Uranium in groundwater in the sedimentary aquifer of the eastern sector of Valle de la Cruz, Córdoba, Argentina

Abstract

Uranium has a extensive distribution in nature, in granite rocks and in various mineral deposits. The presence in the environment is due to leaching and circulation from natural deposits but also from anthropogenic emissions. The objective of this work is to establish the origin and processes that may explain the Uranium dissolved in surface water and groundwater. Also, the Uranium natural background range was estimated and anomalies were detected using statistical methodologies. The uranium values in groundwater resulted generally low. The most likely natural source of uranium in theregion would be the minerals that make up the rocks located in the Comechingones Mountains which are checked out to contain uranium and those belonging to the loessic deposits thatare present throughout the basin. It was statistically estimatedthat the range of natural background values of total uranium in surface water and groundwater is between 0.47 and 17.3 μg/L, with a characteristic value (percentile 0.5) of 8.1 μg/L. Although in surface water, the total uranium values are within the natural background range, some groundwater samples show little high values anomalies, some of which were linked to agriculture and especially concentrated livestock, being uranium correlated to nitrates. The highest U concentrations are linked to more oxidizing sectors and higher pH. The lowest values are located in the wetland area, where the geochemical environment is characterized by a lower pH and a high organic matter content, which makes possible the U retention/precipitation as a consequence of possible formation of U- complexes with carbonates or organic matter or adsorption on iron and/or manganese oxides. Taking into account that the Argentine Food Code does not establish the Uranium limit value for human consumption, the international guideline was used (reference level of 30 μg/L), finding that 80% of the samples are below the mentioned limit.