Ecotoxicological Effects of Psychoactive Pharmaceuticals in Lemna minor: Phytoremediation Potential and Mixture Risk Assessment

Background: The increasing consumption of psychoactive pharmaceuticals has led to their continuous release into aquatic environments. Methods: This study assessed the ecotoxicological responses, phytoremediation capacity, and ecological risk of seven psychoactive pharmaceuticals—citalopram (CIT), sertraline (SER), fluoxetine (FLU), alprazolam (ALP), clonazepam (CLO), risperidone (RIS), and topiramate (TOP)—using Lemna minor under controlled exposure conditions. Plants were exposed to a concentration gradient, and physiological endpoints, including relative growth rate, chlorophyll content, and maximum photosystem II efficiency (Fv/Fm), were evaluated alongside compound removal and abiotic degradation. Results: Dose–response modeling revealed substantial variability in toxicity, with TOP (EC50 = 74.11 ng L−1), CLO (104.8 ng L−1), and RIS (138.5 ng L−1) exhibiting the highest potency, whereas FLU (1751 ng L−1), CIT (89,941 ng L−1), and ALP (465,351 ng L−1) were less toxic. Relative growth rate was the most sensitive endpoint. Mixture exposure did not result in additional toxicity compared to the most responsive individual compounds. Abiotic degradation was negligible for most compounds (<3%), except for SER (~42%) and FLU (~22%). In contrast, L. minor achieved net removal efficiencies of up to 81%, although reductions occurred under mixed conditions. Probabilistic risk assessment indicated a high ecological risk (msPAFtotal = 1.0), with RIS as the dominant contributor.