We performed near edge X-ray absorption spectroscopy (XANES) measurements on the arsenic K-edge of As(III) in solution tinder acidic and basic conditions, after exposure of the solutions to air. Spectra Were recorded for increasing exposure tithes to the X-rays used to perform absorption spectroscopy measurements. We did not find changes for the solution under acidic conditions, whereas we observed significant changes, in the case of solution under alkaline conditions. To interpret these changes, we compared the obtained spectra with XANES spectra of As(III) and As(V) solutions under alkaline conditions, not exposed to air, and used as standards. Principal component fits using these standards indicate an accelerated conversion of As(III) to As(V) due to the exposure to X-rays.