An Approach for Incorporating Information on Chemical Availability in Soils into Risk Assessment and Risk-Based Decision Making, Prepared by: The New England Environmentally Acceptable Endpoints Workgroup

Abstract

A regional workgroup comprised of individuals from regulatory agencies, universities, and consulting companies was formed to develop an approach for incorporating information on chemical availability in soils into risk assessment and riskbased decision making. The approach consists of the following decision framework for including information on chemical availability: (1) Determine the usefulness of incorporating information on bioavailability; (2) Identify information needs from a conceptual model of exposure for the site and from exposure pathways judged critical to the assessment; (3) Identify soil factors that affect bioavailability; (4) Determine the type or form of information (measures and/or models) that can be used within the risk assessment and risk management process; (5) Select methods (measures and/or models) based on the "weight of evidence" or strength of the bioavailability information they will provide and how that information will be used for risk assessment and risk-based decision making; (6) Incorporate information into the risk assessment and risk-based decision making. These factors can be integrated into existing risk-based approaches for site management such as Superfund, state approaches, and the ASTM Risk Based Corrective Action Process (RBCA). Consistent with risk assessment guidance, an assessment of chemical availability in soils must consider current as well as reasonably foreseeable conditions. The approach recognizes that information on chemical availability is contextual and depends on the receptor and pathway. Further, the value of information depends on how well it is accepted and/or validated for use in regulatory decision making. The workgroup identified four principles for selecting methods (measures and/or models) for obtaining information on chemical availability and for evaluating information on chemical availability for use in risk assessments: (1) soil-chemical relevance, (2) pathway relevance, (3) receptor relevance, and (4) acceptance of the method.

Differential Accumulation of Polychlorinated Biphenyl Congeners in the Terrestrial Food Web of the Kalamazoo River Superfund Site, Michigan

“…Taken together, these observations demonstrate that caution should be exercised when applying BSAFs across sites with greatly different PCB concentrations. Similar cautions have been raised in regards to the application of BSAFs from one site to another since there are potential differences in soil and sediment characteristics that may affect bioavailability (32).…”

Tenax extraction mimics benthic and terrestrial bioavailability of organic compounds

“…This so-called linear sorbed fraction has been shown to relate to biodegradation [5,6] and * To whom correspondence may be addressed (d.thulscher@riza.rws.minvenw.nl). also to uptake by organisms [7][8][9][10][11][12]. Since bioavailability seems to be strongly related to the way chemicals are sorbed in sediments and soils, a short overview of the recent insights in sorption mechanisms is presented below.…”

“…Recent research has indicated that it is not the total concentration of a chemical in sediment or soil that is relevant for its bioavailability, but the fraction that can desorb to the surrounding (pore) water within a few hours. This so‐called linear sorbed fraction has been shown to relate to biodegradation [5,6] and also to uptake by organisms [7–12]. Since bioavailability seems to be strongly related to the way chemicals are sorbed in sediments and soils, a short overview of the recent insights in sorption mechanisms is presented below.…”