| Soybean,as an important cash crop with functions of grain,oil and feed,is susceptible to pests and diseases during the growth process,which can reduce its yield and quality.Pydiflumetofen is a representative variety of a new succinate dehydrogenase inhibitor fungicide（SDHI）developed by Syngenta,which has a broad spectrum of fungicidal activity and can be used to control various pests and diseases of soybeans,such as soybeans brown spot and cyst nematode.Because of its good penetration and excellent rainfall resistance,residues of pydiflumetofen in soybeans should not be neglected.Therefore,in this paper,to understand the residue characteristics of pydiflumetofen in soybeans cropping system,field residue trials of pydiflumetofen were conducted and dietary risk assessment was performed,and the research and the results are as follows:1.A residue analysis method for pydiflumetofen in green beans（fresh soybeans）,soybeans,plants and soil were developed based on the Qu ECh ERS method and HPLC–MS/MS technique.The instrument conditions and parameters were optimized,and the sample pretreatments were compared with different extraction solvents for the recovery of pydiflumetofen,while the types and dosages of purification were screened and optimized to achieve the satisfactory purification effect and recovery.The average recoveries of different spiked levels of pydiflumetofen in each matrix ranged from 83.9±1.1%～99.5±1.5%with the RSD of 0.77～7.77%.The correlation coefficient was greater than 0.997 in the range of 0.001～0.5 mg/kg,the LOD was 3.5×10-4～4.1×10-3mg/kg,and the LOQ was 0.01 mg/kg.The results showed that the method has good linearity,high sensitivity,and the recoveries and relative standard deviations were within the specified range,which met the technical requirements for the analysis and detection of fungicide residues.2.The residual degradation behavior of 200 g/L pydiflumetofen suspension in plants,soil,green beans and soybeans was studied at three experimental sites in Changchun,Jilin Province,Chifeng,Inner Mongolia Autonomous Region and Hailun,Heilongjiang Province in 2021.The results showed that the degradation dynamics of pydiflumetofen in plants,soil,green beans and soybeans were in accordance with the first-order kinetic equation,with half-lives of 3.6～5.7 d in plants,7.9～25.7 d in soil,11.9 d～12.8 d in green beans and 10.5 d in soybeans in the Chifeng site.The residues of pydiflumetofen in soybeans at Changchun and Hailun experimental sites were lower than the LOQ values obtained in this study at 14 d,resulting in less than 5 points in the fitting of the ablation curve,and the fitting of the first-order kinetic equation could not be carried out to obtain the corresponding half-lives.The results indicated that the half-life of pydiflumetofen in plants,soil,green beans and soybeans were less than 30 d.It is a readily degradable fungicide.3.The terminal residue experiment research of 200 g/L pydiflumetofen suspension in soybeans fields was conducted at three experimental sites in Changchun City,Jilin Province,Chifeng City,Inner Mongolia Autonomous Region and Hailun City,Heilongjiang Province in2021.The results showed that with three or four applications at 150 g a.i./ha and 225 g a.i./ha and harvest intervals of 21,28 and 35 d,the residues of pydiflumetofen in green beans were0.024～0.869 mg/kg,<0.01～0.046 mg/kg in soybeans,0.193～1.878 mg/kg in soybeans plants,and<0.01～1.236 mg/kg in soil.The MRL values of pydiflumetofen in green beans and soybeans have not been established in China,therefore,based on the final residue data of pydiflumetofen in green beans and soybeans in this paper,it is recommended that China establish its MRL values of 1.0 mg/kg in green beans and 0.06 mg/kg in soybeans.4.The storage stability of pydiflumetofen in green beans and soybeans was studied at-20°C（±2°C）with sampling intervals of 0,14,30,60,90,180 and 270 d.The results showed that the degradation rates of pydiflumetofen in green beans ranged from-0.03 to 22.41%and in soybeans ranged from-2.03 to 22.04%.The degradation rates of pydiflumetofen in both matrixes were less than 30%,indicating that pydiflumetofen could be stored stably for 270 d in green beans and soybeans samples at-20°C（±2°C）.5.The acute and chronic dietary risks of pydiflumetofen in green beans and soybeans were evaluated by combining the registration status of pydiflumetofen in China and the dietary structure of our population.The results showed that the RQa of pydiflumetofen in green beans and soybeans was less than 1%,however,the RQc was 94.12%,which was close to 100%,with the MRL values in dark vegetables and vegetable oils being the main reasons for the increased RQc of pydiflumetofen.The RQ values of pydiflumetofen in green beans and soybeans were less than 100%,indicating no unacceptable risk to public health.However,to further control the risk to human health posed by pydiflumetofen,the registration of pydiflumetofen in crops other than the already registered food variety should be controlled to safeguard human dietary health. |
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