Assessment of heavy metal contamination levels in the soil of the former Poura mine in Burkina Faso (West Africa)

The development of the mining sector in Burkina Faso has its roots in small-scale mining, which has been practiced for many years. However, this activity causes enormous disruption to the environment and threatens the ecosystems around these facilities. The objective of this study is to assess the level of heavy metal contamination in the soil in the area surrounding the former Poura mine. A grid was established for the study site. This grid was tightened to a radius of 600 meters from the ends of each tailing and cyanide tank in the four cardinal directions, taking into account the direction of surface water flow. A distance of 200 meters between sampling points was established. A total of 35 sampling points were identified. Thirteen (13) soil samples were taken from tailings pile 1, eleven (11) from around tailings pile 2, and eleven (11) from the cyanide tank. The results show heterogeneous concentrations of As, Cd, Cr, Cu, Ni, Pb, and Zn in the soil. These vary depending on the metal and the source of pollution. Median manganese concentrations are high in all three sources. Tailings 1 has the highest median with 900 mg.kg⁻¹ of Mn, followed by the cyanide tank, while tailings 2 show lower values. With Mn, the dispersion is asymmetrical for the tailings, with the presence of extreme values. However, with regard to arsenic (As), the median concentrations in the various sources are all very close to 0 mg·kg⁻¹ and do not show any significant difference. The distributions are asymmetrical, particularly for tailings 1 and tailings 2. Consequently, the soils in the area affected by the Poura mine can be considered poor quality in terms of heavy metal content.