Ecotoxicological Assessment and Biodegradation of Prednisone by Aquatic Microorganisms

The increasing consumption of pharmaceuticals associated with global population growth has intensified concerns regarding their release into aquatic environments and potential ecotoxicological effects. In this context, this study evaluated the ecotoxicity and biodegradation of the widely used corticosteroid prednisone. Ecotoxicity assays were performed using aquatic organisms representing different trophic levels: Artemia salina (microcrustacean), Aliivibrio fischeri (marine bacterium), and the cyanobacterium Microcystis novacekii. Biodegradation assays were conducted using M. novacekii. Prednisone was tested at concentrations ranging from 5 to 100 mg/L, corresponding to its maximum solubility in water. All experiments were carried out in accordance with standardized protocols (ABNT NBR 16530, ABNT NBR 15411-3, ISO 11348-3, and OECD 201). No toxic effects were observed for prednisone in any of the tested organisms, as responses at all tested concentrations, including the highest, were not significantly different from the control. Therefore, it was not possible to estimate EC50 values within the tested concentration range. According to the Globally Harmonized System of Classification and Labelling of Chemicals (GHS), substances with effect concentrations above 100 mg/L are considered non-toxic to aquatic organisms. During biodegradation assays, a reduction in prednisone concentration was observed during the growth of M. novacekii, which was associated with an increase in the pH of the culture medium. These results suggest that prednisone degradation occurred indirectly through pH changes caused by cyanobacterial growth rather than through direct metabolic pathways.