Exploring the aquatic photodegradation of two ionisable fluoroquinolone antibiotics – Gatifloxacin and balofloxacin: Degradation kinetics, photobyproducts and risk to the aquatic environment

Abstract

Fluoroquinolone antibiotics (FQs) are ubiquitous and ionisable in surface waters. Here we investigate gatifloxacin (GAT) and balofloxacin (BAL), two widely used FQs, and determine the photochemical reactivity of their respective dissociation species that arise at different pH to understand the relevance and pathways of phototransformation reactions. Simulated-sunlight experiments and matrix calculations showed that neutral forms (HFQs) of the two antibiotics had the highest apparent photolytic efficiency and hydroxyl-radical oxidation reactivity. Based on the pH-dependent photochemical reactivities, the solar apparent photodegradation half-lives (t) in sunlit surface waters ranged from 14.5-169min and was 1-2 orders of magnitude faster than hydroxyl-radical induced oxidation (t=20.9-29.8h). The corresponding pathways were proposed based on the identification of key intermediates using HPLC-ESI-MS/MS. The apparent photodegradation induced defluorination, decarboxylation, and piperazinyl oxidation and rearrangement, whereas hydroxyl-radical oxidation caused hydroxylated defluorination and piperazinyl hydroxylation. The photomodified toxicity of GAT and BAL was examined using an Escherichia coli activity assay. E. coli activity was not affected by BAL, but was significantly affected by the photo-modified solutions of GAT, indicating that primary photo-degradates have a comparable or higher antibacterial activity than the parent GAT. In fresh water and seawater this antibacterial activity remained high for up to 24h, even after GAT had undergone significant photodegradation (>1 half-life), indicating the potential impact of this chemical on microbial communities in aquatic systems.

Monitoring photolysis and (solar photo)-Fenton of enrofloxacin by a methodology involving EEM-PARAFAC and bioassays: Role of pH and water matrix

“…1 and 5 shows that, in general, similar trends can be found between C1 + C2 and ENR relative amount shown by HPLC: a) No destruction of the FQ in photolysis experiments, in line with the low removal of the parent pollutant; b) some decrease in the C1 + C2 components was reached in the other cases following the trend: Fenton at pH = 5.0 b photo-Fenton at pH = 5.0 = Fenton at pH = 2.8 b photo-Fenton at pH = 2.8. This behaviour can be understood by considering that although photolysis is able to remove ENR, it cannot produce important changes in the fluoroquinolone structure (Babić et al, 2013;Ge et al, 2018;Zhang et al, 2019) and only stronger oxidation agents (e.g. •OH) efficiently attack the fluoroquinolone core (An et al, 2010).…”

“…The inhibition halo disappeared after 15 and 30 min for solar photo-Fenton and Fenton processes respectively in MQ at pH 2.8, whereas in photolysis the inhibition halo remained constant even after 120 min of irradiation and not notable decrease of inhibition halos for Fenton performed at pH 5.0 was seen. This might indicate that the destruction of the FQ structure is needed to eliminate the antibiotic properties (Ge et al, 2018(Ge et al, , 2015Rosen et al, 1989).…”

“…In sharp contrast with the low efficiency of the chemical and biotic pathways for FQ removal, photolysis has been described as a major route for the self-remediation of ecosystems containing these substances. Important work has been devoted to study the photodegradation of FQ in different aqueous media (Ge et al, 2018;Zhang et al, 2019). Its photochemical reactivity is attributable to the presence of chromophores which can absorb wavelengths that are within the range of solar radiation reaching the Earth's surface (300 nm b λ) (Babić et al, 2013).…”

Treatment of statins drug (pravastatin and rosuvastatin) in water by electro-Fenton process: Kinetics of degradation/mineralization and optimization of experimental conditions for a biological post-treatment

“…AOPs are effective methods that generate hydroxyl radicals in situ • OH capable to oxidize organic molecules until their mineralization. These radicals may be produced by chemical, photochemical or electrochemical methods [19][20][21] .…”

Elimination of gatifloxacin from water: Treatment by electro-Fenton process and highlighting of a biological post-treatment

“…Among the pollutant antibiotics, there is gatifloxacin (destined to treat sensitive germ infections) where one study has clarified the aqueous photodegradation of this antibiotic, determining degradation kinetics and the formation of photoproducts 10 . Another study has shown that the photodegradation of gatifloxacin in freshwater and seawater is not as faster as in pure water, so, there are the integrative effects of pH and dissolved substances in the solution, such as humic acids, on photodegradation 11 .…”