The Behaviors And Toxic Effects Of Neonicotinoid Pesticides In Model Organisms

Neonicotinoid insecticides play the dominant role in the global pesticides market,but the frequent usage worldwidely have caused serious pest resistance problem and hazardous environmental impacts.Therefore,it has become one of the urgent problems to be solved in the world to explore the environmental friendly substitute for traditional neonicotinoid pesticides.Cycloxaprid and paichongding are novel neonicotinoid pesticide initiatively developed by China with the advantages,such as high efficiency to pest,low toxicity to non-target organisms and environmentally-friendly.They both are promising candidates for traditional neonicotinoid pesticides.Besides,the development of "high efficiency and environmental benefit" single enantiomer helps to reduce pesticide environmental pollution problems.At present,the scientific understanding of the environmental behavior and risk assessment of cycloxaprid and paichongding is still limited,and it is rare to find their biological toxicity effect on non-target environment model organisms.In this research work,by combining isotopic tracing technique,instrumental analysis,biotechnical and toxicological methods,the stereoselective environmental behavior and fate of 14C-cycloxaprid in rats were studied,and Cycloxaprid's and Paichongding' toxic effects on non-target model organisms in aquatic environment(Scenedesmus sp.and Hydra sinensis)were also investigated.The study aims to objectively and comprehensively evaluate and understand the environmental safety of the new type pesticides cycloxaprid and paichongding,and provide reference data for the scientific and rational use of new pesticides.This research also has important scientific and practical significance to ensure the safety of the ecological environment and human health.The main research contents and results were as follows:(1)It's reported that neonicotinoid pesticides has low toxicity to mammals,and it is rare to see neonicotinoids metabolism studies in the model animals.This research work studied the absorption,transportation and elimination of 14C labeled racemic cycloxaprid and its 2 enantiomers in rats,using isotope tracing and HPLC analysis.The results shows that,after oral administration of cycloxaprid in rats,the concentration of cycloxaprid in blood were increased at first,then tended to decrease to a certain level and kept stable.The distribution of cycloxaprid were mostly in organs kidneys,adrenal glands,skin and heart.With time went by,the concentration of cycloxaprid in kidneys,adrenal glands,and heart went down,meanwhile the concentration of cycloxaprid in skin and fat went up.After 24 h oral administration,more than 50%of cycloxaprid were eliminated from rat's body in the form of urine and faeces.The metabolism experiments of racemic cycloxaprid RM and 2 enantiomers SR and RS in rats showed that,there was stereoselectivity in rat's blood metabolism,and the distribution and transportation of RM and SR,RS in rat's organs and tissues appeared differences.After 24 h oral administration,the elimination of RM and SR?RS from rats were 50.4%,59.7%,74.5%,respectively.Enantiomer RS was least accumulated in rat body.Besides,the metabolism of cycloxaprid in rats showed gender differences,and the female rat showed slower rates in the absorption,transportation and elimination of cycloxaprid in its body.(2)As persistent organic pollutants in aquatic environment,neonicotinoid insecticides lead to fatal harms to the organisms in the environment.Cycloxaprid and paichongding are both highly potent substitutes for traditional neonicotinoid pesticides,therefore,it is necessary to carry out toxicity studies of cycloxaprid and paichongding on aquatic organisms.As the primary producer in the biologic chain,algae occupies an important position in the entire ecosystem.This research work investigated toxic effects of on the growth and physiology of cycloxaprid and paichongding on non-target model plant Scenedesmus sp.The research results found that,neonicotinoids had toxicity to,the order of the toxicity were imidacloprid>cycloxaprid>paichongding.Low concentration of paichongding could be used as a nutrient source to promote the growth of Scenedesmus sp..With the increased concentrations of paichongding in algal culture medium,the growth of the algae was greater inhibited,and also,the contents of chlorophyll a,chlorophyll b and total chlorophyll became less.The higher the cycloxaprid concentration,the growth inhibition effect on Scenedesmus sp.was more obvious,the oxidative damage degree on algal cell was greater,which resulted in higher MDA contents in algal cells,as well as higher SOD activity.But when cycloxaprid concentration was too high(>50 mg/L),the balance between the increased oxidative stress and the antioxidant system in algal cells would be destroyed,which could lead to apoptosis or necrosis,then resulted in lower SOD activity.Racemic cycloxaprid and its 2 enantiomers were observed no selective differences on Scenedesmus sp.under oxidative stress conditions.(3)Hydra is a model animal for water quality monitoring,and it is extremely sensitive to the toxic effects.The toxicity of pesticide could cause hydra's morphological changes and death in short period of time,which are obvious and easy to be observe.The research work studied the toxic behavior and effects of cycloxaprid and paichongding on Hydra sinensis.The results showed that,neonicotinoids's toxic effects on hydra leaded to its shrinking and disintegrating,and eventually to death.The higher the pesticides' concentration,the shorter time was needed for hydra's disintegration and death.The 48h LC50 of cycloxaprid and paichongding were 17.25 mg/L,31.67 mg/L,respectively.Therefore,the toxicity of cycloxaprid was higher than paichongding.Besides,the lethal effect on Hydra sinensis of racemic cycloxaprid and its 2 enantiomers were observed no stereoselectivity.