Binding of mercury(II) to dissolved organic matter: The role of the mercury-to-DOM concentration ratio
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Abstract
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.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Binding of mercury(II) to dissolved organic matter: The role of the mercury-to-DOM concentration ratio |
| Series title | Environmental Science & Technology |
| DOI | 10.1021/es025699i |
| Volume | 36 |
| Issue | 16 |
| Year Published | 2002 |
| Language | English |
| Publisher | ACS |
| Contributing office(s) | Toxic Substances Hydrology Program |
| Description | 7 p. |
| First page | 3564 |
| Last page | 3570 |
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