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ENANTIOSELECTIVITY IN THE BIODEGRADATION OF PCB ATROPISOMERS
Citation:
Pakdeesusuk, U., C. M. Lee, D. L. Freedman, J. T. Coates, C S. Wong, W J. Jones, AND A W. Garrison. ENANTIOSELECTIVITY IN THE BIODEGRADATION OF PCB ATROPISOMERS. Presented at 23rd Annual Society of Environmental Toxicology and Chemistry Meeting, Salt Lake City, UT, November 16-20, 2002.
Impact/Purpose:
(1) Use toxicity-based approach to identify DBPs that show the greatest toxic response. (2) Comprehensively identify DBPs formed by different disinfectant regimes for the 'Four Lab Study'. (3) Determine the mechanisms of formation for potentially hazardous bromonitromethane DBPs.
Description:
Microcosms inoculated with sediment from two locations in a contaminated reservoir, Lake Hartwell, SC, USA, degraded certain PCB atropisomers enantioselectively while other atropisomers were degraded in racemic proportions. The microcosms were spiked with either 234-236 PCB (PCB132) or 236-245 PCB (PCB149). After a lag period, the enantiomers of both atropisomers were degraded in equal proportions with no change in the enantiomeric fraction (EF). The first products of dechlorination of both atropisomers were also atropisomers and were degraded enantioselectively. For example, the EF of PCB91 (236-24 PCB), the first product observed during the dechlorination of PCB132, changed from 0.42 to 0.03 over 140 days of incubation. PCB95, the first product observed for the dechlorination of PCB149, also showed a change in EF during the incubation. Microcosms spiked with Aroclor 1254 showed similar behavior in that PCB91 and PCB95 were degraded enantioselectively but PCB149 and PCB136 (236-236 PCB) were not. In all cases, methane production was initiated at the same time that dechlorination of the PCBs began in the microcosms. The chlorination pattern appeared to affect whether the biotransformation was racemic. Results point to the use of chiral analysis in understanding biotransformation mechanisms for PCBs in anaerobic environments.