Spatial Exploration of Trace Metals in Near-Surface Water and Soil in the Bolivian Altiplano

We analyzed soil and groundwater samples from the Bolivian Altiplano for trace metal concentrations, correlations and partitioning trends. Total digestion, sequential extraction and loss on ignition experiments were performed on soil samples. We ran aqueous samples on an ICP-MS. Results were analyzed to identify trace metal concentrations and find any significant correlations. We generated interpolated maps in ArcGIS to spatially analyze results. Results for elevated concentrations of interest were divided into sub-groups of organophilic metals, oxoanions and divalent metals and include vanadium, arsenic, selenium, zinc, nickel, lead, cobalt, uranium, copper and manganese. These elements are likely naturally sourced. We found trends among groupings of depths and location. Arsenic exceeded the World Health Organization (WHO) guideline for all water samples. Some elements of interest were not concentrated in water samples but were present in soil, which could pose an agricultural concern. For organophilic metals, trends were likely due to soil weathering. For divalent metals, solubility was likely the controlling factor. For oxoanions, correlations were probably from strongly held inner-sphere sorption and soil weathering. As soil weathering occurs, oxoanions were likely taken into different phases. The methods we implemented in this paper are very useful for both exploration, risk assessment and prediction via empirical relationships. The visualization of data using of spatially interpolated maps is useful in identifying trends as well as areas of potential risk. This method can be applied in other areas with suspected risks due to anthropogenic contamination or naturally occurring concentrations of trace metals