Enantiomeric profiling of mefentrifluconazole in watermelon across China: Enantiochemistry, environmental fate, storage stability, and comparative dietary risk assessment

Highlights: • Absolute configuration was confirmed to be S-(+)-mefentrifluconazole and R-(−)-mefentrifluconazole. • Rapid enantioseparation was optimized within 2.5 min by 3D response surface RPLC-MS/MS. • Target enantiomers remained stable over 210 days during freezer storage of watermelon. • S-mefentrifluconazole degraded faster than R-mefentrifluconazole in watermelon. • Long-term risk of mefentrifluconazole should be continuously emphasized for urban children. Elucidating the enantiomeric chemistry and enantioselective fate of the novel chiral triazole fungicide mefentrifluconazole is of vital importance for agroecosystem safety and human health. The absolute configuration of mefentrifluconazole was identified firstly as S-(+)-mefentrifluconazole and R-(−)-mefentrifluconazole on a cellulose tris(3-chloro-4-methylphenylcarbamate) chiral phase. A baseline resolution ($\mathrm{Rs},$ 2.51), favorable retention ($\mathrm{RT}$ ≤ 2.24 min), and high sensitivity (LOQ, 0.5 μg/kg) of enantiomer pair were achieved by reversed-phase liquid chromatography tandem mass spectrometry combined with a 3D response surface strategy. Nationwide field trials were undertaken to clarify the enantiomer occurrence, enantioselective dissipation, terminal concentrations, and storage stability of S-mefentrifluconazole and R-mefentrifluconazole in watermelon across China. The original deposition of the sum of enantiomer pair was estimated to be 14.4–163.7 μg/kg, and terminally decreased to < LOQ–59.3 μg/kg 10 days after foliage application. S-mefentrifluconazole preferentially degraded (T_1/2, 3.3–6.0 days), resulting in the relative enrichment of R-mefentrifluconazole (T_1/2, 3.9–6.6 days) in watermelon. A probabilistic model is recommended for the dietary risk assessment, although both acute (%ARfD, 0.435–22.188%) and chronic (%ADI, 1.697–9.658%) risks are acceptable for associated population. The long-term exposures should be continuously emphasized given the increasing applications and persistent fate of mefentrifluconazole, especially for urban children.