The role of environmental waters ionic composition and UV–LED radiation on photodegradation, mineralization and toxicity of commonly used β-blockers

•Photodegradation of metoprolol (MET) and propranolol (PRO) under UV-LED radiation.•Kinetics of photolysis/photocatalysis of MET, PRO, and MET-PRO in environmental waters.•Influence of magnesium and chloride ions on photodegradation of MET-PRO mixture.•DFT and MD computational studies of MET, PRO, and MET-PRO mixture.•Mineralization efficiency and toxicity of mixture in selected mammalian cell lines.