PH07 Environmental Chemistry and Toxicology of Chiral Pollutants
Exhibit Hall
8:00 AM - Thursday
(PH067) Changes in enantiomeric fractions (EF) of PCB atropisomers in composting field and microcosm samples.
Hall, A1, Im, J1, Pressley, H1, Lee, C1, Freedman, D1, 1 Clemson University, Anderson, SC, USA
ABSTRACT- Treatability studies have been on-going at the Department of Energy?s Savannah River Site (SRS) to evaluate the effectiveness of composting of soils from the Chemical Metals and Pesticides (CMP) pits for removing polychlorinated biphenyls (PCBs) and various organochlorine pesticides. Microcosm studies under aerobic and anaerobic conditions have been performed in the laboratory in conjunction with field tests. Achiral analysis of PCB congeners indicates that certain highly chlorinated congeners are removed from anaerobic microcosms of compost soils treated with reduced anaerobic mineral media (RAMM) and molasses with simultaneous appearance of dichlorobiphenyls. Anaerobic microcosms also generate significant amounts of methane. Aerobic microcosms show removal of dichlorobiphenyl congeners. But the evidence for biodegradation is equivocal because the changes are not statistically robust. Chiral analysis of the field samples and microcosms show more definitive evidence that biodegradation has occurred. The enantiomeric fractions (EFs) for four chiral congeners, PCB 84, PCB 91, PCB 95, and PCB 149, were determined using a Chirsal-Dex capillary column installed in a HP 6890 gas chromatograph with an electron capture detector (ECD). Results indicate that microbial dechlorination has occurred in the composted soils. For example, the EF for PCB 84 is 0.25 (0.006), for PCB 91 the EF is 0.41 (0.004), for PCB 95 the EF is 0.65 (0.007), and for PCB 149 the EF is 0.49 (0.005). Standard deviations are included in parenthesis. Three out of the four congeners show an EF below or above 0.5, which indicates a change from the original racemic mixture. Changes in EF with time in the microcosms and field samples will be discussed.
Key words: biodegradation, polychlorinated biphenyls, chiral, enantioselective