Dichloroethene and Vinyl Chloride Degradation Potential in Wetland Sediments at Twin Lakes and Pen Branch, Savannah River National Laboratory, South Carolina
GEOLOGICAL SURVEY RESTON VA
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A series of 14C-radiotracer-based microcosm experiments was conducted to assess the mechanisms and products of degradation of dichloroethene DCE and vinyl chloride VC in wetland sediments at the Department of Energy DOE Savannah River National Laboratory. This project investigated the potential for biotic and abiotic DCE and VC degradation in wetland sediments from the Twin Lakes area of the C-BRP investigative unit and from the portion of Pen Branch located directly down gradient from the CMP investigative unit. Substantial degradation of 1,2-14C DCE and 1,2-14C VC to 14CO2 was observed in all viable sediment microcosms prepared under oxic conditions. These results indicate that microbial mineralization processes, involving direct oxidation or cometabolic oxidation, are the primary mechanisms of DCE and VC biodegradation in Twin Lake and Pen Branch sediments under oxic conditions. Substantial degradation of 1,2-14C DCE and 1,2-14C VC was observed in all viable sediment microcosms incubated under anoxic conditions. Production of 14CO2 was observed in all sediment microcosms under anoxic conditions. In general, the accumulation of mineralization products 14CO2 and 14CH4 was comparable to the accumulation of those reduced daughter products 14C-VC, 14C-ethene or 14C-ethane traditionally identified with chloroethene reductive dechlorination. These results indicate that microbial mineralization processes can be an important component of DCE and VC degradation in Twin Lake and Pen Branch sediments under anoxic conditions. These results demonstrate that an evaluation of the efficiency of in situ DCE and VC biodegradation in Twin Lakes and Pen Branch that is based solely on the observed accumulation of reduced daughter products may underestimate substantially the total extent of contaminant biodegradation and, thus, the contribution of biodegradation to overall contaminant attenuation.
- Organic Chemistry