Geogenic arsenic and other trace elements in the shallow hydrogeologic system of Southern Poopó Basin, Bolivian Altiplano

• Published in: Journal of hazardous materials 2013-11, Vol.262, p.924-940
• Main Authors: Ormachea Muñoz, Mauricio, Wern, Hannes, Johnsson, Fredrick, Bhattacharya, Prosun, Sracek, Ondra, Thunvik, Roger, Quintanilla, Jorge, Bundschuh, Jochen
• Format: Article
• Language: English
• Subjects: Absorption; Adsorption; Alluvial sediments; Arsenic; Arsenic - analysis; Arsenic - chemistry; Bolivia; Bolivian Altiplano; Boron - analysis; Climate; Electrochemistry; Environmental Monitoring - methods; Ferric Compounds - chemistry; Geography; Geologic Sediments - analysis; Geology; Groundwater; Hydrogen-Ion Concentration; Ions; Oxidation-Reduction; Rivers; Trace Elements - analysis; Volcanic rocks; Water; Water Pollutants, Chemical - analysis; Water Supply
• ISSN: 0304-3894; 1873-3336; 1873-3336
• DOI: 10.1016/j.jhazmat.2013.06.078

•Groundwater used as drinking water has elevated concentrations of arsenic and boron.•Sediments are potential sources of arsenic and boron in shallow groundwater.•Fe-oxides and hydroxides are important absorbents of arsenic.•Multiple geochemical processes drive mobilisation of arsenic in groundwater. Environmental settings in the southern area of Lake Poopó in the Bolivian highlands, the Altiplano, have generated elevated amounts of arsenic (As) in the water. The area is characterised by a semiarid climate, slow hydrological flow and geologic formations of predominantly volcanic origin. The present study aimed at mapping the extent of the water contamination in the area and to investigate the geogenic sources and processes involved in the release of As to the groundwater. Ground- and surface-water samples were collected from 24 different sites, including drinking water wells and rivers, in the southern Poopó basin in two different field campaigns during the dry and rainy seasons. The results revealed variable levels of As in shallow drinking water wells and average concentration exceeding the WHO guidelines value. Arsenic concentrations range from below 5.2μg/L (the detection level) to 207μg/L and averages 72μg/L. Additionally, high boron (B) concentrations (average 1902μg/L), and high salinity are further serious concerns for deteriorating the groundwater quality and rendering it unsuitable for drinking. Groundwater is predominantly of the Na–Cl–HCO3 type or the Ca–Na–HCO3 type with neutral or slightly alkaline pH and oxidising character. While farmers are seriously concerned about the water scarcity, and on a few occasions about salinity, there are no concerns about As and B present at levels exceeding the WHO guidelines, and causing negative long term effects on human health. Sediment samples from two soil profiles and a river bed along with fourteen rock samples were also collected and analysed. Sequential extractions of the sediments together with the calculation of the mineral saturation indices indicate that iron oxides and hydroxides are the important secondary minerals phases which are important adsorbents for As. High pH values, and the competition of As with HCO3 and dissolved silica for the adsorption sites probably seems to be an important process for the mobilisation of As in the shallow groundwaters of the region. Continuous monitoring and expansion of monitoring systems are necessary prerequisites for better understanding of the pattern of