Title: Relative contributions of mercury bioavailability and microbial growth rate on net methylmercury production by anaerobic mixed cultures

Abstract

Monomethylmercury (MeHg) is produced in many aquatic environments by anaerobic microorganisms that take up and methylate inorganic forms of Hg(II). Net methylation of Hg(II) appears to be correlated with factors that affect the activity of the anaerobic microbial community and factors that increase the bioavailability of Hg(II) to these organisms. However, the relative importance of one versus the other is difficult to elucidate even though this information can greatly assist remediation efforts and risk assessments. Here in this study, we investigated the effects of Hg speciation (dissolved Hg and nanoparticulate HgS) and microbial activity on the net production of MeHg using two mixed microbial cultures that were enriched from marine sediments under sulfate reducing conditions. The cultures were amended with dissolved Hg (added as a dissolved nitrate salt) and nanoparticulate HgS, and grown under different carbon substrate concentrations. The results indicated that net mercury methylation was the highest for cultures incubated in the greatest carbon substrate concentration (60 mM) compared to incubations with less carbon (0.6 and 6 mM), regardless of the form of mercury amended. Net MeHg production in cultures exposed to HgS nanoparticles was significantly slower than in cultures exposed to dissolved Hg; however, the difference diminished withmore » slower growing cultures with low carbon addition (0.6 mM). The net Hg methylation rate was found to correlate with sulfate reduction rate in cultures exposed to dissolved Hg, while methylation rate was roughly constant for cultures exposed to nanoparticulate HgS. These results indicated a potential threshold of microbial productivity: below this point net MeHg production was limited by microbial activity, regardless of Hg bioavailability. Lastly, above this threshold of productivity, Hg speciation became a contributing factor towards net MeHg production.« less

Authors:

Kucharzyk, Katarzyna H. ^[1]; Deshusses, Marc A. ^[1]; Porter, Kaitlyn A. ^[1]; Hsu-Kim, Heileen ^[1]

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+ Show Author Affiliations

1. Duke Univ., Durham, NC (United States). Department of Civil and Environmental Engineering

Publication Date:

Fri Jul 17 00:00:00 EDT 2015

Research Org.:

Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1454936

Grant/Contract Number:  

SC0006937; SC0006938

Resource Type:

Accepted Manuscript

Journal Name:

Environmental Science: Processes & Impacts

Additional Journal Information:

Journal Volume: 17; Journal Issue: 9; Journal ID: ISSN 2050-7887

Publisher:

Royal Society of Chemistry

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; 59 BASIC BIOLOGICAL SCIENCES