Norfloxacin and gentamicin degradation catalyzed by manganese porphyrins under mild conditions: the importance of toxicity assessment

The current work assessed the degradation degree and the degradation products derived from norfloxacin (NOR) and gentamicin (GEN) using iodosylbenzene and iodobenzene diacetate, in the presence of manganese porphyrin as catalysts. Better results for NOR degradation (> 80%) were obtained when more hydrophobic porphyrins were employed. beta-brominated manganese porphyrins showed a lower GEN degradation (similar to 25%) than the non-brominated ones (similar to 35%), probably due to their steric hindrance. In any case, complete mineralization was achieved neither for NOR nor for GEN, and the assignment of the generated products, complemented by the study of their toxicity, was an important step performed. From the obtained results, no correlation was found between the number of identified products and the reported toxicity value (r(Spearman,NOR) = 0.006; p value = 0.986 and r(Spearman,GEN) = - 0,198; p value = 0.583), which reinforces the idea of synergism and antagonistic phenomena. The higher degradation degree could have led to products of lower steric hindrance and easier penetration into the A. fischeri cells, which subsequently led to an increase in toxicity for these experiments. In most cases, the products presented higher toxicity than the original compound, which raises a concern about their occurrence in environmental matrices.

Automated summary

This study assessed the degradation of norfloxacin and gentamicin using manganese porphyrins as catalysts, finding that more hydrophobic porphyrins led to better norfloxacin degradation. beta-brominated manganese porphyrins showed lower gentamicin degradation compared to non-brominated ones. Although the products generally exhibited higher toxicity than the original compounds, there was no clear correlation between the number of identified products and their toxicity levels.