Exploring the behavior of fluorinated sulfonylureas herbicides, trifloxysulfuron and prosulfuron, under oxidative water treatment processes: Chlorination, ozonation, UV photolysis and hydroxyl radical reactions.

This study is the first to comprehensively compare the transformation pathways of two fluorinated sulfonylurea herbicides, prosulfuron (PSF) and trifloxysulfuron (TFS), during hydrolysis and various oxidative water treatment processes, such as chlorination, ozonation, UV photolysis, and hydroxyl radical reactions. We determined the specific rate constants of chlorination and photolysis quantum yields at 254 nm over a wide pH range. Our results show that TFS is more stable upon UV irradiation and that chlorination rates are faster for TFS. Both pesticides exhibit high rate constants with ozone (k > 104 M⁻¹ s⁻¹) at pH 7.0, indicating transformation within a few seconds at an ozone concentration of 0.5 mg L⁻¹ . At pH 7.0, the apparent second-order rate constants for the reaction with the OH radical are 4.09 × 10⁹ and 4.32 × 10⁹ M⁻¹ s⁻¹ for PSF and TFS, respectively. A total of 16 transformation products (TPs) are proposed for TFS and nine for PSF, including some persistent fluorinated organic compounds. The reaction of hydrolysis, photolysis, chlorination, and ozonation for PSF is limited to cleavage of the sulfonylurea bond. Only reactions with the hydroxyl radical lead to the hydroxylation of the aryl sulfonamide. Upon hydrolysis, SO₂ elimination and intramolecular rearrangement are observed for TFS. Initial transformations of TFS by chlorine, ozone, and the OH radical occur at the 5-position of the pyrimidine ring activated by the two methoxy groups. Finally, QSAR models predict that some hydroxylated and chlorinated TPs would be as toxic as their parent compounds. These findings advance our understanding of the fate of fluorinated pesticides in engineered water systems and highlight critical transformation routes with potential health implications.