Anne%20Fairbrother,%20Randy%20Wentsel,%20Bill%20Wood,%20Keith%20Sappington,%20and%20Pam%20Noyes

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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

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Background

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

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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

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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

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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

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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

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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

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Schedule
Phase I Metals Action Plan Dec 2002
SAB Review
Phase II Issue Papers Aug 2004
Peer Review
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Schedule
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
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Metals and Metalloids of Primary Interest

• Aluminum
• Antimony
• Arsenic
• Barium
• Beryllium
• Boron
• Cadmium
• Chromium
• Cobalt
• Copper
• Iron
• Lead

• Manganese
• Mercury (inorganic)
• Molybdenum
• Nickel
• Selenium
• Silver
• Strontium
• Tin
• Thallium
• Vanadium
• Zinc

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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

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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

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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

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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.

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Natural occurrence of barite
Natural occurrence of barite (USGS)
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Principles

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

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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 organisms ability to regulate and/or store
  the metal.

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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

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Conceptual Model for Metal Risk Assessments
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Assessment Questions

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

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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?

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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

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Bioavailability Issues

• Bioavailability of metals varies widely 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

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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

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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)

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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.

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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

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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

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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 metals kinetics
• Both the exposure route and the form of a metal
  can affect the metals carcinogenic potential and
  its noncancer effects
• Sensitivity to metals varies with age, sex,
  pregnancy status, nutritional status, and genetics

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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

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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

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Essentiality and Toxicity
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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

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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

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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

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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

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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

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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

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Web Sites

• Metals Framework, January, 2007
• http//?
• Issue papers August 2004
• http//cfpub2.epa.gov/ncea/cfm/recordisplay.cfm?de
  id86119

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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