Groundwaters of the Chacopampean Plain of Argentina (provinces of Córdoba, La Pampa, Santa Fe and Buenos Aires) contain levels of arsenic (As) well above the 10 µg L−1 limit established by the Food Argentine Code (Código Alimentario Argentino 2007), same as recommended by WHO (WHO 2004) (10 µg L−1). These groundwaters present high salinity, and the As concentrations are generally well correlated with those of other anions (F, V, HCO3

−, B, Mo). Waters are predominantly oxic, and have high pH values (7.0-8.7). Hence, As is mainly present as As(V) (Smedley et al. 2002). Metal oxides in the sediments (especially of Fe and Mn) are probably the main source of dissolved As as reported by Smedley et al. (2002), although the dissolution of volcanic glass has also been cited by Nicolli et al. (1989) as a potential source.