| The rate, extent and pattern of in situ reductive dechlorination of polychlorinated biphenyls (PCBs) in the sediments of Lake Hartwell, South Carolina, were identified by microcosm studies, analysis of enantiomers of PCB atropisomers, and historical field data. Lake Hartwell located on the border between South Carolina and Georgia was contaminated with an estimated 200,000 kg of PCBs along with the wastewater discharge from a capacitor plant site. Lake Hartwell is distinguished from other sites that have been studied for in situ reductive dechlorination because monitored natural attenuation (MNA) was selected as the PCB-remediation strategy, the relatively warm temperature of Lake Hartwell, and the lack of significant co-contaminants along with PCBs.; Microcosm studies, conducted with the sediments from two locations with the highest PCB contamination, confirmed the presence of a microbial community capable of reductive dechlorination of both Aroclor 1254, one of the commercial PCB mixtures used at the plant site, and 234-236 hexachlorobiphenyl (PCB 132), one of 19 atropisomeric PCBs. Approximately 40% of the total chlorines in Aroclor 1254 were removed in the live treatments following 250–260 days of incubation. The maximum observed dechlorination rates, which were similar to what has been observed for other fresh water ecosystems located in colder climates and containing co-contaminants, were from 0.29 to 0.87 μg-atom Cl− per gram sediment dry weight per week. The final residual products of dechlorinated Aroclor 1254 were similar for the two sites tested. The final congener pattern consisted of PCBs that retained chlorines predominantly at the ortho and para position such as 2−2+26; 24−24+246+245−2; 24−4; 4−4+24−2; and 2-4 chlorobiphenyl. PCB132 was dechlorinated to 236-24 pentachlorobiphenyl (PCB91), which is another atropisomeric PCBs, and 24-26 tetrachlorobiphenyl (PCB51). Further incubation yielded slight amounts of 26-2 trichlorobiphenyl (PCB19).; Analysis of the enantiomers of atropisomeric PCBs was used in conjunction with microcosm studies to elucidate the enantioselectivity of PCB dechlorination in order to provide information in support of the potential application of the enantiomeric fraction (EF) as an indicator for in situ reductive dechlorination. (Abstract shortened by UMI.)... |
