Degradation of (E)- and (Z)-Endoxifen: Kinetics, By-products Identification and Toxicity Assessment.

Abstract

Endoxifen is an effective metabolite of a commonly used chemotherapy agent, tamoxifen. Endoxifen has been detected in the final effluent of wastewater treatment plants. The release of endoxifen into the water environment could bring negative effect to aquatic lives due to its antiestrogenic activity. This research investigated the uses of isolated bacteria strains and ultraviolet (UV) radiation (253.7 nm) to degrade endoxifen in water and wastewater, and the generations of degradation by-products and their toxicity. Biodegradation of endoxifen by isolated bacteria strains from wastewater resulted in inefficient degradation of (E)- and (Z)-endoxifen. However, photodegradation with UV light eliminated endoxifen from water by at least 99.1% after 35 seconds of irradiation with a light dose of 598.5 mJ cm-2. Light intensity and initial concentrations of (E)- and (Z)-endoxifen exhibited positive linear correlations with the photodegradation rates while pH had no effect. Photodegradation of (E)-and (Z)-endoxifen in water generated three photodegradation by-products (PBPs). Toxicity assessments through modeling of the identified PBPs suggest higher toxicity than the parent compounds. Photodegradation of (E)- and (Z)-endoxifen in wastewater at light doses used for disinfection in wastewater treatment plants (WWTPs) resulted in reduction of (E)- and (Z)-endoxifen by at least 30, 44, and 71% at the light doses of 16, 30, and 97 mJ cm-2, respectively. Two of the three PBPs observed in the experiments with water were detected in the experiments in wastewater. Therefore, highly toxic compounds are potentially generated at WWTPs during UV disinfection process if (E)- and (Z)-endoxifen are present in the treated wastewater.