噻虫嗪在保护地和露地菠菜中的消解规律及安全使用

Residue decline study and safe use of thiamethoxam in greenhouse and open field spinach

利用液相色谱-串联质谱仪建立了菠菜中噻虫嗪残留量的检测方法，并根据农药残留登记田间试验方法研究了25％噻虫嗪水分散粒剂在保护地和露地菠菜中的残留规律。结果表明：噻虫嗪在2种栽培条件下的消解动态均符合一级动力学模型，但在保护地菠菜中的消解速率明显比露地的慢，半衰期分别为4.08和1.28 d；25％噻虫嗪水分散粒剂按推荐剂量（有效成分）30 g/hm2和1.5倍推荐剂量45 g/hm2，分别对水喷雾施药2～3次，施药间隔期为7 d，于距离末次施药3、5、7 d采样测定，噻虫嗪在保护地菠菜中的残留量明显高于露地的。我国暂未制定噻虫嗪在菠菜上的最大残留限量（ MRL），参照其在甘蓝上的MRL值（0.2 mg/kg），噻虫嗪在保护地和露地栽培时的安全间隔期分别应为7和3d以上。在菠菜种植中使用噻虫嗪时应根据不同栽培条件设定不同的安全采收间隔期，从而降低其风险。

A simple, fast and easy operation method was developed for determining thiamethoxam residues in spinach by liquid chromatography-mass spectrometer （LC-MS）. The final residue and decline trend of thiamethoxam in greenhouse and open field were studied. The results showed that the decline dynamic of thiamethoxam in spinach in two different cultivation methods accorded with the first-order kinetics, and the decline rate of thiamethoxam in greenhouse spinach was slower than the other. The half-lives of thiamethoxam were 4. 08 d and 1.28 d, respectively. When the spinach in greenhouse and open field was sprayed 2 - 3 times at an interval of 7 d with thiamethoxam 250WDG with recommended dosage of 30 g a. i/hm2 and 1.5 times recommended dosage 45 g a. i/hm2, 3, 5, 7 days after the last application, the final residues of thiamethoxam in greenhouse spinach were higher than thiamethoxam residues in open field spinach at harvesting. There is no MRL of thiamethoxam spinach set in China now. Referring to the MRL of 0. 2 mg/kg in cabbage, the safe intervals of thiamethoxam in greenhouse spinach and in open field spinach should be more than 7 d and 3 d, respectively. From this study, in order to ensure the dietary risk in acceptable level, differentpre-harvest intervals of thiamethoxam in spinach must be set according to different cultivation methods.