title: Binding of mercury(II) to aquatic humic substances: influence of pH and source of humic substances.
abstract: Conditional distribution coefficients (K(DOM')) for Hg(II) binding to seven dissolved organic matter (DOM) isolates were measured at environmentally relevant ratios of Hg(II) to DOM. The results show that K(DOM') values for different types of samples (humic acids, fulvic acids, hydrophobic acids) isolated from diverse aquatic environments were all within 1 order of magnitude (10(22.5 +/-1.0)-10(23.5 +/- 1.0)) L kg(-1)), suggesting similar Hg(ll) binding environments, presumably involving thiol groups, for the different isolates. K(DOM') values decreased at low pHs (4) compared to values at pH 7, indicating proton competition for the strong Hg(II) binding sites. Chemical modeling of Hg(II)-DOM binding at different pH values was consistent with bidentate binding of Hg(II) by one thiol group (pK(a) = 10.3) and one other group (pK(a) = 6.3) in the DOM, which is in agreement with recent results on the structure of Hg(II)-DOM bonds obtained by extended X-ray absorption fine structure spectroscopy (EXAFS).
authors.affiliation: Department of Civil, Environmental, and Architectural Engineering University of Colorado, Boulder, Colorado 80309, USA. mhaitzer@usgs.gov
authors.forename: Markus
authors.initials: M
authors.lastname: Haitzer
authors.forename: George R
authors.initials: GR
authors.lastname: Aiken
authors.forename: Joseph N
authors.initials: JN
authors.lastname: Ryan
mesh_terms: D004784:Environmental Monitoring; D006812:Humic Substances / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008628:Mercury / Q000737:chemistry*; D008956:Models, Chemical; D014873:Water Pollutants / Q000032:analysis
chemical_list: D006812:Humic Substances; D014873:Water Pollutants; D008628:Mercury