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Bioavailability of Contaminants in Soils and Sediments: Processes, Tools, and Applications
scientific evidence is adequate to apply the results within their community. Of the limited cases to date where communities have been presented with bioavailability information, the responses have ranged from strong support to acceptance to strong objection.
Because bioavailability processes for contaminated soils and sediments are inherently part of risk assessment, bioavailability does not present a unique risk communication problem. Thus, the public should be introduced to the concept of bioavailability as being a fundamental component of risk assessment no different from other exposure parameters or toxicity values. The technical components that should be part of any public communication program regarding bioavailability include (1) the factors that affect bioavailability from soils or sediments, (2) the concepts of absolute bioavailability and relative bioavailability, (3) the technical basis for the established toxicity values, (4) the selection of a model for bioavailability studies and why it was chosen, (5) how uncertainty was handled, and (6) how site-specific bioavailability information will be incorporated into the risk assessment. Finally, it should be acknowledged that rarely are bioavailability studies undertaken simply to improve the accuracy of a risk assessment. Rather they are performed to justify site cleanup goals that are more financially or technically feasible, and that involve leaving appreciable amounts of contaminant mass in place, while still being protective of public health and the environment.
Next Steps in the Regulatory Arena
The resistance in some regulatory domains to allowing site-specific measurements of some bioavailability processes to replace default assumptions stems from many factors, including uncertain methodologies and lack of validation, public anxiety and suspicion about motives, and lack of precedent. A viable way to move around these obstacles and achieve more widespread consideration of bioavailability processes in risk-based management of contaminated soils and sediments is to invoke an adaptive management approach, which embraces two ideas. The first is that there should be pilot studies to experiment with different tools and models. The second is that agencies should use the results from such efforts to develop a common systematic approach to determine how and when to incorporate bioavailability concepts into regulations in a consistent manner. Adaptive management concepts are not new, but rather are akin to the scientific method and engineering problem solving. An adaptive management example relevant to bioavailability is the approach recently recommended by EPA for determining the efficacy of dredging and how much PCB-contaminated sediment to dredge from the Hudson River. The plan involves evaluating risks over time and adjusting cleanup plans as performance monitoring data are acquired and analyzed.