Northern Chile has a long history of arsenic (As) contamination. Examples include arsenic found in Chinchorro mummies’ hair and high rates of lung and bladder cancer in the city of Antofagasta. The natural environment of the northern Atacama Region is comparable to areas associated with high natural arsenic concentrations in Chile. To quantify natural concentrations of arsenic of this region, the northern Atacama Region basins were sampled at the El Salado river, the Pedernales salt-flat, and the Río Negro and Laguna Verde hot-springs. Our results show that: (1) to the east of Diego de Almagro, all water samples contain dissolved-As values above 700 μg/L; (2) As bearing phases were not observed in the colloi-dal fraction; (3) As-bearing minerals were found at the Pedernales salt-flat (silicate minerals with ∼20% As), the Potrerillos site (apatite and Fe-oxides), and the El Salado river close to the Potrerillos site (iron oxides); (4) in 80% of the studied sediments there are enzymes that metabolize As, however this phenomenon is nearly absent in the Pedernales salt-flat indicating a high solubility of the As-bearing silicates.