Fluoroquinolone antibiotics sensitized photodegradation of isoproturon

Fluoroquinolone (FQ) antibiotics are a group of contaminants of emerging environmental concern. In the present study, we demonstrated that norfloxacin (NORF) and ofloxacin (OFLO), two typical FQs, have photochemical reactivity analogous to chromophoric dissolved natural organic matter (DOM) in surface waters and can sensitize the photodegradation of isoproturon (IPU), a phenylurea herbicide. Such photochemical reactivity is ascribed to the quinolone chromophore that is excited to a triplet state ((3)FQ*) upon UV-A irradiation. (3)FQ* further reacts with dissolved oxygen to give rise to singlet oxygen. (3)FQ* steady-state concentrations of 6.72 x 10(-15) and 1.27 x 10(-15) M were measured in 10 mu M NORF and OFLO solutions, respectively, under UV365nm irradiation. The degradation of IPU was due to the reaction with (3)FQ*, with bimolecular rate constants of 6.07 x 10(-9) and 1.51 x 10(-10) for (NORF)-N-3* and (OFLO)-O-3*, respectively. Intriguingly, NORF and OFLO per se were unstable and photolyzed during UV-A irradiation, but the photochemical reactivities of the solutions were not lost accordingly. High-resolution mass spectrometry analysis revealed that defluorination and piperazine moiety oxidation were the main photolysis pathways, while the core quinolone structure remained intact. Thus, the photolysis products largely inherited the photochemical reactivity of the parent compounds. Since all FQs share the same quinolone structure, similar photochemical reactivity is expected. The presence of FQs in surface water would affect the transformation and fate of coexisting compounds. To the best of our knowledge, this is the first study examining the environmental behavior of FQs as photosensitizers. The findings greatly advance the understandings of the influence of FQs in aquatic environment. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Fluoroquinolone antibiotics exhibit photochemical reactivity in surface waters, sensitizing the photodegradation of coexisting compounds. The study reveals that fluoroquinolones produce harmful photolysis products under UV irradiation, affecting the transformation and fate of other compounds in aquatic environments.