Speciation, contamination, and risk assessment of potentially toxic elements in soils from mining and non-mining...

Using a sequential extraction scheme, this study investigated the fractions of metals, including As, Cd, Cr, Cu, Hg, Pb, and Zn, in soils from two mining areas (Amansie and Konongo) and a non-mining community (Mampong) in Ghana. The elements were fractionated into exchangeable, carbonate-bound, reducible, oxidizable, and residual forms to assess their mobility and bioavailability. The results showed that Cd, Hg, and Zn had the highest proportions in the mobile fractions (exchangeable and acid-soluble), with Cd in Amansie soil exhibiting 40.67% (2.92 mg/kg) in the exchangeable fraction and 48.97% (3.52 mg/kg) in the acid-soluble fraction, indicating high bioavailability. Enrichment factor (EF) analysis revealed moderate to significant enrichment of Pb, Cd, and Hg in the mining areas (EF > 5), while geo-accumulation index (Igeo) calculations indicated moderate contamination of Pb and Hg in Amansie and Konongo. Ecological risk assessment identified Amansie as posing the highest potential ecological risk (Risk Index = 215), with moderate risks in Konongo (Risk Index = 177) and Mampong (Risk Index = 129). Health risk analysis found low non-carcinogenic risks (Hazard Index < 1) but a potential lifetime cancer risk for children due to Cr exposure. Positive Matrix Factorization identified mining, agriculture, vehicular emissions, and geogenic processes as key sources of soil contamination. These findings highlight the need for policies to regulate mining, encourage sustainable agriculture, and implement soil remediation.