Bioavailability of Soil-borne Chemicals: A Regulatory Perspective

ABSTRACT

U.S. Environmental Protection Agency (USEPA) risk assessment guidance documents dating back to 1989 have articulated the principles for incorporating information on bioavailability into the risk assessment process. However, in the interim period both the methods for obtaining media or route specific measures of bioavailability and the corresponding guidance to incorporate these data have languished. Presently, USEPA is developing guidance to address both of these concerns. This article outlines the broad framework for systematically evaluating the role of bioavailability in site-specific risk assessment from a regulatory perspective. At the same time, in appreciation of the vast horizon of uncharted territory ahead, the focus of USEPA's draft guidance, and consequently this report, is on bioavailability adjustments for soil-borne metals. The article describes a two-stage process. The first stage outlines a paradigm for screening sites to determine if generating site-specific data on the bioavailability of a metal in soil is of technical utility and economically justifiable. The second stage focuses on the collection, analysis, and incorporation of these data into the risk assessment for decision-making purposes.

Keywords:

• metals
• soil
• bioavailability
• risk assessment
• regulatory decisions.

The regulatory perspective described herein is extracted from draft guidance currently under development by a USEPA workgroup on bioavailability. The workgroup is chaired by Mike Beringer (USEPA, Region 7) and receives technical support from Gary Diamond (Syracuse Research Corporation).

Notes

¹ Medium-specific absorption default values are currently available for lead; and medium-specific Reference Doses have been developed for cadmium and manganese.