In collaboration with COWI and DAEPA (Direction de L'Approvisionnement en Eau Potable et de L'Assainissement), the BGS has carried out an investigation of arsenic in groundwaters from the Ouahigouya area of rural northern Burkina Faso.
Previous surveys had shown that some sources of drinking water in the area had concentrations of arsenic above the WHO guideline value for arsenic (10 µg/L) and some villagers were presenting with skin problems consistent with chronic arsenic exposure.
Northern Burkina Faso is an arid area and traditional sources of water have been from shallow hand-dug wells. These are still used by many villagers in the region, although boreholes were drilled in some villages in the 1990s to 2000s to provide drinking water from deeper groundwater sources.
BGS collected 45 samples of groundwater from hand-pumped boreholes and dug wells in villages from the Ouahigouya area. Results of the survey showed:
The high-arsenic groundwaters, that were observed, derive from zones of gold mineralisation in ancient (Lower Proterozoic) volcano-sedimentary rocks. The gold occurs in vein structures along with quartz and altered sulphide minerals (pyrite, chalcopyrite, arsenopyrite).
The source is likely to be the oxidised sulphide minerals and secondary iron oxides in the mineralised zones. Links were also found between the concentrations of dissolved arsenic and the concentrations of dissolved molybdenum and tungsten. These also probably derive from ore minerals and oxides in the mineral veins.
Since discovery of the groundwater quality problems in the region, the Burkina Faso government has taken steps to close many of the problematic wells and install alternative supplies. The government has carried out subsequent sampling and analysis, conducted awareness campaigns and carried out health surveillance.
The discovery of high arsenic concentrations in groundwaters from crystalline basement rocks in northern Burkina Faso reiterates the need for reconnaissance surveys of trace elements (including arsenic) in groundwater from basement aquifers.
Smedley, P L, Knudsen, J, and Maiga, D. 2007. Arsenic in groundwater from mineralised Proterozoic basement rocks of Burkina Faso. Applied Geochemistry, 22, 1074–1092.
Contact Dr Pauline Smedley for further information