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bacterial demethylation of methylmercury in the south
florida ecosystem>
abstract
Methyl-Mercury Degradation Pathways:
A Comparison Among Three Mercury-Impacted Ecosystems
Mark Marvin-DiPasquale1*, Jennifer Agee1,
Chad McGowan1, Ronald S. Oremland1, Martha Thomas2,
David Krabbenhoft3 and Cynthia C. Gilmour4
Published in:
Environmental Science and Technology, 2000, Vol. 34, Pgs. 4908-4916
Click here for entire document
Abstract
We examined microbial methylmercury (MeHg) degradation in sediment of the Florida Everglades, Carson River (NV), and San Carlos Creek (CA), three freshwater environments that differ in the extent and type of mercury contamination, and
sediment biogeochemistry. Degradation rate constant (kdeg) values increased with total mercury (Hgt) contamination both among and within ecosystems. The highest kdeg’s (2.8-5.8 d-1
) were observed in San Carlos Creek, at acid mine drainage impacted sites immediately downstream of the former New Idria mercury mine, where Hgt ranged from 4.5-21.3 ppm (dry wt.). A reductive degradation pathway (presumably mer-detoxification) dominated degradation at these sites, as indicated by the nearly exclusive production of 14CH4 from 14C-MeHg, under both aerobic and anaerobic conditions.
At the upstream control site, and in the less contaminated ecosystems (e.g. the Everglades), kdeg’s were low
(£ 0.2 d-1) and oxidative demethylation (OD) dominated degradation, as evident from 14CO2
production. kdeg increased with microbial CH4 production, organic content and reduced sulfur in the Carson River system, and increased with decreasing pH in San Carlos Creek. OD associated CO
2 production increased with pore-water SO4-2 in Everglades samples, but was
not attributable to anaerobic methane oxidation, as has been previously proposed. This ecosystem comparison indicates that severely contaminated sediments tend to have microbial populations that actively degrade MeHg via mer-detoxification, whereas OD occurs in heavily contaminated sediments as well, but dominates in those less contaminated.
1U.S. Geological Survey, Water Resources Division / MS 480, 345 Middlefield Rd., Menlo Park, CA 94025
2University of California, Dept. of Environmental Toxicology, Santa Cruz, CA 95064
3U.S. Geological Survey, Water Resources Division, 8505 Research Way, Middleton, WI 53562
4The Academy of Natural Sciences, Estuarine Research Center, 0545 Mackall Rd., St. Leonard, MD 20685
* Corresponding Author, Phone: 650-329-4442, Fax: 650-329-4463, e-mail: mmarvin@usgs.gov
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