The apparently very variable potency of the anti-depressant fluoxetine

•Different aquatic species appear to have very different sensitivities to fluoxetine.•Some species of invertebrate appear to be extremely sensitive to fluoxetine.•Many published studies have major limitations.•It is currently unclear whether or not fluoxetine presents an environmental risk. The anti-depressant fluoxetine is widely present in the aquatic environment. Typical river concentrations are in the low ng/L range. Many ecotoxicity studies have assessed the effects of this pharmaceutical on a range of aquatic species. Some studies report that ng, or even pg, per litre concentrations cause effects, whereas other studies report that effects only occur when the water concentration is in the μg/L range. It seems unlikely that all reported effects will be repeatable. Many of the studies have considerable limitations. Currently it is impossible to ascertain what environmental concentrations of fluoxetine pose a risk to aquatic organisms. The key question can be answered only by high quality, reproducible research.