Heavy Metals Contaminations and Ecological Risk Assessment in Soils, Mining Wastes and Sediments of the Ngoura Gold Mining Area, Eastern Cameroon

Abstract

To assess contamination levels, 14 samples were taken from mining sites in the Ngoura gold mining area, to determine the possible ecological hazards of heavy metals (Al, Mn, As, Ba, V, Cr, Ag, Pb, Hg, Y, Th and U). Physico-chemical parameters (pH, OM, CEC, Available P, and EC) were analysed. Using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), heavy metals were identified. The contaminations were estimated using the following methods: enrichment factor (EF), contamination factor (CF), mean contamination index (Im), pollution load index (PLI), geo-accumulation index (I-Geo), and ecological risk index (Ri). Findings indicated that mining materials exhibit acidic to highly alkaline pH (5.2 to 9.8), are non-saline (EC < 250 µS/cm), with low to very high OM (1.20 to 6.51), moderate to very high CEC (14.11 to 45 meq/100g), and very low to medium available phosphorus (7 to 34.34 mg/kg). Heavy metal analysis revealed concentrations (mg/kg) exceeding UCC values: soils near mines: Hg (24.81), Pb (18.99), Th (8.46) mining wastes: Y (97.66), Hg (26.96), Pb (25.85), Th (169.96), U (9.8) residues: Hg (19.49), Pb (30.25), Th (21.12), U (16.5) sediments: Ba (682.75), Y (65.75), Hg (4.2), Pb (26.93), Th (236.65), U (16.15). Contamination indices (EF, I-Geo, CF, Im, PLI) revealed contamination by Hg, Y, Pb, Th, and U, with extreme enrichment of Hg across all materials. I-Geo indicated extreme Hg contamination, while Im confirmed contamination in most samples. Hg posed a very high ecological risk, making it the principal contaminant in the Ngoura mining area. Phytoremediation can help to reduce the contaminations in this study area.