Interactions between dissolved organic matter and mercury in the Florida Everglades

Abstract

Experiments were conducted using organic matter isolated from various surface waters in the Florida Everglades to study the interactions between dissolved organic matter (DOM) and Hg(II). Conditional distribution coefficients (K DOM' ), obtained using an equilibrium dialysis ligand exchange method, were strongly affected by the Hg/DOM concentration ratio. Very strong interactions (K DOM' =10 23.2±0.5 L/kg), indicative of Hg-thiol bonds, were observed at Hg/DOM ratios below approximately 1 μgHg/mgDOM. Above approximately 10 μgHg/mgDOM much lower K DOM ' values (10 10.7±0.5 L/kg) were obtained. DOM-Hg interactions were also studied by HgS (log(K sp )=-52.4) dissolution and precipitation experiments. In the dissolution experiments, a significant amount of Hg was released from cinnabar in the presence of DOM, suggesting strong interactions. Conversely, precipitation of HgS was strongly inhibited in the presence of low concentrations (≤3 mgC/L) of DOM. In both the dissolution and precipitation experiments, organic matter rich in aromatic moieties was more reactive with HgS than less aromatic fractions and sulfur-containing model compounds. These results suggest that DOM can influence the geochemistry of inorganic complexes of Hg in the Everglades, especially HgS, by strong Hg-DOM binding and colloidal stabilization.