Effect-Based Identification of Hazardous Antibiotic Transformation Products after Water Chlorination

Antibiotic transformation products (TPs) generated during water treatment can be considered as an environmental concern, since they can retain part of the bioactivity of the parent compound. Effect-directed analysis (EDA) was applied for the identification of bioactive intermediates of azithromycin (AZI) and ciprofloxacin (CFC) after water chlorination. Fractionation of samples allowed the identification of bioactive intermediates by measuring the antibiotic activity and acute toxicity, combined with an automated suspect screening approach for chemical analysis. While the removal of AZI was in line with the decrease of bioactivity in chlorinated samples, an increase of bioactivity after complete removal of CFC was observed (at >0.5 mgCl₂/L). Principal component analysis (PCA) revealed that some of the CFC intermediates could contribute to the overall toxicity of the chlorinated samples. Fractionation of bioactive samples identified that the chlorinated TP296 (generated from the destruction of the CFC piperazine ring) maintained 41%, 44%, and 30% of the antibiotic activity of the parent compound in chlorinated samples at 2.0, 3.0, and 4.0 mgCl₂/L, respectively. These results indicate the spectrum of antibacterial activity can be altered by controlling the chemical substituents and configuration of the CFC structure with chlorine. On the other hand, the potential presence of volatile DBPs and fractionation losses do not allow for tentative confirmation of the main intermediates contributing to the acute toxic effects measured in chlorinated samples. Our results encourage further development of new and advanced methodologies to study the bioactivity of isolated unknown TPs to understand their hazardous effects in treated effluents.