Study On The Residual Behavior In Tea Garden And Risk Assessment Of Thiamethoxam And Lambd-cyhalothrin

A multi-residue analysis method of thiamethoxam and lambda-cyhalothrin in different madetea, fresh tea leaf, soil and tea infusion has been developed in this paper. Then to be used forstuding the residual degradation dynamics and final residue in tea and soil after22%thiamethoxam·lambda-cyhalothrin CS application in tea field, and the leaching behavior of twokinds of pesticides in tea brewing process. It is also be performed risk assessment to these twokinds of pesticides in tea. All of these can supply scientific basis data for human to use pesticidessafely and appropriately, and keep drinking tea safety.And these main research contents are as follow:1The residues analysis methods of thiamethoxam and lambda-cyhalothrin in made tea, teafresh leaf and soil were established at the same time. The samples were extracted with acetonitrileafter made tea and soil with water soaked and fresh leaf with homogenated, added MgSO4andNaCl, centrifuged after fully vortexed, then cleaned-up by mixing adsorbents of PSA, GCB andFlorisil and detected by GC-ECD. The average recoveries of the methods were between71.2%and105.3%with RSD less than15.8%, the recoveries of green tea were between80.4%and104.7%with RSD less than8.7%; the recoveries of black tea were between78.8%and99.1%withRSD less than7.8%; the recoveries of dark tea were between75.7%and97.8%with RSD lessthan5.6%; the recoveries of tea fresh leaves were between80.4%and105.2%with RSD less than15.8%; the recoveries of soil were between71.2%and105.3%with RSD less than5.3%. Theof the method were less than10μg/kg. The accuracy and precision of the method have reached theresidue analysis methods requirements.2The residual degradation dynamics and final residues of22%thiamethoxam·lambda-cyhalothrin CS in tea and soil were studied by three-field experiments inHunan, Zhejiang and Fujian. The results of residual degradation dynamics showed that theresidual degradation dynamics of thiamethoxam and lambda-cyhalothrin in tea fresh leaf and soilcan be fit by the first order dynamics:C=C0e-kt. The half lives of thiamethoxam were respectively5.8~4.9d in tea fresh leaf and8.5~13.7d in soil, the half lives of Lambda-cyhalothrin wererespectively3.1~5.0d in tea fresh leaf and7.9~14.9d in soil. The results of final residues showedthat tea and soil were treated with the pesticides at recommended dosage effective constituent 22.23g/hm2and1.5times of recommended dosage effective constituent33.345g/hm2in the finalresidual experiment, the maximum residue limits (MRL)of thiamethoxam and lambda-cyhalothrinin made tea on5days after the last spraying were all lower2mg/kg and3mg/kgrespectively.They are lower than the MRL for these two kinds of pesticides in made tea in Japanand our country, suggested safety interval was7d.3The residues analysis methods of thiamethoxam and lambda-cyhalothrin in tea infusionwere established respectively. Thiamethoxam in tea infusion was concentrated by Chem Elutliquid-solid extraction column, eluted by60mL methylene chloride, than detected by GC-ECDafter concentrated; Lambda-cyhalothrin in tea infusion was extracted by methylene chloride,cleaned-up by Florisil column, than detected by GC-ECD. The results showed: The averagerecoveries of thiamethoxam spiked were between73.4%and92.8%with RSDs(n=5)≤9.9%, Theaverage recoveries of lambda-cyhalothrin spiked were between83.9%and101.7%%withRSDs(n=5)≤12.9%, and the limits of quantitation(LOQs) were0.1μg/L and0.05μg/Lrespectively, can meet the demand of the detection.4The influence of the leaching rule from made tea to tea infusion at different leaching time,leaching temperature, tea shape and different residue concentration of two kinds of pesticide werestudied by the analysis methods in made tea and tea infusion above-mentioned. The results showthat the leaching rates of thiamethoxam and lambda-cyhalothrin from made tea to infusion wereincreasing according to the leaching temperature, when the temperature was100℃, the leachingrates of thiamethoxam were83.9%in whole leaf tea and89.1%in broken tea respectively, theleaching rates of lambda-cyhalothrin were0.55%in whole leaf tea and4.1%in the broken tearespectively. When the leaching time at15min, the leaching rates of thiamethoxam weremaximum, which were81.2%in whole leaf tea and88.6%in broken tea. Under the sameconditions, the leaching rates of thiamethoxam in the whole leaf tea and broken tea were close, butthe leaching rate of lambda-cyhalothrin in broken tea was higher than in the whole leaf tea, theleaching rates of two kinds of pesticides were decreasing according to the leaching times in wholeleaf tea. The residue concentration of thiamethoxam in the made tea and tea infusion were meetingthe linear relationship, the equation was Y=0.9267x-0.0336, and the concentration of lambda-cyhalothrin in the made tea and tea infusion were meeting the polynomial relationship, theequation was Y=0.0026x2-0.0023x+0.0096.5On the basis of above research, We conduct risk assessment of thiamethoxam andlambda-cyhalothrin in tea for drinking, according to the MRL of our country, the results showedthat the risk effects of two kinds of pesticidue residues that taken in to human health wereacceptable limits.