Dynamics of Chlorpyrifos Residue in Vegetable Soybean and Techniques for Its Safe Use

In order to monitor chlorpyrifos residue content in vegetable soybean,and apply chlorpyrifos scientifically and safely to control the pests in vegetable soybean,and insure the quality safety of products,the residue dynamics of chlorpyrifos in vegetable soybean was studied by the methods of gas chromatography and field experiment.In addition,techniques for safe use were explored in field demonstration.The results showed that initial chlorpyrifos residue on vegetable soybean was high.The chlorpyrifos residue was higher when treated with 1.08 kg·hm-2 than treated with 0.77 kg·hm-2.Spraying twice led to higher chlorpyrifos residue than single spray.The dynamics of chlorpyrifos residue in vegetable soybean followed first order kinetics.The degradation rates was faster in the early season than in the late season.The half life time(DT50) and time needed for 99% degradation were 2.7 d and 18.2 d in the early season,and the figures were 3.4-3.5 d and 22.7-23.5 d respectively in the late season.In the field demonstration to explore techniques for safe use of chlorpyrifos,conventional application rate and spray method were adopted.Vegetable soybean received twice spray of 0.77 kg·hm-2 of effective component of chlorpyrifos at 7 d intervals.Chlorpyrifos residues in vegetable soybean were all below 0.1 mg·kg-1 25 d after application,and all below 0.05 mg·kg-1 after 28 d.The average residue content was 0.075 mg·kg-1 and 0.030 mg·kg-1,respectively.According to GB2763-2005(for leafy vegetable) and the MRL of Japan,USA and European Union,the products met the Chinese food safety standard after 25 d and met that of Japan,USA and European Union after 28 d.