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 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

Collaboration 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

Purpose 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

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

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

Principles Unlike organic chemicals, metals are neither

created nor destroyed by biological or chemical processesthey 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 metalthe form of the metal or metal compoundthe organism’s ability to regulate and/or

store the metal

Metals FrameworkUtilized the ecological risk assessment

processListed questions assessors should

consider in the phases of risk assessmentIncluded chapters on

Introduction (bioavailability)Environmental chemistryAquatic eco-risk assessmentTerrestrial eco-risk assessment Human health

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 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 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

Soil pH

Soil Organic Matter

Low organic matter

(<2%)

Medium organic matter

(2 to 6%)

Highorganic matter

(6 to 10%)4 < Soil pH < 5.5 Very high High Medium

5.5 < Soil pH < 7 High Medium Low7 < Soil pH < 8.5 Medium Low Very low

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

EPA's Bioavailability Committee Initiated in March, 2007Develops 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: http://www.epa.gov/superfund/health/contaminants/bioavailability/trw.htm

BackgroundBackground 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 ToxicityFor most metals, the free ionic form is most

responsible for toxicityFree-ion activity models are useful for establishing

relative toxicity among metals in different mediaBLM – EPA Water Quality CriteriaFIAM

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 PoisoningInorganic metal compounds rarely biomagnify

across three or more trophic levelsSoil- 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 quantitiesWildlife

Incidental soil ingestion is a proportionally more important pathway for herbivores than for carnivores or invertivores.

Environmental Chemistry Metal speciation affects metal behavior in

environmental media

pH and redox potential affect speciation

Kd values – a coefficient for mobility in soilslimited use of single values

Aging of metals in media reduces bioavailability

Metal sorption behavior affects bioavailability

Metals Framework, March, 2007 http://www.epa.gov/raf/metalsframework

Fairbrother et al., 2007. Ecotoxicology and Environmental Safety. 68: 145-227

EPA Ecological Soil Screening Levels epa.gov/ecotox/ecossl/

Issue papers August 2004: epa.gov/raf/publications/paper risk

assessment-metals.htm

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