Azithromycin and clarithromycin degradation when applying the photo-Fenton process: the role of macrolides complexation with iron and copper

This study aimed to investigate the effect of the complexation of iron and copper, with azithromycin (AZT) and clarithromycin (CLA), on the degradation of the two compounds by the homogeneous photo-Fenton process and to propose an initial degradation pathway. Complex formation of AZT or CLA with iron and copper was observed in different molar ratios: 1:1 for Fe(II)-AZT and Fe(II)-CLA, 1:3 for Cu(I)-AZT, and 1:2 for Cu(I)-CLA. Although Cu(II) was used as the copper source, Cu(I)-macrolide complexes were formed due to a reducing effect of AZT and CLA, which exhibited no degradation when subjected to the photo-Fenton process. On the other hand, Fe(II)-macrolide complexes underwent degradation by up to 83 % after 150 min. The degradation pathway of AZT and CLA involved hydroxylation and/or the loss of the sugar groups from the macrolide ring. These findings reveal a slow-reacting behavior of macrolides under optimal photo-Fenton conditions and their possible behaviour in water matrices, which is connected with the potential for complex formation.