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 (center dot OH) and singlet oxygen ((1)Delta O-2), and, the direct reaction with the triplet excited state, (NOM)-N-3*, also varied but collectively appeared to be the major loss factor. Bimolecular reaction rate constants of the three beta-blockers with (1)Delta O-2 and center dot OH were measured and accounted for 0.02-0.04% and 7.2-38.9% of their loss, respectively. These data suggest that the (NOM)-N-3* contributed 50.6-85.4%. Experiments with various (NOM)-N-3* 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. (C) 2012 Elsevier B.V. All rights reserved.