High Arsenic Enrichment in Water and Soils from Sambayourou Watershed – Burkina Faso (West Africa)

Abstract

Sambayourou is one of the main tributary of Mouhoun River in southwest Burkina Faso. Its watershed is part of area affected by mining operations from Poura gold mine in 80s. Investigations on surface water, ground-water and soil from Sambayourou watershed reveal that enormous vol. of mine wastes from Poura old gold mine is causing acid mine drainage (AMD). This latter is characterized by a red-brick color, a low pH (2.9) and high contents of arsenic and heavy metals: arsenic (753 ppm), iron (4948 ppm), zinc (51 ppm), copper (38 ppm), cobalt (7 ppm) and lead (4 ppm). The oxidn. and acidification of the mine wastes have also resulted in the pollution of some groundwater with concns. of arsenic and lead beyond acceptable stds. Arsenic is the most polluting element of surface water and ground-water. Concerning ground-water contamination, arsenic come from both mine wastes and host rocks. To assess soil contamination, geo-accumulation indexes (Igeo) and enrichment factor (EF) are used. The use of the index of geo-accumulation is based on seven descriptive classes for increasing geo-accumulation index values. The different values of enrichment factor are divided into five groups corresponding to five categories of contamination. According to geo-accumulation values, the soil in Sambayourou watershed is strongly contaminated by arsenic. This situation is confirmed by enrichment factor which indicates a very high enrichment in arsenic. The very high enrichment in arsenic can derive from erosion of host rocks of ores mineralization which contain sulfide minerals as arsenopyrite (FeAsS) and/or from pedogenesis processes. However, mine wastes are assumed to be the main sources of arsenic contamination of soil in Sambayourou watershed. [on SciFinder(R)]