GEOCHEMICAL MECHANISMS AND SPATIO-TEMPORAL VARIATION OF THE MOBILITY OF NATURAL ARSENIC IN SHALLOW GROUNDWATER AND SURFACE WATER IN THE HYDROGEOLOGIC SYSTEM OF LOWER KATARI BASIN, BOLIVIAN ALTIPLANO

Arsenic (As) contamination of drinking water is a world-wide problem. The natural origin of As, its mobility and transport are of great interest in Bolivian Altiplano due to its presence in mineral deposits, brines, hot springs and volcanic rocks. In this study, a geochemical spatial-temporal approach was used to understand the sources and factors that control the mobilization and fate of As in water bodies as well as sediments of Lower Katari Basin (LKB). The results reveal that high levels of As, boron (B), manganese (Mn) and high salinity are present in shallow drinking water wells, which exceed the guideline values of the Bolivian regulation (NB-512) and WHO. The seasonal variation and its impact on water quantity, in addition to the load of solids and liquids of residual origin (Pallina River) represent risk of significant negative health impact for the communities at the banks of the Katari River. The first evaluation of the hydrogeological study indicates that the groundwater flow was observed in the direction southeast - northwest (SE - NW), which are showed in the sectors with interaction between groundwater and surface water. The spatial distribution of As varies considerably due to geological characteristics of the area as well as due to the heterogeneously distributed evaporites in the sediments; however, the highest concentrations of As are found in the alluvial sediments of the northern region. Sequential extraction of sediment along with geochemical modeling (mineral saturation indices) indicates that the iron (Fe) and aluminum (Al) oxides as well as their hydroxides are most important adsorbent minerals of As in central and southern region of LKB. The hydrochemistry of water bodies in LKB is strongly influenced by the interaction with the sediment constituents and by the spatial-temporal variations. Therefore, the determination of the distribution of As among the different geochemical fractions was useful to find the relative proportions of As transported by different chemical mechanisms and their spatial-temporal variation.