Study On Degradation Efficiency And Degradation Pathway Of Organophorus Pesticides By Voltage Electric Field Cold Plasma

Cold plasma technology has been a new type of pesticide removal technology in recent years.Compared with other methods,it has the advantages of high degradation efficiency,short treatment time,and simple operation.Malathion and chlorpyrifos are widely used as organophosphorus pesticides in the cultivation of agricultural products and widely left in water,fruits and vetagebles.The damage of their harm to consumers' health has been received extensively concerned.In this paper,cold plasma was used as a new method to remove pesticide residues.A dielectric barrier discharge cold plasma system was used to study the degradation efficiency and mechanism of cold plasma treatment on malathion and chlorpyrifos,and to identified the degradation products and analyze its degradation pathway.The research provides a new method for the study of degradation of pesticide residues in fruits and vegetables.The specific research content and results are as follows:1.Study on degradation efficiency of malathion and chlorpyrifos in aqueous solution by cold plasma treatment conditionsThe aqueous solution containing malathion and chlorpyrifos was used as the research object.The effects of DBD cold plasma on the degradation efficiency of malathion and chlorpyrifos under different conditions were studied with different discharge voltages,treatment times and initial concentrations of solution.Through the change of active substances in the treatment process,the degradation rule of pesticides was explored.The results showed that discharge voltage,treatment time,and initial solution concentration had significant effects on the degradation efficiency of malathion and chlorpyrifos.The degradation efficiency of malathion and chlorpyrifos was improved with the increase of discharge voltage,the extension of treatment time and the decrease of initial concentration.After the treatment at 80 kV for 180 s,the degradation efficiency of malathion(0.5 ?g/mL)and chlorpyrifos(1.0 ?g/mL)in the solution could reach 64.60%and 62.69%.Through the detection of active substances during the treatment,it was found that the active substances generated by cold plasma to degrade organophosphorus pesticides include:O3,·OH,O·,H2O2,et al.2.Analysis of degradation kinetic model and degradation pathways of malathion and chlorpyrifosBased on the degradation efficiency of malathion and chlorpyrifos under different discharge voltages and initial concentrations,the degradation kinetic model were established to analyze the degradation rule.Fourier transform infrared spectroscopy(FT-IR),liquid chromatography tandem mass spectrometry(HPLC-MS),and ion chromatography(IC)were used to analyze the intermediates produced during the degradation of malathion and chlorpyrifos,and to analyze their degradation pathways.The results showed that under the conditions of DBD cold plasma treatment,the degradation rule of malathion and chlorpyrifos conformed to the first-order degradation kinetic model,and the degradation efficiency increased significantly with the improved of the discharge voltage and the decreased of the initial solution concentration.The degradation of malathion and chlorpyrifos was mainly through the oxidation of the P=S bond and the breaking of the C-S and C-O bonds.The degradation intermediates of malathion were malaoxon,triethyl phosphate,2-butenedioic acid(Z)-,diethyl ester,2-butenedioic acid(E)-,diethyl ester,2dimethoxyphosphinothioylsulfanyl-4-ethoxy-4-oxobutanoic acid and O,O,S-trimethyl phosphorodithioate.Chlorpyrifos degradation intermediates mainly included chlorpyrifos oxon,diethyl phosphate,3,5,6-trichloro-2-pyridinol and ethyl 3,5,6-trichloropyrid in-2-yl hydrogen phosphate xylene phosphate.The more toxic oxidation products could be further degraded into less toxic molecules,and finally into small molecules such as phosphate and sulfate.3.Effects of cold plasma treatment on the degradation efficiency of malathion and chlorpyrifos on lettuce and lettuce qualityThe degradation efficiency of malathion and chlorpyrifos on lettuce was analyzed at different discharge voltages of cold plasma.The changes of lettuce color,ascorbic acid and chlorophyll content under different treatment conditions were explored to determine the optimal treatment conditions.At the same time,the change of microbial content on lettuce during storage period was studied.The results showed that there was no significant difference in the color and chlorophyll content of the lettuce after cold plasma treatment,but the ascorbic acid content in the lettuce was significantly reduced after the treatment time exceeded 120 s.In order to maintain the quality of lettuce during treatment processing,the treatment time was shortened to 120 s.Under this condition,the degradation efficiency of malathion and chlorpyrifos on lettuce could reach 58.96%and 57.88%.At the same time,cold plasma treatment can significantly reduce the number of microbial colonies on lettuce,and could extend the shelf life of lettuce from 8 d to 24 d.