Distribution And Dissipation Of Chlorothalonil And Chlorpyrifos In Greenhouse Crops

Comparing to the open field conditions, greenhouse provides more favorable climate for fast reproduction of pests and diseases, which require extensive application of pesticides for their control, and the hermetic environment in greenhouse alters dissipation behavior of pesticides in crop plants. Therefore, extensive application of pesticides in greenhouse may result in accumulation of residues at levels considerably higher than those in open field. The objectives of this work were to analyze distribution and dissipation of pesticides in greenhouse crops, to provide a way to evaluate the vegetable safety and pesticide pollution in greenhouse.This paper investigated the distribution and dissipation of chlorothalonil (CHT) and chlorpyrifos (CHP) in tomatoes and cucumbers grown in greenhouse and open field conditions. The methods of pesticides measurement in crops have been established. The acetone was employed as extractant, and the extraction time of crops surface pesticides was 5 minutes. The inner pesticides were extracted by mixed solution [V (hexane)∶V (acetone) =6∶4] with ultrasonic wave, and the extraction was concentrated and purified by chromatography column filled with sodium sulfate - silica gel - neutral aluminum oxide, and eluted with mixed solution [V (hexane)∶V (acetone) =9∶1], the average recoveries of CHT and CHP were 92.70~94.48% and 112.80~113.25%, respectively.The distribution of CHT in the crops was full foliage> full fruit, foliage surface>foliage flesh> peel> pulp, while the distribution of CHP in crops was full foliage> full fruit, foliage surface> peel> foliage flesh> pulp. And most of the pesticides were distributed on the surface of fruits and foliages. The average residues of CHT in cucumber and tomato foliage surface were accounted for 91% and 97% of the full foliage, and the CHP accounted for 96% and 71% respectively; while the average residues of CHT in cucumber and tomato peel were 91% and 82% of the full fruit, and the CHP was 91% and 70%, which is the same as the distribution trend in open field.The contents of the two pesticides in crop under greenhouse and open field conditions were generally declined during the experiment periods. The dissipation rates of CHT and CHP in greenhouse were much slower than in open field. After sprayed with recommended dosages, the half- lives of CHT and CHP in cumber full foliage and full fruits were 32.1, 7.4 d and 4.1, 3.3 d, respectively; while the corresponding half-lives in open field were 3.5, 2.0 d and 1.5, 1.5 d, respectively; the half-lives of two pesticides in greenhouse tomato full foliage and full fruit were 22.2, 6.4 d and 3.1, 6.6 d, while the corresponding half-lives of open field were 3.5, 4.0 d and 3.5, 4.0 d, respectively. Those showed that the half-lives of two pesticides in greenhouse were extended with compared to that of in open field. After 14 days application, the CHT in cumber and tomato fruits in facility environment were 7.86 and 8.79 mg/kg, and CHP were 1.01 and 6.51 mg/kg, both of which were higher than the national standard (5.0 and 0.5 mg/kg); while the pesticide residues in open field 7 days after the sprayed were less than that of in greenhouse after 14 days. Moreover, the two pesticide residues in cucumber fruit have met the national standard.