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US EPA Framework for Metals Risk Assessment. Randall Wentsel, Ph.D. 7 September, 2011. Background. Problems PBT process is based on principles developed for organic substances that do not apply to metals PBT process lacks discriminatory power for metals BCF for metals – will be discussed

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us epa framework for metals risk assessment

US EPA Framework for Metals Risk Assessment

Randall Wentsel, Ph.D.

7 September, 2011

  • Problems
    • PBT process is based on principles developed for organic substances that do not apply to metals
    • PBT process lacks discriminatory power for metals
    • BCF for metals – will be discussed
  • The US EPA therefore initiated a process
    • to address issues associated with metals
    • to provide opportunities for external
    • input, peer review and cross-Agency involvement
  • Development of the Framework involved national and international experts in two workshops and five issue papers that supported the development of the document
  • US EPA was active with MERAG development in Europe attending workshops and reviewing documents
  • US EPA was active in Canadian Metals in the Human Environment Research Network
  • Co-sponsored a SETAC workshop on metals issues
  • Present key guiding principles based on the unique attributes of metals
  • Describe how metals-specific attributes and principles may then be applied in the context of existing US EPA risk assessment guidance and practices
  • Outline key metal principles and how they should be considered in existing human health and ecological risk assessment practices
  • Foster consistency across US EPA programs and regions
  • 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
  • Some metals are essential for maintaining proper health of humans, animals, plants, and microorganisms
  • 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
metals framework
Metals Framework
  • Utilized the ecological risk assessment process
  • Listed questions assessors should consider in the phases of risk assessment
  • Included chapters on
    • Introduction (bioavailability)
    • Environmental chemistry
    • Aquatic eco-risk assessment
    • Terrestrial eco-risk assessment
    • Human health
environmental issues in the framework
Environmental Issues in the Framework
  • Limited use of BAF/BCF
  • Incorporation of Bioavailability
  • Background
  • Toxicity – BLM; AVS-SEM
  • Secondary Poisoning
  • Environmental Chemistry
baf bcf issues
BAF/BCF Issues
  • Certain metal compounds are known to bioaccumulate in tissues and this bioaccumulation can be related to their toxicity
  • BCFs for metals vary with species, environmental

conditions, generally show an inverse relationship with media concentration, and are not a predictor of toxicity

  • For soil invertebrates and most plants, metal BAFs are typically less than 1 and usually are based on the total metal in soil and tissue that do not account for bioavailability differences
  • 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 metals
bioavailability issues
Bioavailability Issues
  • Bioavailability of metals and the associated risk vary widely according to the physical, chemical, and biological conditions under which an organism is exposed
  • Bioavailability should be explicitly incorporated into all risk assessments
  • Where data or models are insufficient, assumptions should be clearly articulated

Qualitative bioavailability of metal cations in natural soils to plants and soil invertebrates

epa s bioavailability committee
EPA's Bioavailability Committee
  • Initiated in March, 2007
  • Develops new guidance concerning site assessment and cleanup at hazardous waste sites
  • Evaluates new methods and supports site specific assessments
  • Identifies research needs to address data gaps relevant to contaminant bioavailability in soil site assessment activities
  • EPA’s Bioavailability Committee:
  • 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 owing to differences in geology, hydrology, anthropogenic and natural loads from “nontarget” sources, and other factors
  • It is recommended that, when appropriate, regional- or national- level ecological risk assessments be subdivided into metal-related ecoregions, referred to as metalloregions (McLaughlin and Smolders, 2001)
ecological toxicity
Ecological Toxicity
  • 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 – EPA Water Quality Criteria
    • 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
  • Al and Fe: soil chemistry vs toxicity database
secondary poisoning
Secondary Poisoning
  • Inorganic metal compounds rarely biomagnify across three or more trophic levels
  • Soil- Plant Barrier issues(Chaney, 1980, Chaney et al, 2000)
    • Can assume that most plant species do not bioconcentrate metals (i.e. <1)
    • Pb, As, Cr and Co are not taken up by plants in measurable quantities
  • Wildlife
    • Incidental soil ingestion is a proportionally more important pathway for herbivores than for carnivores or invertivores.
environmental chemistry
Environmental Chemistry
  • Metal speciation affects metal behavior in environmental media
  • pH and redox potential affect speciation
  • Kd values – a coefficient for mobility in soils
    • limited use of single values
  • Aging of metals in media reduces bioavailability
  • Metal sorption behavior affects


web sites
Web Sites
  • Metals Framework, March, 2007
  • Fairbrother et al., 2007. Ecotoxicology and Environmental Safety. 68: 145-227
  • EPA Ecological Soil Screening Levels
  • Issue papers August 2004:
    • risk assessment-metals.htm