Assessment of heavy metal pollution/contamination in soils east and west of the Bamangwato Concessions Ltd (BCL) Cu/Ni mine smelter in Selebi-Phikwe, Botswana

Abstract

The current study evaluated the concentration and levels of pollution by heavy metals in soils around BCL Cu/Ni mine in Selebi-Phikwe, Botswana. Soil samples were collected from four different locations namely 2.5 km east, 2.5km west, 20km west and 55 km west of the mine smelter. Soils were analyzed for metals (Cu, Ni, Pb, Zn, Cr, Fe, Mn, As, Pt, Se, Li, Sn, Co, Cd and Mo) and soil pH was also determined. The results revealed that soil pH is very low (extremely acidic) closest to the mine on the western side and is related to distance from the mine smelter in the direction of prevailing winds which blow from the east towards the west. Heavy metal concentration of Cu, Ni and Fe were higher closer to the mine smelter (2.5 km west) and decreased exponentially with distance from the smelter towards the western side. These heavy metals were lower on the eastern side at 2.5km east compared to the west (2.5 km west). The concentration of heavy metals from the soil followed the order Fe>Cu>Ni>Mn>Cr>Pb>Zn>As>Pt>Se>Li>Sn>Co>Cd>Mo at 2.5 km west, Fe>Cu>Mn>Ni>Cr>As>Zn>Co>Li>Sn>Pb>Se>Cd>Pt>Mo at 20 km west, Fe>Mn>Cr>Co>Zn>Ni>Pb>As>Li>Cu>Sn>Cd>Se>Mo>Pt at 55 km west and Fe>Mn>Cu>Cr>Ni>Pb>Co>As>Zn>Li>Se>Pt>Sn>Cd>Mo at 2.5 km east. The concentrations of Mn, Cu, Ni and Fe were above permissible limits at all four sites for Mn, 2.5 km west for Cu and Ni and 2.5 km west, 20 km west and 2.5 km east for Fe. Mining and smelting in Selebi-Phikwe has resulted in accumulation of heavy metals and soil acidification.