Microbial biotransformation of furosemide for environmental risk assessment: identification of metabolites and toxicological evaluation.

Some widely prescribed drugs are sparsely metabolized and end up in the environment. They can thus be a focal point of ecotoxicity, either themselves or their environmental transformation products. In this context, we present a study concerning furosemide, a diuretic, which is mainly excreted unchanged. We investigated its biotransformation by two environmental fungi, Aspergillus candidus and Cunninghamella echinulata. The assessment of its ecotoxicity and that of its metabolites was performed using the Microtox test (ISO 11348-3) with Vibrio fischeri marine bacteria. Three metabolites were identified by means of HPLC-MS and 1H/13C NMR analysis: saluamine, a known pyridinium derivative and a hydroxy-ketone product, the latter having not been previously described. This hydroxy-ketone metabolite was obtained with C. echinulata and was further slowly transformed into saluamine. The pyridinium derivative was obtained in low amount with both strains. Metabolites, excepting saluamine, exhibited higher toxicity than furosemide, being the pyridinium structure the one with the most elevated toxic levels (EC50 = 34.40 ± 6.84 mg L-1). These results demonstrate that biotic environmental transformation products may present a higher environmental risk than the starting drug, hence highlighting the importance of boosting toxicological risk assessment related to the impact of pharmaceutical waste.