Photosynthetic modulation and oxidative stress in Raphidocelis subcapitata exposed to environmentally relevant concentrations of a ketoconazole based commercial formulation.

Antifungal drugs such as ketoconazole (KTZ) are increasingly detected in aquatic environments, raising concerns about their potential ecotoxicological effects on non-target organisms. In this study, we evaluated the physiological, biochemical, and morphological responses of the freshwater microalga Raphidocelis subcapitata exposed to environmentally relevant concentrations of KTZ. Initially, based on chronic exposure analyses, toxicity was observed at concentrations ≥ 1.9 µg/L, and the IC50 value was 7.2 µg/L after 120 h of exposure. Subsequently, assays using sub-inhibitory concentrations (2.8 and 5.6 µg L⁻¹) were conducted for 96 h and 192 h to evaluate selected endpoints, including changes in growth rate, photosynthetic pigments, cell morphology, lipid production, and oxidative stress, with exposure duration influencing these responses. These findings revealed a dual nature of KTZ toxicity: while low concentrations may stimulate photosynthetic activity, higher levels trigger oxidative stress. In addition, exposure time also influenced the effects observed in R. subcapitata. Our results underscore the importance of multivariate approaches in ecotoxicology and contribute to a deeper understanding of the environmental risks associated with pharmaceutical contaminants in freshwater ecosystems.