Workshop Report on the Application of 2,3,7,8-TCDD Toxicity Equivalence Factors to Fish and Wildlife
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EPA/630/R-01/002 August 2001 www.epa.gov/ncea/raf Workshop Report on the Application of 2,3,7,8-TCDD Toxicity Equivalence Factors to Fish and Wildlife Risk Assessment Forum U.S. Environmental Protection Agency Washington, DC DISCLAIMER This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. ii CONTENTS CONTRIBUTORS TO WORKSHOP DESIGN AND REPORT ........................ iv 1. INTRODUCTION ..........................................................1 2. OBJECTIVES AND DESIGN OF THE EPA/DOI WORKSHOP ......................4 3. WORKSHOP FINDINGS.....................................................6 4. CONCLUSIONS OF THE EPA/DOI WORKSHOP PLANNING GROUP ..............11 5. REFERENCES............................................................18 APPENDICES: A. Workshop Case Study: A Preliminary Problem Formulation for a Retrospective Ecological Risk Assessment Scenario.................................................... A-1 B. Workshop Case Study: A Preliminary Problem Formulation for a Prospective Ecological Risk Assessment Scenario.....................................................B-1 C. Report from the Workshop on the Application of 2,3,7,8-TCDD Toxicity Equivalence Factors to Fish and Wildlife.................................................... C-i I. Introduction ........................................................C-1 II. Opening Presentations...............................................C-2 III. Workshop Proceedings .............................................C-27 IV. Conclusions and Recommendations...................................C-60 Appendices A. Workshop Participants ...................................... C-A-1 B. Agenda.................................................. C–B-1 C. Premeeting Comments.......................................C-C-1 D. Detailed Summaries of Expertise Group Discussions .............. C-D-1 E. Detailed Summaries of Case Study Discussions ...................C-E-1 F. Written Comments from Observers .............................C-F-1 iii CONTRIBUTORS TO WORKSHOP DESIGN AND REPORT EPA Regional Offices EPA Office of Research and Development Patricia Cirone (Region 10) Steven Bradbury Robert Pepin (Region 5) Philip Cook Steve Wharton (Region 8) Michael Devito Tala Henry Cynthia Nolt-Helms U.S. Department of Interior Tim Kubiak (U.S. Fish and Wildlife Service) Donald Tillitt (U.S. Geological Survey) Lisa Williams (U.S. Fish and Wildlife Service) Workshop Case Studies (Appendix A and Appendix B) EPA U.S. Department of Interior Steven Bradbury Tim Kubiak Philip Cook Donald Tillitt Lisa Williams Report from the Workshop on the Application of 2,3,7,8-TCDD Toxicity Equivalence Factors to Fish and Wildlife (Appendix C) Prepared by Eastern Research Group, Inc., an EPA Contractor. Risk Assessment Forum Staff William Wood Scott Schwenk iv 1. INTRODUCTION On January 20-22, 1998, a workshop was held on “The Application of 2,3,7,8-TCDD Toxicity Equivalence Factors to Fish and Wildlife.” The workshop was developed by a joint planning committee of the U.S. Environmental Protection Agency (EPA) and the U.S. Department of the Interior (DOI) and hosted with the support of the Eastern Research Group, Inc. (ERG), a contractor. This introduction provides background about polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) and the development of toxicity equivalence factors (TEFs) to assess their risks. This section is followed by sections that describe the design of the workshop and its results. PCDD, PCDF, and PCB congeners that elicit toxicity through the same aryl hydrocarbon receptor (AhR) mediated mechanisms as 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) are found in a variety of aquatic and terrestrial ecosystems. Exposures of these compounds to fish, and avian and mammalian wildlife have been well documented in a number of settings; examples include the Great Lakes (Gilbertson and Fox, 1977; Kubiak et al., 1989; Yamashita et al., 1993; Devault et al., 1996); the St Lawrence Estuary (Beland et al., 1993); many rivers and lakes of the U.S. (U.S. EPA, 1992a), the arctic (Norstrom et al., 1990), and, similarly, many locations outside of North America. The documented ecological risks associated with exposures of fish and wildlife to 2,3,7,8-TCDD (U.S. EPA, 1993) are magnified through concomitant exposures to other AhR agonists. Because these compounds are typically found as complex mixtures, assessments of ecological risks require both the evaluation of their individual exposures and combined effects. Thus, the need to assess the risks of these classes of compounds may require evaluations of congeners other than 2,3,7,8-TCDD alone or evaluations that are more specific than “total PCBs” or “total PCDDs.” To address the combined AhR-mediated effects of PCDDs, PCDFs, and PCBs, the concept of 2,3,7,8-TCDD toxicity equivalence factors (TEFs) has been proposed to facilitate both human health and ecological risk assessments (e.g., U.S. EPA, 1989; U.S. EPA, 1991; van den Berg et al., 1998). A TEF is a best estimate, from available data for an individual chemical that behaves as an AhR agonist, of the chemical’s potency relative to the potency of the reference chemical, 2,3,7,8-TCDD. Specific relative potency (ReP) data used to determine TEF values generally consist of the ED50, LD50, or LC50 of 2,3,7,8-TCDD divided by the respective ED50, LD50, or LC50 of the chemical. The ReP data base for a chemical may include multiple species, in vitro or in vivo studies, and endpoints ranging from mortality to protein induction (e.g., the enzyme CYP1A1). The World Health Organization (WHO) has defined TEFs as order to half-order of 1 magnitude estimates of relative potency derived from an assessment of available RePs (van den Berg et al., 1998). Initially, TEFs were developed primarily to address human health effects. In 1987, the EPA published an interim report on the toxicity equivalence methodology and proposed TEF values for fifteen 2,3,7,8-chlorine substituted dibenzo-p-dioxin and dibenzofurans for human health risk assessment (U.S. EPA, 1987). At the time the initial TEF values were presented, few in vivo experimental data were available, particularly for the dibenzofurans. Following the EPA-TEF report, the North Atlantic Treaty Organization Committee on the Challenges of Modern Society (NATO-CCMS) also published TEFs for dioxin and dibenzofurans based on scientific consensus (I-TEFs; NATO-CCMS, 1988a,b). The I-TEFs were adopted by EPA in 1989 (U.S. EPA, 1989). TEFs were subsequently expanded to include dioxin-like PCBs (Ahlborg et al., 1994; Safe, 1994; van den Berg et al., 1998). The criteria to include a compound required a structural relationship to the PCDFs and PCDDs, binding to the AhR receptor, and expression of dioxin-specific biochemical or toxicity responses (Ahlborg et al., 1994). TEFs were derived using all the available data and a tier approach to data selection. While the actual TEFs proposed by these reports vary due to data availability and differences in assessing RePs (dose measures, species, end points, in vitro/in vivo, etc.), greater reliance was usually placed on RePs derived from chronic or subchronic in vivo exposures and endpoints associated with overt toxicity, followed by biochemical effects derived from in vivo exposures, followed by biochemical effects derived from in vitro studies, and finally quantitative structure activity relationships. Rather than employing “human-health” TEFs to evaluate risks of PCDDs, PCDFs, and PCBs to fish and wildlife, the need to establish TEFs more appropriate for ecological risk assessments and associated management decisions has been recognized (van den Berg et al., 1998; U.S. EPA, 1992b). In many cases these needs require a greater capability than that used in screening-level risk assessments. Class-specific TEFs are needed to establish aquatic life and wildlife water quality criteria and remediation targets at contaminated sites. For example, development of wildlife criteria for PCBs in the Great Lakes Water Quality Guidance (GLWQG) initially proposed the use of TEFs calculated by Safe (1990). Based on recommendations from the EPA Science Advisory Board (U.S. EPA, 1992b), this approach was not included in the final rule because it was concluded that, although the conceptual basis for the use of TEFs was reasonable, there were insufficient data available to determine the extent to which the TEFs available for human health are appropriate for the species and endpoints of concern in ecological 2 analyses. Currently, EPA and the U.S. Department of Interior (DOI) are jointly addressing the possibility of advancing the use of TEFs in the Great Lakes Water Quality Guidance as new data and methods become available (U.S. Department of the Interior, 1995). In terms of assessing impacted sites, virtually all of the Great Lakes Areas of Concern have PCB- and PCDF- contaminated sediments that require assessment of loading and resultant effects to facilitate risk management decisions. Regulatory decisions for situations with PCDDs, PCDFs, and PCBs that have relied on single chemical estimates for 2,3,7,8-TCDD or total PCBs have been criticized because of the limitations of these approaches. Due to the increasing need for development of TEFs appropriate for use in ecological risk assessments, the WHO convened a meeting of scientific experts in 1997 to derive TEFs