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ENANTIOSELECTIVE REDUCTIVE TRANSFORMATION OF CHIRAL POLYCHLORINATED BIPHENYLS IN LAKE SEDIMENT MICROCOSMS
Citation:
O'Niell, W. L., W J. Jones, A Whittemore, AND J Avants. ENANTIOSELECTIVE REDUCTIVE TRANSFORMATION OF CHIRAL POLYCHLORINATED BIPHENYLS IN LAKE SEDIMENT MICROCOSMS. Presented at Third International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, May 20-23, 2002.
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:
The transformation rates and enantiomeric ratios of two chiral poylchlorinated biphenyls (PCBs), 2,2',3,4',5',6-hexachlorobiphenyl (2,2',3,4',5',6-HCB) and 2,2',3,3',4,4',5,6-octachlorobiphenyl (2,2',3,3',4,4',5,6-OCB), were determined in anaerobic lake sediment microcosms (25oC). Similar experiments were conducted using Arochlor 1260, a mixture of chiral and non-chiral PCB congeners. Experimental treatments consisted of live (natural) sediment slurries, live slurries dosed with an organic nutrient mixture, live slurries dosed with 2,5-dibromobiphenyl (2,5-DBB) (as a "primer"to stimulate dehalogenation activity), live slurries dosed with both the nutrient mixture and 2,5-DBB, and autoclaved controls.
The concentrations of the PCBs in the experimental microcosms were periodically analyzed by high-resolution gas chromatography/electron capture detection (GC/ECD) during a one year period. Analyses were conducted using both standard capillary columns and enantioselective capillary columns, and data were modeled to determine transformation rates. Enantiomer concentrations in transformed and unaltered (control) microcosms were compared to one another to assess enantioselective transformation of the PCB congeners.
Transformation was absent or insignificant in sediment microcosms dosed with Arochlor 1260 or 2,2',3,3',4,4',5,6-OCB, but transformation was observed in microcosms dosed with 2,2',3,4',5',6-HCB. Transformation was observed in the live slurry plus nutrients treatment (89% loss), live slurry treatment (80% loss), live slurry plus 2,5-DBB and nutrients (63% loss), and live slurry plus 2,5-DBB but without nutrients (11% loss). No significant transformation was observed in the autoclaved controls. The 2,2',3,4',5',6-HCB was para-transformed to 2,2',3,5',6-pentachlorobiphenyl (2,2',3,5',6-PeCB) without apparent enantioselective transformation and then meta-transformed enantioselectively to 2,2',5',6-tetrachlorobiphenyl. It is interesting to note that enantioselective transformation occurred for the chiral intermediate (2,2',3,4',6-PeCB) and not for the chiral parent compound (2,2',3,4',5',6-HCB).