Enantioselective toxicity of propranolol on marine diatoms: Assessing growth, energy metabolism and oxidative damage in Phaeodactylum tricornutum

Concern about the presence of pharmaceuticals in aquatic systems has increased in recent years owing to their continued release and the impact they may have on non-target organisms. Over half of these pharmaceuticals are chiral, with enantiomers that may have different pharmacokinetics and effects. However, most studies on their toxicity in marine biota have used racemic mixtures, ignoring the effects of isolated enantiomers. This work examines the potential enantioselective toxic effects of the chiral β-blocker propranolol, widely prescribed for cardiovascular diseases and migraines, and increasingly concerning due to its long-term use and raising consumption. This study used the diatom Phaeodactylum tricornutum as a model organism to assess the effect of each enantiomer on growth, photosynthesis, energy metabolism, and oxidative damage. The results showed that exposure of diatoms to R-propranolol induced growth inhibition due to deficiencies in photochemical metabolism, which was reflected in changes in the photosynthetic pigment profile. Oxidative stress also occurred in cells, resulting in lipid oxidation and DNA damage. In contrast, such effects were not observed for the S-enantiomer at the tested concentrations. This work shows the importance of considering enantiomer-specific effects in ecotoxicological assessments, as the two PRO enantiomers exhibit different toxicities in marine diatoms.