Dynamic Dsitribution, Movement And Domestic Removal Method Of Chlorothalonil And Chlorpyrifos In Greenhouse Plants

The problem of pesticides residue exceeding standard problem in greenhouse cultication has drawn great attention. Based on two years’ field experiments of greenhouse and open field cultivation, the time-dependent distribution, exposure level, migration and transformation of two pesticides chlorthalonil (CHT) and chlorpyrifos (CHP) in cumcumber plants and tomato fruits were discussed in detail by the gas chromatography analysis method with the detection of GC-ECD and GC-MS. Meanwhile, the pesticides distribution among cuticle, pulp and plasma, the permeation pathway and dynamic transfer were discussed. In final, the effectiveness of elution pesticide in cherry tomato were discussed, and an optimized method of removing pesticide was proposed in food processing.Cumcumber and tomato plants growing in both greenhouse and open air were sprayed with CHT and CHP at recommended dosages. The persistence and degradation of the pesticides in cumcumber roots, stems, leaves and fruits as well as tomato fruits over a period of2weeks following spray were determined. The results showed that CHT and CHP residue in greenhouse were higher than open air condition for all detected cumcumber and tomato parts. And at a specific time, the level of CHT in greenhouse cumcumber plants decreased in the order of leave>>fruit>stem>root, and that of CHP in the order of leave>>fruit>>stem≈root The maximum levels of CHT residues in a specific cumcumber plant part were recorded between8and72h after spray while CHP residues were between1-3h. Compared with two pesticides, CHT was more likely to remain on cumcumber and tomato fruits. In terms of the spatial distributions, the pesticide levels were higher in the middle of greenhouse than in other locations alongside the greenhouse due to cross-ventilation in greenhouse. The half-lives of CHT and CHP in cumcumber fruits were7.2d and3.2d while for tomato were5.8d and7.2d, respectively, which were consistent with reported in the literature.Determining the distribution of pesticides in fruits is essential to eliminate pesticide residues during food processing. In this study, the dynamic distribution of two pesticides, chlorothalonil (CHT) and chlorpyrifos (CHP), were determined in different tomato parts following immersion in pesticide solutions. The concentrations of CHT and CHP in tomato followed an order of cuticle> plasma> pulp. However, the plasma initially accumulated the highest pesticide concentration. And the ratio of CHT concentration to that of CHP in plasma was about2.1:1, similar to the ratio in solution, which suggested carpopodium as the entry site for the pesticides tested. The ratio in the cuticle was0.02:1-0.06:1. This was consistent with the ratio of Kow for the two pesticides, manifesting the direct pesticide transfer from solution to cuticle. Following pesticide injection into tomato, the degradation of CHT over96h was described by a first-order decay equation, Ctomato(t)CHT=C0×e-0.0239t. The CHP concentration in tomato remained nearly constant with little degradation detected. Deducting the amount of degradation and migration, volatilization appeared to contribute the most amount of migration of CHT and CHP in tomato.Washing is the most practical way to remove pesticide residues in fruits and vegetables. Two commonly used kitchen dishwashing liquids (detergents) in Chinese market were tested for enhanced removal of chlorpyrifos (CHP) and chlorothalonil (CHT) in cherry tomatoes by soaking the cherry tomatoes in the detergent solutions. The critical micelle concentrations of detergent A and detergent B were about250mg/L and444mg/L, respectively. Detergent A had a higher solubilizing ability for pesticides and hence washing effectiveness than detergent B. The apparent solubility of CHP increased with increasing detergent concentration, while that of CHT remained comparatively invariant independent of detergent concentration within the tested range. The apparent solubility of CHP was also consistently higher in solutions of both detergents as compared to CHT. Due probably to its lower log Kow value, CHT was more readily washed off cherry tomatoes than CHP. In terms of washing, a duration of10-20min was sufficient for removal of pesticides on cherry tomatoes in distilled water and detergent solutions. The effectiveness of removing pesticides increased with increasing detergent concentration from50mg/L to5g/L, with up to80%CHT and42%CHP removed. Multiple washing further increased pesticide removal. Adding10%acetic acid to lower pH or increasing washing temperature favored pesticide removal, but10%NaCl produced the shielding effect and substantially reduced the effectiveness of detergent A for pesticide removal.