M8 PM Chiral Chemistry: Toxicology of Environmental Contaminants and Phase Transfer
Monday, 14 November 2005: 1:50 PM - 5:30 PM in 337-338

(QIN-1117-749913) Difference of Pyrethroid Enantiomers in Their Degradation in Soils.

Qin, S¹, Gan, J¹, ¹ UC, Riverside, Riverside, CA, USA

ABSTRACT- Synthetic pyrethroids contain two or three chiral centers, making them a family of pesticides with the highest number of enantiomers. Our recent studies showed significant differences in aquatic toxicity between the stereoisomers of the same compound. To better understand the ecotoxicological effect and fate of synthetic pyrethroids, chirality in biodegradation of pyrethroid compounds should be also considered. In this study, enantiomers of cis-bifenthrin were isolated on chiral HPLC and the enantiopure isomers were examined individually for their degradation rates in a soil and a sediment at 20°C under either aerobic or anaerobic conditions. The study results show that R-cis-bifenthrin degraded faster than S-cis-bifenthrin under aerobic conditions in both soils. However, under anaerobic condition, S-cis-bifenthrin was found to have a faster degradation rate. Isomer conversion did not occur during degradation in soil. As only biological interactions can be chiral selective, the enantioselectivity observed in degradation of cis-bifenthrin should be a result of different microbial communities under different test conditions. Enantiomers of two other pyrethroids, permethrin and cypermethrin, were also isolated and studied under similar conditions, and the role of microorganisms was further ascertained by including sterilization treatments. These results and their implications will be discussed.

Key words: enantioselective degradation, pyrethroid