Photosynthetic sensitivity of phytoplankton to commonly used pharmaceuticals and its dependence on cellular phosphorus status

Abstract

Recently pharmaceuticals have become significant environmental pollutants in aquatic ecosystems, that could affect primary producers such as microalgae. Here we analyzed the effect of pharmaceuticals on the photosynthesis of microalgae commonly found in freshwater—two species of Chlorophyceae and a member of the Eustigmatophyceae, via PAM fluorometry. As pharmaceuticals, three medicines often consumed in households were chosen: (i) fluoxetine, an antidepressant, (ii) propranolol, a β-blocker and (iii) ibuprofen, an anti-inflammatory and analgesic medicine. The EC₅₀ for the quantum yield of photosystem II in phytoplankton acclimated to inorganic phosphorus (P_i)-replete and P_i-limited conditions was estimated. Acute toxicity experiments over a 5 h exposure revealed that Nannochloropsis limnetica was the least sensitive to pharmaceuticals in its photosynthetic yield out of all species tested. Although the estimation of sub-lethal effects can be vital in contrast to that of LC₅₀s, the EC₅₀ values in all species and for all medicines were orders of magnitude higher than concentrations found in polluted surface water. Chlamydomonas reinhardtii was the most sensitive to fluoxetine (EC₅₀ of 1.6 mg L⁻¹), and propranolol (EC₅₀ of 3 mg L⁻¹). Acutodesmus obliquus was most sensitive to ibuprofen (EC₅₀ of 288 mg L⁻¹). Additionally, the sensitivity to the pharmaceuticals changed under a P_i-limitation; the green algae became less sensitive to fluoxetine and propranolol. In contrast, P_i-limited algal species were more sensitive to ibuprofen. Our results suggest that the sensitivity of algae to pharmaceuticals is (i) highly compound- and species-specific and (ii) dependent on the cellular P status.