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

摘要

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,ko_3=approx 7 M~(-1) s~(-1) and approx 1 M~(-1) s~(-1) at pH=6 for BQM and BQD,respectively).Rate constants for reactions with OH radicals,K_(OH),were determined as approx 7 x 10~9 M~(-1) s~(-1) for BQM and approx 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 muM,236 mug/L).The oxidation products were identified via LC-UV.Concentrations of 0.48 and 0.15 muM 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 ,mug/L Currently,there are no data available on the biological effects of the formed oxidation products.