Ecological Risk Assessment of Soils Near Abandoned Pb–Zn Mines in Nigeria

Abandoned lead–zinc (Pb–Zn) mining sites are major sources of environmental contamination, particularly in developing countries where post-mining management is often inadequate. In Nigeria, historical Pb–Zn mining within the Benue Trough has left numerous abandoned mine lands (AMLs) that continue to release toxic metals into surrounding soils and water systems. However, few studies have assessed their ecological risks and ecosystem-level impacts. This study evaluates the ecological risks associated with abandoned Pb–Zn mine sites in Nigeria to support remediation and sustainable land management.

A total of 49 soil samples were collected from Gimbi/Rikaya and the Abakaliki sites in Nigeria. Metal, mobility, partitioning, and bioavailability were assessed using the BCR three-step sequential extraction procedure. Risk assessment evaluation was conducted using contamination factor (CF), enrichment factor (EF), geoaccumulation index (Igeo), ecological risk index (ERI), and cumulative risk score (CRS). A conceptual site model (CSM) was developed to identify contaminant sources, process and transport mechanisms, exposure pathways, and receptors.

Elevated concentrations of Zn, Pb, Cr, Ni, and Cd were detected in surrounding soils, indicating ongoing dispersion from abandoned mine tailings. Sequential extraction showed that Pb, Cd, and Zn were predominantly associated with exchangeable and reducible fractions, suggesting potential high mobility and bioavailability. Pollution indices classified the sites as strongly polluted with high ecological risks. The CSM identified tailings as the contaminant source, transported via erosion and leaching, ingestion, dermal contact, and inhalation as key exposure pathways affecting terrestrial and domestic receptors.

The study concludes that Abakaliki indicate high metal mobility and ecological risk, with Cd posing the greatest risk in both sites, while cerium was identified as a notable additional contaminant. These results underscore the urgent need for remediation, long‑term monitoring, and stronger mine‑closure practices to protect ecosystems and nearby communities from exposure to contaminants.