Effects Of Mixed Contamination Of Three Pesticides On Degradation Behavior Of Pesticides

In recent years,with the wide application of pesticide mixtures,we often apply many kinds of pesticides to control diseases,insect pests and weeds at the same time.The pesticide residues in the environment are often not a single component,but a mixed form of many kinds of pesticides.Studies have shown that pesticide mixed pollution has an impact on the environmental behavior of pesticides,and the safety assessment based on the results of single pesticide environmental behavior research can not truly and accurately reflect the actual environmental effects of pesticides.Therefore,it is necessary to carry out related research on the environmental behavior of pesticide multi-component residues in the environment.Antibiotics and surfactants are widespread in the environment and may have an impact on environmental behavior.The effects of antibiotics and surfactants on the degradation of pesticides were studied in this paper,taking three common pesticides,chlorfenapyr,cypermethrin and dimethomorph as research objects.And the effects of mixed pollution of three kinds of pesticides on their hydrolysis,photolysis and glass surface photolysis were studied under indoor simulation conditions.The main results are as follows:1.An instrumental method for simultaneous determination of chlorfenapyr,cypermethrin and dimethomorph by high performance liquid chromatography was established.The optimal conditions were EC-C₁₈（4.6×150 mm,4.0μm）column,acetonitrile with water gradient elution,column temperature 35℃and UV detection wavelength 225 nm.Under these conditions,the linearity of the three pesticides was good in the concentration range of 0.1～10 mg/L,the determination coefficient R²was greater than 0.99,and the relative standard deviation RSD was less than 1%.The recoveries of the three pesticides on water and glass slides were 76.9-95.3%,with RSDs<8.5%.The accuracy and precision of the method are good and meet the detection requirements.2.The effect of the mixture of chlorfenapyr,cypermethrin and dimethomorph on hydrolysis was studied by indoor simulation method.The hydrolysis of chlorfenapyr and cypermethrin conformed to the first-order kinetic equation.When any binary pesticide is mixed,there is mutual inhibition between the two pesticides.However,when three pesticides exist at the same time,the hydrolysis half-life of chlorfenapyr and cypermethrin is lower than that of any binary complex system.According to the results of mixed pollution formula,the inhibition of two pesticides on the hydrolysis of another pesticide may be antagonistic in the ternary system.Dimethomorph was stable in water and did not degrade within 120 days.3.The effects of the mixture of chlorfenapyr,cypermethrin and dimethomorph on photolysis in water were studied by indoor simulation method.The photolysis of the three pesticides in water all conformed to the first-order kinetic equation.In the binary system,cypermethrin accelerated the photolysis of chlorfenapyr,while dimethomorph inhibited the photolysis of cypermethrin.In the presence of three pesticides,the photolysis rate of cypermethrin was higher than that of the binary system.According to the results of mixed pollution formula the inhibition of cypermethrin and dimethomorph on the photolysis of chlorfenapyr was antagonistic.For cypermethrin,the photolysis of cypermethrin was inhibited by chlorfenapyr,and dimethomorph,while the inhibition effect of cypermethrin photolysis rate was significantly higher than that of any binary systemin in the ternary system.According to the results of mixed pollution formula,the inhibition of cypermethrin photolysis by chlorfenapyr,dimethomorph is a synergistic effect in the ternary system.For dimethomorph,the photolysis of dimethomorph were all inhibited by chlorfenapyr,cypermethrin.In the ternary system,the photolysis rate of dimethomorphhad was no significant change compared with that of single agent.According to the results of mixed pollution formula,the inhibition of chlorfenapyr and cypermethrin on the photolysis of dimethomorph was antagonistic in the ternary system.4.The effects of the mixture of chlorfenapyr,cypermethrin and dimethomorph on the surface photolysis of glass slides were studied.The photolysis of the three pesticides on the slide surface accords with the first-order kinetic equation.In the binary pesticide slide containing cypermethrin and dimethomorph,the photolysis half-life of chlorfenapyr did not change significantly.While the three pesticides existed at the same time,the photolysis half-life of chlorfenapyr was significantly prolonged.According to the results of mixed pollution formula,the inhibition of cypermethrin and dimethomorph on the surface photolysis of chlorfenapyr was a synergistic effect.The photolysis of cypermethrin was accelerated by chlorfenapyr,dimethomorph in binary system,but the photolysis rate of cypermethrin was significantly delayed in ternary system.According to the results of mixed pollution formula,the inhibition of cypermethrin surface photolysis by chlorfenapyr and dimethomorph was synergistic in the ternary system.For dimethomorph,chlorfenapyr accelerated the photolysis of dimethomorph,while cypermethrin had no significant effect on the photolysis of dimethomorph,but in the ternary system,the photolysis rate of dimethomorph is equal to that of the binary system with chlorfenapyr.According to the results of mixed pollution formula,the inhibition of chlorfenapyr and cypermethrin on the surface photolysis of dimethomorph is similar to the additive effect in the ternary system.5.The effects of p H,surfactant and antibiotics on the degradation of chlorfenapyr,cypermethrin and dimethomorph were studied by indoor simulation method.The hydrolysis rate of chlorfenapyr and cypermethrin was the fastest under neutral condition,and the half-life of degradation from large to small was p H4>p H9>p H7.Both surfactants inhibited the hydrolysis of cypermethrin and chlorfenapyr,and the inhibitory effect of SDS on cypermethrin was stronger than that of CTAB,chlorfenapyr is the opposite.Oxytetracycline can promote the hydrolysis of chlorfenapyr,but inhibit the hydrolysis of cypermethrin.SDS and CTAB significantly promoted the photolysis of chlorfenapyr and delayed the photolysis of dimethomorph in water.It had no significant effect on the photolysis of cypermethrin in water.Oxytetracycline significantly inhibited the photolysis of cypermethrin and dimethomorph in water,but had no significant effect on the photolysis of chlorfenapyr.