RESUMO
Fenpiclonil is an agricultural phenylpyrrole fungicide, which raise the concern about its ecotoxicological effects. In this paper, we investigate the indirect photochemical transformation mechanisms, environmental persistence and eco-toxicity of fenpiclonil initiated by various active oxidants (1O2, â¢OH and SO4â¢â¾) in aquatic environments. The results shown that 1O2 can react with pyrrole ring by cycloaddition pathways to form the endo-peroxides. In addition, â¢OH and SO4â¢â¾ initial mechanisms are calculated, suggesting that â¢OH-initiated mechanisms play a dominant role in the degradation process of fenpiclonil at high rate constants (2.26 ×109 M-1 s-1, at 298 K). The kinetic calculation results indicate that high temperature is more favorable for the degradation of fenpiclonil. To better understand the adverse effects of the transformation products formed during the subsequent reaction of â¢OH-adduct IM10, the computational toxicology has been used for the toxicity estimation. The results show that aquatic toxicity of these products decrease with degradation process, especially the decomposition products (TP3 and TP4). However, TP1 and TP2 are still toxic and developmental toxicant. The study provides guidance for further experimental research and industrial application of fungicide degradation from the perspective of theoretical calculation.
Assuntos
Radical Hidroxila , Poluentes Químicos da Água , Cinética , Oxirredução , Pirróis , Oxigênio Singlete , Sulfatos/toxicidade , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/toxicidadeRESUMO
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 â¢OH/1O2-initiated process were systematically studied using quantum chemistry and computational toxicology. The results indicate that the two favorable pathways of â¢OH/1O2-initiated reactions are both occurred in pyrrole ring. It can conclude that the rate constants of â¢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.