Ozonation of Carbamazepine in Drinking Water: Identification and Kinetic Study of Major Oxidation Products

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Abstract

Kinetics and product formation of the anti-epileptic drug carbamazepine (CBZ) were investigated in lab-scale experiments during reactions with ozone and OH radicals. Ozone reacts rapidly with the double bond in CBZ, yielding several ozonation products containing quinazoline-based functional groups. The structures for three new oxidation products were elucidated using a combination of mass spectrometric and NMR techniques. The three products were determined to be 1-(2-benzaldehyde)-4-hydro-(1H,3H)-quinazoline-2-one (BQM), 1-(2-benzaldehyde)-(1H,3H)-quinazoline-2,4-dione (BQD), and 1-(2-benzoic acid)-(1H,3H)-quinazoline-2,4-dione (BaQD). Additional kinetic studies of the ozonation products showed very slow subsequent oxidation kinetics with ozone (second-order rate constants, kO3 = approximately 7 M(-1)s(-1) and approximately 1 M(-1)s(-1) at pH = 6 for BQM and BQD, respectively). Rate constants for reactions with OH radicals, kOH, were determined as approximately 7 x 10(9) M(-1)s(-1) for BQM and approximately 5 x 10(9)M(-1)s(-1) for BQD. Thus, mainly reactions with OH radicals lead to their further oxidation. A kinetic model including ozone and OH radical reactions allows a prediction of the time-dependent product distribution during ozonation of natural waters. In Rhine River water, CBZ spiked at 500 ng/L was completely oxidized by ozone with applied doses > or =0.3 mg/L. To confirm that the two major ozonation products BQM and BQD are produced as a result of the ozonation of a CBZ-containing natural water, Lake Zurich water samples were spiked with CBZ (1 microM, 236 microg/L). The oxidation products were identified via LC-UV. Concentrations of 0.48 and 0.15 microM for BQM and BQD, respectively, were measured for an ozone dose of 1.9 mg/L. BQM and BQD were also identified in ozonated water from a German waterworks containing CBZ in its raw water with 0.07-0.20 microg/L. Currently, there are no data available on the biological effects of the formed oxidation products.

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