publications > paper > binding of mercury(II) to dissolved organic matter
Binding of Mercury(II) to Dissolved Organic Matter: The Role of the Mercury-to-DOM Concentration RatioMarkus Haitzer, *, **, *** U.S. Geological Survey, Water Resources Division, 3215 Marine Street, Boulder, Colorado 80303, and
Abstract | Figures | Tables | Bibliography The binding of Hg(II) to dissolved organic matter (DOM; hydrophobic acids isolated from the Florida Everglades by XAD-8 resin) was measured at a wide range of Hg-to-DOM concentration ratios using an equilibrium dialysis ligand exchange method. Conditional distribution coefficients (KDOM') determined by this method were strongly affected by the Hg/DOM concentration ratio. At Hg/DOM ratios below approximately 1 µg of Hg/mg of DOM, we observed very strong interactions (KDOM' = 1023.2±1.0 L kg-1 at pH = 7.0 and I = 0.1), indicative of mercury-thiol bonds. Hg/DOM ratios above approximately 10 µg of Hg/mg of DOM, as used in most studies that have determined Hg-DOM binding constants, gave much lower KDOM' values (1010.7±1.0 L kg-1 at pH = 4.9-5.6 and I = 0.1), consistent with Hg binding mainly to oxygen functional groups. These results suggest that the binding of Hg to DOM under natural conditions (very low Hg/DOM ratios) is controlled by a small fraction of DOM molecules containing a reactive thiol functional group. Therefore, Hg/DOM distribution coefficients used for modeling the biogeochemical behavior of Hg in natural systems need to be determined at low Hg/DOM ratios.
a Analyzed on dried samples and reported here on an ash-free basis. b The relative content of reduced sulfur was measured by sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy (27).
a (+) = good, (0) = fair, (-) = bad, (?) = not known. b Chelate formation with DOM is regarded more likely than formation of DOM-Hg-OH. c HgBrn is only competitive with HgDOM at low pH, where H+ competition decreases Hg-DOM binding but does not affect Hg-Br binding. d Based on number of literature values, agreement between data, and IUPAC recommendation.
a Overall binding constants. b Corrections for the experimental temperature of 22 °C using the van't Hoff equation are not significant. c IUPAC tentative recommendation (19). d IUPAC recommendation (19).
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* Corresponding author phone: 303 541 3009; fax: 303 447 2505; e-mail: mhaitzer@usgs.gov; address: U.S. Geological Survey, 3215 Marine Street, Boulder, CO 80303. Related information: SOFIA Project: Interactions of Mercury with Dissolved Organic Carbon in the Florida Everglades
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