| The extensive use of pesticides in conventional agricultural practices has resulted in continuous and serious environmental pollution. Because of this, public concern over the residues of pesticides in environment, food and related commodities has increased over the last decades.To evaluate the risk of pestieide residues, the analytical method for determine residues of thiacloprid, flubendiamide and its metabolite NNI-des-iodo in rice, paddy soil and water were developed, and their residue dynamics were studied in this paper. In order to provide scientific evidences for the reasonable and safe application of39.6%flubendiamide and thiacloprid suspension concentrate in rice field. The main research contents were shown as follows:(1) A method for determination of thiacloprid, flubendiamide and its metabolite NNI-des-iodo residues in paddy soil and water of environment was developed by ultra performance liquid chromatography (UPLC). The paddy water was extracted with ethyl acetate and the organic phase was concentrated to constant. The paddy soil was extracted using acetone-water and the extract was purified by liquid-liquid distribution. The average recoveries were82.2%～106.2%with variation coefficients0.8%～3.8%. The minimum quantitative concentration of thiacloprid, flubendiamide and its metabolite NNI-des-iodo in water was0.4μg·L-1,0.9μg·L-1,1.0ug·L-1,0.002mg·kg-1,0.003mg·kg-1,0.004mg·kg-1in soil. The UPLC method of thiacloprid, flubendiamide and its metabolite NNI-des-iodo residues in rice for quantitative determination was established. Rice samples were first extracted with acetonitrile, and followed by cleanup with NH2-Carb columns. The average recoveries were77.8%～94.3%, with variation coefficients of1.2%～4.4%. The method detection limit were0.002～0.004mg·kg-1in rice straw,0.001～0.002mg·kg-1 in rice grain and0.001-0.003mg-kg-1in rice hull. Test results are to meet the requirements of residue analysis.(2) The residue analysis rule, degradation dynamic and final residue of39.6%flubendiamide and thiacloprid suspension concentrate in rice, water and soil were studied through two-year field experiment in Fujian, Nanjing and Tianjin. The rice, water and soil were treated with the pesticides at1.5times of the recommendation dosage. Digestion dynamic test results shown that the degradation process followed the first-degree reaction model. The results shown that flubendiamide was degraded slowly in soil, with a half-life of17.3-34.7days,9.8-23.1days in water,3.5-23.1days in plants. Residues of metabolite NNI-des-iodo in soil were0.020-0.055mg-kg-1and0.002-0.019mg-L-1in water, but not detected in rice plants. It is worth noting that digestion rate of flubendiamide in soil of Fujian and Nanjing is relatively slow, especially in2012year, and the half-life were more than a month, so it could be thought that flubendiamide may be affected on soil pollution.(3) The rice and soil were treated with the pesticides at recommendation dosage and1.5times of the recommendation dosage, as the final residue experiment. Collect the harvest of rice and soil samples for testing. The results shown that thiacloprid and flubendiamide residues in brown rice were0.011-0.303mg-kg-1, ND-0.121mg-kg-1, ND-0.063mg-kg-1and ND-0.380mg-kg-1, ND-0.200mg-kg-1, ND-0.079mg-kg-1in10,20,30days after the last sprayed pesticides. In addition, thiacloprid and flubendiamide residues in rice hull and straw were significantly higher than brown rice. The highest residues of thiacloprid and flubendiamide in rice hull were7.022mg-kg-1and9.781mg-kg-1,2.083mg-kg-1and5.581mg-kg-1in rice straw. Third, final residue results shown that residue detection rate of thiacloprid and flubendiamide in soil was higher, they also have a certain level of residues. It could be further confirmed that pollution of the two pesticides in soil has a certain influence.(4) At present, the maximum residue limits (MRL) of thiacloprid in rice is0.02mg·kg-1in European and Codex Alimentarius Commission (CAC), and MRL of flubendiamide in corn is0.02mg·kg-1in CAC. Refered to the standards for maximum residue limits, two doses of39.6%flubendiamide and thiacloprid were sprayed in rice for two times at recommended dosage, the average residues of the two pesticides were higher than0.02mg·kg-1. It has shown that food safety may be relatively serious of the residue of thiacloprid and flubendiamide in brown rice after spraying under application of86.4g·hm-2at the safely interval of20days.(5) According to the final residues, thiacloprid in rice hull were0.107～7.022mg·kg-1and0.016～2.083mg·kg-1in rice straw, and flubendiamide in rice hull were ND-9.781mg·kg-1and0.168～5.581mg-kg-1in rice straw. If the rice hull and straw were used for feeding, high attention should be paid on the risk of harm to livestock and poultry.(6) It suggested that people should give full consideration to the final residual properties of the two pesticides in rice and safety for human and animals, when making MRL of thiacloprid and flubendiamide in rice and the reasonable application of39.6%flubendiamide and thiacloprid suspension concentrate in rice field. |
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