Photodegradation of propranolol in surface waters: An important role of carbonate radical and enhancing toxicity phenomenon

Antihypertensive propranolol (PRO) is frequently detected in surface waters and has adverse effects on aquatic organisms. In this study, its photochemical fate in surface water with the aspect of kinetics, products and toxicity were investigated employing steady-state photochemistry experiments and ecotoxicity tests. The results showed that photodegradation of PRO was enhanced in river water than that in phosphate buffer where dissolved organic matter (DOM), NO3−, and HCO3− played important roles. DOM accelerated the photodegradation mainly through generation of excited triplet-state DOM while NO3− played dual roles in the photodegradation. The reaction between excited triplet-state PRO and HCO3− can generate carbonate radical (CO3·-) to promote the photodegradation. The second-order reaction rate constant between PRO and CO3·- was determined to be (3.4 ± 0.8) × 108 M−1 s−1. Eight photodegradation products were identified in the studied river water sample. Finally, the toxicity evaluated by Vibrio fischeri increased after photodegradation and three photodegradation products were responsible for the increasing toxicity, which was concluded from the significant correlation between toxicity parameters and quantity of the photodegradation products.