| With the improvement of our living standard and the enhancement the awareness on health and environmental protection, People are becoming increasingly worried about food safe. In recent years, the problems of food and environmental pollution caused by pesticide residues are attracting more and more attention from government and the public. China is a major tea-producing country with more than2million hm2plantations and has become the first in the world tea production. At the same time, China’s tea exports exceeded300000tons. Tea leaves are directly processed without washing or other treatments and the tea are directly drunk after brewed by boiling water. Therefore, the problem of pesticide residues in tea is more concerned by the public.Imidacloprid is a neonicotinoid pesticide with the features of broad-spectrum, high efficiency, low toxicity and low-residue. Pests are not easy to develope a resistance to it. Imidaclorpid had been registered in china and used widely in tea garden to control leafhopper and spiniferus. Imdacloprid is more effective than buprofezin, permethrin, pirimicarb, cartap and other pesticides. Established Maximum Residue Limit (MRL) for imidacloprid in tea is0.5mg/kg in china, while it is0.05mg/kg in EU. The HPLC analysis method for measuring imidacloprid residue in tea was established and the degradation dynamics of imidacloprid residue in fresh tea leaves, tea processing and the transfer potential form made tea to infusion in hot water was studied. The main results were as follows:1. A method for determination of imidacloprid residue in tea with HPLC-UV was developedA method was established for analysis of imidacloprid residue in tea by High Performance Liquid Chromatography (HPLC) with UV detector. Through the comparation of extract efficiencies of several solvent and the clean-up capacities of different SPE cartridges, the results show that after soaked with water, extracted by acetonitrile, cleaned up with the Envi-Carb/PSA cartridge, imidacloprid was eluted with6ml acetonitrile solution from the cartridge and detected with HPLC, the samples was spiked at the level of0.050mg/kg～0.50mg/kg, and the recovery of Imidacloprid range from92.0%～97.6%with RSD less than3.8%. Practical determination limit was0.050mg/Kg. It has been proposed to be the analytical method for determination the imidacloprid in tea. The pretreatment method was simple, sensitive and less organic solvent consumption.2. Studies on the dissipation behavior of imidacloprid residues in tea, tea processing and its transfer potential form tea to infusion in hot waterThe degradation dynamics of70%imidacloprid wettable powder’s residues in fresh tea leaves, the imidacloprid residues degradation rates in different tea processing and imidacloprid transfer potential form tea to infusion in hot water were studied. The result shows that the original depositions of imidacloprid in the fresh tea leaves and tea are different in different pesticides usage. In recommended and double dose area, the original deposition of imidacloprid in the fresh tea leaves are7.11mg/kg and13.88mg/kg respectively, the original deposition of imidacloprid in green tea leaves are27.80mg/kg and42.39mg/kg respectively and the residues degradation dynamics followed the first-order kinetic. The imidacloprid dissipation rates in recommended dose and double dose area are similar, the average digestion coefficient (k) is0.2712±0.0124. Half-life of imidacloprid is2.67days in fresh tea leaves in recommended dose. Half-life of imidacloprid is2.65days for recommended dose in green tea leaves, the time required for the residue level of0.5mg/kg is12.43days, for the residue level of0.05mg/kg is21.23days. The average imidacloprid dissipation rate in different tea processing was found to be19.69%in green tea,27.93%in black tea and50.48%in oolong tea, respectively. The percent transfer of imidacloprid residues from made tea to infusion was62.09%in green tea,66.38%in black tea and52.94%in oolong tea. |
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