Studies On Determination Method And Degradation Dynamic Of Acetamiprid Residues In Tea

Tea, as one of China’s special economic product, is the most popular beverage in theworld. More than60countries have tea garden and100countries people are drinking teain the world. China, the biggest tea producer and tea exporter, with a tea output of200000tons, has achieved$400million foreign exchange earnings per year, which is one of thelargest contributors to the local fiscal revenue. Pesticide residues in tea are an unavoidableissue and should not be neglect, and it is also the key factor which brings negativeinfluence to our country’s tea exports. Acetamiprid, a kind of new nicotine chemicals, withcharacteristics of broad spectrum, suction, available, low toxicity, high activity, usage andlong validity, is widely used in the prevention numerous sucking pests of vegetables, fruitsand tea in our country. The MRL values have been fixed for acetamiprid on tea0.1mg/kgin EU and50mg/kg in Japan, The MRL values has not been fixed for acetamiprid on tea inChina. In this paper, the determination methods of acetamiprid residues in fresh tea leaves,made tea and tea infusion were established. The acetamiprid degradation in tea processingand infusion in the different season were also studied. The specific contents are as follows:1. Analytical methods of acetamiprid residue in fresh tea shoots，made tea andtea infusion were establishedComparing with different solvent for extracting of acetamiprid, the results show thatacetonitrile as extraction solvent, got good effect with least the matrix interference. Andthen application of different SPE column for purifying effect, Envi-Carb/LC-NH₂columnacquire better purifying effect. Finally we established the residue methods of acetamipridby HPLC: Tea samples were extracted by acetonitrile and Nacl Alkaline saturated solution,and then cleaned up with the Envi-Carb/NH₂cartridge, finally eluted with10mlacetonitrile. acetamiprid recoveries in tea, fresh tea were in the range of68.46%¹03.61%at spike level of0.1¹.0mg/kg with relative standard deviations （RSD） less than13.6%.When spiked at the level of0.033⁰.333mg/L in infusion, the recovery was in the range of72.95%¹03.75%with RSD less than7.6%. Practical determination limit in tea, fresh teaand infusion respectively was0.07mg/kg,0.09mg/kg and0.002mg/L. Due to fastness andeffectiveness, the proposed method could be used for routine monitoring of the acetamipridresidues and safety assessment research in the tea.2. Study on dynamics of acetamiprid in fresh tea shoots and made teaWith reference to the agricultural industry standard of People’s Republic NY/T788-2004in pesticide residue test method, different dosages of acetamiprid wassprayed in summer of2010and in spring of2011respectively in tea field: recommendedapplication rate （effective constituent22.5g/hm²） and twice the recommended applicationrate （effective constituent45g/hm²）. Fresh tea leaves were plunked after spraying at0,1,3,5,7,10,14,17,21and31days, Acetamiprid residues in fresh tea shoots and made teawere determined, the results show that: the degradation of acetamiprid were all accordedwith the first-order kinetics equation.In summer of2010, the degradation equation of acetamiprid was C=2.2918e^-0.2499tinfresh tea shoots with recommended application rate （22.5g/hm²） treatment and the half-lifewas2.77days; The degradation equation of acetamiprid was C=4.2968e^-0.2533twith twicethe recommended application rate （45g/hm²） treatment and the half-life was2.74days. thedegradation equation of acetamiprid was C=6.2817e^-0.1744tin green tea with recommendedapplication rate （22.5g/hm²） treatment and the half-life was3.97days; The degradationequation of acetamiprid was C=13.121e-0.1709twith twice the recommended application ratetreatment （45g/hm²） and the half-life was4.06days.In spring of2011, the degradation equation of acetamiprid was C=1.9786e^-0.2208tin freshtea shoots with recommended application rate （22.5g/hm²） treatment and the half-life was3.14days; The degradation equation of acetamiprid was C=3.3387e^-0.1732twith twice therecommended application rate treatment （45g/hm²） and the half-life was4.00days. thedegradation equation of acetamiprid was C=5.4252e^-0.2193tin green tea with recommendedapplication rate （22.5g/hm²） treatment and the half-life was3.16days; The degradationequation of acetamiprid was C=12.746e-0.2141twith twice the recommended application ratetreatment （45g/hm²） and the half-life was3.24days. The degradation equation ofacetamiprid was C=5.9876e^-0.1957tin black tea with recommended application rate（22.5g/hm²） treatment and the half-life was3.54days；The degradation equation ofacetamiprid was C=11.22e^-0.1967t, with twice the recommended application rate treatment（45g/hm²） and the half-life was3.52days.3. Fate of acetamiprid residues during tea manufactureIn summer of2010, average degradation rate of acetamiprid in green tea manufacturewas15.0%,17.7%,17.7%,19.4%,5.1%,13.8%at the PHI of0,1,3,5,7,10days withrecommended application rate treatment，respectively, with average14.8%; Degradationrate of acetamiprid was8.6%,1.1%,2.4%,3.5%,2.9%,2.8%respectively, in the samedays as application rate treatment, with average3.6%.In the spring of2011, the degradation of acetamiprid in green tea manufacture was 41.2%,36.7%,31.3%,21.3%,16.8%,42.9%,45.5%,50.0%at the PHI of0,1,3,5,7,10,14,21days with recommended application rate treatment, respectively, with average35.7%;Degradation rate of acetamiprid was19.9%,29.4%,33.5%,14.6%,11.6%,21.6%,20.7%,54.8%in the same days as recommended application rate treatment, with average25.8%.Whereas the average degradation in black tea manufacture was41.7%,36.2%,20.4%,26.5%,32.1%at the PHI of0,1,3,5,7days with recommended application rate treatment,respectively, with average31.4%; Degradation rate of acetamiprid was28.3%,39.9%,33.5%,26.7%,27.0%, respectively, in the same days as application rate treatment, withaverage29.1%.4. The dissipation behavior of acetamiprid from made tea to infusion andpreliminary safety assesment of acetamiprid in teaThe average transfer percent of acetamiprid residue from green tea to infusion was94.2%,69.4%,77.7%,81.7%after sparing acetamiprid1,3,7,10days in summer of2010,respectively. The average percent transfer of acetamiprid residues were77.4%and84.1%from green tea and black tea to infusion at the PHI （picking harvest interval） of5daysrespectively in spring of2011. The average transfer percent of acetamiprid residue frommade tea to infusion is80.8%in two seasons. If the final exposed residue levels werecalculated as0.1mg/kg （MRLs of EU）,50mg/kg （MRLs of Japan） or0.12mg/kg （residueat the PHI14days with application rate treatment in spring） and dissolution rate in teainfusion was80.8%, the safety coefficient was1211,2.42and1000respectively.