Study On Enantioselective Environmental Behavior Of Chiral Pesticides

Research on enantioselective environmental behavior of chiral pesticides was a hot spot of environmental chemistry. In this paper, the enantioselective degradation of organophosphorus pesticides and synthetic pyrethroid pesticides in different soils was studied in details. Further research focused on the chiral stability of enantiopure pesticide enantiomers as well as the influence of soil nature on degradation of pesticides. Following experimental results were conducted:1) Enantiomeric separation of chiral pesticidesEnantiomers of five pesticides were successfully separated using chiral HPLC, and elution order of malathion and profenophos enantiomers was further concluded.2) Enantioselective determination of chiral pesticides in soilsMalathion, profenophos,β-cypermethrin andβ-cyfluthrin were extracted from soil by Matrix Solid-phase Dispersion (MSPD) method and enantioselective determination of the four pesticides in soils was accomplished using achiral and chiral HPLC in combination with MSPD technique.3) Enantioselective degradation of malathion in soilsThe degradation of malathion in different soils showed the half-lives of malathion were 3.5 h and 4.3 h in Tianjin yellow soil, and 1.6 h and 2.2 h in Wuhan red soil on 21℃and 25℃. Malathion was degraded faster in Tianjin yellow soil than in Wuhan red soil. Further chiral analysis demonstrated the enantioselectivities during the degradation of malathion in two soils. It was further observed obviously that the enantioselectivity of malathion in Wuhan red soil was much higher than in Tianjin yellow soil. No obvious degradation of malathion was observed in sterilized soils, indicating the enantioselective degradation of malathion was mainly biologically mediated.4) Enantioselective degradation of profenophos in soilsThe enantioselective degradation of profenophos was mainly biologically mediated in five soils. Profenophos was degraded fast in five soils with half-lives ranging from 4.2 h to 433.2 h. Further chiral analysis demonstrated that different enantioselectivity was showed in different soils. In Tianjin and Hubei alkaline soils, the (+)-enantiomer was degraded faster than the (-)-enantiomer. However, in Baoding alkaline soil both enantiomers were degraded at similar rates, and in Hubei and Guangdong acidic soils the enantioselectivity was reversed. At last, during the degradation of enantiomer pure (+)-profenophos, no enantiomerization was observed in both nonsterilized and sterilized soils. The soil pH mainly influenced the degradation rate of profenophos and had no effect on the enantioselectivity.5) Enantioselective degradation ofβ-cypermethrin andβ-cyfluthrin in soilsThe degradation of cis-β-cypermethrin and trans-β-cypermethrin in Wuhan acidic red soil showed the half-lives of cis-β-cypermethrin were 150.7 h and 87.7 h, and the half-lives of trans-β-cypermethrin were 157.5 h and 95.0 h, respectively the trans-isomer of the two pesticides was degraded faster than corresponding cis-isomer. It was further observed obviously that the enantioselectivity ofβ-cyfluthrin was much higher thanβ-cypermethrin for both cis-isomer and trans-isomer.