HR: 0800h
AN: B11B-0412    [Abstracts]
TI: Competitive binding between mercury and copper for reduced sulfur binding sites on dissolved organic matter from the Florida Everglades
AU: * Gerbig, C A
EM: chase.gerbig@colorado.edu
AF: Univ of Colorado, Dept of Civil, Environmental and Arechitectural Engineering, Boulder, CO 80309-0428, United States
AU: Aiken, G R
EM: graiken@usgs.gov
AF: US Geological Survey, 3215 Marine Street, Boulder, CO 80303, United States
AU: Ryan, J N
EM: joe.ryan@colorado.edu
AF: Univ of Colorado, Dept of Civil, Environmental and Arechitectural Engineering, Boulder, CO 80309-0428, United States
AB: The interaction of mercury and dissolved organic matter (DOM) strongly influences the biogeochemistry of mercury in the Florida Everglades. Previous laboratory-based studies of simple systems at environmentally relevant concentrations of mercury(II) (a soft Lewis acid) and DOM found strong conditional binding constants (log K_HgL' = 28-31). These large constants result from the interaction of mercury(II) with reduced sulfur (a soft Lewis base) sites on DOM. Reported conditional binding constants for other metals with DOM (e.g. log K_CuL' = 11-14), suggest that metals of borderline Lewis acidity would not compete with mercury(II) for the strongest binding sites at environmentally relevant concentrations. However, the small proportion of strong binding sites responsible for mercury(II) binding have proven to be susceptible to competitive effects from borderline metals. Equilibrium dialysis experiments using organic matter isolated from the Florida Everglades were designed to determine the effects of competitive binding between copper(II) and mercury(II) on DOM binding sites. These experiments demonstrated that copper(II), a borderline Lewis acid, effectively competed for strong DOM sites at concentrations only 1-2 orders of magnitude greater than experimental mercury(II) concentrations (which ranged from 0.05 to 0.2nM). Our results indicate that the reduced sulfur sites responsible for Hg(II) binding on DOM also have high affinities for borderline metals. Interactions of copper(II) and DOM were also investigated in the absence of mercury(II). These results further substantiate the significance of a small concentration of strong binding sites on DOM. At low copper(II) to DOM ratios, preliminary results indicate that the binding interactions between copper(II) and DOM are significantly greater than previously reported and are close to those measured for DOM-mercury(II) binding. We conclude that currently available binding constants for metals of interest (borderline Lewis acids) are inadequate for assessing competitive effects with mercury(II)-DOM binding at low metal to DOM ratios. In the environment, copper(II) may be found at concentrations several orders of magnitude greater than mercury(II) concentrations and the concentration of copper(II) may significantly exceed the concentration of strong binding sites on DOM. Potential competition between mercury and borderline metals may influence mercury speciation and significantly affect the biogeochemical modeling of mercury in aquatic systems.
DE: 0400 BIOGEOSCIENCES
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0461 Metals
DE: 0489 Trace element cycling (4875)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting