Increased acute toxicity to fish caused by pharmaceuticals in hospital effluents in a pharmaceutical mixture and after solar irradiation

•Irradiation significantly increased the acute toxicity of the pharmaceutical mixtures to fish.•Mixing of pharmaceuticals caused a synergistic increase in toxicity.•The pre-irradiated pharmaceutical mixture induced strange behaviors in the fish.•Reference threshold of mixing pharmaceuticals toxicity has been tested.

Hospital effluents are an important source of residual drugs and other classes of pharmaceuticals in aquatic environments. The raw wastewater from the studied hospital exhibited acute toxicity to vertebrate organisms, and Cyprinus carpio was the most sensitive organism tested. A mixture of 19 commonly used pharmaceuticals caused acute toxicity to C. carpio with an LC50 value of 60.68 mg L−1 after 96 h. This study demonstrated that irradiation for 1–5 days significantly increased the acute toxicity of the pharmaceuticals to fish, leading to increased mortality after a 2-h exposure and approximately 40% of the surviving fish died within 28 days. The pre-irradiated pharmaceutical mixture also induced strange behaviors in the fish that survived the test. The synergistic increase in toxicity caused by the photolysis and mixing of pharmaceuticals cannot be ignored and warrants further examination.