Residues of prothioconazole and trifloxystrobin in wheat and their dietary risk assessment

To investigate the residue patterns and dietary intake risk of 30% prothioconazole + trifloxystrobin suspension concentrate (SC) in wheat after application, experiments were conducted on its dissipation dynamics in wheat grains at 4 trial sites and final residues in wheat grains and straw at 12 trial sites in China. The formulation was applied twice at 5-day intervals at the recommended dosage of 180 g a. i./hm². And an analysis method of QuEChERS (quick, easy, cheap, effective, rugged, and safe) pretreatment method with a ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed. After extraction by shaking with an acetonitrile-aqueous solution and purification using C₁₈, the sample was separated by ACQITY UPLC BEH C₁₈ column (50 mm × 2.1 mm, 1.7 μm). With aqueous 0.1% formic acid-acetonitrile as mobile phase, it was detected by electrospray positive ion (ESI⁺) scanning and multiple reaction monitoring (MRM) mode, and quantified using external standard method. The results showed that the dissipation of prothioconazole-desthio, trifloxystrobin and trifloxystrobin acid in wheat grains all conformed to first-order reaction kinetic models, with half-lives of 2.2-10.2 d, 1.9-4.0 d and 3.7-10.3 d, respectively; Except that the final residue of prothioconazole-desthio at the experimental site in Shanghai was 0.026 mg/kg, which was lower than the national maximum residue limit of 0.1 mg/kg, the terminal residues of the three substances were all lower than the limit of quantification of 0.02 mg/kg in wheat grains at all experimental sites; The highest final residual amounts of the three substances in wheat straw were 0.67, 0.52, and 0.14 mg/kg, respectively. The long-term risk quotient contribution rates of prothioconazole-desthio and trifloxystrobin residues in wheat grains to the dietary intake of Chinese residents were 3% and 0.8%, respectively. The short-term risk quotient of prothioconazole-desthio residue was also at a low level (due to the lack of relevant data, the risk to women of childbearing age has not been assessed). These results showed that, when 30% prothioconazole + trifloxystrobin SC was applied to wheat, the dietary intake risks of prothioconazole-desthio and trifloxystrobin to Chinese residents were both very low, but the short-term dietary intake risk of prothioconazole-desthio to women of childbearing age needs to be confirmed.