Residue levels and dietary risk evaluation of prothioconazole-desthio and kresoxim-methyl in cucumbers after field application in twelve regions in China

A commercial formulation called prothioconazole·kresoxim-methyl 50% water dispersible granule (WG), used to control the powdery mildew, is under registration for use on cucumbers. Therefore it is urgent to validate the reliability of the recommended good agricultural practices (GAP) conditions (187.5 g a.i. ha−1, three sprays with a 7-d interval, and a pre-harvest interval of 3 d) by conducting field trials in 12 regions in China, as required by national regulations, with a subsequent risk assessment. The residues of prothioconazole-desthio and kresoxim-methyl in field samples were determined using QuEChERS coupled with high-performance liquid chromatography – tandem mass spectrometry (HPLC-MS/MS). On the suggested pre-harvest interval (PHI, 3 d), the residual concentrations of prothioconazole-desthio (no maximum residue limit set in China) and kresoxim-methyl (maximum residue limit = 0.5 mg/kg) in cucumbers were 0.01–0.020 and 0.01–0.050 mg/kg, respectively. The acute risk quotients of prothioconazole-desthio in cucumbers were no higher than 0.079% for Chinese consumers. The chronic dietary risk quotient of kresoxim-methyl and of prothioconazole-desthio for different groups of consumers in China ranged from 2.3% to 5.3% and from 1.6% to 4.6%, respectively. Thus, prothioconazole·kresoxim-methyl 50% WG sprayed on cucumbers under the recommended GAP information can pose a negligible risk for Chinese consumers.