title: Aqueous photodegradation of sethoxydim herbicide: Qtof elucidation of its by-products, mechanism and degradation pathway.
abstract: The photochemical fate of sethoxydim herbicide in water was studied under simulated sunlight radiation (Suntest apparatus). This compound exhibited a rapid degradation rate in water with a half-life of approximately 1h, which is in accordance with the high calculated value of the quantum yield (Φ=0.26). Consequently, the photolysis of sethoxydim should be considered as an efficient route of sethoxydim removal in aqueous media. During the photodegradation studies, ten by-products were detected, and their identification was accomplished using high-performance liquid chromatography (HPLC) coupled with quadrupole time-of-flight mass spectrometry (Qtof) and electrospray ionization in positive mode (ESI+). A detailed and exhaustive study of the mass spectra of the precursor ions and their MS/MS fragmentation patterns allowed for their identification. The photodegradation products resulted from the cleavage and isomerization of the NO bond of the oxime, oxidation of the sulfur atom, oxidative CS bond cleavage and Beckmann rearrangement followed by intramolecular cyclization. Additionally, the reactive species involved and a plausible mechanism for the photodegradation of sethoxydim in water are discussed. Finally, based on the identified products, a rational pathway for the photodegradation of sethoxydim in water is proposed.
authors.affiliation: DTVPF - Unit of Plant Protection Products, INIA, Ctra. de La Coruña, Km. 7.5, 28040 Madrid, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Sevilla-Morán
authors.affiliation: DTVPF - Unit of Plant Protection Products, INIA, Ctra. de La Coruña, Km. 7.5, 28040 Madrid, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: López-Goti
authors.affiliation: DTVPF - Unit of Plant Protection Products, INIA, Ctra. de La Coruña, Km. 7.5, 28040 Madrid, Spain.
authors.forename: José Luis
authors.initials: JL
authors.lastname: Alonso-Prados
authors.affiliation: DTVPF - Unit of Plant Protection Products, INIA, Ctra. de La Coruña, Km. 7.5, 28040 Madrid, Spain. Electronic address: sandin@inia.es.
authors.forename: Pilar
authors.initials: P
authors.lastname: Sandín-España
mesh_terms: D003512:Cyclohexanones / Q000032:analysis / Q000737:chemistry*; D006207:Half-Life; D006540:Herbicides / Q000032:analysis / Q000737:chemistry*; D007700:Kinetics; D013058:Mass Spectrometry; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010782:Photolysis; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*
chemical_list: D003512:Cyclohexanones; D006540:Herbicides; D014874:Water Pollutants, Chemical; C049437:sethoxydim
keywords: By-products; Degradation pathway; Photolysis; Qtof; Sethoxydim