Study On The Residual Behaviour Of Avermectins And Monosultap In Pakchoi And Soil

Pesticides has brought a large number of substantial growth in agricultural production, but the issue of pesticide residue in environment due to the irrational use of pesticides brought has caused widespread concern. Therefore, the investigation of contamination behavior of pesticides in environment and agricultural products is important for protection of agricultural environment, promoting agricultural production safety and protection of human health significance.This paper studied the residual pollution behaviour of avermectins and monosultap in pakchoi and soil. By field experiment, the paper investigated the analysis methods and the degradation dynamics of avermectins and monosultap in pakchoi and soil,so that ,we can get the base data and science basis for make a safe use regulation and MRL of avermectins and monosultap in pakchoi. The main results were showed as follows:1. Residue analysis method of HPLC for detecting avermectins in pakchoi and soil was established. The avermectins in soil could be extracted with water and acetone (20 mL:50 mL), then re-extracted with dichloromethane three times. The avermectins in pakchoi could be extracted with water and acetone 1:1, then re-extracted with petroleum ether and acetonitrile. The constant volume was finished with methanol, after being concentrated by evaporation. At last, the avermectins was detected by HPLC-DAD. The sensitivity, precision and accuracy of the test method could meet the requirement of pesticide residue determination.2. Residue analysis method of GC for detecting monosultap in pakchoi and soil was established. The monosultap in pakchoi and soil were acidized by 0.1 mol·L^-1 HCl,adjusted pH value to 8.5⁹.0, then add 4 mL 1 mol·L^-1 sodium sulfide, so monosultap could turn into nereistoxin on the condition of water bath, which was re-extracted with pentroleum. The constant volume was finished with n-hexane, after being concentrated by evaporation. At last, the monosultap was detected by GC-ECD detector. The sensitivity, precision and accuracy of the test method could meet the requirement of pesticide residue determination.3. The law of residual degradation dynamic and its final residues of 20% avermectins & monosultap WP in pakchoi and soil were studied by a two-year and two-field trial in Tianjin and Jiangsu province. The pakchoi and soil were treated with the pesticides at 1.5 times of the recommended dosage. It is shown that the residual degradation procedure was up to the mathematic pattern: C=C0e-kt.The half life of avermectins and monosultap is less than 30 days,so they could be degraded in pakchoi and soil, easily.4. 20% avermectins & monosultap WP was sprayed one or one point five times at recommended dosage. Gathered the pakchoi and soil sample at 1 d, 3 d and 5 d before the last application for detecting. The consequence indicated that the maximum residue limit of avermectins and monosultap in pakchoi and soil were 0.0436 mg·kg ^-1 and 0.0428 mg·kg ^-1 at 5 d after the last employed pesticides.5. The maximum residue limits (MRL) of avermectins and monosultap in pakchoi and soil had not be made in our country, at present. Related standards have: The MRL of avermectins of Japan positive list in cabbage is 0.01 mg·kg ^-1. The MRL of avermectins of chinese NY in leafvegetables is 0.05 mg·kg ^-1, the MRL of monosultap in cabbage is 0.2 mg·kg ^-1. So it is safe of the residue of avermectins and monosultap in pakchoi and soil on the 5th day after applying 1.5 times of the recommendation dosage at 2-3 times at an interval of 7 d when the pakchoi grow five to eight leafs.