Arsenic speciation and trace element analysis of the volcanic rio Agrio and the geothermal waters of Copahue, Argentina

Surface water originating from the Copahue volcano crater-lake was analysed for total arsenic and four arsenic species: arsenite (iAs(III)), arsenate (iAs(V)), monomethylarsonic acid (MA(V)) and dimethylarsinic acid (DMA(V)) and other trace elements (Fe, Mn, V, Cr, Ni, Zn). A novel in-field technique for the preconcentration and separation of four arsenic species was, for the first time, used for the analysis of geothermal and volcanic waters. Total arsenic levels along the rio Agrio ranged from <0.2-3783 mu g/l As-T. The highest arsenic levels were recorded in the el Vertedero spring (3783 mu g/l As-T) on the flank of the Copahue volcano, which feeds the acidic rio Agrio. Arsenite (H3AsO3) predominated along the upper rio Agrio (78.9-81.2% iAs(III)) but the species distribution changed at lago Caviahue and arsenate (H2AsO4-) became the main species (51.4-61.4% iAs(V)) up until Salto del Agrio. The change in arsenic species is potentially it result of an increase in redox potential and the formation of iron-based precipitates. Arsenic speciation showed a statistically significant correlation with redox potential (r=0.9697, P=0.01). Both total arsenic and arsenic speciation displayed a statistically significant correlation with vanadium levels along the river (r=0.9961, P=0.01 and r=0.8488, P=0.05, respectively). This study highlights that chemical speciation analysis of volcanic waters is important in providing ideas on potential chemical toxicity. Furthermore there is a need for further work evaluating how arsenic (and other trace elements), released in volcanic and geothermal streams/vents, impacts on both biota and humans (via exposure in thermal pools or consuming commercial drinking water). (C) 2012 Elsevier B.V. All rights reserved.