A Preliminary Study On Residue And Degradation Of Pyrethroids In Vegetables

Pyrethroids are broad-spectrum insecticides, and sprayed frequently on the vegetables and the fruiters to prevent and to cure the plant diseases and pests. Because pesticide residues of most vegetables frequently exceeded the acceptable level, it is important for safety to study the degradation of Pyrethroids in different kinds of vegetables. This experiment builded up the methods of GC to determine the three pesticides of Cypermethrin, Fenvalerate, Deltamethrin; and studied the degradation of the three pesticides in Vigna sesquipedalis, Xue li hong and Hong cai tai. As follows the results:1. This study used Agilent6890N GC with HP-5 capillarty column to detect the residue pesticides in the vegetables. The minimal determination concentration scope of this method was from 0.002mg/kg to 0.005mg/kg; the average recoveries scope was from 86.5% to 98.6%; the average RSD scope was from 2.3% to 7.8%. The method was applied to the determination of the three Pyrethroids in actual samples with satisfactory results.2. The results of the degradation experiments showed that initial residue concentration and degradation rate were different in Vigna sesquipedalis, Xue li hong and Hong cai tai for each of Cypermethrin, Fenvalerate, Deltamethrin. The half life of Cypermethrin was 3.15 days in the leaves of Vigna sesquipedalis, 2.63 days in the fruits of Vigna sesquipedalis, 2.95 days in Xue li hong and 3.09 days in Hong cai tai. The half life of Fenvalerate was 4.85 days in the leaves of Vigna sesquipedalis, 3.63 days in the fruits of Vigna sesquipedalis , 3.54 days in Xue li hong and 3.97 days in Hong cai tai. The half life of Deltamethrin was 3.01 days in the leaves of Vigna sesquipedalis, 2.77 days in the fruits of Vigna sesquipedalis , 2.61 days in Xue li hong and 3.23 days in Hong cai tai.3. As the result of the research about of concentration, each of the three pesticides had the trend that the residue increased with the increase of concentration. Based on the edible safety of vegetables and the need to prevent the plant diseases and pests, in vegetable production, recommended maximum size were suggest to be used to spray pesticides. The sprayed dosage of Cypermethrin ranged from 20 to 30ml/667m~2, of Fenvalerate from15 to 40ml/667m~2, of Deltamethrin from 20 to 40ml/667m~2. The range of the safety interval of Cypermethrin was from 3 days to 9 days, the safety interval of Fenvalerate was from 7 days to 11 days and sometime longer, the safety interval of Deltamethrin was from 3 days to 7 days.4. The times of spraying pesticides had a bit of effects on residues of the pesticides...