Carbon Isotope Fractionation of PCE and TCE During Dechlorination by Vitamin B12 |
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| Authors: | GF Slater B Sherwood Lollar S Lesage S Brown |
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| Institution: | Greg Slater;, Ph.D., is currently a Canada Research Chair nominee and assistant professor at McMaster University, whose interests are in the application of compound specific isotope analysis to understand the fate and transport of organic compounds in the environment. He has a B.Sc. in environmental chemistry and a Ph.D. in geology from the University of Toronto. Barbara Sherwood Lollar;, Ph.D., is a professor of geology and chemistry (in the field of stable isotope geochemistry) at the University of Toronto. Her research interests focus on the application of compound specific stable isotope analysis to constrain sources and fates of ground water contaminants. She has a B.A. from Harvard University, and a Ph.D. from the University of Waterloo. Suzanne;Lesage, Ph.D., is currently chief of the Groundwater Remediation Project of the Aquatic Ecosystem Management Research Branch, National Water Research Institute, Environment Canada, and is involved in the development and assessment of ground water and sediment remediation technologies. She is also an adjunct professor in the Botany Department at the University of Toronto. She has a B.Sc. in biochemistry from the University of Ottawa, and a Ph.D. in chemistry from McGill University. Susan Brown;has been a research technician in ground water remediation at the National Water Research Institute, Environment Canada, since 1990. She has a B.Sc. in biology and a B.A. in management economics from the University of Guelph, Ontario. |
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| Abstract: | Reductive dechlorination of perchloroethylene (PCE) and trichloroethylene (TCE) by vitamin B12 is an analogue of the microbial reductive dechlorination reaction and is presently being applied as a remediation technique. Stable carbon isotopic analysis, an effective and powerful tool for the investigation and monitoring of contaminant remediation, was used to characterize the isotopic effects of reductive dechlorination of PCE and TCE by vitamin B12 in laboratory microcosms. In laboratory experiments, 10 mg/L vitamin B12 degraded >90% of the initial 20 mg/L PCE with TCE, the primary product of PCE degradation, accounting for between 64% and 72% of the PCE degraded. In experiments with TCE, 147 mg/L vitamin B12 degraded >90% of the initial 20 mg/L TCE with cis -dichloroethene ( c DCE), the primary product of degradation accounting for between 30% and 35% of the TCE degraded. Degradation of both PCE and TCE exhibited first-order kinetics. Strong isotopic fractionation of the reactant PCE and of the reactant TCE was observed over the course of degradation. This fractionation could be described with a Rayleigh model using enrichment factors of ?16.5%o and ?15.8%o for PCE, and ?17.2%o and ?16.6%o for TCE. Fractionation was similar in all experiments, with a mean enrichment factor of ?16.5%o ± 0.6%o. The occurrence of such large enrichment factors indicates that isotopic analysis can be used to monitor the dechlorination of PCE and TCE by vitamin B12 and remediation of ground water plumes. Evidence indicates that isotopic fractionation is taking place during complexation of the chlorinated ethenes to vitamin B12, as has been suggested for reductive dechlorination by zero valent iron. The differences between e values for this reaction and those observed for anaerobic biodegradation of the chlorinated ethenes suggest that there may be differences in the rate-determining step for these two processes. |
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