Isomer-specific ecotoxicity and occurrence of ibuprofen: Underestimated risks in aquatic ecosystems

Ibuprofen (IBU) is used as a racemic mixture despite enantiomeric pharmacological differences. However, its stereoselectivity in aquatic ecosystems remains inadequately characterized, leading to potential environmental risk uncertainties. This study presents a comprehensive, integrated, multi-tiered evaluation of the enantioselective ecotoxicity, environmental fate, and ecological risk of IBU in aquatic environments. Chronic toxicity tests with D. magna and recombinant yeast nuclear receptor assays demonstrated significant enantio-selective effects, with S-IBU exhibiting as much as 8-fold greater toxic potency than R-IBU at environmentally relevant concentrations. Using chiral-specific toxicity data from our experiments and the literature, the predicted no-effect concentration (PNEC) for S-IBU was significantly less than those for racemic IBU and R-IBU. Environmental monitoring across the Wenyu River basin revealed prevalent IBU contamination with a detection rate of 96.8 % and maximum concentration of 431.7 ng/L, with predominance of S-IBU with an enantiomeric fraction of 0.57-1.0 in surface waters and wastewater treatment plant effluents. Ecological risk assessment indicated that IBU posed moderate to great risks to aquatic ecosystems, with 93.5 % of sites exceeding PNEC. These findings demonstrate that conventional risk assessments using only racemic IBU substantially underestimate ecological hazards. This highlights the necessity for enantioselective toxicity assessment and monitoring in chiral chemicals risk management.