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Sulfide Controls on Mercury Speciation and Bioavailability to Methylating Bacteria in Sediment Pore Waters

Addition/Correction

Janina M. Benoit,*^†^‡ Cynthia C. Gilmour,^† Robert P. Mason,^‡ and Andrew Heyes^†

The Academy of Natural Sciences, Estuarine Research Center, 10545 Mackall Road, St. Leonard, Maryland 20685, and The University of Maryland, Center for Environmental and Estuarine Studies, Chesapeake Biological Laboratory, P.O. Box 38, Solomons, Maryland 20688

Environ. Sci. Technol., 1999, 33 (6), pp 951–957

DOI: 10.1021/es9808200

Publication Date (Web): February 3, 1999

Corresponding author e-mail: benoit@acnatsci.org; phone: (410)586-9700; fax: (410)586-9705.

†

The Academy of Natural Sciences.

‡

The University of Maryland.

Abstract

A chemical equilibrium model for Hg complexation in sediments with sulfidic pore waters is presented. The purpose of the model was to explain observed relationships between pore water sulfide, dissolved inorganic Hg (Hg_D), and bulk methylmercury (MeHg) in surficial sediments of two biogeochemically different ecosystems, the Florida Everglades and Patuxent River, MD. The model was constructed to test the hypothesis that the availability of Hg for methylation in sediments is a function of the concentration of neutral dissolved Hg complexes rather than Hg²⁺ or total Hg_D. The model included interaction of mercury with solids containing one or two sulfide groups, and it was able to reproduce observed Hg_D and bulk MeHg trends in the two ecosystems. The model is consistent with HgS⁰ as the dominant neutral Hg complex and the form of Hg accumulated by methylating bacteria in sulfidic pore waters. The model-estimated decline in HgS⁰ with increasing sulfide was consistent with the observed decline in bulk sediments MeHg. Since bacterial Hg uptake rate is one of the factors affecting methylation rate, Hg complexation models such as the one presented are helpful in understanding the factors that control MeHg production and accumulation in aquatic ecosystems.

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