Study Of Etoxazole Stereoselective Environmental Behavior In Orchard And Toxicology Effect

In recent years,chiral pesticides have been widely used in agriculture,most of which are produced and applied in the form of racemates.The enantiomers often show stereoselective bioaccumulation,metabolism,bioactivity,toxicity,and environmental behavior when they enter into the ecological system.However,in the conventional risk assessment,enantiomers of chiral compounds are considered as one compound,which therefore causes the unreliable results of risk evaluations and pose potential threats to our health and the ecological safety.In this work,we selected etoxaozle as the target pesticide,which is one of the most frequently used pesticides in the orchards and,its bioactivity,ecotoxicity,environmental behavior and bioaccumulation were systemically investigated in enantiomeric level.We hope the results obtained here will provide additional information that contributes to the comprehensive evaluation of the risks posed by the application of etoxazole.First,the chiral separation of etoxazole enantiomers was developed using HPLC-MS/MS and SFC-MS/MS,respectively.Baseline separation of etoxazole was achieved by systemically optimizing the separation parameters including chiral stationary phase(CSP),organic modifier,flow rate,system pressure and column temperature.In the HPLC-MS/MS system,the method achieved an Rs value of 1.51 with retention time of 2.06 min and 2.54 min for the two enantiomers.Meanwhile,in the SFC-MS/MS system,the method achieved an Rs value of 5.81 with retention time of 0.47 min and 0.81 min.The absolute configuration of etoxazole enantiomers was determined using an optical rotation detector and the elution order was also confirmed under different conditions of chromatography.Second,the enantioselective dissipation of etoxazole was investigated in three species of fruits and open-field soil samples.Significant enantioselectivity was observed as follows:(+)-(S)-etoxazole was preferentially dissipated in grapes and strawberries grown in greenhouse condition,whereas(-)-(R)-etoxazole degraded faster than its antipode in apples and soil under open-field condition.Third,stereoselective bioactivity of etoxazole enantiomers was assessed against two target organisms(Tetranychus urticae and Tetranychus cinnabarinus eggs).The result indicated that a significant difference was found in the bioactivity among etoxazole enantiomers,and the order of bioactivity observed was(+)-(S)-etoxazole > Rac-etoxazole >(-)-(R)-etoxazaole.Additionally,the ovicidal activity of(+)-(S)-etoxazole against Tetranychus urticae and Tetranychus cinnabarinus eggs was about 16 and 24 times higher,respectively,than that of(-)-(R)-etoxazole.Fourth,the acute toxicity of chiral etoxazole was assessed toward non-target aquatic organisms(Daphnia magna and Danio rerio).The result showed that a significant difference was found in the acute toxicity among etoxazole enantiomers.The toxicity order was(+)-(S)-etoxazole > Rac-etoxazole >(-)-(R)-etoxazaole in Daphnia magna and(-)-(R)-etoxazole >(+)-(S)-etoxazole > Rac-etoxazole in Danio rerio.Inconsistent order of etoxazole isomer toxicity was observed toward different aquatic organisms:(+)-(S)-etoxazole showed nearly 8.7 times higher acute toxicity than(-)-(R)-etoxazole toward Daphnia magna,whereas(-)-(R)-etoxazole was 4.5 times more toxic to Danio rerio than(+)-(S)-etoxazole.Fifth,the stereoselective determination of etoxazole in zebrafish and water samples was developed using SFC-MS/MS combined with a modified QuEChERS pretreatment and then applied to estimate stereoselective bioaccumulation and elimination in zebrafish.The results indicated that etoxazole enantiomers showed enantioselective bioaccumulation in zebrafish,with the preferential accumulation of(-)-R-etoxazole.Sixth,the potential toxic effects of etoxazole on zebrafish were explored,and activities of antioxidant enzymes were determined in the liver of zebrafish.The results indicated that significant changes were observed in the SOD and GST activities and in the MDA levels,which indicated the occurrence of oxidative stress in the liver of zebrafish.Therefore,the present work can facilitate the accurate risk evaluation of etoxaozle in orchard.Developing(+)-(S)-etoxazole to supersede its racemate could reduce the use of pesticides and environmental pollution.