HYDROCHEMICAL ASSESSMENT AND OCCURRENCE OF ARSENIC IN THE LOWER BASIN OF KATARI RIVER, BOLIVIAN ALTIPLANO

Lake Titicaca is the largest lake in South America and the highest navigable lake in the world, however, because of the increasing number of inhabitants the lake is being polluted by waste water and solid waste. Recent studies indicate that the Cohana bay area within the lake has several environmental problems mainly caused by different contaminants such as heavy metals, nutrients and bacterial. These problems are caused by the urban and industrial waste and by mining activities carried out upstream the Katari river which discharges into the Cohana bay.

Hydrochemical investigations were performed in order to better understand the environmental conditions of Katary river; a total of 37 water samples were collected including 31 groundwater samples and 6 surface water samples. Field measurements were performed with a portable multiparameter and water samples were collected for the analysis of cations, anions, trace elements and arsenic (As) Anions were analyzed in an ion chromatograph while cations were analyzed in a flame atomic absorption spectrometer. Arsenic and other trace elements were analyzed in a graphite furnace atomic absorption spectrometry.

Results show the pH ranging from 6.7 to 9.0, ORP ranging from +168 mV to +246 mV and EC ranging from 253 to 4674 mS/cm; high EC values are related to the presence of salt deposits in the area. Surface waters are predominantly Na-HCO₃ type, while groundwater are predominantly Ca-HCO₃ type. Dissolved As concentration ranges from 2.1 to 89.7 μg/L; more than 43% of the samples exceeded the As WHO guideline (10 μg/L). The presence of As is attributed to the oxidation of sulfide minerals such as arsenopyrite and to the mobilization from volcanic rocks. The distribution of trace elements shows diversity of concentrations; Zinc concentrations range from below detection limit (bdl) to 279 μg/L. Among the redox sensitive elements iron and mangenese showed wide variability in the ranges: from bdl to 419 μg/L and from bdl to 137 μg/L respectively. Elevated As concentrations in groundwater in the study area is big concern because groundwater in the area is used for human consumption. Further studies in this area will be carried out to understand the mobilization and transport of As and its potential health impacts on the local population.