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THE REDUCTIVE TRANSFORMATION OF PERCHLORATE IN A FRESH WATER SEDIMENT: LABORATORY BATCH STUDIES
Citation:
Simon, R. AND E J. Weber. THE REDUCTIVE TRANSFORMATION OF PERCHLORATE IN A FRESH WATER SEDIMENT: LABORATORY BATCH STUDIES. Presented at 20th Annual Society of Environmental Toxicology and Chemistry Meeting, Philadelphia, PA, November 14-18, 1999.
Description:
Perchlorate is widely used as a propellant in solid rocket fuel, and has recently been found in ground, surface, and drinking water, in many cases above the interim action level of 18 ppb. Perchlorate is recalcitrant to chemical reduction, however, studies of perchlorate in pure cell cultures and biotechnical systems have demonstrated that microbial reduction does occur. To determine if the reduction of perchlorate would occur under environmentally relevant conditions, laboratory batch experiments using local river sediment and associated site water have been conducted. Perchlorate and its reduction products (chlorate, chlorite, and chloride), as well as redox sensitive species, including nitrate, nitrite, ferrous iron, and sulfate, were measured as a function of time. Perchlorate was reduced to chloride quantitatively in lactate-amended Oconee River (OR) sediment slurries. The addition of lactate was necessary to induce reducing conditions sufficient for the reductive transformation of the perchlorate. Raising the initial concentration of perchlorate from 10 to 60 ppm increased the half-life of the parent compound from 4 to 11 days. At higher aqueous concentrations of perchlorate (100, 1000, and 10,000 ppm), the reduction of perchlorate was not observed, though the microbial activity as indicated by production of carbonate did not change significantly. We speculate that the higher concentrations of perchlorate were toxic to the nitrate-reducing bacteria thought to be responsible for the reduction of the perchlorate. Experimental evidence suggested that nitrate inhibits perchlorate reduction. The lag-phase for the reduction of perchlorate was increased from 2 to 15 days in an OR sediment that had been amended with 60 ppm sodium nitrate, though all of the nitrate had been reduced after four days. Furthermore, the lag-phase for the reduction of perchlorate decreased upon dosing OR sediment with perchlorate after the removal of the indigenous nitrate was observed.