Chiral Degrading Characters Of Pyrethroid Pesticide By Microorganism

Pyrethroid insecticides are an important species of chiral pesticides,but their pollution to the environment is also one of the difficulties faced by human beings.Microbial remediation of pesticides has been an important topic in scientific research.Microbial degradation is the main route for pesticides dissipation in the environment.Moreover,pyrethroids are chiral compounds and different stereo and enantiomers in one pyrethroid often show different biological activity,ecological toxicity and environmental dissipation process.Knowledge on enantioselective degradation behavior of pyrethroids are useful for better understanding the chiral profiles as well as accurate evaluation of ecological risks of pyrethroid pesticides.In this paper,?-cyfluthrin and fenpropathrin,two important pyrethroid insecticides,were selected to systematically study their stereo and enantioselective degradation behavior in soil and by screened dominant microbial strains.The analysis was achieved by the combination of achiral and chiral high-performance liquid chromatography.The experimental contents were as follows:1)Stereo and enantioselective degradation of ?-cyfluthrin in soilThe stereo and enantioselective degradation of ?-cyfluthrin was investigated in Shijiazhuang yellow soil and Wuhan red soil.The results showed the half-lives were 6.80 d and 7.53 d in Shijiazhuang soil and Wuhan soil,respectively.The degradation of trans-isomer was faster than the corresponding cis-isomer in both soils.Significant enantioselectivity was also observed and the degradation of various enantiomers was followed an order 1R-trans-?S>1S-trans-?R>1R-cis-?S>1S-cis-?R in both soils.Moreover,the results showed ?-cyfluthrin was degraded more easily under alkaline conditions,and the enantioselectivity in Wuhan red soil was higher than that in Shijiazhuang yellow soil.2)Microbial screening,identification and enantioselective biodegradation of ?-cyfluthrinThree dominant microbial strains of z-1,z-2 and h-1,capable of degradation of ?-cyfluthrin were isolated from Shijiazhuang yellow soil and Wuhan red soil.z-1 was identified as Lysine fusiform bacillus,and z-2 and h-1 were idenfied as Microbacterium and Trichosporon,respectively.On this basis,the stereo and enantioselective degradation of ?-cyfluthrin by the three strains were studied in details.The results showed the cis-isomer was degraded faster than the trans-isomer with strains z-1 and z-2,whereas the trans-isomer showed higher degradation rate for strain h-1.Moreover,the trans-isomer exhibited some enantioselectivity when ?-cyfluthrin was degraded by strain z-2.However,there was no enantiomer selectivity for the degradation with strains z-1 and h-1.At last,the influence of pH on the biodegradation was studied.The results showed the alkaline environment was more favorable for the biodegradation,which was consistent with ?-cyfluthrin degradation in soil.3)Microbial screening,identification and enantioselective degradation of fenpropathrinA bacterial strain w-10,capable of degradating fenpropathrin,was isolated from sludge by enrichment culture.w-10 was identified as Alcaligenes faecalis based on analysis of physiological properties and 16 S rDNA sequence.The biodegradation of fenpropathrin by strain w-10 was studied in details.The results showed the degradation followed first-order kinetics,and no enantioselectivity was observed for the two enantiomers of fenpropathrin.The biodegradation conditions were optimized and the optimal conditions were determined to be: temperature 30?,pH 7.0 and inoculum concentration 5%.At last,the degradation activity of w-10 to other pyrethroids was investigated.As a result,permethrin and ?-cyfluthrin could be degraded by w-10 at fairly fast degradation rates.The cis-isomer was degraded faster than the trans-isomer for permethrin,whereas the trans-isomer was found to degrade faster than the cis-isomer for ?-cyfluthrin.Moreover,some enantioselectivity was observed for trans-?-cyfluthrin,and the corresponding ER value reached 1.13 after 8 days incubation.