You are here:
CHANGES IN ENANTIOMERIC FRACTIONS DURING MICROBIAL REDUCTIVE DECHLORINATION OF PCB132, PCB149, AND AROCLOR 1254 IN LAKE HARTWELL SEDIMENT MICROCOSMS
Citation:
Pakdeesusuk, U., W J. Jones, C. M. Lee, A W. Garrison, W. L. O'Niell, D. L. Freedman, J. T. Coates, AND C S. Wong. CHANGES IN ENANTIOMERIC FRACTIONS DURING MICROBIAL REDUCTIVE DECHLORINATION OF PCB132, PCB149, AND AROCLOR 1254 IN LAKE HARTWELL SEDIMENT MICROCOSMS. ENVIRONMENTAL SCIENCE & TECHNOLOGY 37(6):1100-1107, (2003).
Impact/Purpose:
Elucidate and model the underlying processes (physical, chemical, enzymatic, biological, and geochemical) that describe the species-specific transformation and transport of organic contaminants and nutrients in environmental and biological systems. Develop and integrate chemical behavior parameterization models (e.g., SPARC), chemical-process models, and ecosystem-characterization models into reactive-transport models.
Description:
Enantioselectivity of microbial reductive dechlorination of chiral PCBs in sediments from Lake Hartwell, SC, was determined by microcosm studies and enantiomer-specific GC analysis. Sediments from two locations in the vicinity of the highest levels of PCB contamination were used as inocula. Dechlorination activity was monitored by concentration decreases in the spiked chiral PCBs and formation of dechlorination products using both achiral and chiral chromatography. Live microcosms spiked with PCB132 (234-236) exhibited dechlorination of PCB132 to PCB91 (236-24) and PCB51 (24-26). Meta-dechlorination was the dominant mechanism. Microcosms spiked with PCB149 (245-236) exhibited preferential para-dechlorination of PCB149 to PCB95 (236-25), followed by meta-dechlorination to PCB53 (25-26) and subsequently PCB19 (26-2). Dechlorination of chiral PCB132 and PCB149 was not enantioselective. In Aroclor 1254-spiked microcosms, reductive dechlorination of PCB149 also was non-enantioselective. These results suggest that dechlorinating enzymes responsible for dehalogenation of the chiral PCB132 and PCB149 congeners bind both enantiomers equally. Reductive dechlorination of PCB91 and PCB95, however, occurred in an enantioselective manner indicating that the dechlorinating enzymes for these PCBs are enantiomer-specific. The chlorine substitution pattern on the biphenyl ring appears to influence whether reductive dechlorination of chiral PCB congeners is enantioselective. Enantioselective PCB dechlorination by the microbial population of Lake Hartwell sediments occurs for select chiral PCBs; thus, certain chiral PCBs may be useful as markers for in situ reductive dechlorination. These results represent the first evidence of stereoselective reductive dechlorination of PCBs under controlled conditions.