Effects of Non-steroidal Anti-inflammatory Drugs (Ibuprofen and Diclofenac) and Their Mixtures on the Growth of Three Green Algae

Ibuprofen (IBU) and diclofenac (DFN) are the most widely consumed non-steroidal anti-inflammatory (NSAIDs) worldwide. Since they are not completely metabolized in the human body, the unaltered active ingredients can reach aquatic ecosystems through domestic effluents. The aim of this study was to analyse the toxic effects of IBU and DFN, individually and in mixtures, on three freshwater green algae strains, the international standard strain Raphidocelis subcapitata and two native strains, Ankistrodesmus fusiformis and Tetradesmus obliquus. Bioassays were carried out according to the 72-h algal growth inhibition test. The concentration-response curve of the mixture was compared to predicted effects based on both the concentration addition (CA) and the independent action (IA) models. The two drugs tested individually were toxic to all three algal strains, with EC50 values <100 mg L-1. According to these values, the most sensitive strain was R. subcapitata (IBU = 20 mg L-1 and DFN = 8 mg L-1). The most resistant strain was T. obliquus (IBU = 74.1 mg L-1 and DFN = 92.7 mg L-1) and the A. fusiformis strain showed intermediate sensitivity (IBU = 26.7 mg L-1 and DFN = 14.6 mg L-1). The mixtures showed a synergistic effect on R. subcapitata, an additive effect on A. fusiformis, and an antagonistic effect on T. obliquus. Neither the CA nor the IA model was appropriate for predicting the toxicity of the mixtures. In conclusion, IBU and DFN showed toxic effects on the algae growth at the concentrations tested. Individual and mixed toxicity was different according to the species. These differences could be species-specific, showing the importance of including native strains in ecotoxicological studies to evaluate the potential effects of pollutants in regional aquatic environments.