A geochemical approach for source apportionment and environmental impact assessment of heavy metals in a Cu–Ni mining region, Botswana

Soil pollution by heavy metals is increasing continuously in developing countries due to industrial activities such as mining. This study addresses the distribution, potential risk to human health, and ecological risk of heavy metals (Cu, Ni, Cr, Co and Zn) taken from the soil in the vicinity of a relinquished Cu–Ni mine in Selibe Phikwe, Botswana. Furthermore, source apportionment of heavy metals was also conducted through Positive Matrix Factorization (PMF). The geochemical analysis results showed that the mean Cu, Ni, Cr, Pb, Co and Zn concentrations in the soil reached 141.65, 132.30, 87.64, 4.30, 8.97 and 37.15 mg/kg, respectively. Although Hazard Quotient (HQ) calculations results suggest that non-cancerous risks of the target heavy metals are low under the present conditions, the Hazard Index (HI) calculation results indicate a potential non-carcinogenic risk of Cr (HI > 1) for children. The mean values for cancer risk (CR_total) also reached 3.00 × 10^–5 in children and 5.59 × 10^–5 in adults. The findings also suggested a potential ecological risk resulting from Cu and Ni in the region. The PMF model effectively revealed that Pb, Zn, and Co were mainly geologic, while anthropogenic sources were primarily responsible for the Cr, Ni, and Cu enrichment in soils. This study suggests that inexpensive risk mitigation efforts such as phyto-capping should be implemented, particularly in areas with slag piles and tailings dams.