Free Radical Destruction of β-Blockers in Aqueous Solution

Abstract

Many pharmaceutical compounds and metabolites are currently found in surface and ground waters which indicates their ineffective removal by conventional water treatment technologies. Advanced oxidation/reduction processes (AO/RPs) are alternatives to traditional water treatment, which utilize free radical reactions to directly degrade chemical contaminants. This study reports the absolute rate constants for reaction of three β-blockers (atenolol, metoprolol, and propranolol) with the two major AO/RP radicals; the hydroxyl radical (•OH) and hydrated electron (e−aq). The bimolecular reaction rate constants for •OH are (7.05 ± 0.27) × 109, (8.39 ± 0.06) × 109, and (1.07 ± 0.02) × 1010, and for e−aq they are (5.91 ± 0.21) × 108, (1.73 ± 0.03) × 108, and (1.26 ± 0.02) × 1010, respectively. Transient spectra were observed for the intermediate radicals produced by hydroxyl radical reactions. In addition, preliminary degradation mechanisms and major products were elucidated using 60Co γ-irradiation and LC-MS. These data are required for both evaluating the potential use of AO/RPs for the destruction of these compounds and for studies of their fate and transport in surface waters where radical chemistry may be important in assessing their lifetime