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PT17 Assessment and Remediation of Mercury Contaminated Sites
(PT264) An assessment of mercury loads, sources, and potential for bioaccumulation in Oregon's Willamette Basin.
Rubin, J1, Mrazik, S1, Hamel, A1, Lut, A1, Johnson, Y1, Foster, E1, Hope, B1, 1 Oregon Department of Environmental Quality, Portland, OR, USA
ABSTRACT- There are currently multiple fish consumption advisories in Oregon′s Willamette Basin demonstrating that mercury is bioaccumulating in fish to levels that adversely affect public health. These advisories and the subsequent listing of the Willamette River on the State′s 303(d) list of impaired waterbodies necessitate the development of a Total Maximum Daily Load (TMDL) for mercury. One of the primary goals of the TMDL was to establish water column guidance values protective of the beneficial use of fish consumption. A basin-specific aquatic Food Web Model (FWM) was employed to bring regional specificity to estimates of mercury biomagnification and mercury guidance values. The FWM focused on resident fish species identified as species of concern, those occupying critical niches in the aquatic food web, or those of concern to stakeholders. The FWM considered the direct uptake of mercury from water, uptake through feeding, loss of the chemical via elimination, and dilution as a function of age. The model was repeatedly applied to organisms at each trophic level to simulate mercury transfer from primary and secondary producers, through a variety of intermediate fish species, to top level predacious fish. Probabilistic techniques were used to propagate stochastic variability and uncertainty throughout the model to provide a range of estimates for the mercury guidance values. The model was calibrated with fish tissue, sediment and surface water data from the Willamette Basin. An independent mass balance analysis of mercury inputs and outputs was also developed to determine the mass load of mercury at various locations along the river and to identify and quantify the potential sources of mercury contributing to this load. Mean estimates of relative source load contributions were developed for each source category considered in the analysis. These independent analyses were used to develop preliminary reduction targets for mercury sources in the Willamette Basin.
Key words: methylmercury, mercury, bioaccumulation, tmdl
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