Enhanced ozonation of ciprofloxacin in the presence of bromide: Kinetics, products, pathways, and toxicity

Although the ozonation of common antibiotics, such as ciprofloxacin (CIP), in water has been well studied, the influence of bromide that is present at high levels in seawater, is essentially unknown. In this study, we investigated the effect of bromide on the reaction kinetics, formation of transformation products (TPs), reaction pathways, and toxicity in the ozonation of CIP. Bromide significantly accelerated the transformation of CIP by ozone, likely due to the formation of reactive bromine species. Based on time-of-flight high-resolution mass spectrometry and suspect screening, a total of 26 TPs, including 13 previously unknown products, were identified in artificial seawater, while only 9 of them were found in pure water without bromide. The transformation of CIP in artificial seawater was found to involve four major processes: oxidation at the piperazinyl moiety with the addition of hydroxyl group(s) to the ring and ring cleavage, oxidation at the quinolone moiety, and bromination. In contrast, the ozonation of CIP in pure water occurred only at the piperazinyl moiety. In addition, bromide also enhanced the removal of toxicity towards Escherichia coli. This study suggests that careful consideration should be taken when using ozone to treat antibiotics contaminated water in the presence of bromide. (c) 2020 Elsevier Ltd. All rights reserved.