DoD is responsible for the management of thousands of sites with organic compounds and metals contamination in soils and sediments. The current regulatory paradigm for characterizing the level of contamination in soils and sediments, for the most part, does not include measures of the actual bioavailability of these contaminants to human or ecological receptors. There is a growing body of evidence, however, that suggests that some of these contaminants are less available to cause harm to humans or ecological receptors than is suggested by extrapolating effects based on total soil or sediment concentration measurements. As a result, cleanup levels expressed as bulk soils or sediment concentrations may not correlate with actual risks.

Physical and chemical sequestration processes can reduce the potential for exposure and uptake by living organisms. These changes in bioaccessibility and bioavailability, however, are in most cases not addressed when setting risk-based cleanup criteria. Providing explicit assessments of contaminant bioavailability can result in setting more technically defensible cleanup goals. Such assessments also can establish more realistic cleanup priorities, while still ensuring protection of human health and the environment. Though there is increasing interest in incorporating site-specific bioavailability measurements into site management decisions, many of the methods being considered have not undergone critical review or validation.

SERDP and ESTCP convened a workshop in 2008, Research and Development Needs for Understanding and Assessing the Bioavailability of Contaminants in Soils and Sediments, to determine future research and demonstration needs in the area of bioavailability and its use in the risk-based remedial decision-making process at DoD sites. Specific objectives included the following:

• Examine the current state of the science and technology for understanding and assessing bioavailability processes in soils and sediments that may affect risk-based remedial action decisions
• Evaluate current and potential future applications of bioavailability concepts and assess barriers to their implementation
• Identify and prioritize research and demonstration opportunities that, if addressed, can facilitate regulatory acceptance and field implementation of bioavailability concepts to support risk assessments at DoD sites.

Research and demonstration efforts on bioavailability focus on either upland soil or aquatic sediment issues. Exposure pathways and contaminants of concern differ depending on whether soil or sediment is contaminated. Of the many research needs identified in the 2008 Workshop, SERDP and ESTCP efforts are focused on addressing critical research issues, including:

• Improving the understanding of the bioavailability of metals in aquatic sediments through improved tools and techniques to assess site-specific bioavailability of metals in sediments, and through the development of improved modeling methods for predicting metal availability and benthic toxicity in oxic sediments.
• Improving the understanding of the impact of contaminant bioavailability in aquatic sediments on higher trophic level organisms, including the uptake, assimilation, and efflux of metals in benthic organisms and fish that prey on benthic organisms. Also, improving understanding of PCB uptake, accumulation, and biomagnification through the food chain.
• Developing a better understanding of the mechanism and permanence of the binding of contaminants to upland soil components.
• Determining how bioavailability over time is affected by key biological and chemical processes in upland soils.

As these research efforts mature, the knowledge gained can be used in setting more technically defensible cleanup goals and establishing more realistic cleanup priorities, while still ensuring the protection of human health and the environment. An improved understanding of bioavailability issues will increase the confidence levels of the site managers to incorporate site-specific bioavailability measurements into site management decisions.