Effect of dissolved organic matter source and character on microbial Hg methylation in Hg–S–DOM solutions
Dissolved organic matter (DOM) is a key component of fate and transport models for most metals, including mercury (Hg). Utilizing a suite of diverse DOM isolates, we demonstrated that DOM character, in addition to concentration, influences inorganic Hg (Hg(II)i) bioavailability to Hg-methylating bacteria. Using a model Hg-methylating bacterium, Desulfovibrio desulfuricansND132, we evaluated Hg-DOM-sulfide bioavailability in washed-cell assays at environmentally relevant Hg/DOM ratios (∼1–8 ng Hg/mg C) and sulfide concentrations (1–1000 μM). All tested DOM isolates significantly enhanced Hg methylation above DOM-free controls (from ∼2 to >20-fold for 20 mg C/L DOM solutions), but high molecular weight/highly aromatic DOM isolates and/or those with high sulfur content were particularly effective at enhancing Hg methylation. Because these experiments were conducted under conditions of predicted supersaturation with respect to metacinnabar (β-HgS(s)), we attribute the DOM-dependent enhancement of Hg(II)i bioavailability to steric and specific chemical (e.g., DOM thiols) inhibition of β-HgS(s) growth and aggregation by DOM. Experiments examining the role of DOM across a wide sulfide gradient revealed that DOM only enhances Hg methylation under fairly low sulfide conditions (≲30 μM), conditions that favor HgS nanoparticle/cluster formation relative to dissolved HgS species.
Citation Information
Publication Year | 2013 |
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Title | Effect of dissolved organic matter source and character on microbial Hg methylation in Hg–S–DOM solutions |
DOI | 10.1021/es400414a |
Authors | Andrew M. Graham, George R. Aiken, Cynthia Gilmour |
Publication Type | Article |
Publication Subtype | Journal Article |
Series Title | Environmental Science & Technology |
Index ID | 70189563 |
Record Source | USGS Publications Warehouse |
USGS Organization | National Research Program - Central Branch |