Microbial Methylmercury Production in Soil
Map of southwestern Alaska showing locations of three of the abandoned mercury mines: Red Devil, Cinnabar Creek, and Red Top. [Large version of study area map]
Mercury in the Terrestrial Environment at Abandoned Mercury Mines in Alaska
We compared mercury (Hg) concentrations, speciation, and distribution in vegetation (willow and alder) and soil samples collected from abandoned mercury mines and background sites in southwestern Alaska. Mine site samples were collected from areas that were surface mined. Tailings samples were taken from remaining material after mercury ore was processed by roasting or flotation. Retort samples were taken from undisturbed areas near the ore processing facilities. Background samples were collected from areas upstream from any mining activity and from areas nearby that have similar environmental characteristics but no Hg enrichment. Total Hg and methylmercury (MeHg) concentrations were greater in vegetation and soil samples from the mine and tailings sites compared to samples from the retort and background sites. There was no correlation between total Hg concentrations in vegetation and total Hg concentrations in soil or between total Hg and MeHg concentrations in vegetation or soil. However, the percent MeHg was greater in samples from the retort and background sites compared to samples from the mine sites and was greater in vegetation samples than in corresponding soil samples at all sites. The percent divalent Hg [Hg(II)] was also greater in soil samples from the retort and background areas. The greater proportions of reactive Hg species, such as Hg(II), in soils at these sites could explain the greater percent MeHg in vegetation and soil in samples from background sites. Reactive Hg species are more readily accumulated in vegetation and are more readily methylated than solid phases like HgS. In the surface mined and tailings areas Hg is mostly in the form of cinnabar (HgS). Mercury methylation rates in soils, determined by 203HgCl2 incubation experiments, were low overall (< 0.4%/day) but are higher in soil samples from the retort and background sites than in the mined or tailings areas.
Native (liquid) mercury (Hg) from the Cinnabar Creek mine. [Large version of mercury/cinnabar photo]
Abstracts, Presentations, and Posters for Professional Technical Meetings
Bailey, E.A., and Hines, M.E., 2003, Mercury in the terrestrial environment [abs.]: Sixth International Symposium on Environmental Geochemistry (ISEG), Edinburgh, Scotland, September 7-11, 2003. (Abstract and presentation)
Gray, J.E., and Bailey, E.A., 2003, The Southwestern Alaska Mercury Belt, in Gray, J.E., ed., Geologic Studies of Mercury by the U.S. Geological Survey, U.S. Geological Survey Circular 1248, p. 19-22. Available online at: http://pubs.usgs.gov/circ/2003/c1248/.
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