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• June 18, 2008

The Superfund Basic Research Program (SBRP), in collaboration with the Environmental Protection Agency (EPA) Technology Innovation Program, presents the 2008 edition of Risk e Learning: "Bioavailability - Metals, Organics, and Use at Hazardous Waste Sites". This series of online seminars focuses on the science and policy issues of incorporating bioavailability into risk and exposure assessments. Largely drawing from the successful SBRP Bioavailability Workshop: "Assessing Bioavailability as a Determinant of Pollutant Exposure" held in Tampa, FL (February 2008), the web seminar series features SBRP-funded and other academic researchers and EPA senior staff. The first seminar "Bioavailability of Metals" was May 28th, the second seminar "Bioavailability of Organic Compounds: Methods and Case Studies" was June 11th, and the third seminar "Use of Bioavailability Information at hazardous Waste Sites" is June 18th.

This, the third of the three sessions, will feature Mr. Mike Beringer, U.S. EPA Region VII toxicologist, and Dr. Mark Maddaloni, U.S. EPA Region II toxicologist.

Site-specific bioavailability is an important consideration in determining potential threats to human health that are posed by metals-contaminated soils at waste sites. It is important to consider bioavailability because metals may be absorbed to a lesser or greater extent following ingestion of contaminated soils as compared to the fraction absorbed in the studies used to establish toxicity values, such as a reference dose or a cancer slope factor. U.S. EPA's Office of Superfund Remediation and Technology Innovation (OSRTI) has led an effort to develop guidance on evaluating and incorporating bioavailability adjustments into human health risk assessments. The guidance outlines a decision framework for deciding when to collect and incorporate site-specific bioavailability information; recommends a process for documenting the data collection, analysis, and site-specific implementation of a validated method; as well as provides recommended method validation and regulatory acceptance criteria for evaluating alternative methodologies. OSRTI has used these criteria to evaluate two separate methodologies for predicting the relative bioavailability of lead in soil and soil-like materials. OSRTI has determined that both an in vivo swine bioavailability bioassay and an in vitro bioaccessibility assay have sufficiently satisfied these criteria. Thus, they are considered regulatory methodologies appropriate for determining the relative bioavailability of lead for quantitative use in site-specific risk assessments. Mr. Beringer's presentation will summarize the bioavailability guidance document and the basis for OSRTI's decision regarding the two methodologies for predicting lead relative bioavailability.

EPA's bioavailability guidance provides a framework for using bioavailability/bioaccessibility data to inform and refine site specific risk assessments. In the case of lead, which benefits from well-characterized studies on the absorption of this metal when bound to soil, the guidance is highly prescriptive. For many other metals that have limited characterization of their absorption profiles, the guidance is more open to interpretation. The bioavailability guidance will be "test driven" so to speak in a situation where the roadmap is less detailed. In this presentation Dr. Maddaloni will go over a case study involving a RCRA Corrective Action site with arsenic-contaminated soil.

The session will be moderated by Dr. Fred Pfaender, Professor of Environmental Microbiology, Environmental Sciences and Engineering, and Public Health.

• Mr. Mike Beringer, U.S. EPA Region VII toxicologist (beringer.michael@epa.gov)
• Dr. Mark Maddaloni, U.S. EPA Region II toxicologist (maddaloni.mark@epa.gov)

• Dr. Fred Pfaender, Professor of Environmental Microbiology, Environmental Sciences and Engineering, and Public Health, University of North Carolina at Chapel Hill (gregdad@email.unc.edu)
• Justin Crane, MDB, Inc. (jcrane@michaeldbaker.com)

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