HR: 0800h
AN: B11B-0398    [Abstracts]
TI: Importance of Sulfate-Reducing Bacterial Activity in Controlling Mercury Methylation in Anoxic Estuarine Sediment Slurries
AU: * Han, S
EM: s7han@ucsd.edu
AF: Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0202, United States
AU: Obraztsova, A
EM: obraztso@usc.edu
AF: Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0202, United States
AU: Obraztsova, A
EM: obraztso@usc.edu
AF: Department of Earth Science, University of Sourthern California, 3651 Trousdale Pkwy, Los Angeles, CA 90089-0740, United States
AU: Pretto, P
EM: patrizia.pretto@unipd.it
AF: Department of Histology, Microbiology and Medical Biotechnology, University of Padova, Via A. Gabelli 63, Padova, 35121, Italy
AU: Deheyn, D D
EM: ddeheyn@ucsd.edu
AF: Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0202, United States
AU: Gieskes, J
EM: jgieskes@ucsd.edu
AF: Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0202, United States
AU: Tebo, B M
EM: tebo@ebs.ogi.edu
AF: Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0202, United States
AU: Tebo, B M
EM: tebo@ebs.ogi.edu
AF: Department of Environmental and Biomolecular Systems, OGI School of Science & Engineering, Oregon Health & Science University, 20000 NW Walker Rd, Beaverton, OR 97006, United States
AB: Solution speciation of dissolved Hg has been considered an important factor controlling Hg methylation in anoxic sediments. Our previous research with sediments from the Venice Lagoon, Italy, however, has shown that the Hg methylation rate is affected by the activity of sulfate-reducing bacteria, which varies widely within the lagoon. To understand the role of sulfate-reducing bacterial activity in monomethylmercury (MMHg) production, we amended anoxic sediment slurries collected from Venice Lagoon with inorganic Hg and potential electron acceptors (sulfate or hydrous Fe(III) oxide) or metabolic byproducts of sulfate and Fe(III) reduction processes (sulfide or Fe(II)) and after 48h measured sulfate reduction rates, MMHg concentrations, and concentrations of dissolved Hg, Fe, sulfate, and sulfide. Addition of sulfide (final concentration: 0.2-6.3 mM) but not sulfate (final concentration: 29-54 mM) resulted in an exponential decrease in sulfate reduction rates and MMHg production with increasing concentrations of sulfide. These findings suggest that the negative relationship between dissolved sulfide and MMHg concentrations often found in freshwater and estuarine sediments can be caused by the decreased activity of sulfate-reducing bacteria. Addition of either Fe(II) (0-6.1 mM) or Fe(III) (0-3.5 mM) resulted in similar trends in MMHg production, an initial increase and subsequent decrease, as a function of added Fe, with a noticeable reduction in MMHg production in Fe(III)-amended slurries. Reduced Hg methylation in Fe(III)-amended slurries associated with the decrease in the sulfate reduction rate may be due to the enhanced activity of Fe(III)-reducing bacteria. Dissolved Hg concentrations in sulfide-, Fe(II)-, and Fe(III)-amended slurries were controlled mainly by FeS precipitation, which limits the availability of Hg for methylation in active sulfate-reducing slurries. Monomethylmercury production, however, was not correlated to the modeled concentrations of HgS⁰ and Hg(HS)₂⁰. Overall, our results suggest that the activity of sulfate-reducing bacteria and the availability of dissolved Hg are critical factors controlling MMHg production in anoxic estuarine sediments.
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0489 Trace element cycling (4875)
DE: 4875 Trace elements (0489)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting