乐果及其代谢物氧乐果在不同生育期豇豆中的残留消解动态

为明确不同生育期豇豆上施用乐果可能产生的残留风险,以40%乐果乳油按有效成分设低（540 g/hm2）、中（600 g/hm2）和高（900 g/hm2）3个施药剂量,开展了苗期、结荚期2次施药和结荚期3次施药3种场景下的田间模拟试验,按照一定的时间间隔采集成熟豇豆样品,采用乙腈提取,C18分散净化,超高效液相色谱-串联质谱检测。结果表明:乐果和氧乐果在豇豆中的定量限均为0.01 mg/kg,在0.01~2 mg/kg添加水平下,乐果和氧乐果的平均回收率在77%~101%,相对标准偏差为3.1%~17%。距苗期最后一次施药后10 d,乐果在豇豆中的残留量各处理均低于中国国家标准中规定的最大允许残留限量（MRL）值0.5 mg/kg,最高为0.043 mg/kg;但其代谢物氧乐果残留量在施药后14 d,仅540 g/hm2的处理低于其MRL值0.02 mg/kg,施药后18 d仍有检出,最高为0.013 mg/kg。于结荚期2次和3次施药条件下,豇豆中乐果的残留量分别于施药后3 d和5 d即低于其MRL值（0.5 mg/kg）;而其代谢产生的氧乐果在施药后10 d仅540 g/hm2处理在豇豆中的残留量低于其MRL值。表明乐果使用后的残留超标风险主要源于其代谢物氧乐果。因此,建议豇豆结荚期不宜施用乐果,对其在苗期施用也应严格限制。

Residue and dissipation of dimethoate and omethoate in Vigna unguiculata at different periods of planting

To evaluate the residues of dimethoate in Vigna unguiculata after its application during different growth periods, pesticide residue was determined in three scenes, including seedling stage, fruiting stage with application twice and fruiting stage with application thrice. 40% Dimethoate emulsifiable concentrate was sprayed at different active ingredient dosages (540, 600 and 900 g/hm²) and samples were collected at intervals. Residues were extracted with acetonitrile, cleaned by dispersed purification with C₁₈ and determined with UPLC-MS/MS. The results showed that LOQ of dimethoate and omethoate were both 0.01 mg/kg. At the spiking level of 0.01-2 mg/kg, the average recoveries ranged from 77% to 101% and the RSD was 3.1%-17%. During the seedling stage and 10 days after the final application, the highest residue of dimethoate was 0.043 mg/kg, which was lower than MRL value. However, other than the 540 g/hm² treatment group, the residue of its metabolite omethoate at 14 days after the application was over the MRL value (0.02 mg/kg). The metabolite was still 0.013 mg/kg at 18 days after the application. In terms of fruiting stage with application twice and thrice, the residues of dimethoate were reduced to below 0.5 mg/kg 3 days and 5 days after the application, respectively. Meanwhile, the detected concentration of metabolite omethoate was still as high as 0.036 mg/kg after 10 days, and only the residue of the lowest dosage treatment could meet the requirement of MRL value. Based on these results, it could be concluded that the risk of over MRL value was mainly due to the metabolite omethoate. As a consequence, the application during fruiting period should be prohibited, while seedling period application should be exactly controlled.