Degradation of fluopyram in water under ozone enhanced microbubbles: Kinetics, degradation products, reaction mechanism, and toxicity evaluation

The degradation of fluopyram (FLP) was investigated under ozone-microbubble treatment (OMBT). Kinetic models were established to study the influence of three treatments: ozonated water, microbubbles (MCB), and OMBT. FLP degraded completely in OMBT, and a clearance rate of 89.8-100% was achievable. Three direct transformation products [product 1 (F1), product 2 (F2), and product 3(F3)] were isolated and identified using a hybrid ion trap-orbitrap mass spectrometer. Moreover, a transformation theory of FLP degradation was developed according to targeted fragmentation, accurate mass measurements, and degradation profiles. These analyses showed that the products originated from a series of chemical reactions involving dechlorination, hydroxyl substitution, cleavage and oxidation, and were further confirmed based on molecular electrostatic potential and molecular orbital theory. In addition, the stability and toxicity of FLP and its transformation products were tested using the Toxicity Estimation Software Tool (T.E.S.T.) and the Ecological Structure Activity Relationships (ECOSAR) program. Products F1, F2 and F3 were found to be toxic substances, but their toxicity to aquatic organisms was lower than that of FLP. However, they were more toxic to rats than FLP, and their physicochemical properties were more stable. Overall, OMBT is a highly effective method for FLP removal during wastewater treatment. (C) 2020 Elsevier Ltd. All rights reserved.