Residue Analysis And Dietary Risk Assessment Of Metaflumizone And Methoxyfenozide In Rice

Rice is the main food crop in our country,and the planting area accounts for about one-third of the country’s total planting area.Because rice is vulnerable to diseases and insects,so people spray a lot of pesticides to ensure the yield of rice,making it be the biggest food crop for pesticide consumption.Because farmers use pesticides blindly,there is a misconception that the higher the dosage,the higher the concentration,the better the effect,which leads to the unsafe use of pesticides in rice production.This not only damages the environment,affects the quality safety and the export of rice,even threatens the people’s edible safety.In this paper,the residual determination method of metaflumizone and methoxyhydrazide on rice was established by high performance liquid chromatography-tandem mass spectrometry（HPLC-MS/MS）after the effective dosage was determined by field test.The aim is to provide reliable technical support for the safety evaluation of metaflumizone and methoxyhydrazide in rice and to provide basis for the safe use of the two pesticides.The research work of this paper is mainly carried out from the following aspects:1.A high performance liquid chromatography-tandem mass spectrometry（HPLC-MS/MS）method for simultaneous determination of two pesticides in rice was established.The chromatographic and mass spectrometry conditions of the instrument were established,and the extraction and purification methods were screened and optimized.The results showed that the rice plant,seed and soil samples were extracted with acetonitrile.The water samples were extracted by reverse extraction with ethyl acetate.C₁₈ was used as purifying agent in rice plants,brown rice,rice husk and soil samples.The standard curve equation y=875826x-137.55,correlation coefficient r=0.9998,average recovery rate 78.7-104.4%,relative standard deviation1.3-9.4%;The standard curve equation y=2E+06x+3907.9,the correlation coefficient r=0.9964,the average recovery rate 79.2-107.1%,the relative standard deviation 1.3-5.0%,the sensitivity and accuracy of the method meet with the pesticide residue standard.2.The decline dynamic of metaflumizone and methoxylhydrazide on rice plant、soil and field water were measured.In 2017,a three-land-a-year dynamic experiment was conducted.The results showed that the half-life of metaflumizone in rice plants and soil was 2.4-11.4 d and3.0-6.8 d respectively.Because the original deposition of metaflumizone in field water was very small,the dynamic regression equation could not be established in three experiments,so the half-life of metaflumizone in field water could not be calculated.The half-life of methoxyfenozide in rice plant,soil and field water was 1.3-10.2 d,3.0-6.8 d and 0.8-1.4 d,respectively.The half-life of the two pesticides,t_1/2,is less than 30 d.3.The final residues of metaflumizone and methoxylhydrazide on rice plant、brown r ice、rice husk and soil were determined.Final residue tests were conducted in three places a year in 2017.The results showed that when low dose of 750g/hm ²（150g a.i./hm²）and high dose of 1125 g/hm ²（225g a.i./hm ²）were administered once and twice,t he residual amounts of metaflumizone and methoxyhydrazine in plants were 0.123-1.072mg/kg and 0.300-4.757 mg/kg,respectively.The residues in rice husk were 0.040-0.636 mg/kg and 0.142-2.257 mg/kg,respectively.The residues in soil were 0.013-0.562mg/kg and 0.025-1.150 mg/kg,respectively.The final residue test was carried out in 2018.The results showed that when the si ngle dose of 750g/hm ²（150g a.i./hm²）was administered for 21 days and 28 days,th e residual amount of metaflumizone and methoxyhydrazine in the plant was 0.105-2.282mg/kg and 0.094-9.192mg/kg,respectively.The residues in brown rice were less than0.01 mg/kg,0.01-0.571 mg/kg and 0.089-2.445 mg/kg,respectively.4.According to the results of this study,the dietary risk was evaluated by combinin g the maximum allowable residues of two pesticides in brown rice.The risk quotient on brown rice was lower than 9.14×10^-4 and 1.14×10^-3,respectively and was far less than 1,which indicated that the dietary risk of the drug was low and safe to eat.