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Bacterial Mercury Methylation At The Sediment-Water Interface Of Mercury Contaminated Sediments
Citation:
Fimmen, R. L., R. Darlington, P. L. Lehocky, V. Lai, B. Sass, S. Chattopadhyay, AND P. RANDALL. Bacterial Mercury Methylation At The Sediment-Water Interface Of Mercury Contaminated Sediments. Presented at Battelle 10th International In Situ and On-Site Bioremediation Conference, Baltimore, MD, May 05 - 08, 2009.
Impact/Purpose:
Microcosm incubation studies were conducted to investigate the transformation of Hg to MeHg and the factors that affect MeHg production. Lake-sediments were used in the microcosm incubations to examine the influence of (1) an organic carbon amendment (as lactate) and (2) sulfate on the observed ORP and MeHg production.
Description:
Bench scale experiments were conducted to improve our understanding of bacterial mediation of mercury transformation (methylation), specifically those factors which govern the production of methyl mercury (MeHg) at the sediment-water interface. The greatest cause for concern regarding mercury contamination is bioaccumulation into higher trophic levels in aquatic food webs, from bacteria to plankton, micro- and macro-invertebrates, and ultimately to herbivorous and piscivorous fish. The dominant form of mercury in the fatty tissue of fish is MeHg, a potent mammalian neurotoxin even at very low concentrations. MeHg is formed mainly in suboxic and anoxic sediments by the interaction of inorganic Hg with organic matter and microorganisms. The conversion of Hg to MeHg is widely accepted to be governed by the action of sulfate reducing bacteria (SRB), which enzymatically catalyze the methylation of inorganic Hg. The exact mechanism of methylation is not known, but it is believed that during heterotrophic organic carbon metabolism, passive uptake of inorganic Hg occurs through the cell membrane of methylating bacteria. Due to the lack of information regarding the sedimentary biogeochemical conditions, which promote mercury methylation, microcosm incubation studies were conducted to investigate the transformation of Hg to MeHg and the factors that affect MeHg production. Microcosm incubations using lake-sediments were designed to examine the influence of (1) an organic carbon amendment (as lactate)and (2) sulfate on the observed oxidation-reduction potential (ORP) and MeHg production. Sediments used int his study were obtained from a site known to be impacted by mercury contamination. Incubations were analyzed for both the rate and extent of MeHg production. Methylation rates were estimated by analyzing MeHg and Hg after 48 hrs, 7 d , 10 d, 14 d, 28 d, and 42 d. The production of dissolved gases as a proxy for metabolic utilization of carbon substrate was also monitored. In all treatments amended with sulfate and SRB, MeHg (97 ng/g-sediment dry weight (DW)) was produced after only 48 hrs of incubation. MeHg concentrations then increased to 122 ng/g-sediment DW at day 28 of the incubation. The concentration of sedimentary MeHg, however, declined after 28 d to 110 ng/g-sediment DW.
URLs/Downloads:
Bacterial Mercury Methylation at the Sediment-Water Interface of Mercury Contaminated Sediments (PDF, NA pp, 150 KB, about PDF)Conference Program
