| Widespread application of chiral pesticides results in their occurrence in the organism, plant, soil, water and other environmental systems. In general, the enantiomers of chiral compounds are different in biological activities, enantioselective behavior and eoctoxicity because of their different interactions with enzymes and other naturally occurring chiral molecules. However, most of the chiral pesticides are still marketed and applied in racemates. Consequently, the application and envinormental safety of chiral pesticides have been the new concern of scientific researches. So far, the environmental behaviors and eoctoxicity of chiral pesticides have received limited research. In this study, the enantiomeric separation, environmental behaviors, bioaccumulation and biotoxicity of several typical chiral pesticides were investigated.(1) A sensitive and convenient chiral liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed and validated for measuring epoxiconazole stereoisomers in grape and soil. Then the proposed method was successfully applied to investigate the possible stereoselective degradation of Rac-epoxiconazole in grape and soil under field conditions. The results of field experiment showed that the dissipations of epoxiconazole stereoisomers in grape followed first-order kinetics (R2>0.92) and stereoselectivity occurred in2h after spraying. The (-)-stereoisomer of expoxiconazole with half-life of9.3d degraded faster than (+)-stereoisomer with that of13.2d, which would resulted in relative enrichment of (+)-stereoisomer in grape. However, the stereoisomeric dissipations of expoxiconazole in soil were triphasic ("increase-decrease-steady") with lower dissipation rates, although it also occurred with preferential degradation of (-)-stereoisomer under field condition.(2) The separation of triadimefon (TF) and its major metabolite triadimenol (TN) including their simultaneous stereoseparation was studied; using two different polysaccharide-type chiral stationary phases inculding Cellulose-tris(3,5-dimethyphenylcarbamate)(CDMPC) and Amylose-tris(3,5-dimethylphenylcarbamate)(ADMPC) on reverse-phase high-performance liquid chromatography. Compared with two chiral stationary phases, CDMPC exhibited higher resolving ability for TF and TN. And after the optimization of other chromatographic conditions such as the mobile phase composition, a good enantioseparation of two enantiomers of TF and four stereoisomers of TN was successfully achieved. Then we developed a sensitive and rapid analytical method for simultaneous determination of TF and TN stereoisomers in wheat, straw, and soil by LC-MS/MS.Racemic triadimefon (TF) was applied to wheat and soil at three sites (Beijing, Huaibei, and Zhengzhou in China) under open field conditions. Its enantioselective degradation and stereoselective transformation to the major metabolite, triadimenol (TN), in wheat straw, grain and soil were investigated. At all three sites, the degradation of TF enantiomers in straw and soil followed first-order kinetics, In soil from Beijing and Zhengzhou,,R-(—)-TF was preferentially degraded; however, preferential enantioselective degradations were not observed in soil from Huaibei or in the straw from all sites. There were noticeable differences in the stereoselective formation of TN stereoisomers in all straw and soil samples. Different TN concentrations were found in the order of SR-(-)-TN> RR-(+)-TN>RS-(+)-TN>SS-H-TN in straw, and RR-(+)-TN>SS-(-)-TN> SR-(-)-TN> RS-(+)-TN in soil. Neither TF nor TN was found in wheat grain at harvest.(3)The toxicity of each isomer and racemate of hexaconazole (HZ) to two aquatic orgnisms including Daphnia magna (D. magna), adult zebrafish (Danio rerio), zebrafish embryos and larvae (3d old) were tested. For the aquatic organisms metioned above, significant enantioselectivity were observed in the acute toxicity and development toxicity among the enantiomers of HZ. The order of the acute toxicity to the aquatic organisms of the enantiomers of HZ was (-)-HZ> Rac-HZ>(+)-HZ. At specified stages (24,48,72,96and120hour postfertilization), spontaneous movement, survival, heart beats and hatching as well as non-lethal malformation like crooked body or edema were recorded in detail in zebrafish embryo tests. The results indicated that the (-)-enantiomer of HZ enantioselectively inhibited of hatching and heart beats of embryos and induced significantly more crooked body, yolk sac edema, pericardial edema than (+)-enantiomer. Moreover,(-)-enantiomer also enantioselectively caused morphological impairments, and inhibited the free swimming of the larvae of zebrafish.(4) The enantioselective bioaccumulation of indoxacarb in adult zabrafish and the effects of two indoxacarb enantiomers on zebrafish embryos and larvae were studied. The results demonstrated that the accumulation of (-)-R-indoxacarb was approximately13-fold more than that of (+)-S-indoxacarb in adult zabrafish, indicating a clear enantioselectivity of indoxacarb in bioaccumulation. The depuration of the two enantiomers followed first-order kinetics and the average half-lives of (-)-R-indoxacarb and (+)-S-indoxacarb were4.2and2.4d, respectively.The results also indicated that (-)-R-indoxacarb was more toxic than (+)-S-indoxacarb to embryo-larval zebrafish in causing mortality, inhibition of hatching and heart beats, and in inducing yolk sac edema, pericardial edema and crooked body. The enantioselective toxicity of indoxacrb was consistent with its enantioselectivity in bioaccumulation. The Rac-indoxacarb had the least potency of development toxicity as compared to its two enantiomers. |
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