ELEVATED CONCENTRATIONS OF FLUORIDE, BORON AND ARSENIC IN GROUNDWATER USED FOR HUMAN CONSUMPTION IN THE MUNICIPALITY OF SAN PEDRO, SANTA CRUZ, BOLIVIA

Groundwater is the main source for drinking water in rural areas in San Pedro Municipality located in the western part of department of Santa Cruz in Bolivia. This preliminary study is undertaken to determine the drinking water quality of 19 wells installed at different villages wide scattered along the municipality. Field investigations include the determination of the pH, electrical conductivity, dissolved oxygen and temperature using a portable multiparameter kit and alkalinity using a digital titrator. Water samples were collected in replicate, filtered samples for major anion and filtered acidified samples for major cation and trace element analyses.

Groundwater pH are circum-neutral to alkaline, with dissolved oxygen in a range from 3.2 to 6.8 mg/L and the electrical conductivity in a range from 482 to 1379 µS/cm. The predominant water type is Na-Cl-HCO₃. High concentrations of fluoride was noted in all water samples in a range varying from 1.6 to 5.8 mg/L. Arsenic concentrations were typically below the WHO drinking water guideline and the Bolivian standard (0.87 to 6.91 µg/L) except for two samples with high As concentrations of 20.8 and 124 µg/L respectively. The concentrations of boron were in a range of 150 to 2699 µg/L. High concentrations of these elements can have serious health effects on the population exposed and it is necessary to apply low cost remediation technologies for ensuring the drinking water safety.

It is necessary to understand the sources of fluoride, arsenic and boron and the geochemical mechanism for mobilization in these groundwater that are probably controlled by weathering, dissolution/precipitation of carbonates, gypsum, halite and plagioclase mineral phases.