X-ray absorption spectroscopic evidence for the complexation of Hg(II) by reduced sulfur in soil humic substances
- Kansas State Univ., Manhattan, KS (United States). Dept. of Agronomy
- Swedish Univ. of Agricultural Sciences, Umeaa (Sweden). Dept. of Forest Ecology
- Univ. of Wisconsin, Madison, WI (United States). Dept. of Soil Science
- Univ. of Minnesota, St. Paul, MN (United States). Dept. of Soil, Water, and Climate
Analysis of Hg(II) complexed by a soil humic acid (HA) using synchrotron-based X-ray absorption spectroscopy (XAS) revealed the importance of reduces sulfur functional groups (thiol (R-SH) and disulfide (R-SS-R)/disulfane (R-SSH)) in humic substances in the complexation of Hg(II). A two-coordinate binding environment with one oxygen atom and one sulfur atom at distances of 2.02 and 2.38 {angstrom}, respectively, was found in the first coordination shell of Hg(II) complexed by humic acid. Model calculations show that a second coordination sphere could contain one carbon atom and a second sulfur atom at 2.78 and 2.93 {angstrom}, respectively. This suggests that in addition to thiol S, disulfide/disulfane S may be involved with the complexation of Hg(II) in soil organic matter. The appearance of carbon atom in the second coordination shell suggests that one O-containing ligand such as carboxyl and phenol ligands rather than H{sub 2}O molecule is bound to the Hg(II). The involvement of oxygen ligand in addition to the reduced S ligands in the complexation of Hg(II) is due to the low density of reduced S ligands in humic substances. The XAS results from this experiment provided direct molecular level evidence for the preference of reduced S functional groups over oxygen ligands by Hg(II) in the complexation with humic substances.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- OSTI ID:
- 318714
- Journal Information:
- Environmental Science and Technology, Journal Name: Environmental Science and Technology Journal Issue: 2 Vol. 33; ISSN ESTHAG; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
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