Interval Variable Estimate Std. Err. Lower Conf. Limit Upper Conf. Limit c 3.565 1.09332 1.42214 5.70787 beta_0 6.06284e-009 3.09921e -008 -5.46806e -008 6.68063e -008 beta_l 6.3958e- 008 3.37242e -007 -5.97025e -007 7.24941e -007 beta_2 0 NA beta_3 6.69836e-008 3.08585e -007 -5.37832e -007 6.718e -007 NA - Indicates that this parameter has hit a bound implied by some inequality constraint and thus has no standard error. Log(likelihood) # Param AIC Fitted Model -82.6066 5 175.213 Data Summary CLASS C F I U Total DOSE 0 46 0 4 0 50 0.74 21 0 28 0 49 1.2 16 0 34 0 50 1.6 8 0 42 0 50 Benchmark Dose Computation Risk Response = Incidental Risk Type = Extra Specified effect = 0.01 Confidence level = 0.9 T ime = 105 BMD = BMDL = BMDU > 0.00978798 0.0052444 0.0783038 17cv1906 Sierra Club v. EPA ED_001523_00004237-00094 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene MultistageWeibullModel. (Version: 1.6.1; Date: 11/24/2009) Solutions are obtained using donlp2 -intv, (c) by P. Spellucci Input Data File: FMLAd3Io.(d) Tue May 02 09:58:502017 Female Mouse LungC + I+U Grouped Incidental Risk 3-stage MSW model The form of the probability function is: Pfresponse] = l-EXP{-(t - t_0)Ac * (beta_0+beta_l*doseAl+beta_2*doseA2+beta_3*doseA3)} The parameter betas are restricted to be positive Dependent variable = CLASS Independent variables = DOSE, TIME Total number of observations = 200 Total number of records with missing values = 0 Total number of parameters in model = 6 Total number of specified parameters = 1 Degree of polynomial= 3 User specifies the following parameters : t_0 = 0 Maximum number of iterations= 16 Relative FunctionConvergencehas been set to: le-008 Parameter Convergence has been set to: le- 008 Default Initial Parameter Values c = 3.02326 t_0 = 0 Specified beta_0= 7.4445e-008 beta 1 = 8.31425e-007 beta 2 = 0 beta 3 = 6.42289^007 Asymptotic Correlation Matrix of Parameter Estimates Page C-11 17cv1906 Sierra Club v. EPA ED_001523_00004237-00095 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene Page C-12 ( *** The model parameter(s) -t_0 -beta_2 have been estimated at a boundary point, or have been specified by the user, and do not appear in the correlationmatrix ) c beta_0 beta_l beta_3 c 1 -0.99 -0.99 -0.99 beta_0 -0.99 1 0.98 0.98 beta_l -0.99 0.98 1 0.97 beta_3 -0.99 0.98 0.97 1 Variable c beta_0 beta_l beta_2 beta_3 Parameter Estimates Estimate 3.59456 5.28712e-009 5.52071e-008 0 5.93591e-008 Std. Err. 1.08684 2.68702e -008 2.89531e -007 NA 2.72143e -007 95.0% Wald Confidence Interval Lower Conf. Limit Upper Conf. Limit 1.4644 5.72473 -4.73775e -008 5.79518e -008 -5.12264e -007 6.22678e -007 -4.74031e -007 5.92749e -007 NA - Indicates that this parameter has hit a bound implied by some inequality constraint and thus has no standard error. Log(likelihood) # Param Fitted Model 82.6739 5 Data Summary CLASS C F I U Total DOSE 0 46 0 4 0 50 0.74 21 0 28 1 50 1.2 16 0 34 0 50 1.6 8 0 42 0 50 Benchmark Dose Computation Risk Response = Incidental Risk Type = Extra Specified effect = 0.01 Confidence level = 0.9 Time = 105 BMD = e>.00988202 BMDL = 0.0052649 BMDU > 0.0790561 AIC 175.348 17cv1906 Sierra Club v. EPA ED_001523_00004237-00096 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene APPENDIXD ABOUT RAMBOLL ENVIRON 17cv1906 Sierra Club v. EPA ED_001523_00004237-00097 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene ABOUT RAMBOLL ENVIRON A premier global consultancy, Ramboll Environ is trusted by clients to manage their most challenging e nvironmental, health and social issues. We have earned a reputation for technical and scientific excellence, innovation and client service. Our independent science-first approach ensures that our strategic advice is objective and defensible. We apply integrated multidisciplinary services and tailor each solution to our client's specific needs and challenges. At the end of 2014, ENVIRON joined forces with Ramboll, Northern Europe's leading engineering, design and managementconsultancy, to create a global practice called Ramboll Environment and Health. Together we provide an even higher level of serviceto our clientsand addresssomeof the most importantissuesfacingour global community, including the environmental and health implications of urbanization, climate change and resource scarcity. Ramboll Environ's network of experts includes more than 2,100 employees across 130 offices in 28 countries around the world. Clients will continue to benefit from our unique ability to bring clarity to issues at the intersection of science, business and policy. 17cv1906 Sierra Club v. EPA ED_001523_00004237-00098 Basisfor Correctionof US EPA's2010 ToxicologicaReviewof Chloroprene APPENDIX E EXPER.r BIOGRAPHIES 17cv1906 Sierra Club v. EPA ED_001523_00004237-00099 ENVIRON P ROBINAN GENTRY Principal/Operations Director - Gulf Coast ENVIRONMENT & HEALTH Dr. Robinan Gentry is a toxicologist with over 25 years of experience in toxicological issues relevant in the determination of the potential safety or risk associated with exposure to chemicals. Over her career, she has been a principal investigator or contributing author for numerous safety and risk assessments for both government and industry. She has worked as a government subcontractor in which she developed toxicological profiles for the US EPA IRIS program, ATSDR and FDA. Many assessments in which she has been involved has been to incorporate innovative quantitative approaches at that time (e.g., benchmark dose modelling, probabilistic assessments, PBPK modelling, in vitro to in vivo extrapolation, genomics data). She is a published author in the development of risk assessment methods, including Physiologically Based Pharmacokinetic (PBPK) models, and their application into both the cancer and non-cancer risk assessment process. EXPERIENCE Quantitative Risk Assessments Managed numerous human health risk assessments and projects related to the development of criteria and other health effects documents, including application of benchmark modelling; conducted detailed analyses of guidance used in the determination of acute toxicity exposure levels and comparison of USEPA's and California's Proposition 65's risk assessment methods for multiple chemicals; quantified margin of exposures and cancer slope factor using existing kinetic and mechanism of action for multiple compounds. Toxicological Reviews Prepared toxicological reviews for USEPA's Office of Pesticide Programs and Program for Toxic Substances (OPPTS), FDA's Center for Food Safety and Nutrition, the Agency of Toxic Substances and Disease Registry (ATSDR), contributing author for development of Drinking Water Criteria Documents for several radionuclides and chloroform; development of weight-of-evidence evaluations and systemic reviews for multiple chemicals including formaldehyde, methyl salicylate and arsenic. Pharmacokinetics and PBPK Modelling Served as principal investigator or co-investigator for several PBPK modelling projects, including the development of models in multiple species for constituents such as coumarin, arsenic, acrylic acid and isopropanol. 1/1 CV, P ROBINAN GENTRY CONTACT INFORMATION P Robinan Gentry rqentry@ramboll.com +1 (318) 3982083 Ramboll Environ 3107 Armand Street Monroe, LA 71201 United States of America CREDENTIALS PhD, Toxicology, Utrecht University, The Netherlands Diplomate. American Board of Toxicology, 2002; recertified, 2007,2011 MS, Pharmacology & Toxicology, Northeast Louisiana University BS, Toxicology, Northeast Louisiana University 17cv1906 Sierra Club v. EPA ED_001523_00004237-00100 RAMB ENVIRON KENNETH A MUNDT Principal ENVIRONMENT & HEALTH Dr. Kenneth Mundt is Health Sciences Practice Network Leader. He brings 30 years of experience in applying epidemiological concepts and methods to understand human health risks from environmental, occupational and consumer product exposures. Dr. Mundt specializes in the pragmatic interpretation of epidemiological evidence in evaluating disease causation and supporting science-based regulation and decision-making. Previously, Dr. Mundt served 11 years on the Graduate Faculty of the School of Public Health and Health Sciences, University of Massachusetts at Amherst. He received his PhD in Epidemiology at the University of North Carolina at Chapel Hill, and is a Fellow in the American College of Epidemiology. EXPERIENCE HIGHLIG Epidemiological Studies Managed multidisciplinary teams in designing, conducting and interpreting occupational epidemiological studies of workers involved in rubber, porcelain, chemical and steel industries, as well as military and other professionals. Health Risks Evaluation and Communication Responded to observed and perceived health problems related to occupational, environmental and consumer product exposures. Teaching and Scholarship Frequent participant in scientific meetings, training courses, and litigation proceedings. Consistent publication record. Scientific Regulatory Support Provided scientific evaluation and support to various regulatory and policy processes, including oral and written comments, statistical re-analysis of data from key studies, preparation of commentaries and technical communications, identification of new research opportunities, critical review and meta-analyses of epidemiological evidence, integration of scientific evidence from diverse lines of inquiry, organize and manage expert panels and topical symposia. Critical Reviews and Syntheses Comprehensively identified, systematically critically reviewed and synthesized the epidemiological literature on human health risks associated with numerous occupational, environmental and consumer product exposures. CONTACT INFORMATION Kenneth A Mundt kmundt@ramboll.com + 1 (413) 8354360 Ramboll Environ 28 Amity Street Suite 2A Amherst, 01002 United States of America CRED PhD, Epidemiology University of North Carolina MS, Epidemiology University of Massachusetts MA, English University of Virginia AB, English Dartmouth College 17cv1906 Sierra Club v. EPA ED_001523_00004237-00101 ENVIRON ENVIRONMENT & HEALTH SONJA SAX Senior Environmental Health Scientist Dr. Sonja Sax is an environmental health scientist with over 15 years of exposure and health risk assessment experience. She has particular expertise in airborne gases and particles, and has performed indoor and outdoor air quality investigations, managed several large environmental projects, conducted critical evaluations of toxicology and epidemiology studies, and helped prepare technical and expert reports. Sonja has authored and co-authored several publications, presented her research and consulting work at various conferences and testified before scientific panels. Sonja earned an MS and doctorate in environmental health from the Harvard T.H. Chan School of Public Health, where she also served as a postdoctoral fellow. EXPERIENCE HIGHLIGHTS Critical Reviews and Syntheses Conducted an extensive literature search on the toxicity and health effects of different chemical compounds including cobalt alloys found in dental materials, diesel exhaust, carbon black, welding fumes, particulate matter and sulfur dioxide. Systematic Reviews Conducted weight-of-evidence evaluation of cardiovascular and respiratory effects from exposures to ozone. Results were published in several peer-reviewed manuscripts. Litigation Support Contributed to the preparation of expert reports in litigation projects involving different chemical exposures (e.g., vinyl chloride, asbestos, carbon black, particulate matter, sulfur dioxide, and pesticides). Exposure and Risk Assessment For numerous projects prepared technical analyses on exposures and potential health effects associated with various pollutants (e.g., particulate matter, sulfur dioxide, nitrogen dioxide, arsenic, and pesticides). Exposure assessments included air dispersion modeling. Regulatory Comments Provided written and oral comments to the Clean Air Scientific Advisory Committee on exposure and health effects data and their bearing on US EPA's National Ambient Air Quality Standards for particulate matter and ozone. Indoor Exposure and Risk Assessment Conducted analyses of residential exposures to chemicals (e.g., formaldehyde from wood products, vapor intrusion of tetrachloroethylene, mercury from wallboard, and flame retardants from various indoor sources). 1/1 CV, SONJA SAX, LAST UPDATED 2017/03 CONTACT INFORMATION Sonja Sax ssax@ramboll.com + 1 (413) 835-4358 Ramboll Environ 28 Amity Street Suite 2A Amherst, 01002 United States of America CRED: ScD, Environmental Health Sciences Harvard School of Public Health MS, Environmental Health Management Harvard School of Public Health BA, Biological Chemistry Wellesley College 17cv1906 Sierra Club v. EPA ED_001523_00004237-00102