The Degradation Of Thiacloprid In Soil And Water Environment

Pesticides that enter the environment are affected by chemical and biological factors and eventually degrade into new products that pose a threat to the agricultural environment.Studying the degradation rules and degradation products of pesticides in the environment is of great significance for the rational scientific use of pesticides and the accurate evaluation of environmental risks.In this experiment,thiacloprid was the research object,using UHPLC-QTOF/MS to study the degradation characteristics of thiacloprid in the environment and the identification of degradation products.The main results are as follows:1.An analytical method was established to determine thiacloprid in soil and different aqueous solution.Samples were extracted using 1%(v/v)formic acid-acetonitrile for thiacloprid in soil and different aqueous solution,using PSA for purification and detected by UPLC-QTOF/MS.Good linearities of thiacloprid were obtained in the range of 0.01-10 mg/L,the regression equation is y=50836x+9923.4(R~2>0.9994).The average recovery in soil matrix was 79.6%~101.2%in spiked level of 0.01,0.1,1.0 and 10.0 mg/kg with the relative standard deviation between 2.0%and 4.9%,for the aqueous solution,the average recovery was 87.1%~113.3%with the relative standard deviation between 0.1%and 7.8%.This method meets the requirements of pesticide residue analysis.2.The half-life of thiacloprid under aerobic conditions in Dongbei soil,Hebei soil and Hunan soil were 24.0 d,11.0 d and 9.3 d,respectively.Thiacloprid was stable in the black soil of northeastern China under anaerobic conditions of soil,and the degradation rate was 19.5%at 96 days;the half-life of thiacloprid under aerobic conditions in Hebei soil and Hunan soil was 39.6 d and 96.1 d.The degradation rate of thiacloprid in soil under aerobic conditions is faster than that under anaerobic conditions.At 25°C,there was a small difference in the hydrolysis of thiacloprid in pH=4,pH=7,and pH=9 buffer solutions,with half-lives of 138.6 d,173.25 d,and 173.25 d,respectively.In ultrapure water,the degradation rate was only 24.6%after 124 days of culture.At a treatment temperature of25°C,the photolysis half-life of thiacloprid at pH=7 was 11.95 h;pH=9,was 11.75 h;ultrapure water,was1.95 h;while at pH=4,the degradation rate was only 33.4%after 168 h.3.UHPLC-QTOF/MS was used to acquire MS information from samples and then the data was processed by UNIFI to identify the degradation products of thiacloprid.A total of 6 compounds were identified in environment samples,which were M271,M287,M269,M295,M279,M267.The main reactions of thiacloprid in environment are oxidation reaction,reduction reaction,hydrolysis reaction and oxidation dichlorination reaction.The proposed degradation pathway of thiacloprid in environment was investigate.The potential energy profile for reactions of thiacloprid and water was also calculated.