Photochemical fate of beta-blockers in NOM enriched waters

Beta-blockers, prescribed for the treatment of high blood pressure and for long-term use after a heart attack, have been detected in surface and ground waters. This study examines the photochemical fate of three beta-blockers, atenolol, metoprolol, and nadolol. Hydrolysis accounted for minor losses of these beta-blockers in the pH range 4–10. The rate of direct photolysis at pH 7 in a solar simulator varied from 6.1 to 8.9 h− 1 at pH 7. However, the addition of a natural organic matter (NOM) isolate enhanced the photochemical loss of all three compounds. Indirect photochemical fate, generally described by reactions with hydroxyl radical (OH) and singlet oxygen (1ΔO2), and, the direct reaction with the triplet excited state, 3NOM⁎, also varied but collectively appeared to be the major loss factor. Bimolecular reaction rate constants of the three beta-blockers with 1ΔO2 and OH were measured and accounted for 0.02–0.04% and 7.2–38.9% of their loss, respectively. These data suggest that the 3NOM⁎ contributed 50.6–85.4%. Experiments with various 3NOM⁎ quenchers supported the hypothesis that it was singly the most important reaction. Atenolol was chosen for more detailed investigation, with the photoproducts identified by LC–MS analysis. The results suggested that electron-transfer could be an important mechanism in photochemical fate of beta-blockers in the presence of NOM.

► Photochemical degradation of beta-blockers in the simulated natural waters. ► Reactive Oxygen Species play a minor role in the indirect photodegradation. ► The loss of beta-blockers results from direct reaction with 3DOM⁎.