Identification of photoproducts of fungicide cyprodinil and elucidation of transformation mechanism in water using LC-IT-TOF-MS/MS technique

• Photodegradation of cyprodinil in aqueous solution was firstly reported in this study.
• Six main TPs were identified based on mass spectra data and DFT quantum calculations.
• Kinetic evolutions of the TPs were also investigated during UV–visible irradiation.
• A tentative transformation pathway was proposed based on the identified TPs.
• Factors affecting the cyprodinil photodegradation were explored.

This study aimed at investigating photodegradation of cyprodinil in aquatic solution under the simulated natural light or UV–visible irradiation (290–800 nm) using LC-MS/MS techniques. Effects of pH, nitrate ion, Fe (III), humic acid and TiO2 on photolysis kinetics of cyprodinil were explored. The photodegradation followed first-order reaction kinetics, and linear accelerating effects of Fe (III), nitrate ion and TiO2 with concentrations ranging from 0.1 to 5.0 mg L−1 on photodegradation were remarkably observed. HA at low concentration ranges (<3.0 mg L−1) enhanced cyprodinil photodegradation while the photocatalytic rate was weakened with more addition of HA. The degradation rate in alkaline solutions was greater than in acidic solutions. Six main transformation products (TPs) were separated and identified based on mass spectra data and density functional theory (DFT) quantum calculations, and their kinetic evolutions were also investigated. Ultimately, a tentative transformation mechanism was proposed based the identified TPs and their kinetic evolutions. The results indicated that one α-H on pyridine ring of cyprodinil was hydroxylated to form TPs 1. TPs 1 underwent a series of photochemical reactions involving ring-opening, addition of one H2O molecule and demethylation on three-member ring to form TPs 2, which was further hydroxylated on benzene ring to form TPs 6. TPs 3–5 were three isomers from Hofmann-Martius rearrangement of cyprodinil. These findings were of utmost importance for elucidating environmental fate of cyprodinil in aquatic ecosystem and further environmental risk evaluation.