PHYSICOCHEMICAL CHARACTERIZATION AND ECOLOGICAL RISK ASSESSMENT OF MIXED TOXIC METALS AND RADIONUCLIDES IN CONTAMINATED TIN MINE TAILINGS IN SELECTED AREAS AROUND JOS, PLATEAU STATE, NIGERIA

Abstract

Tin-mine tailings in Jos Plateau State, Nigeria, contain elevated levels of toxic metals (Pb, Cd, Cr) and naturally occurring radionuclides (U, Th, K), yet few studies have quantified the ecological risks associated with these wastes. This study characterizes physicochemical properties and contaminant levels in tailings collected from four dumpsites, Zawan A, Kuru A, Sharubutu, and Rim, and compares them with adjacent farmland soils. Tailings and control samples (500 g each) were pretreated and analyzed via atomic absorption spectrophotometry and gamma spectrometry. Soil pH, electrical conductivity, bulk density, organic matter, texture, and cation exchange capacity (CEC) were assessed. Toxic metals were evaluated using contamination indices: Contamination Factor (CF), Metal Pollution Index (MPI), Pollution Load Index (PLI), Geo-accumulation Index (Igeo), Nemerow Pollution Index, Enrichment Factor (EF), Degree of Contamination (Cd), and Potential Ecological Risk Index (PERI). Principal Component Analysis (PCA) was conducted to explore relationships among metals and soil properties, and radionuclide activity (²³⁸U, ²³²Th, ⁴⁰K), absorbed dose rates, and annual effective dose were quantified. Heavy metal concentrations (Pb: 11.5–50.5 mg/kg; Cd: 1.8–5.1 mg/kg; Cr: 1.2–5.1 mg/kg) varied by site, with Pb highest in Kuru A and Cd highest in Rim. Ecological risk indices indicated moderate to high pollution at Zawan A and Rim (Cd > Cr > Pb). While most farmland soils remained of acceptable quality, dumpsites exhibited moderate contamination and localized ecological risk (total degree-of-contamination: Rim > Zawan A > Kuru A > Sharubutu). PCA revealed correlations between Cd and CEC/silt content, highlighting anthropogenic origins. Radionuclide activity at dumpsites exceeded adjacent farmland levels, but remained below global average values; absorbed dose and effective annual dose rates were within safe thresholds (<1), indicating non-controlled radiation risk. However, ecological indices flagged localized ecological concerns. This study underscores the need for targeted remediation and environmental management interventions at contaminated tailing sites, especially those near communities. It also recommends continuous monitoring of contaminant migration, evaluation of human exposure pathways, and policy-based controls on tailings management in mining-impacted regions.