豇豆不同生长时期施用毒死蜱的膳食风险

近年来,禁用农药毒死蜱在豇豆中被高频检出,已成为豇豆中农残超标率居高不下的关键问题之一。为明确毒死蜱在豇豆播种期、苗期、结荚期使用后的残留及其膳食风险,进行了田间模拟残留试验,将采集的成熟豇豆通过乙腈提取,C18分散净化,经超高效液相色谱-串联质谱方法测定豇豆中毒死蜱残留量,并进行了膳食风险评估。试验结果表明,毒死蜱在豇豆中的方法定量限为0.01 mg·kg^-1,在0.01~5 mg·kg^-1添加水平下,毒死蜱的平均回收率为76.3%~88.3%,相对标准偏差(RSD)为2.7%~6.4%;播种期、苗期、结荚期一次施药和结荚期二次施药后,成熟期采收的豇豆样品中均无毒死蜱检出;结荚盛期一次施药后,残留消解曲线为Ct=1 726.6e^-0.431t(R²=0.981 5),符合一级动力学方程,半衰期为1.6 d;施药后10 d,豇豆中毒死蜱残留量降至0.05 mg·kg^-1以下,慢性膳食摄入风险和急性膳食摄入风险均小于100%;毒死蜱在播种期和苗期的使用,不会导致成熟期豇豆中残留超标,可以安全使用;始花期后的使用需控制10 d以上的采收间隔期;结荚盛期须禁止使用毒死蜱。综上表明,在尚未制定毒死蜱在豇豆生产中精准施用规范的背景下,我国禁止毒死蜱在豇豆生产中的使用是十分必要的。

Degradation and dietary risk of chlorpyrifos after its application during different periods of cowpea planting

In recent years, the banned pesticide chlorpyrifos was frequently detected in cowpeas, which has become one of the key problems of high pesticide residue over standard rate in cowpeas. The degradation and risk assessment of chlorpyrifos in the different growth stages (sowing, seedling and podding) of cowpea were investigated. In field experiments, chlorpyrifos was applied to the different growth stages of cowpea. Cowpea samples were collected at mature stage, which were extracted with acetonitrile and purified by C18. The residue concentrations of chlorpyrifos was determined by UPLC-MS/MS, and dietary risk assessment was calculated. The limit of quantitation (LOQ) value of chlorpyrifos in cowpea samples was 0.01 mg·kg^-1. The average recoveries of chlorpyrifos in cowpea samples at four spiked levels (0.01, 0.1, 1 and 5 mg·kg^-1) ranged from 76.3% to 88.3% with relative standard deviation (RSD) in the range of 2.7%-6.4%. When applying chlorpyrifos at sowing stage, seedling stage and podding stage (one application and two applications), the residue concentrations of chlorpyrifos in cowpea samples were below LOQ. When once application at high podding stage, the degradation curve was Ct=1 726.6e^-0.431t (R²=0.981 5), fitting the first-order kinetic equation, and the half-life was 1.6 d. Ten days after applying, the concentrations of chlorpyrifos in cowpea samples were below 0.05 mg·kg^-1. The risks of chronic and acute dietary intake were lower than 100%. Therefore, the applying of chlopyrifos at sowing period and seedling period of cowpea will not lead to the residual concentrations exceeding the MRL, but the preharvest interval was at least 10 days after applying chlopyrifos at podding period, and the use of chlorpyrifos in the peak pod period should be prohibited. In conclusion, it is very necessary to prohibit the use of chlorpyrifos in cowpea production in China under the background that the precise application of chlorpyrifos in cowpea production has not been formulated.