XANES Spectroscopy Studies of Cr(VI) Reduction by Thiols in Organosulfur Compounds and Humic Substances

• Published in: Environmental science & technology Vol. 35; no. 6; pp. 1134 - 1141
• Main Authors: Szulczewski, Melanie D, Helmke, Philip A, Bleam, William F
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.03.2001
• Subjects: Applied sciences; Carcinogens, Environmental - analysis; Carcinogens, Environmental - chemistry; Chemicals; Chromium; Chromium - analysis; Chromium - chemistry; cysteine; Cysteine - chemistry; Decontamination. Miscellaneous; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; glutathione; Glutathione - chemistry; Humic Substances - chemistry; Hydrogen-Ion Concentration; Industry; Oxidation-Reduction; Pollution; Pollution, environment geology; Scientific imaging; Soil and sediments pollution; Soil Pollutants; Soils; Spectrum analysis; Sulfur - chemistry; thiols; Cysteine; Thiol; XANES spectrometry; Sulfur Organic compounds; In situ; Soil pollution; Heavy metal; Chemical reduction; Chromium III; Decontamination; Reaction mechanism; Humic acid; Chromium VI; Glutathione; Functional group
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es001301b

The reduction of Cr(VI) by the thiol-containing compounds cysteine and glutathione and by reduced sulfur in humic substances was monitored with sulfur and chromium X-ray absorption near-edge structure (XANES) spectroscopy in chromium-contaminated soils. Reaction of humic acids with Cr(VI) resulted in a reduction of the peak area of thiols and an increase in the peak area of disulfides in the sulfur XANES spectra. Analysis of the sulfur XANES spectra in various systems indicates that the reduction of Cr(VI) by humic substances involves a thiol/disulfide redox couple analogous to that of the Cr(VI) reduction by the simple thiol-containing compounds cysteine and glutathione. A fraction of the hexavalent chromium present in industrially-contaminated soils was not reducible by thiols. Reduction of Cr(VI) to Cr(III) in soils by thiols has little effect on the pH of the system in contrast to the pH decrease resulting from reduction by Fe(II).