Study On The Accumulation, Degradation And Toxicity Of The Chiral Pesticide Dinotefuran In Rana Nigromaculata Tadpole

Neonicotinoids are a class of pesticides widely used in agriculture,with high insecticidal activity and broad selective insecticidal spectrum against pests.Dinotefuran is a third-generation neonicotinoid compound,which has certain ecotoxicity to aquatic organisms.In this paper,taking the aquatic animal Rana nigromaculata tadpoles as the model organism,the selective enrichment,degradation and toxicity effects of dinotefuran in Rana nigromaculata tadpoles were carried out at the enantiomeric level.The main research contents and conclusions are as follows:1.A method for the determination of dinotefuran enantiomers in Rana nigromaculata tadpoles and water samples was established by Superchiral R-AD chiral column and liquid chromatography tandem mass spectrometry(LC-MS/MS).The results showed that the linear relationship was good in the range of 0.01-10 mg /L.The average recovery of R-(–)-dinotefuran and S-(+)-dinotefuran in the matrix of Rana nigromaculata tadpoles were 86.83-98.91%,the relative standard deviation(RSDs)were <10.2%,the limit of quantification(LOQ)and limit of detection(LOD)were 0.01mg/kg and 0.003 mg/kg,respectively,the stability,accuracy and precision of the method meet the requirements of pesticide residue analysis.2.Acute and subchronic toxicity tests were carried out.The results showed that the order of acute toxicity of dinotefuran to Rana nigromaculata tadpoles was R-(–)-dinotefuran>Rac-dinotefuran>S-(+)-dinotefuran.After exposure to 0.2 and 2mg/L solution for 28 days,compared with the control group,the growth of Rana nigromaculata tadpoles were delayed by measuring R-(–)-dinotefuran and Rac-dinotefuran,and the effect of R-(–)-dinotefuran were greater than Rac-dinotefuran,while S-(+)-dinotefuran had no significant effect on its growth.3.The enrichment and degradation of dinotefuran enantiomers in Rana nigromaculata tadpoles exposed to dinotefuran were studied.The results showed that the tadpoles of Rana nigromaculata had significant stereoselectivity for dinotefuran and preferentially enriched R-(–)-dinotefuran;Rana nigromaculata tadpoles can quickly eliminate the enantiomer of dinotefuran,and S-(+)-dinotefuran was preferentially degraded.The EF value of the stereoisomer of dinotefuran in water is basically maintained at about 0.5,indicating that dinotefuran has no stereoselectivity in water environment.The BCF value of the two isomers of dinotefuran is less than10,which belongs to low enrichment pesticide in Rana nigromaculata tadpoles.4.The tadpoles of Gosner stage 26 were exposed to 0.2,2 mg/L dinotefuran and its enantiomer for 28 days,and the results of thyroid hormone content and related gene expression in the tadpoles showed that: After 28 d of exposure to 0.2 and 2 mg/L of Rac-dinotefuran and R-(–)-dinotefuran in Rana nigromaculata,the thyroid hormone T3 and T4 in the head were disturbed with their contents decreased significantly.Rac-dinotefuran and R-(–)-dinotefuran had thyroid endocrine disrupting effects on the tadpoles of the Rana nigromaculata tadpoles;compared with the control group,the dio2 gene m RNA level in the brain tissue of the tadpoles in the low concentration treatment group was significantly decreased.Under Rac-dinotefuran treatment,the expression level of dio3 gene in the low and high concentration treatment groups was significantly increased compared with the control group.In this study,both low and high concentrations of R-(–)-dinotefuran induced a significant decrease in the relative expression of trα and trβ genes in the head of the Rana nigromaculata tadpoles,while the relative expression of Rac-dinotefuran at low concentrations showed no significant change.5.To study the oxidative stress of dinotefuran to Rana nigromaculata tadpoles.The results showed that dinotefuran affected the antioxidative enzyme activities of Rana nigromaculata tadpoles,and detoxified by increasing the enzyme activity levels of glutathione reductase;dinotefuran and its enantiomers induced oxidative stress in Rana nigromaculata tadpoles,the contents of superoxide dismutase,glutathione S-transferase,acetylcholine esterase and malondialdehyde in Rana nigromaculata tadpoles changed significantly.