A Preliminary Study On Residue And Degradation Of Pesticide In Different Vegetables

Dimethoate, Deltamethrin and Cypermethrin are broad-spectrum insecticides, and are sprayed frequently on the vegetables and the fruiters to prevent and to cure the plant diseases and pests. As pesticide residues of most commercial vegetables exceeded the acceptable level, it is important to study the degradation of the three pesticides in different kinds of vegetables. This study reported degradation behavior of pesticides in different vegetables. There are lots of factors affecting the pesticide residues in vegetable.1. The results of the degradation experiments showed that initial residue concentration and degradation rate were different in Chinese cabbage, Lettuce, Pepper and Radish for each of Dimethoate, Deltamethrin and Cypermethrin. The descending order of initial residue concentration was as follows: Lettuce >Chinese cabbage> Pepper> roots of Radish. But the descending order of the half life was as follows: Chinese cabbage > Lettuce > root of Radish >Pepper except Deltamethrin. The half life of Dimethoate was 1.62 days in Chinese cabbage, 1.74 days in Lettuce, 2.65 days in root of Radish, and 3.38 days in Pepper. The half life of Deltamethrin was 2.50 days in Chinese cabbage, 2.12 days in Lettuce, 2.71 days in root of Radish, 3.89 days in Pepper. The half life of Cypermethrin was 2.14 days in Chinese cabbage, 2.15 days in Lettuce, 2.47 days in root of Radish, 3.52 days in Pepper. The results showed that these three pesticides do not empoison vegetable if they are used following the concentration of recommended maximum size.2. As the result of the research about the effects of concentration, each of the three pesticides had the trend that the residue increased with the increase of concentration. For the effective factors of the residue of pesticides, the residue of pesticides had positive relations with initial residue concentration. In vegetables production, recommended maximum size or double of the recommended maximum size were suggest to be used to spray pesticides. The sprayed concentrations of Dimethoate ranged from 400mg/L to 800mg/L, of Deltamethrin from 25mg/L to 50mg/L, of Cypermethrin from 45mg/L to 90mg/L. The range of the safety interval of Dimethoate was from 3.2days to 11.2 days. The range of the safety interval of Deltamethrin was from 3.1days to 11 days. The range of the safety interval of Cypermethrin was from 1.7days to 9.4 days.3. The times of spraying pesticides had a bit of effects on residues of the pesticide in vegetables. But the speed of the pesticide degradation of the Chinese cabbage planted in autumn was more than twice as fast as that of the Chinese cabbage planted in spring.4. The degradation of the pesticide residues in the roots of radish is faster than that inthe leaves of radish. In spring, the half life of the Dimethoate was 3.87 days in the roots of radish, 3.47 days in the leaves of radish. In autumn, the half life of the Dimethoate was 2.88 days in the roots of radish, 2.65 days in the leaves of radish. After 20 days sprayed pesticides, in spring, the residues of Dimethoate in the roots of radish were 0.1851mg/kg, that of Deltamethrin 0.050mg/kg, that of Cypermethrin 0.0421mg/kg. But the residues of Dimethoate in the leaves of radish were 1.014mg/kg, that of Deltamethrin 0.2981mg/kg, that of Cypermethrin 0.3568mg/kg. In the autumn, the residues of Dimethoate in the leaves of radish were 0.2541mg/kg, that of Deltamethrin 0.1052mg/kg, that of Cypermethrin 0.1055mg/kg, but the residues of Deltamethrin and Cypermethrin cannot be detected, except Dimethoate with 0.0545mg/kg-residue.5. The degradation of the residues of pesticide in the vegetables planted in autumn was faster than that in the vegetables planted in spring. The safety interval of Dimethoate of the Chinese cabbage planted in spring was 13.2 days, and in autumn 7.2days. These of the roots of radish planted in spring and autumn were 10.2 days and 6.6days, and these of the leaves of radish were 17.9 days and 11.2 days. The safety interval of Deltamethrin of the Chinese cabbage planted in spring was 9.7 days, and in autumn 6.5days. These of the roots of radish planted in spring and autumn were 8.7 days and 5.2days, and these of the leaves were 14.3 days and 10.1 days. The safety interval of Cypermethrin of the Chinese cabbage planted in spring was 7.3 days, and 4.9 days in autumn. These of the roots of radish planted in spring and autumn were 6.1 days and 4.5 days, and these of the leaves were 11.5 days and 9.0 days.