We investigated the relevance of the interaction between Fe and As in iron-rich sediments for As attenuation in surface waters of the Chilean Altiplano, under climatic conditions of extreme altitude (>4,000 masl) and aridity (<310 mm year-1). Our results show that As concentrations in aqueous phase were attenuated (>70%) due to stabilization processes in Fe-rich sediments. Total As content in Fe sediment profiles exceeds 0.9 g kg-1 and in the surface is higher than 4 g kg-1. As and Fe show perfect correlation in the Fe sediment profiles indicating a close connection between Fe minerals and As mobilization. Altogether, these results indicate that As attenuation is controlled by stabilization processes onto Fe minerals on the surface and at depth, thus controlling the discharge of As-rich runoff to the surface waters. © 2014 Taylor & Francis Group.