Photodegradation of selected β-blockers in aqueous fulvic acid solutions: Kinetics, mechanism, and product analysis

Abstract

The photodegradation of the widely used β-blockers atenolol and metoprolol were investigated in the presence of fulvic acid (FA) under simulated sunlight. Both atenolol and metoprolol undergo indirect photodegradation in the FA solutions. The triplet excited state of FA (3FA∗) was verified to be main reactive species responsible for the photosensitized degradation of β-blockers. An electron transfer mechanism for the interaction between β-blockers and 3FA∗ was proposed on the basis of a series of experiments. Magnetic property of metal ions exhibited significant impact on photosensitized degradation. Diamagnetic metal ions such as Mg2+, Ca2+, Zn2+, and Al3+ negligibly affected the degradation. In contrast, paramagnetic metal ions including Mn2+, Cu2+, Fe3+, and Cr3+ markedly inhibited the reactions in the order of Cr3+ < Fe3+ < Cu2+ < Mn2+. The inhibition was related to the complexation ability with FA. By LC-ESI-MS/MS analysis, deisopropyl-atenolol (metoprolol) was identified as the main photosensitized product. The degradation pathways of β-blockers involving electron transfer processes were proposed. This finding strongly suggests that 3FA∗ was important reactive species for the degradation of β-blockers in natural waters.