Comprehensive Understanding of the Phototransformation Process of Macrolide Antibiotics in Simulated Natural Waters

This study investigated the transformation kinetics and pathways of four widely used macrolides (MLs), including roxithromycin, azithromycin, erythromycin, and clarithromycin, in dissolved organic matter (DOM) solutions under simulated solar irradiation. The results suggest that the triplet excited state of DOM plays an important role in the phototransformation of MLs. The transformation products (TPs) of MLs in the presence of natural organic matters were identified by liquid chromatography high-resolution mass spectrometry (LC-HRMS). Statistical analysis data mining procedures, including Venn diagrams and hierarchical clustering, were used to extract the TPs of the MLs. Multiple TPs for the selected MLs (roxithromycin (39), azithromycin (22), erythromycin (19), and clarithromycin (19)) were identified based on the structural information within the MS2 spectra. Most of the TPs are reported here for the first time. These TPs were mapped to the "photometabolome" networks of the MLs via linkage analysis. The results suggest that demethylation and hydroxylation are the most common reactions during the phototransformation of MLs. The products formed via N-demethylation of the desosamine moiety constitute the most abundant TPs. Overall, the combination of statistical analyses and linkage analyses of HRMS data could be a useful and promising method for predicting the degradation processes of ML antibiotics.