Enantioselective Toxicity of Ibuprofen to Earthworms: Unraveling the Effect and Mechanism on Enhanced Toxicity of <i>S</i>-Ibuprofen Over <i>R</i>-Ibuprofen

With the global implementation of wastewater reuse, accurately assessing the soil ecological risk of chiral pollutants from wastewater necessitates a comprehensive understanding of their enantioselective toxicity to soil animals. Ibuprofen (IBU) is the most prevalent chiral pharmaceutical in municipal wastewater. However, its enantioselective toxicity toward soil animals and the underlying mechanism remain largely unknown. In this study, the toxicity of IBU enantiomers, <i>S</i>-IBU and <i>R</i>-IBU, to earthworms was evaluated at environmentally relevant concentrations (10 and 100 μg/L), simulating wastewater reuse for irrigation. The results demonstrated that IBU adversely affects the growth, reproduction, regeneration, defense systems, and metabolic processes of earthworms, with <i>S</i>-IBU exhibiting stronger toxic effects than <i>R</i>-IBU. The bioavailability assessment revealed that <i>S</i>-IBU was more readily absorbed by earthworms and converted to its enantiomer within earthworms than <i>R</i>-IBU. This is consistent with molecular docking results showing that <i>S</i>-IBU had stronger affinities for functional proteins associated with xenobiotic transport and transformation. The findings of this study highlight that <i>S</i>-IBU poses a higher risk than <i>R</i>-IBU to soil organisms under wastewater reuse scenarios and that the chirality of chemical pollutants in wastewater deserves more attention when implementing wastewater reuse. In addition, our study underscores that the differences in bioavailability and bioactivity may account for the enantioselective toxicity of chiral pollutants.