The Degradation Behaviors And Products Of Imidaclothiz In Soil And Water

The natural degradation behaviors of pesticides in the environment included chemical degradations and biodegradations.Hydrolysis and photolysis were important chemical degradation pathways of pesticides while biodegradation in soil and plant degradation were major biodegradation processes.As pesticides might degrade into products with high toxicity,which would pose threats to environmental safety and non-target organisms,it was of great significance to study the natural degradation behaviors and degradation mechanisms of pesticides and ecological toxicities of pesticides degradation products for the assessment of environmental fate and the evaluation of ecological risk of pesticides.Imidaclothiz is a fourth-generation neonicotinoid insecticide developed by our country.At present,few researches focused on the environmental behaviors and degradation products of it at home and abroad,so the environmental risks of imidaclothiz and its degradation products cannot be objectively evaluated.Therefore,on the basis of the high resolution,high sensitivity and accurate molecular mass measurement characteristics of UHPLC-QTOF/MS,quantum chemistry theory and reference standard comparison method,we studied the degradation behaviors,products and mechanisms of imidaclothiz in different types of soil and aqueous solutions.And the major experimental results were listed as follows:1.An instrumental analytical method of imidaclothiz using UHPLC-QTOF/MS was established.Using this method,in the range of 0.05¹0 mg/L,good linear relationship between the concentration of imidaclothiz solution and peak area was achieved.Then,pretreatment methods of imidaclothiz in black soil,red soil and fluvo-aquic soil and four kinds of aqueous solutions were established with average recoveries in the range of 75.16¹06.45%and RSDs in the range of 3.25%⁹.33%,which could satisfy the experiment needs and be used in the pretreatments of the samples in imidaclothiz degradation experiments.2.The degradation behaviors of imidaclothiz in different types of soil and aqueous solutions were studied by soil degradation,hydrolysis and photolysis experiments.The results showed that imidaclothiz was stable in black soil,red soil and fluvo-aquic soil under aerobic conditions,and the degradation rate of imidaclothiz was a little faster under anaerobic condition.Under anaerobic condition,the half-lives of imidaclothiz in black soil and fluvo-aquic soil was 18.24 days?easily degraded?and53.32 days?medium degradation?,respectively.The hydrolysis rate of imidaclothiz was increased?half-life was 4.95 d?in the buffer solution of pH9 at 50?,while it degraded slowly under other conditions,so the hydrolysis stability of imidaclothiz was confirmed.The photolysis half-lives of imidaclothiz in buffer solutions at pH4,pH7 and pH9 and in ultra-pure water were 16.50 h,14.75 h,2.46 h and 2.63 h,respectively,which indicated that it was little difficult for imidaclothiz to degrade under acidic and neutral conditions and easy to degrade under alkaline conditions.3.UNIFI software was used to identify the degradation products of imidaclothiz.10 good matched degradation products which conforming to the degradation trend were identified.The retention time and secondary mass spectrogram of the two compounds was compared using reference standard comparison method,and the validity of the two degradation products was verified.Density Functional Theory of Quantum chemistry on the level of B3LYP/6-3l g?d?calculations was used for the structure optimization of reactants,transition states,intermediates and products,frequency calculation,transition state calculation,IRC verification,zero-point energy correction and activation energy calculation by Gaussian 16 proceeding.And the processes of three degradation reaction were explicated.4.The acute toxicity of imidaclothiz to Daphnia magna and Apis mellifera L.was determined by experiments,and the results showed that it was low toxic to Daphnia magna(48h EC₅₀ is 12.798 mg a.i./L)and high toxic to Apis mellifera L(48h LD₅₀ is 0.835?g a.i./bee).The reliability of prediction result of ECOSAR was verified by comparision between the predicted and measured values of the acute toxicity of imidaclothiz to Daphnia magna.Then ECOSAR software was used to predict the acute toxicity and chronic toxicity of imidaclothiz and its degradation products to three aquatic organisms.The results showed that the degradation process of imidaclothiz could produce degradation products with higher toxicities.