SPATIAL VARIABILITY AND HYDROGEOCHEMISTRY OF GEOGENIC: ARSENIC, BORON AND LITHIUM IN THE HYDROLOGICAL SYSTEM OF THE LAUCA RIVER BASIN IN BOLIVIA

Arsenic (As) contamination in drinking water is a global issue, and reports from various regions offer valuable data for mapping its distribution, predicting occurrences, and understanding its spatial variability. However, studies related to the presence of As with the co-occurring geogenic contaminants (GCs) like Boron (B), and Lithium (Li) in hydrological systems, especially in areas with unusual geological characteristics like the Lauca River Basin (LRB) of the Bolivian Antiplano (BA), has remained scanty. This study investigates the natural occurrence of high concentrations of As, B, and Li using an integrated approach with GIS based mapping, geostatistics, and hydrogeochemistry.

Several field and laboratory parameters were analyzed from 171 water samples collected from the different water bodies of the LRB hydrological system, including major ions and trace elements using IC and ICP-MS. In addition to confirming high concentrations of As in water, we found remarkably high concentrations of B and Li in the different water bodies. The analytical results revealed that the concentration of As, B and Li in rivers reaching as high as 1895 μg/L, 10806 μg/L and 14432 μg/L respectively. In springs, concentration of As ranged up to 862 μg/L, B up to 20093 μg/L and Li up to 14691 μg/L, while the maximum concentrations of As, B and Li in hot springs were found to be 6797 μg/L, 40872 μg/L and 6872 μg/L respectively. The highest concentrations of As, B and Li were 4619 μg/L, 64414 μg/L and 19789 μg/L in the wetlands respectively. In lagoons, the maximum concentrations of As, B and Li were 3489 μg/L, 188982 μg/L and 35886 μg/L respectively. The river waters are predominantly of Na-Cl-HCO₃-type, while the water samples in the springs, wetlands, and lagoons are mainly of Na-Ca-Cl-SO₄-HCO₃-type. On the other hand, the hot springs are predominantly of Na-Cl-HCO₃-B-type. The average pH of the water bodies is slightly alkaline, and the conductivity values are high in sources near the Coipasa salt flat. These unusual hydrogeochemical characteristics are compatible with extremely arid volcanic areas with high evaporation rates containing evaporative deposits and geothermal fluids. Continuous and vigilant monitoring of BA’s water resources is critical not only to safeguarding public health but also to conserving the environment and promoting the sustainable use of these water sources.