Photo-Conversion of Phenytoin to Ecotoxicological Substance Benzophenone by Ultraviolet Light Irradiation in Aqueous Media

Abstract

To determine the fate and behavior of pharmaceuticals in the aquatic environment, in this study, we investigated the photo-conversion of phenytoin (PH), which is one of the antiepilepsy drug, induced by ultraviolet light (UV) irradiation in the aqueous media. The degradation of PH and the generation of its photoproducts were monitored by means of high-performance liquid chromatography (HPLC). Based on the fragmentation patterns in electrospray ionization time-of-flight mass spectrometry (ESI-TOF/MS/MS) and coupling patterns in nuclear magnetic resonance (NMR) spectrum, the main photoproduct of PH was determined as benzophenone. Evaluation of toxicity by means of luminescent bacteria test (ISO11348) indicated that a PH solution was nontoxic, whereas a UV-irradiated PH solution and a benzophenone solution were toxic (EC₅₀: 19.46 mg/L and 24.40 mg/L). It was shown that benzophenone has a contribution to the increase of ecotoxicity of PH solution for luminescent bacteria after UV irradiation. This is the first report of the photo-conversion of PH to benzophenone induced by UV irradiation in the absence of photo-catalysts. These results indicate that the importance of evaluating not only parent compounds but also their photoproducts for the risk assessment of pharmaceuticals in the aquatic environment.