Origin and geochemistry of arsenic in surface and groundwaters of Los Pozuelos basin, Puna region, Central Andes, Argentina

• Published in: The Science of the total environment Vol. 697; p. 134085
• Main Authors: Murray, Jesica, Nordstrom, D. Kirk, Dold, Bernhard, Romero Orué, Maria, Kirschbaum, Alicia
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 20.12.2019; Elsevier
• Subjects: Altiplano-Puna; Applied Geochemistry; Arsenic redox speciation; Closed basin; Environmental Sciences; Evaporation; Tillämpad geokemi; UNESCO Biosphere Reserve; Altiplano-Puna; Evaporation; Arsenic redox speciation; Closed basin; UNESCO Biosphere Reserve
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.134085

Los Pozuelos is a closed basin in the Puna region of NW Argentina, Central Andes. This is a semi-arid region where closed basins are the most important feature for the hydrologic systems. The center of the basin is occupied by a fluctuating playa lake called Los Pozuelos lagoon, which constitutes a UNESCO Biosphere Reserve. This is one of the most populated closed basins in the Argentinian Puna and residents use groundwater for drinking and cooking. Lowest concentrations of As and dissolved solids are in the headwaters of the rivers (1.46–27 μg/L) and the highest concentrations are in the lagoon (43.7–200.3 μg/L). In groundwater, arsenic concentrations increase from the outer ring aquifer (3.82–29.7 μg/L) composed of alluvial-alluvial fan sediments to the inner lacustrine aquifer (10–113 μg/L) that surround the playa lake. Moreover, high concentrations of As during the dry season (90.2 and 113 μg/L), Na/K mass ratios (0.2 and 0.3), and formation of Na-rich efflorescent salts suggest that high evaporation rates increases As concentration, while rainwater dilutes the concentration during the wet season. As(V) is the dominant species in all the water types, except for the lagoon, where As(III) occasionally dominates because of organic matter buildup. There are at least three potential sources for As in water i) oxidation of As sulfides in Pan de Azúcar mine wastes, and acid mine drainage discharging into the basin; ii) weathering and erosion of mineralized shales; iii) weathering of volcanic eruptive non-mineralized rocks. Because it is a closed basin, the arsenic released from the natural and anthropogenic sources is transported in solution and in fluvial sediments and finally accumulates in the center of the basin where the concentration in water increases by evaporation with occasional enhancement by organic matter interaction in the lagoon. [Display omitted] •There are at least three different geogenic sources of arsenic in the basin.•Concentrations of As in waters increase to the center of the basin.•A(V) is the dominant specie in all the water types.•The presence of A(III) in the lagoon indicates reductive conditions.•The closed basin effect, and high evaporation increase As in waters.