title: Formation of Mercury Sulfide from Hg(II)-Thiolate Complexes in Natural Organic Matter.
abstract: Methylmercury is the environmental form of neurotoxic mercury that is biomagnified in the food chain. Methylation rates are reduced when the metal is sequestered in crystalline mercury sulfides or bound to thiol groups in macromolecular natural organic matter. Mercury sulfide minerals are known to nucleate in anoxic zones, by reaction of the thiol-bound mercury with biogenic sulfide, but not in oxic environments. We present experimental evidence that mercury sulfide forms from thiol-bound mercury alone in aqueous dark systems in contact with air. The maximum amount of nanoparticulate mercury sulfide relative to thiol-bound mercury obtained by reacting dissolved mercury and soil organic matter matches that detected in the organic horizon of a contaminated soil situated downstream from Oak Ridge, TN, in the United States. The nearly identical ratios of the two forms of mercury in field and experimental systems suggest a common reaction mechanism for nucleating the mineral. We identified a chemical reaction mechanism that is thermodynamically favorable in which thiol-bound mercury polymerizes to mercury-sulfur clusters. The clusters form by elimination of sulfur from the thiol complexes via breaking of mercury-sulfur bonds as in an alkylation reaction. Addition of sulfide is not required. This nucleation mechanism provides one explanation for how mercury may be immobilized, and eventually sequestered, in oxygenated surface environments.
authors.affiliation: †ISTerre, Université Grenoble Alpes, CNRS, 38000 Grenoble, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Manceau
authors.affiliation: †ISTerre, Université Grenoble Alpes, CNRS, 38000 Grenoble, France.|‡Institut Néel, Université Grenoble Alpes, CNRS, 38000 Grenoble, France.
authors.forename: Cyprien
authors.initials: C
authors.lastname: Lemouchi
authors.affiliation: §Laboratoire Chrono Environnement, Université de Franche-Comté, CNRS, 25030 Besançon, France.
authors.forename: Mironel
authors.initials: M
authors.lastname: Enescu
authors.affiliation: ∥Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS, 2 Rue de la Houssinière, 44322 Nantes, France.
authors.forename: Anne-Claire
authors.initials: AC
authors.lastname: Gaillot
authors.affiliation: †ISTerre, Université Grenoble Alpes, CNRS, 38000 Grenoble, France.
authors.forename: Martine
authors.initials: M
authors.lastname: Lanson
authors.affiliation: †ISTerre, Université Grenoble Alpes, CNRS, 38000 Grenoble, France.
authors.forename: Valérie
authors.initials: V
authors.lastname: Magnin
authors.affiliation: ⊥European Synchrotron Radiation Facility (ESRF), 71 Rue des Martyrs, 38000 Grenoble, France.
authors.forename: Pieter
authors.initials: P
authors.lastname: Glatzel
authors.affiliation: #Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, 428 UCB, Boulder, Colorado 80309-0428, United States.|∇U.S. Geological Survey, 3215 Marine Street, Boulder, Colorado 80303, United States.
authors.forename: Brett A
authors.initials: BA
authors.lastname: Poulin
authors.affiliation: #Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, 428 UCB, Boulder, Colorado 80309-0428, United States.
authors.forename: Joseph N
authors.initials: JN
authors.lastname: Ryan
authors.affiliation: ∇U.S. Geological Survey, 3215 Marine Street, Boulder, Colorado 80303, United States.
authors.forename: George R
authors.initials: GR
authors.lastname: Aiken
authors.affiliation: ‡Institut Néel, Université Grenoble Alpes, CNRS, 38000 Grenoble, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Gautier-Luneau
authors.affiliation: @Department of Earth and Environmental Sciences, University of Illinois at Chicago, MC-186, 845 West Taylor Street, Chicago, Illinois 60607, United States.
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Nagy
mesh_terms: D008628:Mercury / Q000032:analysis*; D017669:Mercury Compounds / Q000032:analysis*; D008962:Models, Theoretical; D053758:Nanoparticles / Q000737:chemistry; D009930:Organic Chemicals / Q000737:chemistry*; D012987:Soil / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013455:Sulfur / Q000032:analysis; D013816:Thermodynamics; D014867:Water / Q000737:chemistry; D056928:X-Ray Absorption Spectroscopy
chemical_list: D017669:Mercury Compounds; D009930:Organic Chemicals; D012987:Soil; D013438:Sulfhydryl Compounds; D014867:Water; D013455:Sulfur; D008628:Mercury; C034211:cinnabar