Norfloxacin Oxidative Degradation and Toxicity in Aqueous Media: Reciprocal Effects of Acidity Evolution on Metal Cations and Clay Catalyst Dispersion

The ozonation of norfloxacin (NOF), a widely used fluoroquinolone antibiotic, in the presence of Na⁺, Fe²⁺, Cu²⁺, Ni²⁺, and Co²⁺ cations and their montmorillonite-supported counterparts was investigated. The NOF degradation and the toxicity of the ozonized mixtures towards an aquatic organism (<i>Lemna minor</i>) were evaluated in terms of changes in its frond number, chlorophyll content, photosynthesis efficacy, and production of reactive oxygen species (ROS). The evolution over time of the NOF degradation grade and the toxicity were discussed in terms of <i>i.</i> the observed changes in the interactions of the cation and clay catalyst with NOF molecules; <b><i>ii.</i></b> the pH decay, during ozonation. Ion-exchange and Lewis acid-base interactions appear to govern NOF adsorption and clay catalyst dispersion in correlation with the progressive formation of acidic species in the aqueous media. These findings reveal promising prospects for tailoring optimum oxidative water treatments with minimum toxicity and for predicting their environmental impacts on aquatic media.