Residue Dissipation Of Four Pesticides On Vegetables In Comparison With The Greenhouse And The Field

Nowadays, greenhouse vegetables is the main source of market vegetables, because the high temperature and humidity in greenhouse induced using excessive pesticides, the phenomenon of pesticide residue over standard becomes serious. Imidacloprid, dimethomorph, chlorothalonil and beta-cypermethrin are widely used in greenhouse. The present study involved three sections:(1) An improved analytical method was developed for quantification of four pesiticides in the vegetables;(2) The degradation of the four pesticides in the vegetables were studied in greenhouse and field;(3) The influences of environment factors in degradation of four pesiticides were studied. The aim of this study was to find out the differences of the degradation of pesticides between greenhouse and field and the main environmental factor. This paper made a forecast of pesticides prospective development in the greenhouse.The methods for the quantification of four pesiticides in four crops were established by HPLC and GC, respectively. Results showed that the recoveries of imidacloprid and dimethomorph ranged from80.86%-97.57%and79.41%-95.74within its respective linear range (0.01～10mg/L); The recoveries of chlorothalonil and beta-cypermethrin ranged from80.87%-102.89%and77.94%-95.13%, within its respective linear range (0.001～1mg/L).The degradation dynamics showed that the degradation half-lives of imidacloprid in spinach, cucumber, tomato, celery in the greenhouse were5.35d,4.47d,3.53d and4.27d, while in the field were3.08d,2.22d,1.84d and1.58d, lower than that in the field. The half-lives of dimethomorph in spinach, cucumber, tomato, celery in the greenhouse were6.49d,2.78d,3.07d and5.86d, while in the field were4.74d,1.70d,2.48d and4.03d. The half-lives of chlorothalonil in spinach, cucumber, tomato, celery in the greenhouse were7.22d,2.42d,2.97d and5.59d, while in the field were5.0d,1.95d,1.51d and3.92d. The half-lives of beta-cypermethrin in spinach, cucumber, tomato, celery in the greenhouse were6.88d,2.39d,3.49d and3.Old, while in the field were3.0d,1.94d,2.08d and2.12d. The degradation rates of the four pesticides in spinach, cucumber, tomato, celery in the greenhouse were lower than that in the field. In the process of experiment, there is great difference of light intensity and rainfall in the greenhouse and field, while the temperature of greenhouse is closed to the field.Our study showed that the photolysis rate tested with4200Lux and8300Lux of imidacloprid, dimethomorph, chlorothalonil and beta-cypermethrin were rapid, the light intensity increase twice, the photolysis rate also increase twice.Imidacloprid is steady in acid conditions, it degraded faster while pH was higher, dimethomorph is steady in the range of pH4-9, chlorothalonil and beta-cypermethrin also degraded faster while pH was higher. Temperature had a significant effect on the four pesticides’hydrolysis, which were increased with temperature increasing. The rainfall study showed that continuous rainfall have stronger scour to pesticides than interrupted rainfall.Through residual test of four pesticides in greenhouse and open field vegetables and environmental factor simulation,the preset study preliminarily found the rainfall, light intensity and temperature were the main environmental factors which caused the differences of residues between greenhouse and field.