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Methylmercury Formation in Mercury-Treated River Sediments During in situ Equilibration¹

ABSTRACT

An in situ experiment was established at two environmentally different river sites (one each on the Wisconsin and Fox rivers) to evaluate the extent of methylmercury (MeHg) production in and Hg loss from sediments treated with mercuric chloride (HgCl₂) or phenylmercuric acetate (PhHgAc). Bulk sediment was collected from each river site, treated with approximately 1, 10, or 100 ppm Hg (oven-dry basis) as HgCl₂ or PhHgAc, and returned to the river site with untreated controls for 2, 4, or 12 weeks of equilibration with the aquatic environment. After each sample retrieval, the sediments were analyzed for total Hg using an aqua regia digest and flameless atomic absorption spectrophotometry and for MeHg by gas chromatography using a modified extraction procedure which is described.

Results suggest that Hg losses from stationary sediments are minimal and that sediment transport is probably the major source of Hg movement in a river system. In both sediments, more MeHg was produced from PhHgAc than from a similar concentration of HgCl₂, and MeHg concentration increased as the Hg treatment with either compound was increased. The MeHg concentrations found in the Wisconsin River sediments were substantially higher than in the Fox River sediments with a similar Hg treatment. The large differences in MeHg production between these two sediments may be partially attributed to their chemical dissimilarities. The Wisconsin River sediment is acidic and contains more organic materials compared to the Fox River sediment which is more alkaline and contains larger amounts of sulfide sulfur.

Key Words: Mercury transformations • toxic elements • biological methylation

¹ Contribution from the Department of Soil Science, University of Wisconsin, Madison, WI 53706. Research supported by the College of Agricultural and Life Sciences, Univ. of Wis., Madison, and Wisconsin Dept. of Natural Resources (Project 133-8233). Presented before Div. A-5, Amer. Soc. Agron., 2 Nov. 1972, Miami Beach, Florida.

² Former Research Assistant and Associate Professor of Soil Science, respectively. The senior author is now Assistant Professor, Dept. of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824.

Received for publication June 8, 1973.