Publication Date


Document Type


Committee Members

Amy Burgin (Committee Member), William Fitzgerald (Committee Member), Chad Hammerschmidt (Committee Chair)

Degree Name

Master of Science (MS)


Monomethylmercury (MMHg) is the toxic form of mercury (Hg) that biomagnifies in food webs, and human exposure to MMHg occurs predominantly via consumption of fish. The primary source of MMHg to the marine environment is thought to be in situ sedimentary production by benthic microorganisms, namely sulfate-reducing bacteria (SRB). I collected sediments from the continental shelf (stations 2 and 6) and slope (station 9) of the NW Atlantic Ocean, and amended them with various inhibitor and promoter solutions to target specific functional groups capable of Hg transformations. I also added stable enriched Hg isotopes to quantify gross Hg methylation and gross MMHg demethylation, which were detected with inductively couple plasma mass spectrometry (ICPMS). Hg isotope results suggest that biotic methylation accounted for at least 60% of gross Hg methylation and 0-40% of gross MMHg demethylation. Methanogens probably did not have a major role in MMHg production or demethylation at any of the stations. Iron-reducers (FeRB) were not primary Hg methylators, but iron-reduction (via a Fenton-like reaction) or Fe(III) limitation appear to have influenced MMHg demethylation. Nitrogen cyclers possibly were important in Hg methylation and MMHg demethylation may have been limited by nitrate. SRB were likely important producers of MMHg in nearly all of the sediments. Results of this study support previous research that SRB are important Hg methylators in sulfate-rich, marine environments. This study also highlights the potential importance of iron and nitrogen cycling in MMHg demethylation in marine sediments.

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Department or Program

Department of Earth and Environmental Sciences

Year Degree Awarded