Mapping of Arsenic Pollution in Burkina Faso Using a New Field Measurement Technique

Abstract. Arsenic is a major pollutant of groundwater with evident health impacts on affected populations. Since twenty years, these issues have been highlighted in West Africa. The magnitude of groundwater arsenic contamination is still not sufficiently known in these countries. There is a need to predict exactly in which areas and in which kind of geology arsenic is found in order to give more certainty in the implementation of new boreholes. The main objectives of the study are to: Measure the reliability of a new field measurement technique by comparison with a proven laboratory measurement technique; Map arsenic pollution in south western Burkina Faso to show a link between arsenic contamination and (i) geology and (ii) physico-chemical parameters of water. We have compared measurements taken using the Wagtech Metalyser (in-field measurement) with a reliable laboratory technique (ICP-MS). 103 boreholes were analyzed for arsenic and major ion concentrations. All samples contain arsenic but only 10% with a concentration above 10 µg/L (WHO guideline). The correlation between arsenic measurements with both techniques is quite good (Correlation coefficient = 0.91) but there is a big difference for values under 10 µg/L (Correlation coefficient = -0.56) and values above 10 µg/L (Correlation coefficient = 0.97). There is a better reliability of the field technique for values above 10 µg/L. The mapping of arsenic contamination shows that 79% of boreholes with elevated arsenic concentrations are located on volcano-sedimentary formations. Also we found a significant relationship between arsenic in groundwater and gold mining.