Kinetics of Aqueous Ozone-Induced Oxidation of Some Endocrine Disruptors

This study investigated aqueous ozone-induced oxidation of six endocrine disruptors (EDs: 4-n-nonylphenol, bisphenol A, 17α-ethinylestradiol, 17β-estradiol, estrone, and estriol). In the first part, ED ozonation kinetics were studied over a pH range of 2.5−10.5 at 20 ± 2 °C and in the presence of tert-butyl alcohol. Under these conditions, for each studied compound, the apparent ozone rates presented minima at acidic pH (pH < 5) and maxima at basic pH (pH > 10). In the second part, to explain this pH dependence, elementary reactions, i.e., reactions of ozone with neutral and ionized ED species, were proposed, and the intrinsic constants of each of them were calculated. The reactivity of ozone with ionized EDs (i.e. 1.06 × 109−6.83 × 109 M-1 s-1) was found to be 104−105 times higher than with neutral EDs (i.e. 1.68 × 104 M-1 s-1−2.21 × 105 M-1 s-1). At pH > 5, ozone reacted to the greatest extent with dissociated ED forms. Finally, to assess the potential of ozone for inducing ED oxidation in water treatment conditions, the expected removal rates for each of the studied EDs were determined on the basis of the kinetic study at pH = 7 and 20 ± 2 °C. For all EDs considered, O3 exposures of only ∼2 × 10-3 mg min L-1 were calculated to achieve ≥95% removal efficiency. The ozonation process could thus highly oxidize the studied EDs under water treatment conditions.