HR: 17:15h
AN: B52F-06 INVITED     [PDF]
TI: Organic Sulfur Associated with Aquatic Humic Substances
AU: * Aiken, G
EM: graiken@usgs.gov
AF: U. S. Geological Survey, 3215 Marine Street, Boulder, CO 80303
AU: Vairavamurthy, M A
EM: vmurthy@bnl.gov
AF: Brookhaven National Laboratory, Energy Sciences and Technology Department, Upton, NY 11973
AU: Ravichandran, M
EM: ravi.ravichandran@amec.com
AF: AMEC Earth and Environmental, Inc, 1395 S. Marietta Parkway Bldg 300, Ste 210, Marietta, GA 30067
AB: This study examines the speciation and reactivity of organic sulfur associated with dissolved organic matter isolated from a variety of freshwater environments and the Pacific Ocean. The isolates, which included aquatic humic substances, were obtained using XAD resins and exhibited a wide range of elemental compositions, aromatic carbon contents, and molecular weights. Organic sulfur contents for the samples ranged from 0.4% to 1.9% of the atomic composition and were strongly dependent on the redox chemistry of the environments whence the samples originated, especially with regard to potential interactions with sulfide in sulfate reducing environments. The speciation of the sulfur associated with these samples was investigated using X-ray adsorption near edge spectroscopy (XANES). The samples, all obtained from oxic environments, contained reduced sulfur moieties. Reduced sulfur content (thiophene, organic sulfides and thiols) ranged from 22-70%. In general, humic acid fractions were found to have the largest percentage of reduced sulfur, followed by the fulvic acid and hydrophobic acid fractions. Hydrophilic fractions of the DOC contained a large percentage of oxidized organic sulfur (sulfonate and sulfate moieties). To assess the significance of reduced S content on interactions with soft metals, an environmentally significant process, the binding strength and binding capacity of Hg with organic matter isolated from the Florida Everglades were determined using equilibrium dialysis ligand exchange. Based on elemental analyses and XANES, the DOM sample from the Everglades used in our binding experiments had a reduced-S content of approximately 1.0%. Very strong interactions (K$_{DOM}$' = 10$^{23.2\pm0.5}$ L kg$^{-1}$) were observed at Hg/DOM ratios below approximately 1 $\mu$g Hg per mg DOM. Only a small fraction (approximately 2%) of the reduced-S groups were involved with the strongest interactions between Hg and DOM, suggesting that the binding of Hg to DOM under natural conditions (very low Hg/DOM ratios ranging from 0.01 to 10 ng of Hg/mg of DOM) is controlled by a small fraction of DOM molecules containing reactive sulfur functional groups.
DE: 0330 Geochemical cycles
DE: 0400 Biogeosciences
DE: 1045 Low-temperature geochemistry
DE: 1055 Organic geochemistry
DE: 1065 Trace elements (3670)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting