Potentially Harmful Elements in Mine Pond Water from Derelict Tin and Columbite Workings in Barkin-Ladi, Jos Plateau, Nigeria: Contamination Status and Human Health Risk

Derelict tin and columbite mine ponds are a defining feature of the Jos Plateau landscape, yet many continue to be used by rural communities for drinking, domestic chores, livestock watering, and crop irrigation long after active mining has ceased. This study assessed the concentrations of twelve potentially harmful elements (PHEs: As, Cu, Pb, Cr, Fe, Zn, Mn, Cd, Ni, Se, Mo and Hg) in water from twenty georeferenced abandoned and active mine ponds in Barkin-Ladi Local Government Area, Plateau State, north-central Nigeria, and evaluated the associated contamination status and human health risk. Samples were analysed by Atomic Absorption Spectrometry and interpreted against WHO drinking-water guidelines using the Contamination Factor (CF) and Pollution Load Index (PLI), together with non-carcinogenic health risk indices (Estimated Daily Intake, Hazard Quotient and Hazard Index) for adult and child receptors. Arsenic and lead exceeded WHO guidelines at fourteen and sixteen of sixteen detection sites respectively (means 7.7 and 7.7 times the guideline value), cadmium exceeded its guideline at thirteen of sixteen sites, and mercury reached contamination factors in the hundreds to low thousands at several locations (peaking at approximately 1,500 at site W13), a signature consistent with historical gold amalgamation practice associated with artisanal small-scale mining rather than tin ore weathering alone. A discrete, spatially isolated chromium detection at site W9 (2.1 times the guideline) pointed to a localised rather than basin-wide source. Every sampled location returned a Pollution Load Index above unity, and the cumulative adult Hazard Index exceeded the safety threshold of 1.0 at all twenty sites (range 1.20 to 18.02), rising to 2.81-42.05 for children, with the most severe contamination concentrated in a spatially coherent upper cluster of ponds (W11-W20) accounting for every value exceeding HI = 10. These findings, benchmarked against comparable studies from Thailand, southwest Nigeria, and northern Nigeria, place this site among the more severely contaminated legacy mining water resources reported in the recent literature, identify mine pond water as the principal, and most urgent, exposure pathway in this legacy mining landscape, and support prioritizing arsenic, lead, cadmium and mercury for regulatory attention and remedial intervention ahead of any further domestic or agricultural use of these waters.

potentially harmful elements; mine pond water; artisanal mining; hazard index; contamination factor; Jos Plateau

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