Lead, Cadmium and Zinc in Agricultural Soils and Irish Potatoes around an Abandoned Tin-Mining Area of Jos-South, Nigeria

Abstract

Decades of tin extraction on the Jos Plateau have left behind heavily reworked ground, including open pits, spoil heaps and slurry deposits, much of which has gradually been absorbed back into local farming. This paper re-examines a field investigation of that reclamation process, focusing on how much lead (Pb), cadmium (Cd) and zinc (Zn) have built up in the farm soils and Irish potato (Solanum tuberosum) tubers grown around three disused mining excavations at Dahwol-Vwana village, Kuru District, Jos-South Local Government Area, Plateau State. Paired soil and tuber samples were drawn from fifteen points encircling the excavations, with soil taken 10–20 cm beneath the surface of established potato ridges; a comparatively undisturbed site supplied the control material. After wet-acid digestion, metal content was determined by atomic absorption spectrometry (AAS). Soil concentrations spanned 0.0445–3.9343 mg kg⁻¹ for Pb, 0.0086–0.1200 mg kg⁻¹ for Cd and 0.0751–39.0302 mg kg⁻¹ for Zn, while tuber concentrations spanned 0.0741–1.5042, 0.0081–0.0931 and 0.1038–88.0503 mg kg⁻¹, respectively. Every soil sample remained below the international guideline values used for comparison, yet all three metals were consistently higher than in the control soil. Measured against the food-safety benchmarks adopted in the source study, tuber Cd remained within limits throughout, whereas Pb exceeded 0.1 mg kg⁻¹ in eleven of twelve tuber samples and Zn exceeded 15 mg kg⁻¹ in four samples. Taken together, the findings suggest that although the bulk soils were not heavily contaminated by the standards applied, localised enrichment of Pb and Zn in the edible tuber tissue is sufficient to justify continued monitoring of food crops raised on reclaimed mine land.