Effects Of Surfactants And Catechin On The Photolysis Of Chlorothalonil On The Surface Of Pepper

Methods of photolysis of chlorothalonil on pepper surface were established. The photochemical degradation of chlorothalonil on pepper surface was studied through adding chlorothalonil and foreign materials on pepper surface. The present study examined the effects of the different kinds of surfactants and catechin on photochemical degradation of chlorothalonil in aqueous solution and on the plant surface under high-pressure mercury lamp,and sunlight illumination respectively. Under the sunlight the photochemical degradation of chlorothalonil on pepper surface was studied by covering film or not to imitate greenhouse environmentResidues of chlorpyrifos were extracted from pepper with acetonitrile, then mechanical shocked after ultrasonic extraction and determined by HPLC. The method detection limit (MDL)of chlorpyrifos in the samples of pepper was0.2mg/kg-2.0mg/kg, the average recoveries and coefficient of variations of the method were89.13%-96.44%and2.426-4.96%. These results showed that both the methods accorded with demands of residue analysis of pesticides.The effects of three different kinds of surfactants on photochemical degradation of chlorothalonil are different under high-pressure mercury lamp. The SDS has the photo-sensitization effect on photochemical degradation of chlorothalonil and the sensitization rate is18.89%; The Span-20has the photo-sensitization effect on photochemical degradation of chlorothalonil and the sensitization rate is21.28%; The CTAB has the photo-quenching effect on photochemical degradation of chlorothalonil and the quenching rate is21.34%.Under the high-pressure mercury lamp, the low doses of SDS and Span-20has the photo-sensitization effect on photochemical degradation of chlorothalonil, while the dosage increased the photo-sensitization effect weakened gradually even into the quenching effect. When the added doses of SDS is0.5:1, the photo-sensitization effect is the strongest and the photolysis of chlorothalonil rate is the maximum(19.81%); When the added doses of Span-20is0.5:1, the photo-sensitization effect is the strongest and the photolysis of chlorothalonil rate is maximum(31%); CTAB has the photo-quenching effect on photochemical degradation of chlorothalonil and with the increase of adding amount, quenching effect increased. When the added dose is10:1, the rate is38.11%.The effect of the surfactants on photochemical degradation of chlorothalonil under the sunlight is the similar with the effect under the high-pressure mercury lamp. The low doses of SDS and Span-20has the photo-sensitization effect on photochemical degradation of chlorothalonil, while CTAB has the photo-quenching effect. When the added doses of SDS is0.5:1, the photo-sensitization effect is the strongest and the photolysis of chlorothalonil rate is the maximum(33.91%); When the added doses of Span-20is1:1, the photo-sensitization effect is the strongest and the photolysis of chlorothalonil rate is maximum(62.77%); CTAB has the photo-quenching effect on photochemical degradation of chlorothalonil and with the increase of adding amount, quenching effect increased. When the added dose is10:1, the rate is90.21%.The half-life of chlorothalonil on the surface of pepper of covered film is greater than the natural state. It showed that plastic film deferred the speed of photolysis of chlorothalonil on the pepper. The effect of the surfactants on photochemical degradation of chlorothalonil under the natural state is the similar with the effect under the state of plastic film, but the photo-sensitization rate of SDS and Span-20reduced and the photo-quenching rate increased.Three kinds of catechin have the photo-sensitization effect on photochemical degradation of chlorothalonil under the high-pressure mercury lamp and the trend of the sensitization effect is the same, but the sensitization rate of three kinds of catechin is different. The photo-sensitization rate of ECG is15.08%. The photo-sensitization rate of EGC is22.58%. The photo-sensitization rate of EGCG is12.57%.The effect of the catechin on photochemical degradation of chlorothalonil under the natural state is the similar with the effect under the high-pressure mercury lamp. Three kinds of catechin have the photo-sensitization effect on photochemical degradation of chlorothalonil. Generally speaking, the sensitization effect is added gradually with the enhancing of the ratio. When the ratio reached a certain degree, the effect has a tendency to gradually decline.The half-life of chlorothalonil under the covered film is greater than the natural state. The effect of the catechin on photochemical degradation of chlorothalonil on the pepper covered film is the similar with the effect under the natural state. Three kinds of catechin have the photo-sensitization effect on photochemical degradation of chlorothalonil and the photo-sensitization rate is appropriate to the natural state.