Dynamics of Arsenic in Pozuelos basin, Central Andes, Argentina

MURRAY JESICA; KIRSCHBAUM ALICIA; NORDSTROM DARRELL KIRK; DOLD BERNHARD

PARIS

Congreso; GOLDSCHMIDT; 2017

High concentrationsof arsenic (As) in groundwater occur in the Central Andes. Groundwater with Aslevels above WHO guidelines (10 μg/L) is the main source of drinking water forAndean communities in Pozuelos basin. Pozuelos is a semi-arid closed basin witha playa lake (PL) on its depocenter. In Pozuelos, there are at least threepotential sources for As in groundwater i) As sulfides in mining wastes, andacid mine drainage (AMD); ii) rich Au-As mineralized shales; and iii) volcaniceruptive non-mineralized rocks.In Pozuelos,AMD has the highest concentration of As (0.7 ? 44 mg/l), decreasing ingroundwater (8.22 ? 113 μg/L) and rivers (1.7 ? 20 μg/L) and increasing againin the PL (~ 200 µg/L). The As(V) concentration is much greater than theAs(III) concentration in AMD, groundwater and rivers, while As(III) ≈ As(V) concentration in the PL.Oxidation promotes higher As(V) concentration in shallow groundwater, riversand AMD. High evaporation could increase As concentrations in PL, but therelative increase of As(III) suggests biological reduction processes. Despite theobvious source of As in sulfides for As-bearing groundwater in Pozuelos, theseare localized sources and redox and sorption processes often immobilize As fromAMD sources. Arsenic does not correlate well with any other parameter in water,but high concentrations of B and Li coupled to As could indicate volcanicsources. High concentrations of B and Li are also found in AMD.Environmentalisotopes (δ34SSO4, δ18OSO4, δ18OH2O,δDH2O) in combination with water geochemistry will contribute tounderstanding more about multiple As sources, mobility and behavior undersemi-arid conditions in this region of Central Andes. High resolution drillingand spectroscopic analysis in selected samples will contribute to elucidateAs-bearing conditions in the aquifer of Pozuelos basin.