Arsenic (III) is a common by product of mining activity. This contaminant can have a high environmental impact because it might accumulate in the food chain and seriously affect human health. The purpose of this study is to develop a method to remove arsenic (III) using the photo catalyst TiO2-N activated by visible light. The catalyst TiO2 Degussa P-25 was doped with nitrogen in order to narrow the energy gap and to work with radiation in the visible range. A multi variable approach was used in order to optimize the removal of arsenic, varying the concentration of the catalyst and the pH, maintaining the initial concentration of As (III) in 3 mg L–1. Two optima were determined, in one of which As (III) was reduced by 96.7% at pH 2, and in the other As was reduced by 80% at pH 7. Furthermore, the toxicity of the As (III) solutions was determined using Daphnia magna before and after the photochemical treatment. Mortality in the initial concentration was 87%. After the treatment at pH 2.0, a significant reduction in toxicity was recorded, with a mortality of only 30%.