Indirect photodegradation of fludioxonil by hydroxyl radical and singlet oxygen in aquatic environment: Mechanism, photoproducts formation and eco-toxicity assessment.

Fludioxonil has been proven valuable as a broad-spectrum fungicide. However, there are concerns about its risk posed to non-target organisms in aquatic environments. In this paper, the mechanism, photoproducts transformation and eco-toxicity of fludioxonil during •OH/1O2-initiated process were systematically studied using quantum chemistry and computational toxicology. The results indicate that the two favorable pathways of •OH/1O2-initiated reactions are both occurred in pyrrole ring. It can conclude that the rate constants of •OH and 1O2 are 1.23 × 1010 and 3.69 × 107 M-1 s-1 at 298K, respectively, which results in half-lives of <2 days in surface waters under sunlit near-surface conditions. Based on toxicity assessments, these photoproducts showed a decreased aquatic toxicity but the majority products are still toxic. This study gives more insight into the chemical transformation mechanism of fludioxonil in aquatic environments.