Study On Residual Detection And Degradation Rule Of Thiophanate-methyl And Tebuconazole In Cucumber

Pesticide residues have become the main problem of threatening produce security. Therefore,considering the current situation of pesticide residue in agricultural products, it is necessary to researchresidue and contamination behavior of pesticides.In order to provide experimental data for residual rule of48%thiophanate-methyl&tebuconazoleWP, residue analysis method of thiophanate-methyl and tebuconazole in cucumber and soil, degradationrule and its final residues were studied. The main contents were shown as follows:1. A residue analytical method was established to extract tebuconazole, thiophanate-methyl and itsmetabolite carbendazim from cucumber and soil. The pesticides were extracted with acetone, salting-outby lead acetate and sodium chloride, cleaned up with dichloromethane, after being concentrated byevaporation, the residues were reconstituted with methanol, finally detected by GC, HPLC. Becausecarbendazim is the toxic metabolite of thiophanate-methyl, the residues of thiophanate-methyl mustinclude carbendazim. The result of recovery test showed: the minimum detectable concentrations oftebuconazole, thiophanate-methyl and carbendazim were0.005,0.015,0.013mg/kg; the minimumdetectable limits were0.1×10^-10,0.29×10^-9,0.25×10^-9g; the recovery rates were88.4%⁹6.1%,85.3%⁹3.9%,84.9%⁹1.1%; the relative standard deviations （RSD） were1.9%⁴.2%,3.5%⁴.7%,1.8%⁴.5%respectively. The study results indicated this method was correct and precision to meet therequirements of the residual analysis.2. Degradation dynamic of thiophanate-methyl and tebuconazole in cucumber and soil was studied.The samples were treated with the pesticides at1.5times of the highest recommended dosage in fieldexperiment, the degradation procedure in line with the mathematic pattern: CT=C0e-KT. The half lives oftebuconazole were4.8⁶.4d in cucumber,6.8⁹.0d in soil, the half lives of thiophanate-methyl were5.2⁵.5d in cucumber,3.7⁵.1d in soil. Both of them could be degraded easily.3. The final residues were obtained in cucumber and soil by a two-year three fields experiment. Inthe experiment, the highest recommended dosage and1.5times of the highest recommended dosage hadbeen set up, times of spray pesticides were three and four, gathered the samples for detecting at1,2,35d after the last application. The results showed: the final residues of tebuconazole andthiophanate-methyl were0.031⁰.138mg/kg,0.024⁰.146mg/kg respectively on the third day after thelast sprayed pesticides.4. Now, the MRLs of thiophanate-methyl and tebuconazole in cucumber have not been set up inChina. In Japan the MRL of tebuconazole is0.2mg/kg in cucumber. According to FAO/WHOregulation, thiophanate-methyl’s MRL is0.5mg/kg. After applying the highest recommended dosageand3times of spray pesticides, highest residues （HR） of tebuconazole and thiophanate-methyl were0.115,0.092mg/kg in cucumber on the third day after the last employed pesticides. In addition,thiophanate-methyl and tebuconazole’s residues were all less than the criteria above in the harvest time.So, their final residues in cucumber were safe.