more protective risk estimates, for example by refining a default relative bioavailability factor or identifying an important exposure pathway that was overlooked.

Consideration of bioavailability processes could also be used to improve evaluation of remediation technologies. For example, dredging is a common remediation technology applied to contaminated sediments. In certain cases, natural burial processes have isolated the contamination to the extent that contact between sensitive species and the contaminated matrix is not possible (a situation that can be evaluated through the use of coring studies). Dredging may promote the release of contaminants to the water column, possibly resulting in an increase in mobility and hence bioavailability. In such cases, decision-makers need to consider whether an increase in bioavailability is consistent with the goals of site remediation.

This chapter examines the developments needed in both science and decision-making approaches to promote better consideration of bioavailability processes in remediation and management of contaminated soil and sediment. The chapter examines limitations in our current understanding of bioavailability processes and their implications and what can be done to overcome these limitations. Scenarios in which consideration of bioavailability processes has the greatest potential to impact decision-making are identified, with the hope of focusing science and technology development efforts on these situations. The chapter concludes by recommending specific steps that can be taken to move forward with consideration of bioavailability processes at individual sites, in regulation and decision-making, and in scientific research.

CURRENT LIMITS OF KNOWLEDGE

As demonstrated in Chapter 3, bioavailability of contaminants in soils and sediments to human and ecological receptors is governed by a wide range of physical, chemical, and biological processes. Qualitative and quantitative understanding of some of these processes is substantial, but for other processes there is much to be learned. For example, there is much about contaminant–solid interactions that is only weakly understood. While conceptual models exist for many kinds of contaminant–solid interactions, tools to test these models are often inadequate or nonexistent. As a result, there is significant uncertainty in the models used to describe contaminant–solid interactions and in the parameter values employed in these models. As some description of contaminant–solid interaction will usually be needed for assessment of risk associated with contaminated soils and sediments, the model and parameter uncertainty will transfer directly to the exposure assessment in a risk analysis.

All models and parameters used in exposure assessment have a certain degree of uncertainty associated with them, including those used in bioavailability process considerations. In screening-level assessments for contaminated soils and sediments, this uncertainty is often recognized and dealt with by assuming



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