Phototransformation of three selected pharmaceuticals, naproxen, 17α-Ethinylestradiol and tetracycline in water: Identification of photoproducts and transformation pathways

Transformation products (TPs) may be formed during various processes, however, it was proved that one of the main mechanisms responsible for degradation of pharmaceuticals in natural waters is photolysis. Three compounds were selected, tetracycline (TC), 17-alpha-ethinylestradiol (EE2) and naproxen (NAP), for degradation experiments which were performed using a xenon lamp emitting light with a spectrum closely approximating that of natural sunlight. Identification of photodegradation products was achieved via liquid chromatography coupled with high resolution quadrupole time-of-flight mass spectrometry (LC-QTOE-MS) providing accurate mass measurements and MS/MS experiments for structural elucidation. Results indicate that degradation of compounds under the study follows pseudo-first-order kinetics. Photolysis rate constants (k) were determined and half-lifes (t(1/2)) calculated to be 11, 120, and 13 min for TC, EE2 and NAP, respectively. Xenon lamp irradiation led to the formation of several photoproducts. Many of them have been identified for the first time. LC-QTOF-MS analysis allowed for the identification of seven, four, and eight TPs of TC, EE2 and NAP, respectively. Finally, the presence of parent compounds and identified TPs was investigated in various real-world water samples. Only three degradation products of 17-alpha-ethinylestradiol and naproxen were detected in wastewater effluent and treated water samples. Quantitative structure-activity relationship (QSAR) approach was applied in order to estimate physical-chemical properties of selected pharmaceuticals and their TPs. This allowed predicting the fate of all analytes in the aqueous environment.