Study On Pollution Characteristics And Bioavailability Of Neonicotinoid Pesticides In Farmland Soil In Shaanxi

Neonicotinoid Pesticides(NPs)are a class of pesticides widely used after organochlorine and organophosphorus.As a large agricultural province,Shaanxi cannot avoid the problem of pesticide contamination while agriculture is developing rapidly,which,together with the differences in different natural conditions in the three regions of northern,central,and southern Shaanxi,may lead to a more complex and uncertain pesticide contamination problem.More scholars have conducted relevant studies on pesticide contamination in agricultural soils and agricultural products in Shaanxi Province,but mainly focused on traditional typical pesticides such as organochlorine and organophosphorus,while there are fewer studies on the distribution and risk assessment of neonicotinoid pesticide residues in agricultural soils in different regions of Shaanxi.In this study,115 soil samples collected from different areas in northern,central and southern Shaanxi were used to determine the residues of neonicotinoid pesticides such as Imidacloprid,Thiamethoxam,Clothianidin and Acetamiprid in different areas and to investigate the characteristics of neonicotinoid pesticide residues in different land-use types.The ecological risk assessment was conducted using the risk quotient method,and the ecological risk of nicotine pesticides in different land-use types was investigated;the human health risk assessment was conducted using the US EPA health risk assessment model,and the health risk of neonicotinoid pesticides on different populations was investigated;the biological effects of neonicotinoid pesticides were determined based on the Tenax three-phase desorption kinetic equation,and the effects of soil pH,soil organic matter,aging time and other factors on the bioavailability of neonicotinoid pesticides were investigated using the single point extraction method.The effects of soil pH,soil organic matter and aging time on the bioavailability of neonicotinoid pesticides were investigated using single-point extraction method;the bioavailability relationships between simulated and actual soil at different soil pH and organic matter contents were studied.The main findings are as follows.(1)There were significant differences in the residues of neonicotinoid pesticides in farmland soils from different regions and land-use types in Shaanxi.The detection rates and residues of Thiamethoxam(94.40,14.85 μg/kg)in northern Shaanxi,Imidacloprid(66.2%,113.71 μg/kg)in central Shaanxi,and Thiamethoxam(31.3%,184.32 μg/kg)in southern Shaanxi were relatively high,and both indicators of neonicotinoid pesticide detection rates and maximum residues were relatively high compared with other regions in China,and the residues of neonicotinoid pesticides in greenhouse soils were generally higher than those in field soil.The correlation between different types of neonicotinoid pesticides and between neonicotinoid pesticides and soil properties varied greatly.(2)There are significant differences in the ecological risk of neonicotinoid pesticides in agricultural soils in different regions and land-use types in Shaanxi.In northern Shaanxi,Thiamethoxam was mainly of medium risk;in central Shaanxi,Imidacloprid was mainly of high risk;in southern Shaanxi,the problem of the high ecological risk of Imidacloprid and Thiamethoxam was more prominent.The overall ecological risk of neonicotinoid pesticides in greenhouses is higher than that in fields,and their non-carcinogenic risk levels are in the range of 10-8 to 10-5,which is far below the safety standard of 1 and will not have significant adverse effects on human health.However,it should be noted that children are more sensitive to neonicotinoid-based pesticides and more prominently affected than adults.(3)The effects of soil pH,organic matter content and aging time on the bioavailability of neonicotinoid pesticides were investigated by single-site extraction using Tenax sequential extraction of four neonicotinoid pesticides to fit the kinetic equation of three-phase desorption,and the effects of soil pH,organic matter content and aging time on the bioavailability of neonicotinoid pesticides were investigated by single-site extraction using artificial simulated soil as a substrate:the bioavailability of four neonicotinoid pesticides were always:Thiamethoxam>Acetamiprid>Imidacloprid>Clothianidin,which may be related to their structure.This may have some relationship with their structure.Soil pH was positively proportional to the bioeffect of neonicotinoid pesticides,while soil organic matter content and soil aging time were inversely proportional to the bioeffect of neonicotinoid pesticides.(4)The relationship between simulated soil and actual soil bioavailability of neonicotinoid pesticides showed that although the actual soil effectiveness concentration was lower,the actual soil bioavailability under the influence of soil pH and soil organic matter was consistent with the simulated soil bioavailability pattern,indicating that the method of using simulated soil to determine the bioavailability of neonicotinoid pesticides under the influence of different soil pH and organic matter was well applied.