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Bioavailability of Contaminants in Soils and Sediments: Processes, Tools, and Applications
Next Steps in the Scientific Arena
Expansion of bioavailability considerations into risk assessment and remedial decision-making requires improved scientific understanding and models for a number of key bioavailability processes. Investment in mechanistic understanding and models will prove more profitable in the long-term than reliance on empirical knowledge because models have greater predictive power for a broader range of situations. As part of this research effort it will be important to draw ties between mechanistic understanding and more operational tests for bioavailability with studies that, for example, quantitatively examine both the form of a contaminant and its biological uptake. Other areas in need of attention include contaminant–solid interactions (especially the nature and effects of aging on contaminant release rates), the feeding ecology of animals, and how organisms bioaccumulate and transfer contaminants to their predators. Better understanding of whether and when associations between contaminants and soils and sediments can be made permanent should be a future research goal. The results from such research are needed before bioavailability explanations can be used with confidence to determine the amounts of soil and sediment to be remediated.
Much information on bioavailability of contaminants comes from industry-funded studies at specific sites, particularly for human health risk assessments. Such studies are usually, and understandably, not conducted in a way that advances understanding of fundamental underlying processes. Over the last decade, EPA has supported studies on mobility of chemicals in the environment, uptake relevant to assessing ecological risks, and bioavailability processes that might affect bioremediation. Yet despite this research investment, progress in understanding these bioavailability processes is limited. Unless a greater commitment is made to fund bioavailability studies from a research rather than industry-driven perspective, progress in developing information that can be used to advance human health and ecological risk assessments will be slow.