| Abstract
| - The speciation of mercury(II) in the aquatic environmentis greatly affected by the presence of ligands capable offorming extremely strong complexes with Hg(II). In this study,a novel competitive ligand exchange (CLE) techniquewas used to characterize Hg(II)-complexing ligands insamples collected from three municipal wastewater treatmentplants, a eutrophic lake, a creek located downstream ofan abandoned mercury mine, and a model water containingdissolved Suwannee River humic acid. These samplescontained 3.3−15.9 mg/L dissolved organic carbon and wereamended with 1.0−1.7 nM Hg(II) for CLE analysis. Resultsindicated that all samples contained labile Hg(II)-complexing ligands with conditional stability constantssimilar to those of reduced sulfur-containing ligands. Twowastewater effluent samples also contained approximately0.5 nM of ligands that formed extremely strong Hg(II)complexes that did not dissociate in the presence ofcompeting ligands. The conditional stability constant ofthese extremely strong or nonlabile complexes (i.e., cKHgL)were estimated to be greater than 1030, for the reactionHg2+ + L‘ = HgL. The third wastewater sample and theeutrophic lake sample contained lower concentrations, 0.07−0.09 nM, of nonlabile Hg(II)-complexing ligands. Theresults suggested that these extremely strong Hg(II)-complexing ligands should account for most of the dissolvedHg(II) species in municipal wastewater effluent and maydominate Hg(II) speciation in effluent-receiving waters.
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