Complex pollution of Fluoroquinolone antibiotics and metal oxides/metal ions in water: a review on occurrence, formation mechanisms, removal and ecotoxicity

Fluoroquinolone antibiotics (FQs) form complex pollutants when they coexist with metal ions or oxides in water. These complexes alter the physicochemical properties and ecotoxicological effects of all of these three components, posing significant challenges to water treatment processes and drinking water safety. Previous studies have primarily focused on individual pollutants with little research on complex pollutants as a whole. This study summarizes the research status of complex pollutants in water environments. First, the occurrence of complex pollutants in the water was recorded. Second, the interaction mechanisms between FQs and metal ions/oxides are summarized. Complex pollution by FQs and metal ions mainly occurs through chelation reactions, whereas FQs and metal oxides are prone to adsorption and oxidation reactions. In this regard, the functional groups of FQs influence the reaction by modifying the electron transfer ability and steric hindrance, altering the reaction intensity owing to the differences in electron affinity and steric hindrance effects. Metal oxides affect complex pollution formation through differences in adsorption and oxidation capabilities. Subsequently, the effect of complex pollutants on the removal of FQs, metal ions, and metal oxides was evaluated. In particular, complex pollution affects the oxidative removal of FQs by modifying the oxidation pathways and influencing the efficiency of oxidants. In addition, complex pollution affects the photodegradation of FQs by modifying FQs' activity, electron capture, and reaction activation energy. Finally, the toxicological effects of the complex pollution were assessed to provide valuable insights into the prevention and treatment of complex pollution processes.