Enantiomer-Specific Microbial Biotransformation of Chiral POPs

1 Enantiomer-Specific Microbial Biotransformation of Chiral POPs 

The nonracemic compositions in the Arctic Ocean are due to microbial degradation of a-HCH both in tributary waters and within the oceanic water column. About 7% of a-HCH was enantioselectively degraded, with preferential elimination of the (-l-)-enantiomer, in streams draining into Amituk Lake on Cornwallis Island in the Canadian Archipelago [124]. In the lake itself, (—)-a-HCH was enriched (mean ER = 0.77) at 15-21 m depth [125]. 

Although not as well studied, nonracemic compositions of other legacy OC pesticides, as well as of a-HCH in other waters, have been observed. The Arctic Ocean was depleted in (—)-heptachlor epoxide in all regions surveyed, while cis- and tra 5-chlordane were nearly racemic [121]. Lake Ontario was also enriched in (—)-a-HCH (mean ER of 0.85), with enantiomer compositions that did not vary with depth but did vary in the presence of racemic sources such as precipitation and water from the tributary Niagara River [128]. The York River in Chesapeake Bay had microbial consortia that degraded (+)-a-HCH upstream [129, 130]. However, greater microbial activity was observed in more brackish waters 

Little work has been done on POP enantiomers in wastewater and activated sludge, in part because other sources to the environment exist compared to some emerging pollutants such as drugs [29]. One of the few studies to investigate behavior of chiral legacy POPs in 

While brominated flame retardants, including HBCDD, were reductively dehalogenated in laboratory anaerobic microcosms of sewage sludge, such degradation was not enantio-selective for the three major HBCDD isomers in that study [136]. 

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