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Framework for Inorganic Metals Risk Assessment

Explore the challenges with the PBT framework and develop a comprehensive guide for assessing metal risks, focusing on bioavailability and hazard potential. Includes key principles, guiding methods, models, and approaches. Schedule and phases outlined for implementation.

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Framework for Inorganic Metals Risk Assessment

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  1. Framework for Inorganic Metals Risk Assessment Anne Fairbrother, Randy Wentsel, Bill Wood, Keith Sappington, and Pam Noyes Office of Research and Development SETAC North America Annual Conference November 2006

  2. Background • There has been considerable interest in the Agency’s assessments on metals and metal compounds • promulgation of the Toxics Release Inventory (TRI) lead rulemaking • development of the Agency’s Waste Minimization Prioritization Tool

  3. Challenge to the PBT Framework as Applied to Metals • PBT framework is based on principles developed for organic substances that do not apply to metals • PBT framework does not distinguish between metal elements, metal compounds, or particulate size • There is a major disconnect between the forms selected for toxicity testing and those in the marketplace

  4. Challenge to the PBT Framework as Applied to Metals • BCFs for metals • vary with species and environmental conditions • show an inverse relationship with concentration • are not a predictor of toxicity • Speciation and bioavailability are more meaningful than persistence when evaluating hazard potential

  5. Challenge to the PBT Framework as Applied to Metals • PBT framework lacks discriminatory power for metals All metals would satisfy the criteria to be a PBT

  6. Metals Framework • Develop a cross-Agency guidance for assessing metal and metal compounds • discussions within the Agency, with external stakeholders and with Congress • provide opportunities for external input, peer review and cross-Agency involvement

  7. Metals Framework • Develop a comprehensive framework that could be the basis of future Agency actions • Provide a consistent set of key guiding principles to be considered in assessing risks posed by inorganic metals • Identify available methods, models, and approaches for use in metals risk assessments • Foster consistency across EPA programs and regions

  8. Schedule Environ Chemistry Eco Effects Bioavail. Bioaccum. Human Health Exposure Phase I: Metals Action Plan Dec 2002 SAB Review Phase II: Issue Papers Aug 2004 Peer Review

  9. Schedule Phase III: Draft Metals Framework June 2004 Phase III: Draft Metals Framework Dec 2004 Peer Input Workshop July 2004 SAB Review Feb 2005 - 2006 IntraAgency Review July 2006 InterAgency Review August 2006 Phase IV: Final Document and Agency Implementation Jan 2007

  10. Aluminum Antimony Arsenic Barium Beryllium Boron Cadmium Chromium Cobalt Copper Iron Lead Manganese Mercury (inorganic) Molybdenum Nickel Selenium Silver Strontium Tin Thallium Vanadium Zinc Metals and Metalloids of Primary Interest

  11. Framework TOC Executive Summary Ch 1 – Intro Ch 2 – Framework overview Ch 3 – Environmental Chemistry, Transport, and Fate Ch 4 – Human Health Ch 5 – Aquatic EcoRisk Ch 6 – Terrestrial EcoRisk Ch 7 -- References

  12. Ch 1. Introduction • Purpose and audiences • Metals Framework Scope • Metals Assessment Context • National ranking and categorization • National risk assessments • Regional and local risk assessments • Key Principles to Consider

  13. Ch 1. Introduction • Purpose and audiences • Metals Framework Scope • Metals Assessment Context • National ranking and categorization • National risk assessments • Regional and local risk assessments • Key Principles to Consider

  14. Principles • Metals are naturally occurring constituents in the environment and vary in concentrations across geographic regions. • All environmental media have naturally occurring mixtures of metals, and metals often are introduced into the environment as mixtures.

  15. Natural occurrence of barite Natural occurrence of barite (USGS)

  16. Principles • Some metals are essential for maintaining proper health of humans, animals, plants, and microorganisms.

  17. Principles • Unlike organic chemicals, metals are neither created nor destroyed by biological or chemical processes • They can transform from one species to another (valence states) and can convert them between inorganic and organic forms. • The absorption, distribution, transformation, and excretion of a metal (toxicokinetics) within an organism depends on • the metal • the form of the metal or metal compound • the organism’s ability to regulate and/or store the metal.

  18. Ch 2. Framework Over view • Human Health and Ecological Risk Assessment: Planning and Problem Formulation • Metal Conceptual Model • Assessment Phase • Bioavailability • Characterization of Exposure • Characterization of Effects / Hazard Analysis • Risk Characterization

  19. Conceptual Model for Metal Risk Assessments

  20. Assessment Questions • Principles are translated into assessment questions to assist in their consideration • Questions drafted for all phases of the risk assessment

  21. Example Assessment Questions • BACKGROUND: How should background (natural and anthropogenic) levels for metals be characterized for the selected spatial scale of the assessment? • MIXTURES: Are toxicological effects of metal mixtures being incorporated in the effects assessment? • ESSENTIALITY: How will both toxicity and deficiencies of essential metals be characterized? • METAL FORMS: Since environmental chemistry is a primary factor influencing metal speciation and subsequent transport, uptake, and toxicity, how will it be included in the risk assessment?

  22. Ch 3. Environmental Chemistry, Transport, and Fate • Introduction and Terminology • Hard and soft acids and bases • Transformations • Aquatic chemistry • Ground water and metals mobility • Sediment chemistry • Soil chemistry • Atmospheric behavior / chemistry • Metal Transport and Fate • Aquatic and terrestrial transport pathways • Atmospheric fate and transport

  23. Bioavailability Issues • Bioavailability of metals varieswidely according to the physical, chemical, and biological conditions under which an organism is exposed. • Bioavailability should be explicitly incorporated into all risk assessments • Trophic transfer can be an important route of exposure for metals • but biomagnification of inorganic forms of metals in food webs is generally not a concern in metals assessments

  24. BAF/BCF Issues • Certain metal compounds are known to bioaccumulate in tissues and this bioaccumulation can be related to their toxicity. • The latest scientific data on bioaccumulation do not currently support the use of bioconcentration factor (BCF) or bioaccumulation factor (BAF) values when applied as generic threshold criteria for the hazard potential of inorganic metal

  25. BAF/BCF Issues • Single value BAF/BCFs hold the most value for site-specific assessments • extrapolation across different exposure conditions is minimized • For regional and national assessments, BAF/BCFs should be expressed as a function of media chemistry and metal concentration for particular species (or closely related organisms)

  26. Environmental Chemistry • Metal speciation affects • toxicity, volatilization, photolysis, sorption, atmospheric deposition, acid/base equilibria, polymerization, complexation, electron-transfer reactions, solubility and precipitation equilibria, microbial transformations, and diffusivity • Speciation includes • free metal ions, metal complexes dissolved in solution and sorbed on solid surfaces, and metal species that have been co-precipitated in major metal solids or that occur in their own solids.

  27. Environmental Chemistry • pH and redox potential affect speciation • Kd values • limited use of single values • Aging of metals in media reduces bioavailability • Metal sorption behavior affects bioavailability

  28. Ch 4. Human Health Risk Assessment for Metals • Metals Principles • Human Exposure Assessment • Background • Bioavailability • Susceptible populations • Environmental release, transport and fate • Route-specific differences in effects • Integrated exposures • Biomarkers • Hazard Characterization • Mixtures • Essentiality • Forms of metals • Toxicokinetics / toxicodynamics • Metal toxicity • Dose-response assessment • Risk Characterization

  29. Human Health • The organ or tissue in which metal toxicity occurs may differ from the organ or tissue(s) in which the metal bioaccumulates and may be affected by the metal’s kinetics • Both the exposure route and the form of a metal can affect the metal’s carcinogenic potential and its noncancer effects • Sensitivity to metals varies with age, sex, pregnancy status, nutritional status, and genetics

  30. Human Health • Metals attached to small airborne particles are of primary importance for inhalation exposures. • Because the diets of humans and other animals are diverse, there may be wide variability in the dietary intake of some metals (e.g., in seafood) • results in temporal, geographic or cultural variability of responses

  31. Human Health • Essentiality should be viewed as part of the overall dose-response relationship for those metals shown to be essential • Zinc IRIS document is an example RFDs should not be below RDAs

  32. Essentiality and Toxicity

  33. Aquatic Ecological Risk Assessment for Metals • Metals Principles • Characterization of Exposure • Background • Forms of metals • Exposure pathway analysis • Fate and transport of metals • Bioavailability and bioaccumulation • Characterization of Effects • Essentiality • Toxicokinetics / toxicodynamics • Metal mixtures • Critical body residues • Risk Characterization

  34. Terrestrial Ecological Risk Assessment for Metals • Metals Principles • Characterization of Exposure • Natural occurrence of metals • Forms of metals • Exposure routes • Soil transport and fate models • Toxicokinetics / toxicodynamics • Soil invertebrate exposure • Plant exposure • Wildlife exposure • Characterization of Effects • Essentiality • Toxicity tests • Metal mixtures • Critical body residues • Plant and invertebrate toxicity • Wildlife toxicity • Risk Characterization

  35. Ecological • Background levels refers to those concentrations of metals that derive from natural as well as anthropogenic sources that are not the focus of the risk assessment • metal concentrations vary widely over space and time • are partially responsible for distributions of plants and wildlife

  36. Ecological • For aquatic organisms, routes of exposure include • absorption across respiratory organs, dermal absorption, sediment ingestion, and food ingestion • For terrestrial organisms, routes of exposure include • binding to roots, foliar uptake, dermal absorption, food, water, and soil ingestion, or inhalation

  37. Ecological • For most metals, the free ionic form is most responsible for toxicity • Free-ion activity models are useful for establishing relative toxicity among metals in different media • BLM • FIAM • Sediment toxicity is reduced by acid volatile sulfides, organic carbon and other factors that bind free ions and decrease bioavailability • Soil toxicity is affected by pH, CEC, and % organic matter

  38. Ecological • Inorganic metal compounds rarely biomagnify across three or more trophic levels • Effects addition models are a useful first approximation of acute toxicity of metal mixtures • Critical body or tissue residues can be used for effects estimations but few data are available for metals

  39. Web Sites • Metals Framework, January, 2007 http://? • Issue papers August 2004 http://cfpub2.epa.gov/ncea/cfm/recordisplay.cfm?deid=86119

  40. Core Technical Panel Co-leads: Anne Fairbrother ORD/NHEERL Randy Wentsel OW/OST Steering Committee: Bill Wood ORD/NCEA/RAF Steve Devito OEI/OIAA Alec McBride OSWER/OSW Dave Mount ORD/NHEERL Keith Sappington ORD/NCEA Pam Noyes ORD/NCEA/RAF Gary Bangs ORD/NCEA/RAF

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