Kinetic study, byproducts characterization and photodegradation pathway of profoxydim in a biochar water soil system

The study focused on the photodegradation of profoxydim, a low-toxicity cyclohexanedione herbicide commonly used in rice crops, under simulated sunlight conditions. Profoxydim’s behavior in paddy field conditions is not well understood, and this research aimed to fill that gap, particularly examining the effect of commonly utilized organic amendments such as biochar (BC) on its degradation. Results indicated that profoxydim degrades rapidly, with a half-life of 2.4 ± 0.3 h in paddy water and 1.03 ± 0.1 h in paddy soil. However, when BC was introduced, the degradation slowed significantly, extending the half-lives to 3.1 ± 0.2 h in water and 3.07 ± 0.5 h in soil. The study identified five degradation products (DPs) using TOF mass accuracy measurements and MS/MS spectra fragmentation. Two of these DPs were found to be more stable than profoxydim itself. Additionally, the research proposed a novel photodegradation pathway, highlighting processes such as homolytic C-N bond cleavage, photoisomerization, and photoinduced oxidation. The study’s findings contribute new insights into the environmental fate of profoxydim, offering a deeper understanding of its transformation in rice paddy fields and aiding in the assessment of potential risks associated with its residues in agricultural environments.