Pii: S0043-1354(00)00457-7

This study investigates the oxidative transformation of diethylenetriaminepentaacetate (DTPA), a synthetic ligand, during drinking water ozonation. The rate coefficients for the reactions of CaDTPA and ZnDTPA with ozone were determined to be 6200 and 3500 150M 1 s , respectively. The reactivity of Fe(III)DTPA towards ozone was found to be much lower ð510 M 1 s Þ, but near neutral pH the reactivity of the Fe(III)-complexes is dominated by [Fe(III)(OH)]DTPA . For the reaction of Fe[(III)(OH)]DTPA with ozone a rate coefficient of 2:4 0:2 10M s 1 was measured. The rate coefficients of the reactions of the ZnDTPA-and Fe(III)DTPA with OH radicals have been determined by a competitive method as 2:4 0:4 10 and 1:5 0:1 10 M s , respectively at pH 1⁄4 7. The degradation of low concentrations of DTPA complexes during ozonation was investigated in natural waters under drinking water relevant conditions. Based on our findings CaDTPA and ZnDTPA are judged as easily degradable. Fe(III)DTPA complexes showed a somewhat lower reactivity, but were still typically degraded by one order of magnitude at ozone dosages of 20 mM ð1 mg L Þ in the three natural waters tested. Molecular ozone was found to be the major oxidant for the metal–DTPA complexes during ozonation. # 2001 Elsevier Science Ltd. All rights reserved Key words}ozonation, hydroxyl radical, drinking water, DTPA, EDTA, ligands, oxidation kinetics