Unveiling the photodegradation of tralkoxydim herbicide and its formulation in natural waters: Structural elucidation of transformation products and toxicity assessment

Pesticide degradation products (DPs), as emerging contaminants, are being detected in aquatic environments due to the widespread use of their active substances and pose potential risks to aquatic ecology and human health. However, their identification is challenging due to the many environmental conditions that influence their degradation processes. The photodegradation of the herbicide tralkoxydim and its formulation has been studied in ultrapure, spring and river waters and has shown rapid degradation. The photodegradation of tralkoxydim was slower in natural water and in the presence of humic acids (HA) than in ultrapure water, with half-lives of 5.1 h for river water and 1.1 h for ultrapure water. For the first time, three degradation products were identified in aquatic media using HPLC-TOF-MS/MS. These include photoisomerization, photolysis of the N-O bond of the oxime resulting in the tralkoxydim imine (major DP), and cyclization leading to tralkoxydim oxazole. Quantitative structure-activity relationship (QSAR) models were employed to approximate the potential ecotoxicological and environmental impacts of tralkoxydim and its DPs. Additionally, the toxicity of the isolated DPs was evaluated using a standard microtest bioassay with Vibrio fischeri bacteria. The results show that tralkoxydim imine and tralkoxydim oxazole exhibit high toxicity.