Solar-Light-Mediated\nPhototransformation of Herbicide\nTribenuron-Methyl Initiated by Its Coexisting Nitrate Ion in Sunlit\nAgricultural Drainages

Understanding the environmental fate of chemical herbicides\nis\ncrucial to sustainable agriculture. Due to their joint-use with nitrogen\nfertilizers, their residues often coexist with NO<sub>3</sub><sup>–</sup> in agricultural drainages. In this study, tribenuron-methyl\nwas used as a model to evaluate the role of NO<sub>3</sub><sup>–</sup> in the phototransformation of chemical herbicides, which was characterized\nby a two-stage process. Initially, a slow hydrolysis occurs (<i>k</i><sub>obs</sub> = 2.573 × 10<sup>–4</sup> min<sup>–1</sup>), producing two hydrolysis products: methyl-2-(aminosulfonyl)-benzoate\n(MSB) and 2-methyl-4-methylamino-6-methoxy-1, 3, 5-triazine (MMT),\nwhich can be significantly accelerated by solar irradiation (<i>k</i><sub>obs</sub> = 2.152 × 10<sup>–2</sup> min<sup>–1</sup>). Subsequently, MSB undergoes a rapid NO<sub>3</sub><sup>–</sup>-initiated photodegradation process (<i>k</i><sub>obs</sub> = 2.251 × 10<sup>–2</sup> min<sup>–1</sup>). MMT was identified as the refractory unit and undergoes a slow\nNO<sub>3</sub><sup>–</sup>-initiated photodegradation process\n(<i>k</i><sub>obs</sub> = 4.494 × 10<sup>–4</sup> min<sup>–1</sup>). The underlying mechanisms were elucidated\nthrough electron paramagnetic resonance spectroscopy and reactive\nspecies quenching experiments. This study fills a knowledge gap on\nthe interaction between NO<sub>3</sub><sup>–</sup> and chemical\nherbicides, highlighting the pivotal role of NO<sub>3</sub><sup>–</sup> in the phototransformation of chemical herbicides.