The Possibility Of Irradiaiton To Degrade Pesticide Residues In Green Tea Manufacturing Processes

Green tea is one of the six major health drinks in the world, it is rich in theanine,polyphenols and caffeine, etc. and these substances have good effects on human health.However, pesticide residue in tea can not be ignored while drinking it. Currently, thetechniques on pesticide residue degradation in water and soil have been reported in manypapers, but the researches of agricultural products and tea are rarely. The effect of60Co-γirradiation on the degradation of pesticide residues was studied.10kinds of pesticidesincluding pyrethroid, organophosphate, organochlorine and neonicotinoid were irradiatedat the same conditions and the result showed that at10kGy irradiation dose thedegradation rate of pyrethroid insecticides was higher than other insecticides. A furtherirradiation experiment on pyrethroid insecticides showed that Fenpropathrin andDeltamethrin had the maximum degradation. The two pesticides’ degradation rate atdifferent radiation dose and different concentrations were studied and their degradationproducts were analysed, too. The degradation rate of Fenpropathrin and Deltamethrinunder irradiation and green tea manufacturing processes was investigated. The mainfindings are as follows:1. After irradiation under10kGy dose, pyrethroid insecticides’ degradation rate inorganic solvents is higher than degradation rate in the glass surface. In hexane degradationrate of pyrethroid insecticides is about70%while the degradation rate of the glass surfaceis generally lower than50%. Neonicotinoid insecticides’ degradation rate in the glasssurface is higher than the degradation rate in acetonitrile, but no more than10%. Thedegradation rate of organophosphate and organochlorine pesticides in the glass surface arequite different because of different pesticides, all are less than50%.2. A further irradiation confirmation experiment on pyrethroid insecticides, includingFenpropathrin, Bifenthrin, Deltamethrin, shows that: Degradation rate of insecticide insingle standard sample is higher than in mixed standard sample. Descending order ofdegradation rate: deltamethrin> fenpropathrin> bifenthrin. After10kGy dose irradiation,3pesticides’ degradation rates in single standard sample and mixed standard sample are53.6%,23.0%,16.0%and37.2%,13.8,10.8%respectively.3. The degradation of Fenpropathrin and Deltamethrin at different radiation dose anddifferent concentration are studied and the result indicates that in the same concentration,degradation rate increases with increasing radiation dose. When the concentration ofFenpropathrin standard solution is20μg/mL, the degradation rates at5,10,15kGy radiation dose are32.6%,46.6%,60.2%separately. When the concentration ofDeltamethrin standard solution is20μg/mL, the degradation rates at5,10,15kGy radiationdose are51.1%、71.6%、82.9%. Under the same irradiation dose, the degradation ratedecreases with increasing concentration. At15kGy radiation dose, the degradation ratesare60.2%、55.1%while the concentration of Fenpropathrin standard solution are20μg/mL、50μg/mL, and the degradation rates are82.9%、78%while the concentration ofDeltamethrin standard solution are20μg/mL、50μg/mL.4. The radiolysis products of Fenpropathrin and Deltamethrin have been studied and itindicates that the radiolysis products of the two insecticides are the same. After searchingthe mass spectral library and analyzing their mass spectra we find that these products areS-α-cyano-3-phenoxy benzy alcohol and phenoxybenzoic acid, both of them are importantintermediate in pesticides industry; after searching the relevant databases and analysingthe structure of the products，we guess that the toxicity of radiolysis products did notincrease.5. The two insecticides’ irradiation degradation in fresh tea leaves and in green teahave been studied. The result indicates that Fenpropathrin content in irradiated fresh tealeaves and green tea has no obvious difference, irradiation degradation rates in fresh tealeaves and in green tea are7.3%、2.2%. Deltamethrin content in fresh tea leaves before andafter irradiation has obvious difference and the irradiation degradation rate is14.7%,Deltamethrin content in green tea before and after irradiation also has obvious differenceand the degradation rate is12.1%. Moisture content in tea has different effect on irradiationdegradation rate to different pesticides. In general, the average irradiation degradation ratesof these two pesticides in fresh tea leaves are7.3%and14.7%.6. The degradation of Fenpropathrin and Deltamethrin under the green tea processinghave been studied and the results indicate that: The Fenpropathrin content after green teamanufacturing processing has significant change and the process degradation rate couldreach16.4%; while the deltamethrin content has no obvious change and the processingdegradation rate is only4.2%.