Environmental concentrations of pharmaceuticals directly affect phytoplankton and effects propagate through trophic interactions.

Pharmaceuticals are found in freshwater ecosystems where even low concentrations in the range of ng L may affect aquatic organisms. In the current study, we investigated the effects of chronic exposure to three pharmaceuticals on two microalgae, a potential modulation of the effects by additional inorganic phosphorus (P) limitation, and a potential propagation of the pharmaceuticals' effect across a trophic interaction. The latter considers that pharmaceuticals are bioaccumulated by algae, potentially metabolized into more (or less) toxic derivates and consequently consumed by zooplankton. We cultured Acutodesmus obliquus and Nannochloropsis limnetica in P-replete and P-limited medium contaminated with one of three commonly human used pharmaceuticals: fluoxetine, ibuprofen, and propranolol. Secondly, we tested to what extent first level consumers (Daphnia magna) were affected when fed with pharmaceutical-grown algae. Chronic exposure, covering 30 generations, led to (i) decreased cell numbers of A. obliquus in the presence of fluoxetine (under P-replete conditions) (ii) increased carotenoid to chlorophyll ratios in N. limnetica (under P-limited conditions), and (iii) increased photosynthetic yields in A. obliquus (in both P-conditions). In addition, ibuprofen affected both algae and their consumer: Feeding ibuprofen-contaminated algae to P-stressed D. magna improved their survival. We demonstrate, that even very low concentrations of pharmaceuticals present in freshwater ecosystems can significantly affect aquatic organisms when chronically exposed. Our study indicates that pharmaceutical effects can cross trophic levels and travel up the food chain.