Photochemical degradation mechanisms and ecotoxicity of propranolol in natural water under simulated and natural sunlight irradiation

The widespread use of propranolol (PRO) has led to its detection in all types of natural water bodies, and it is hazardous to both aquatic organisms and humans. In this study, the photochemical transformation of PRO in the natural environment was investigated using both simulated and outdoor light experiments. The photo-degradation of PRO was found to be faster in Pearl river water and the dissolved organic matter (DOM) solutions than that in pure water under sunlight irradiation. Quenching experiments show that the excited triplet states DOM ((DOM)-D-3*) played a major role while center dot OH and O-1(2) played minor roles in PRO degradation. The secondary reaction rate constants of (DOM)-D-3* with PRO were determined to be (4.32 similar to 6.38) x 10(8) M-1 s(-1). DOM with high steady-state concentrations of the generated reactive species has higher photochemical reactivity for PRO photodegradation. Total of seven products were identified in in pure water, Pearl River water and three DOM solutions. The degradation of PRO can be mainly through hydroxyl addition, dehydration, naphthalene removal and isopropyl removal reactions. The reaction sites predicted by frontier electronic density calculations can further infer degradation pathways. The ecotoxicity of degradation products was found to be decreased relative to PRO through Ecological Structure Activity Relationship (ECOSAR) program.

Automated summary

The photo-degradation of propranolol (PRO) was found to be faster in Pearl river water and dissolved organic matter (DOM) solutions compared to pure water. The reaction rate constants of DOM with PRO were determined to be (4.32 × 10^8 M^−1 s^−1) to (6.38 × 10^8 M^−1 s^−1). The degradation products were found to have decreased ecotoxicity compared to PRO.