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Issue Paper on the Bioavailability and Bioaccumulation of Metals

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Issue Paper on the Bioavailability and Bioaccumulation of Metals ISSUE PAPER ON THE BIOAVAILABILITY AND BIOACCUMULATION OF METALS DRAFT John Drexler,1 Nicholas Fisher,2 Gerry Henningsen,3 Roman Lanno,4 Jim McGeer,5 Keith Sappington6 Contributing Author: Michael Beringer7 Submitted to: U.S. Environmental Protection Agency Risk Assessment Forum 1200 Pennsylvania Avenue, NW Washington, DC 20460 Contract #68-C-98-148 Submitted by: ERG 110 Hartwell Avenue Lexington, MA 02421 August 2003 1University of Colorado, Boulder, CO 2State University of New York, Stony Brook, NY 3H&H Scientific Services, Centennial, CO 4Ohio State University, Columbus, OH 5Natural Resources Canada, Ottawa, ON 6NCEA, ORD, U.S. EPA, Washington, DC 7U.S. EPA Region 7, Kansas City, KS NOTICE This paper has been developed in support of an ongoing effort within the U.S. Environmental Protection Agency (EPA) to develop an integrated framework for metals risk assessment. In September 2002, the cross-Agency technical panel, organized under the auspices of the Agency’s Science Policy Council, discussed plans for the development of the framework and associated guidance with the Agency’s Science Advisory Board (SAB). During the advisory, the SAB affirmed the importance of incorporating external input into the Agency’s effort. As part of the effort to engage stakeholders and the scientific community and to build on existing experience, the Agency commissioned external experts to lead the development of papers on issues and state-of-the-art approaches in metals risk assessment for several key topics. Topics identified include: environmental chemistry; exposure; ecological effects; human health effects; and bioavailability and bioaccumulation. (Some individual EPA experts contributed specific discussions on topic(s) for which he or she has either specific expertise or knowledge of current Agency practice). Although Agency technical staff, as well as representatives from other Federal agencies, reviewed and commented on previous drafts, the comments were addressed at the discretion of each respective author or group of authors. Therefore, the views expressed are those of the authors and should not be construed as implying EPA consent or endorsement. This draft paper is being made available for public comment consistent with EPA’s commitment to provide opportunities for external input. Science-based comments received on this paper will be made available to authors for final disposition. The material contained in this paper may be used in total, or in part, as source material for the Agency’s framework for metals risk assessment and EPA’s evaluation of this material will therefore include consideration of the Assessment Factors recently published by EPA for use in evaluating the quality of scientific and technical information. The draft framework, as an Agency document, will undergo scientific peer review by the SAB. Development of this draft paper was funded by EPA through its Risk Assessment Forum under contract 68-C-98-148 to Eastern Research Group, Inc. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. ii TABLE OF CONTENTS 1. PROBLEM STATEMENT, CONCEPTUAL FRAMEWORK, AND DEFINITIONS ............ 1 1.1 Conceptual Framework ................................................................................................ 2 1.2 Definitions ................................................................................................................... 3 1.2.1 Bioaccessibility or Environmental Availability ............................................ 3 1.2.2 Bioavailability ............................................................................................... 3 1.2.3 Bioaccumulation ........................................................................................... 6 1.2.4 Other Definitions .......................................................................................... 7 2. PRINCIPLES ON BIOAVAILABILITY AND BIOACCUMULATION ................................ 7 2.1 Principles and Issues Common to Both Aquatic and Terrestrial Systems ................... 7 2.2 Membrane Interactions with Metals: Physicochemical Factors in Transfer of Metals Across Membranes ................................................................................................. 9 2.2.1 Factors That Modify Absorption .................................................................. 9 2.3 Toxicokinetics (ADME) and Bioaccumulation of Metals ......................................... 10 3. CURRENT AGENCY PRACTICE ......................................................................................... 10 3.1 Site-Specific Assessments ......................................................................................... 10 3.1.1 Superfund Program ..................................................................................... 11 3.1.2 Ambient Water Quality Criteria ................................................................. 12 3.2 National-Scale Assessments ...................................................................................... 13 3.2.1 Assessing Health Risks of Lead Exposure ................................................. 13 3.2.2 Derivation of Reference Doses (RfDs) ...................................................... 13 3.2.3 National Risk Assessments ......................................................................... 14 3.2.4 National Criteria and Screening Levels ...................................................... 14 3.3 National Hazard Ranking and Classification ............................................................. 16 3.3.1 Toxics Release Inventory (TRI) ................................................................. 16 3.3.2 Waste Minimization Prioritization Tool ..................................................... 17 4. CURRENT STATE OF THE SCIENCE ON BIOACCUMULATION AND BIOAVAILABILITY ISSUES ........................................................................................ 18 4.1 Aquatic ....................................................................................................................... 18 4.1.1 Aquatic Exposure ........................................................................................ 18 4.1.2 Dietary Exposure ........................................................................................ 19 4.2 Bioaccumulation of Metals in Aquatic Biota ............................................................ 20 4.2.1 Uptake Mechanisms .................................................................................... 20 4.2.2 Accumulation Strategy ............................................................................... 21 4.2.3 Trophic Transfer ......................................................................................... 23 4.2.4 Adaptation and Acclimation ....................................................................... 25 4.2.5 Intra/Intercellular Speciation ...................................................................... 26 4.2.6 Empirical Models/Methods ......................................................................... 27 4.2.7 Metabolism/Detoxification ......................................................................... 37 4.2.8 Biomonitoring as a Tool for Bioaccumulation ........................................... 39 4.3 Terrestrial ................................................................................................................... 40 iii 4.3.1 Human ......................................................................................................... 42 4.3.2 Wildlife ....................................................................................................... 50 4.3.3 Plants ........................................................................................................... 53 4.3.4 Soil Community: Invertebrates and Microorganisms ................................. 57 4.4 Speciation: Its Role in Assessing Bioavailability in the Terrestrial Environment .... 65 4.4.1 Speciation .................................................................................................... 66 4.4.2 Tools ........................................................................................................... 68 4.5 Predictive Assays for Terrestrial Mammals ............................................................... 70 5. FUTURE DIRECTIONS TO IMPROVE CURRENT AGENCY PRACTICE ...................... 76 5.1 Aquatic-Based Assessments ...................................................................................... 76 5.2 Research Needs .......................................................................................................... 87 5.2.1 Aquatic ....................................................................................................... 87 5.2.2 Terrestrial .................................................................................................... 87 6. LITERATURE CITED ............................................................................................................ 88 iv LIST OF TABLES Table 1. Mean concentration factors (on a wet weight or, for phytoplankton cell volume basis) of metals in marine organisms............................................. 33 Table 2. Examples of relative bioavailability adjustments (RBA) in human health risk assessment............................................................................ 49 Table 3. Where bioavailability information is used in ecological risk assessment..........50 Table 4. Examples of including bioavailability processes
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