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DEVELOPMENT OF AN ECOLOGICAL RISK ASSESSMENT METHODOLOGY FOR ASSESSING WILDLIFE EXPOSURE RISK ASSOCIATED WITH MERCURY-CONTAMINATED SEDIMENTS IN LAKE AND RIVER SYSTEMS
Citation:
KNIGHTES, C. D. AND R. B. AMBROSE. DEVELOPMENT OF AN ECOLOGICAL RISK ASSESSMENT METHODOLOGY FOR ASSESSING WILDLIFE EXPOSURE RISK ASSOCIATED WITH MERCURY-CONTAMINATED SEDIMENTS IN LAKE AND RIVER SYSTEMS. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-06/073 (NTIS PB2006-114098), 2006.
Impact/Purpose:
The objective of this task is to develop, support and transfer a wide variety of tools and mathematical models that can be used to support watershed and water quality protection programs in support of OW, OSWER, and the Regions.
Description:
Mercury is an important environmental contaminant with a complex chemistry cycle. The form of mercury entering an ecosystem from anthropogenic and natural sources is generally inorganic, while the environmentally relevant form is in the organic form, methylmercury. Therefore, the risk assessor is presented with several challenges in developing remediation strategies for a mercury contaminated river, lake, or pond. To assist with ecological risk assessments for mercury in these systems, a screening level tool was developed. First, the data requirements needed to develop such an assessment and to generally implement a fate and exposure model were specified and are provided herein. Second, a process-based, steady-state risk-assessment model, SERAFM (Spreadsheet-based Ecological Risk Assessment for the Fate of Mercury) was developed and is presented herein also. The SERAFM model (SERAFM) incorporates the chemical, physical, and biological processes governing mercury transport and fate in a surface water body including: atmospheric deposition; watershed mercury transport, transformations, and loadings; solid transport and cycling within the water body; and water body mercury fate and transport processes. SERAFM is comprised of a series of sub-modules that are linked together in series, so that each part is viewed as a building block within the general modeling framework. SERAFM estimates exposure mercury concentrations in the sediment, water column, and food web, and calculates hazard indices for exposed wildlife and humans. Because mercury risk assessments are complicated due to the different source types, that is, from historical loadings of mercury from current atmospheric deposition and watershed loadings, SERAFM simultaneously calculates exposure conditions for three different scenarios at any given site. These are: 1) the historical case of mercury-contaminated sediments; 2) suggested clean-up levels necessary to protect the most sensitive species, if possible; and 3) background conditions that would be present if there were no historical contamination. The sub-modules within SERAFM include: mercury loading (watershed and atmospheric deposition); abiotic and biotic solids balance (soil erosion, settling, burial, and resuspension); equilibrium partitioning; water body mercury transformation and transport processes; and wildlife risk calculations. The spreadsheet structure of SERAFM permits dismantling and reassembling of specific sub-modules to allow model flexibility and to maintain model transparency.