Inspection And Management System For Pesticide Residues In Leafy Vegetable

The invention and application of pesticides greatly increase the output of crop production. With the excessive and fallacious use of pesticides, their residues in food, however, cause a lot of ill-influence on human's health. In recent years, poisoning accidents caused by the pesticide residues in vegetables were reported frequently in the country, which seriously threaten the consumers' health. People have since been aware of pesticide residues in vegetables production. Undoubtedly it is of great importance and the foundation of controlling pesticide residues and assuring the food safety that a study on inspection and management system for pesticide residues in leafy vegetables conducted. Therefore, our research conducted include residual dynamics of mixture of pesticide, pesticides in different season vegetables, low residual levels insecticides screening and its environmental safety assessment, and removal method for pesticides residues in cabbage leaf surfaces. The main results are listed as follows.1. Residual dynamics in mixture of pesticide, autumn Chinese cabbage and spring cabbagePesticides residual dynamics of chlorpyrifos, dimethoate, cyhalothrin, cypermethrin, fenvalerate, deltamethrin and chlorothalonil in the autumn Chinese cabbage (Brassica chinensis L.), spring cabbage (Brassica oleracea L. Var. capitata) and its mixture were studied. The results indicated that mixed use of pesticides did not have significant effects on pesticide residue levels, initial concentrations and half-lives. When the autumn Chinese cabbages were treated once at recommended middle rates, the half-lives of the seven pesticides in the vegetable were 4.71, 5.28, 2.85, 3.50, 5.40, 4.34 and 3.96 days respectively. Thus, based on the recommended pre-harvest intervals, the residual levels of all pesticides were within the MRLs except for chlorpyrifos. When the autumn Chinese cabbages were treated four times at maximal rates at 5 day intervals, the half-lives of chlorpyrifos, cypermethrin and chlorothalonil in the vegetable were 4.92, 3.78 and 5.93 days respectively, so that, based on the recommended pre-harvest intervals, the residual levels of chlorpyrifos and chlorothalonil exceeded the MRL, but the residual level of cypermethrin was within the MRL. In the spring cabbage, if the cabbages were treated one time at recommended middle dosage of pesticides, the half-lives of the seven pesticides in the vegetable were 2.03, 1.57, 1.64, 2.34, 2.16, 1.51 and 1.80 days, respectively. And all pesticides maximum residue limits were not exceeded according to the recommended pre-harvest interval. However, if the vegetables were treated four times at the maximal dosage with a five-day's interval, the half-life of chlorpyrifos, cypermethrin and chlorothalonil in the vegetable were 2.90, 2.62 and 4.06 days, respectively, and the final residual amount of chlorothalonil exceeded its MRL on cabbage, but the final residual amounts of cypermethrin and chlorpyrifos were below its MRLs on the cabbage. Pesticides residues data in autumn Chinese cabbage and spring cabbage clearly showed that the pesticides residues were dependent on the frequency and rate of pesticide application and on the weather conditions immediately following spraying.2. Screening high efficacy and low residual insecticides on leafy vegetables and insecticide residual dynamics in fieldRoom bioassay, field efficacy and residual dynamics were carried out to evaluate pesticides (permethrin, tetramethrin, bifenthrin, dichlorvos, phoxim and 50:50 binary mixtures of pyrethroid and organophosphate) against two pests (Pieris rapae and Plutella xylostella). Room bioassay results showed the efficacy against Pieris rapae and Plutella xylostella of pyrethroids were higher than organophosphates. All tested insecticides efficacy against Pieris rapae were better than Plutella xylostella. The 50:50 binary mixtures of pyrethroid and organophosphate showed synergism or additive. Field effectiveness results showed that the field efficacy against Pieris rapae and Plutella xylostella of binary mixtures of pyrethroid and organophosphate aboved 90%. The insecticides are safe to crops at the dosages. The initial concentrations and half-lives were decreased when the insecticides were used in mixture. In pollution-free vegetable production, these insecticides mixtures can effectively control the pest in vegetables, decrease pesticide residues, and improve the quality and safety level of vegetables.3. Acute toxicity to non-target organism of low residual level insecticidesAcute toxicities to zebrafish and silkworm of two organophosphorus insecticides (dichlorvos and phoxim), four pyrethroid insecticides (permethrin, tetramethrin and bifenthrin) were determined. The data indicated that the acute toxicities to zebrafish of all tested pyrethroids were special high, phoxim were high (48, 72 and 96 h exposure) or middle (24 h exposure), but dichlorvos were low grade. The acute toxicities to zebrafish of 50:50 binary mixtures permethrin or bifenthrin with organophosphates were special high too; however, the mixtures of tetramethrin with organophosphates were high grade. The joint effects of pyrethroid and organophosphate were additive, except for the mixture of bifenthrin with dichlorvos, it showed antagonism (72 h exposure). Acute toxicities to silkworm of all tested insecticides were high, except for bifenthrin, it showed special high grade. Acute toxicities to silkworm of all tested 50:50 binary mixtures of pyrethroid and organophosphate were high, except for the mixture of tetramethrin and dichlorvos, it showed middle grade. The joint effects of all tested 50:50 binary mixtures were additive, except for the mixture of tetramethrin with dichlorvos, it showed antagonism (24 and 48 h exposure). Therefore, these insecticides should be prohibited in or near to paddy, pond and mulberry orchards, to avoid side effect on non-target organism.4. Removal techniques of pesticide residues in cabbage leaves surfaceRemoval efficacies of organophosphates (dimethoate and chlorpyrifos), orgnaochlorine (p,p-DDT andγ-666), pyrethroids (deltamethrin and cypermethrin) and fungicide chlorothalonil residues in cabbage leaves surface caused by different concentrations of salt solution, acetum, tap water, refrigeration and cooking were simulation studied in laboratory. In the same treatment concentration and time, effect of acetum on 7 pesticide residues in cabbages surfaces were high than salt solution. The tap water treatment was the worst. There are no significant effects on pesticide residues in cabbage that refrigeration 12-48 h. The removal efficacy caused by stir-frying was above 65%, and the effects on organophosphates, pyrethroids and fungicide chlorothalonil were greater than organochlorine. It is suggested that citizens should wash cabbage carefully and stir-frying before eat it. Raw eating current situation of pesticide application on cabbage is not encourages.