Ecotoxicological assessment of the interactions between paracetamol and ibuprofen on the freshwater microalgae pseudokirchneriella subcapitata

Emerging contaminants, such as drugs for human and veterinary use, are of growing concern due to their potential toxic effects on aquatic organisms. The anti-inflammatories paracetamol and ibuprofen are among the most consumed drugs worldwide and have been found in aquatic ecosystems such as rivers and lakes. The aim of this work was to evaluate the toxicity of paracetamol and ibuprofen and their interactions on the microalga Pseudokirchneriella subcapitata. For this purpose, increasing concentrations of both pharmaceutical compounds were prepared, toxicity bioassays were performed with P. subcapitata, while for interactions, binary mixtures were prepared in the following ratios: 4:1, 1:4, and 1:1 according to the CI20 previously determined. The interactions were determined according to the concentration-addition and synergy-ratio models. The results show that the toxicity of ibuprofen was higher than paracetamol (72-h CI20 of 12.7 and 23.9 mg/L, respectively). The interactions were classified as antagonistic. In conclusion, the results suggest a low environmental risk for primary producers such as the microalgae P. supcapitata, since the concentrations that cause toxic effects are higher than those reported in natural aquatic ecosystems such as lakes and rivers in different parts of the world. On the other hand, the joint presence of both drugs inhibits their individual toxicities on P. subcapitata.