title: Effect of dissolved organic matter source and character on microbial Hg methylation in Hg-S-DOM solutions.
abstract: 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 desulfuricans ND132, 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.
authors: Department of Chemistry, Grinnell College, Noyce Science Center, 1116 Eighth Avenue, Grinnell, Iowa 50112-1690, United States. grahaman@grinnell.edu
authors: Andrew M
authors: AM
authors: Graham
authors: George R
authors: GR
authors: Aiken
authors: Cynthia C
authors: CC
authors: Gilmour
mesh_terms: D045285:Desulfovibrio desulfuricans / Q000378:metabolism*; D017753:Ecosystem; D006812:Humic Substances; D008628:Mercury / Q000378:metabolism* / Q000493:pharmacokinetics; D008745:Methylation; D053758:Nanoparticles / Q000737:chemistry; D013440:Sulfides / Q000737:chemistry
chemical_list: D006812:Humic Substances; D013440:Sulfides; D008628:Mercury