HR: 14:40h
AN: B13F-04    [Abstracts]
TI: The Role of Dissolved Organic Matter in Environmental Mercury Methylation by Sulfate- Reducing Bacteria
AU: * Moreau, J W
EM: jwmoreau@usgs.gov
AF: Water Resources Division, United States Geological Survey, 8505 Research Way, Middleton, WI 53562, United States
AU: * Moreau, J W
EM: jwmoreau@usgs.gov
AF: Department of Geology and Geophysics, University of Wisconsin at Madison, 1215 W. Dayton St., Madison, WI 53706, United States
AU: Roden, E E
EM: eroden@geology.wisc.edu
AF: Department of Geology and Geophysics, University of Wisconsin at Madison, 1215 W. Dayton St., Madison, WI 53706, United States
AU: Gerbig, C
EM: gerbigca@gmail.com
AF: Department of Civil, Environmental and Architectural Engineering; University of Colorado at Boulder, Engineering Center ECOT 441, Boulder, CO 80309, United States
AU: Gerbig, C
EM: gerbigca@gmail.com
AF: Water Resources Division, United States Geological Survey, 3215 Marine Street, Boulder, CO 80303, United States
AU: Kim, C S
EM: cskim@chapman.edu
AF: Department of Physical Sciences, Chapman University, One University Drive, Orange, CA 92866, United States
AU: Aiken, G R
EM: graiken@usgs.gov
AF: Water Resources Division, United States Geological Survey, 3215 Marine Street, Boulder, CO 80303, United States
AU: DeWild, J F
EM: jfdewild@usgs.gov
AF: Water Resources Division, United States Geological Survey, 8505 Research Way, Middleton, WI 53562, United States
AU: Krabbenhoft, D P
EM: dpkrabbe@usgs.gov
AF: Water Resources Division, United States Geological Survey, 8505 Research Way, Middleton, WI 53562, United States
AU: Krabbenhoft, D P
EM: dpkrabbe@usgs.gov
AF: Department of Geology and Geophysics, University of Wisconsin at Madison, 1215 W. Dayton St., Madison, WI 53706, United States
AB: Methylmercury (MeHg) production in the environment is controlled by many factors, including biogeochemical controls on mercury bioavailability. Strong focus has been placed on the role of sulfide concentration in determining mercury speciation and cellular uptake. However, in natural waters, dissolved organic matter (DOM) is both ubiquitous and important in influencing mercury speciation and bioavailability. We revisit this issue with experimental results from methylation assays of sulfate-reducing bacteria with a pure culture, and through synchrotron-based characterization of mercury in simulated natural waters. Pure cultures of Desulfobulbus propionicus, a sulfate-reducing bacterium (SRB) capable of fermentative growth, were allowed to methylate a mercury isotopic tracer present at <100 ng/L and equilibrated with ~1 μM aqueous sulfide and ~40 mg/L DOM. Fermentative growth conditions allowed control over ambient sulfide concentrations to favor the predicted dominance of dissolved HgS⁰. The DOM used was a hydrophobic fraction isolated from Florida Everglades surface water. Results showed that 5-10% of the mercury isotopic tracer was methylated in both DOM-amended and DOM-free cultures. In DOM-amended cultures, 10-20% greater cell growth was observed, suggesting an apparent slower rate of methylation in DOM-free cultures and a beneficial contribution of DOM to cell growth. We note that as much as ~10% of ambient mercury associated with DOM was also methylated, possibly explaining the observed difference in methylation rates in terms of dilution of the total bioavailable mercury pool for DOM-amended cultures. Our observations suggest that, in some cases, DOM- partitioned mercury is subject to microbial methylation at environmentally significant rates. The nature of mercury- sulfide-DOM interaction was investigated in separate experiments. No precipitation was observed in solutions containing DOM and equimolar Hg²⁺ and aqueous sulfide at concentrations supersaturated with respect to metacinnabar. The equilibrated Hg-S-DOM solution was loaded on hydrophobic chromatography resin and subjected to 100 μM glutathione extraction. Spectra from DOM-partitioned mercury-sulfide exhibited high similarity to metacinnabar despite the absence of precipitation. Lower mercury concentrations and better resins are being tested in order to evaluate the role of DOM-associated nanoparticulate or colloidal metacinnabar in mercury bioavailability for methylation by SRB.
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0432 Contaminant and organic biogeochemistry (0792)
DE: 0448 Geomicrobiology
DE: 0461 Metals
DE: 0497 Wetlands (1890)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting