Study On Deposition,Adsorption And Dissipation Of Four Pesticides On Three Leafy Vegetables

Our country is the world vegetable production and consumption of the biggest country,vegetables in our country agricultural production play an important role.In recent years,the problem of excessive pesticide residues in vegetables occurs from time to time,which not only affects import and export trade,but also poses a threat to people’s health.Leafy vegetables are the most important part of vegetable industry,and the detection rate of pesticide residues is relatively high.The formation of pesticide residues mainly includes deposition,absorption and dissolution.Existing studies have revealed the law of pesticide dissolution in leafy vegetables,but there are few studies on the deposition behavior affecting the initial residues,and the adsorption mechanism kinetics of pesticides in vegetables from leaf surface to body is less,which prevents scholars from exploring the law of pesticide residue formation more scientifically.In this paper,three leafy vegetables such as spinach,cabbage and lettuce were taken as the research object,and imidacloprid,acetamidine,thiamethoxam and fenvalerate were taken as representative pesticides.The deposition,absorption and dissolution laws of four kinds of pesticides on three leafy vegetables after application of foliar spray were studied to provide theoretical reference for the safe use and risk assessment of pesticides in vegetables.It is of great significance to promote the safe production of vegetables and guarantee the quality and safety of agricultural products.The main research contents and results of this paper are as follows:(1)The effects of temporal and spatial changes,water consumption,dosage forms and leaf area index on the original deposition of pesticides were studied.The deposition test of four pesticides on three leafy vegetables was carried out to explore the deposition dynamics of pesticides at different time(0.5-8 h)after application,and the deposition distribution in the leaf surface,roots and soil of vegetable crops at 2 h after application.Two leafy vegetables,spinach and lettuce,and two pesticides,imidacloprid and acetamidine,were selected.The influence of different factors on the original deposition of pesticide on leafy vegetables was further explored.The results showed that 2 hours after application could be used as the choice to determine the original deposition amount.The proportion and distribution of pesticide deposition were affected by different foliar structure characteristics.It was confirmed that the factors such as water dosage,pesticide dosage form and crop leaf area all affected the original pesticide deposition to a certain extent.With the increase of water added,the original deposition decreases.The difference of deposition amount of different dosage forms of pesticide on two kinds of leafy vegetables was related to the characteristics of leafy vegetables and pesticide itself.There was a negative correlation between the amount of pesticide deposition and leaf area index.The smaller the leaf area index was,the larger the amount of pesticide deposition was.(2)The adsorption kinetics of pesticide from leaf surface to body was revealed.The residual adsorption test of four pesticides on three kinds of leafy vegetables was carried out.Vegetables were cleaned after being picked by simulating normal edible soaking and cleaning,and the adsorption behavior of pesticides after deposition on the surface of leafy vegetables was studied.The results of adsorption dynamic test showed that the pesticide residues in leaf cabbage increased first and then decreased after the application of four kinds of pesticides,indicating that the adsorption of pesticides from surface to body occurred.When different pesticides were sprayed on the same vegetable,the adsorption equilibrium rate was different.The same pesticide sprayed on the same kind of vegetables,its adsorption equilibrium time and concentration are not the same.It was confirmed that both the properties of pesticides and the types of leaf vegetables would have an effect on the adsorption of pesticides.For the first time,the quasi-first-order adsorption kinetic equation and the exponential equation of dissolution first-order kinetic equation were combined to obtain the pesticide residue enrichment equation of simulated pesticides from the surface of vegetables to the body,and the pesticide residue data were fitted with the equation.(3)The dissolution kinetics curve and the final residue of pesticides were analyzed.The dynamic test of residual dissolution of four pesticides on three kinds of leafy vegetables was carried out to determine the half-life of degradation of four pesticides in three kinds of leafy vegetables,and to confirm that four pesticides are easy to degrade in three kinds of leafy vegetables.The differences in the dissolution rates of four pesticides on three leafy vegetables indicated that the properties of pesticides and the types of leafy vegetables would affect the dissolution rates of pesticides.The final residue test results showed that the application times would affect the final residue amount and safety interval of pesticide on leaf and vegetable crops.