Mercury(II) Sorption to Two Florida Everglades Peats: Evidence for Strong and Weak Binding and Competition by Dissolved Organic Matter Released from the Peat

Environ. Sci. Technol., 36 (19), 4058 -4064, 2002. 10.1021/es0114005 S0013-936X(01)01400-6
Web Release Date: August 29, 2002

Mercury(II) Sorption to Two Florida Everglades Peats: Evidence for Strong and Weak Binding and Competition by Dissolved Organic Matter Released from the Peat

R. Todd Drexel, Markus Haitzer, Joseph N. Ryan,* George R. Aiken, and Kathryn L. Nagy

Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, Colorado 80309-0428, U.S. Geological Survey, Water Resources Division, 3215 Marine Street, Boulder, Colorado 80303, and Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309

Received for review November 2, 2001

Revised manuscript received June 12, 2002

Accepted June 13, 2002

Abstract:

The binding of mercury(II) to two peats from Florida Everglades sites with different rates of mercury methylation was measured at pH 6.0 and 0.01 M ionic strength. The mercury(II) sorption isotherms, measured over a total mercury(II) range of 10^-^7.4 to 10^-^3.7 M, showed the competition for mercury(II) between the peat and dissolved organic matter released from the peat and the existence of strong and weak binding sites for mercury(II). Binding was portrayed by a model accounting for strong and weak sites on both the peat and the released DOM. The conditional binding constants (for which the ligand concentration was set as the concentration of reduced sulfur in the organic matter as measured by X-ray absorption near-edge structure spectroscopy) determined for the strong sites on the two peats were similar (K_peat,s = 10^21.8±0.1 and 10^22.0±0.1 M^-¹), but less than those determined for the DOM strong sites (K_dom,s = 10^22.8^±^0.1 and 10^23.2^±^0.1 M^-¹), resulting in mercury(II) binding by the DOM at low mercury(II) concentrations. The magnitude of the strong site binding constant is indicative of mercury(II) interaction with organic thiol functional groups. The conditional binding constants determined for the weak peat sites (K_peat,w = 10^11.5^±^0.1 and 10^11.8^±^0.1 M^-¹) and weak DOM sites (K_dom,w = 10^8.7^±^3.0 and 10^7.3^±^4.5 M^-¹) were indicative of mercury(II) interaction with carboxyl and phenol functional groups.

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