Degradation of hormones in tap water by heterogeneous solar TiO2-photocatalysis: Optimization, degradation products identification, and estrogenic activity removal

Hormones are one of the most hazardous classes of Contaminants of Emerging Concern (CEC) found in tap water, being significantly recalcitrant regarding traditional water treatment processes. In this work, the hormones estrone, 17β-estradiol, 17α-ethinylestradiol, and estriol, present in tap water, were degraded by heterogeneous solar photocatalysis in a flat-plate photochemical reactor (recycle mode) using TiO2 (P25, Evonik) as the photocatalyst. A fully automated analytical method based on online SPE and LC-UV was developed and validated for monitoring those molecules. For a fixed amount of sample (125 μL), the limit of quantification was 10 μg L−1 (for all four hormones) with coefficients of variation smaller than 20%, and accuracy between 80% and 120%, all of which are acceptable figures for this kind of determination. The reactional system was optimized with the aid of a 22 factorial design. At optimized conditions (pH ≈ 6.8, flow rate 250 mL min−1), the removal of the four hormones (250 μg L−1 each) was approximately 85% after 3 h of treatment. However, even after 9 h of treatment, it was not possible to completely remove the estrogenic activity (MCF-7 cells) of the treated tap water. The structures of some degradation products were proposed.