Ozonation of carbamazepine in drinking water: Identification and kinetic study of major oxidation products
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, 3M-quinazoline-2-one (130,M), 1-(2-benzaldehyde)(1 (1H,3H)-quinazoline-2,4-dione (130), and 1-(2-benzoic acid)(1H, 3M-quinazoline-2,4-dione (BaQD). Additional kinetic studies of the ozonation products showed very slow subsequent oxidation kinetics with ozone (second-order rate constants, k(O3) = similar to 7 M-1 s(-1) and similar to 1 M-1 s-1 at pH 6 for BQM and BOO, respectively). Rate constants for reactions with OH radicals, k(OH), were determined as similar to 7 x 10(9) M-1 s(-1) for BQM and similar to 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 >= 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 mu M, 236 mu g/L). The oxidation products were identified via LC-UV. Concentrations of 0.48 and 0.15 mu M 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 mu g/L. Currently, there are no data available on the biological effects of the formed oxidation products.