Spatial variability of heavy metals in soils and vegetation and associated risk to grazing animals in the abandoned gold mine in Francistown, Botswana

The environmental impact of the abandoned Monarch Gold Mine in Botswana was analysed based on the concentrations of As, Mn, Cu, Cr and Zr in tailings and its vicinity, and the plants growing in the area. Results showed that the soil in the tailings dam (TD) and in the vicinity of the tailings dam (VTD), and the river sediments (RS) were severely contaminated with pollution load index (PLI) ranging from 1.89 to 2.86 in decreasing magnitude from TD>VTD> RS. The main contaminant is As but Cu, Cr and Zr are all also slightly above the critical values for soil. The TD has fewer plant species than VTD and accumulated elevated levels of these heavy metals (HM). The livestock grazing on these plants also consume the soil which could result to HM bioaccumulation. Therefore, proper management of the site is recommended to prevent the spread of pollutants and exposure to HM by animals and humans.