Bioaccumulation factors (BAFs) are currently being used by the U.S. Environmental Protection Agency (U.S. EPA) to develop water quality criteria for the protection of wildlife and human health. The goal of this work was to calculate national default BAFs for methylmercury in freshwater (lenthic/lotic) and coastal (estuarine) environments and to determine if there are differences in the bioaccumulation of mercury between these different systems. GLEC devised a literature search strategy to obtain all pertinent literature since the early 1990s (i.e., since the employment of "ultra clean" techniques). GLEC then extracted all applicable data and used these data to derive BAFs for methylmercury. Calculations were based on the following approaches: 1) direct method - quotient of methylmercury in aquatic animals (trophic levels 2,3 and 4) to dissolved methylmercury in the water column, 2) indirect method - estimated as above by using a conversion factor to convert total dissolved mercury to dissolved methylmercury in the water column, and 3) a modification of the approach outlined in the Great Lakes Water Quality Initiative Technical Support Document (EPA-820-8-95-005). Methylmercury and total mercury forms were evaluated to determine which forms of mercury result in the best prediction of mercury accumulation. In addition to the BAFs, the partitioning of total mercury and methylmerury between the dissolved and particulate phase in the different systems were calculated using two approaches (direct dissolved fraction and derivation from KD and TSS). Data gaps were identified and the uncertainty associated with each default BAF estimate calculated.
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