The occurrence of arsenic and other trace elements in groundwaters of the southwestern Chaco-Pampean plain, Argentina

The Argentinian Chaco-Pampean plain is a large sedimentary basin, which southern part, covering about 1.9 millions of km(2), encompasses the provinces of Cordoba, Santa Fe, San Luis, Buenos Aires and La Pampa where water demand is mainly satisfied by groundwater. Its quality for human consumption is significantly impaired by the elevated presence of arsenic (As) and other geogenic trace elements. In this paper we investigated the nature and extent of the occurrence of arsenic and other selected trace elements (Fe, Mo and V) in groundwater in the Northern region of La Pampa. To achieve this aim, analytic results from 164 samples were taken into consideration. These samples were collected from community wells located in the study area. For 42 of these samples, determinations of the arsenic species were available. The hydrochemical characterization indicates that these groundwaters are predominantly of Na-HCO3 and Na-SO4-Cl type with variable salinity and high pH and alkalinity. These properties would favor the As mobilization by desorption from the solid phase. Most of the groundwaters revealed As concentrations over 10 mu g/L, while guideline values of iron and molybdenum are exceeded in some cases. Arsenic is predominantly found as As(V) which represents between 92 and 97% of the total arsenic. This is consistent with the oxidizing conditions of the hydrogeochemical system.