J. Phys. IV France 107 (2003) 573
DOI: 10.1051/jp4:20030368

Mercury methylation in mine wastes collected from abandoned mercury mines in the USA

J.E. Gray¹, M.E. Hines², H. Biester³ and B.K. Lasorsa<sup>4

1</sup>  U.S. Geological Survey, P.O. Box 25046, MS 973, Denver, CO 80225, U.S.A.
²  University of Massachusetts, Department of Biological Sciences, Lowell, MA 01854, U.S.A.
³  University of Heidelberg, Institute of Environmental Geochemistry, 69120 Heidelberg, Germany
⁴  Battelle Marine Sciences Laboratory, 1529 West Sequim Bay Road, Sequim, WA 98382, U.S.A.

Abstract
Speciation and transformation of Hg was studied in mine wastes collected from abandoned Hg mines at McDermitt, Nevada, and Terlingua, Texas, to evaluate formation of methyl-Hg, which is highly toxic. In these mine wastes, we measured total Hg and methyl-Hg contents, identified various Hg compounds using a pyrolysis technique, and determined rates of Hg methylation and methyl-Hg demethylation using isotopic-tracer methods. Mine wastes contain total Hg contents as high as 14000  /g and methyl-Hg concentrations as high as 88 ng/g. Mine wastes were found to contain variable amounts of cinnabar, metacinnabar, Hg salts, Hg°, and Hg° and Hg ²⁺ sorbed onto matrix particulates. Samples with Hg° and matrix-sorbed Hg generally contained significant methyl-Hg contents. Similarly, samples containing Hg° compounds generally produced significant Hg methylation rates, as much as 26%/day. Samples containing mostly cinnabar showed little or no Hg methylation. Mine wastes with high methyl-Hg contents generally showed low methyl-Hg demethylation, suggesting that Hg methylation was dominant. Methyl-Hg demethylation was by both oxidative and microbial pathways. The correspondence of mine wastes containing Hg° compounds and measured Hg methylation suggests that Hg° oxidizes to Hg ²⁺, which is subsequently bioavailable for microbial Hg methylation.

© EDP Sciences 2003