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Return to Project List Project Title: Bioavailability and Reactivity of Atmospheric Mercury in Surface Waters of the Great Lakes Region Synopsis: Mercury (Hg) is a mobile contaminant that accumulates in Great Lakes waters from anthropogenic sources. Until recently, it was widely believed that mercury was converted from organic to methyl mercury (MeHg) mostly after deposition from the atmosphere. However, recent measurements show that MeHg concentrations in rain are substantially higher than surface waters of the Lake Superior, and may therefore be a significant source to algae growing in surface waters and their dependant food web. The contribution of this atmospheric MeHg to aquatic food webs depends on the bioaviailability of MeHg after contact and equilibration with surficial lake water. If bioavailability is high, uptake may be almost instantaneous; if bioavailability is low, the impacts may be reduced by photodegradation and particle scavenging. Partitioning of inorganic Hg may be just as important because newly-deposited Hg(II) may be rapidly bound to particles that settle to known zones of methylation. The research objectives of this project include a quantitative assessment of: (1) The bioavailability of MeHg contained in wet and dry deposition in surface waters; In particular, the influence of both lake-water composition, and the constituents of wet and dry deposition, on atmospheric MeHg bioavailability (2) The reactivity of inorganic Hg(II) contained in wet and dry deposition in the surface waters; In particular, the potential influence of particle scavenging on selective transport of newly deposited atmospheric Hg(II) to zones of methylation. Chemicals Studied: Organic and inorganic mercury will be measured in both wet and dry deposition and the bioavailability of each form of mercury in the samples will be assessed. Geographic Areas: Samples will be taken at Devils Lake and Milwaukee, Wisconsin. Water samples will be obtained from Lake Michigan offshore of Milwaukee. The processes being studied (deposition and uptake by biota) are similar throughout the Great Lakes region and the results and implications will therefore be applicable to the region as a whole. Project Duration: Samples will be taken from summer of 2004 through fall of 2005. Laboratory experiments and analysis will continue until early 2006. Final results and reports will be available by summer of 2006. Methods Used: Our field and laboratory approach includes the collection of wet and dry deposition samples from urban, rural, and open water locations. We will use relevant dilutions of wet and dry deposition in lake water and measure Hg biouptake by a standard algal culture in laboratory experiments. Measurements of speciation and the partitioning behavior of mercury will be collected to assess the influence of mercury binding ligands and particles on the bioavailability and potential transport of Hg(II) to zones of methylation. Potential Results and Implications: This research will help identify key atmospheric
sources, pathways, and chemical speciation of Hg associated with increased
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