Photolytic fate of (E)- and (Z)-endoxifen in water and treated wastewater exposed to sunlight.

Endoxifen is the main active metabolite of a common cytostatic drug, tamoxifen. Endoxifen has been recently detected in the final effluent of municipal wastewater treatment plants. The antiestrogenic activity of endoxifen could bring negative effects to aquatic life if released to the water environment. This study elucidated the fate and susceptibility of (E)- and (Z)-endoxifen (2 µg mL-1, 1:1 wt ratio between the two easily interchangeable isomers) in wastewater and receiving surface water to sunlight. Phototransformation by-products (PBPs) and their toxicity were determined. Sunlight reduced at least 83% of endoxifen concentration in wastewater samples, whereas in surface water samples, 60% of endoxifen was photodegraded after 180 min of the irradiation. In ultrapure water samples spiked with endoxifen, PBPs were mainly generated via con-rotatory 6π-photocyclization, followed by oxidative aromatization. These PBPs underwent secondary reactions leading to a series of PBPs with different molecular weights. Eight PBPs were identified and the toxicity analysis via the Toxicity Estimation Software Tool revealed that seven of these PBPs are more toxic than endoxifen itself. This is likely due to the formation of poly-aromatic core in the PBPs due to exposure to sunlight. Therefore, highly toxic PBPs may be generated if endoxifen is present in water and wastewater exposed to sunlight. The presence, fates and activities of these PBPs in surface water especially at locations close to treated wastewater discharge points should be investigated.

Photodegradation of (E)- and (Z)-Endoxifen in water by ultraviolet light: Efficiency, kinetics, by-products, and toxicity assessment.

Endoxifen is an effective metabolite of a common chemotherapy agent, tamoxifen. Endoxifen, which is toxic to aquatic animals, has been detected in wastewater treatment plant (WWTP) effluent. This research investigates ultraviolet (UV) radiation (253.7 nm) application to degrade (E)- and (Z)-endoxifen in water and wastewater and phototransformation by-products (PBPs) and their toxicity. The effects of light intensity, pH and initial concentrations of (E)- and (Z)-endoxifen on the photodegradation rate were examined. Endoxifen in water was eliminated ≥99.1% after 35 s of irradiation (light dose of 598.5 mJ cm-2). Light intensity and initial concentrations of (E)- and (Z)-endoxifen exhibited positive trends with the photodegradation rates while pH had no effect. Photodegradation of (E)- and (Z)-endoxifen in water resulted in three 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 WWTPs (16, 30 and 97 mJ cm-2) resulted in reductions of (E)- and (Z)-endoxifen from 30 to 71%. Two of the three PBPs observed in the experiments with water were detected in the wastewater experiments. Therefore, toxic compounds are potentially generated at WWTPs by UV disinfection if (E)- and (Z)-endoxifen are present in treated wastewater.