Photocatalytic Degradation of Parabens in Aquatic Environment: Kinetics and Degradation Pathway

Parabens are p-hydroxybenzoic acid ester compounds widely used as preservatives in foods, cosmetics, toiletries and pharmaceuticals. These compounds exert a weak estrogenic activity as determined by in vitro estrogen receptor assay and in vivo uterotrophic assay. The photocatalytic degradation of parabens (butylparaben and ethylparaben), as a function of pH and initial concentration of parabens, was investigated in the presence of TiO2 photocatalyst (P-25, Degussa). Experiments conducted at pH 4 with O-2-sparged concentration of 15 mg/L showed that in terms of the photocatalytic efficiency the catalysts were slightly superior to those tested at pH 6-11. The intrinsic reaction rates of 2.08 x 10(2) and 1.81 x 10(2) mu mol L(-1)min(-1) were estimated, and Langmuir-Hinshelwood model adsorption constants K were calculated as 0.05 and 0.06 L/mu mol for butylparaben and ethylparaben, respectively. Ten organic intermediates appeared during the photocatalytic degradation of parabens, and were identified by LC/MS/MS. In addition, a tentative reaction pathway was proposed.