Study On The Residual Dynamics And Safety Assessment Of 72%Mancozeb·Cymoxanil WP In Soil And Potatoes

In order to provide basis for residual rule of 72% Mancozeb·Cymoxanil WP, analysis methods of 72% Mancozeb·Cymoxanil residue and degradation in soil and potatoes and its final residues were studied. 72% Mancozeb·Cymoxanil has three active ingredients which are Mancozeb, ETU and Cymoxanil, the results were shown as follows:1. A detection method of Mancozeb residues in potatoes and soil by gas chromatography was established. The study results about the method for determining Mancozeb through static-head-space-sampling technique suggested that it was a rapid analysis method with high accuracy and good reappearance. Its average analysis cycle time is 5 min .Through the study about the conditions of static-head-space-sampling altered, the optimal operation conditions were as follows: equilibrium temperature 60℃, equilibrium time 60min, salting out reagent sodium chloride and its concentration was 2.0g/100mL, the volume of head space gas injected was 1.0 mL, and the influence of sampling times on results could be overlooked. The method was simple and easy to operation.2. Residue analysis method of ETU in potatoes and soil was established. ETU is strong polar compound, which is difficult detected by generic chromatogram technique. The method of ramification was adopted. After samples were distilled with methanol, the solution were mixed with benzyl chloride,and circumfused to make S-benzyl-ETU in mixed solution of methanol and water. The ramification was purified by LLE, and could be detected by GC.3. Residue analysis method of Cymoxanil was established in potatoes and soil. The Cymoxanil in leafage and culm could be extracted with ethyl acetate, and then re-extracted with ethyl acetate. The Cymoxanil in soil could be extracted with acetone, and then re-extracted with dichloromethane. After being concentrated by evaporation, the extracts were cleaned up by a column chromatography on florisil. The final residue can be detected by C18 in UV of high sensitivity. The accuracy, reappearance and precision of the method well satisfied the essential rules of pesticide residue determination.4. Degradation dynamic of 72% Mancozeb·Cymoxanil in soil and potatoes was studied by a two-year field experiment in Tianjin and Anhui province. The soil and potatoes were treated with pesticide at 3260 gai ha^-1. Samples of soil and potatoes were analysised at different time, then the degradation procedure was corresponding to the mathematic pattern: C=Coe-kt. The result showed that 72% Mancozeb·Cymoxanil was degraded easily in soil and potatoes.5. With sprayed 72% Mancozeb·Cymoxanil on potatoes and soil three or four times at recommended dosage, at the interval of 3d and 7d, the results were as follows: at three times, the final residue of Mancozeb was 0.0143⁰.1981mg·kg^-1 in potatoes, ETU was ND⁰.0341mg·kg^-1, Cymoxanil was ND⁰.0172mg·kg^-1, and at four times, the final residue of Mancozeb was 0.0079⁰.3227mg·kg^-1in potatoes, ETU was ND⁰.0284mg·kg^-1, Cymoxanil was ND⁰.0308mg·kg^-1. The result showed that it was safe to use 72% mancozeb·cymoxanil at this recommended dosage, 3⁴ times, 7d interval by safety assessment.