Elucidation of the environmental reductive metabolism of the herbicide tritosulfuron assisted by electrochemistry and mass spectrometry

The environmental impact of pesticides and other pollutants is, to a great extent, determined by degradation and accumulation processes. Consequently, degradation pathways of pesticides have to be elucidated before approval by the authorities. In this study, the environmental metabolism of the sulfonylurea-herbicide tritosulfuron was investigated using aerobic soil degradation studies, during which a previously unidentified metabolite was observed using high performance liquid chromatography and mass spectrometry. The new metabolite was formed by reductive hydrogenation of tritosulfuron but the isolated amount and purity of the substance were insufficient to fully elucidate its structure. Therefore, electrochemistry coupled to mass spectrometry was successfully applied to mimic the reductive hydrogenation of tritosulfuron. After demonstrating the general feasibility of electrochemical reduction, the electrochemical conversion was scaled up to the semi-preparative scale and 1.0 mg of the hydrogenated product was synthesized. Similar retention times and mass spectrometric fragmentation patterns proved that the same hydrogenated product was formed electrochemically and in soil studies. Using the electrochemically generated standard, the structure of the metabolite was elucidated by means of NMR spectroscopy, which shows the potential of electrochemistry and mass spectrometry in environmental fate studies.