title: Mercury speciation in marine sediments under sulfate-limited conditions.
abstract: Sediment profiles of total mercury (Hg) and monomethylmercury (MMHg) were determined from a 30-m drill hole located north of Venice, Italy. While the sediment profile of total Hg concentration was fairly constant between 1 and 10 m, that of the MMHg concentration showed an unexpected peak at a depth of 6 m. Due to the limited sulfate content (<1 mM) at the depth of 6 m, we hypothesized that the methylation of inorganic Hg(II) at this depth is associated with the syntrophic processes occurring between methanogens and sulfidogens. To test this hypothesis, anoxic sediment slurries were prepared using buried Venice Lagoon sediments amended with HgCl(2), and we monitored MMHg concentration in sediment slurries over time under two geochemical conditions: high sulfate (1-16 mM) and limited sulfate concentrations (<100 microM). After day 52 and onward from the addition of inorganic Hg(II), the MMHg concentrations were higher in sulfate-limited slurries compared to high sulfate slurries, along with methane production in both slurries. On the basis of these results, we argue that active methylation of inorganic Hg(II) occurs under sulfate-limited conditions possibly by syntrophic processes occurring between methanogens and sulfidogens. The environmental significance of syntrophic Hg(II) methylation should be further studied.
authors.affiliation: Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0202, United States of America. shan@gist.ac.kr
authors.forename: Seunghee
authors.initials: S
authors.lastname: Han
authors.forename: Priya
authors.initials: P
authors.lastname: Narasingarao
authors.forename: Anna
authors.initials: A
authors.lastname: Obraztsova
authors.forename: Joris
authors.initials: J
authors.lastname: Gieskes
authors.forename: Aaron C
authors.initials: AC
authors.lastname: Hartmann
authors.forename: Bradley M
authors.initials: BM
authors.lastname: Tebo
authors.forename: Eric E
authors.initials: EE
authors.lastname: Allen
authors.forename: Dimitri D
authors.initials: DD
authors.lastname: Deheyn
mesh_terms: D019015:Geologic Sediments / Q000737:chemistry*; D017404:In Situ Hybridization, Fluorescence; D008628:Mercury / Q000032:analysis*; D012623:Seawater / Q000737:chemistry*; D013431:Sulfates / Q000737:chemistry*; D014871:Water Microbiology
chemical_list: D013431:Sulfates; D008628:Mercury