In the Abakaliki area of Southern Benue Trough which is mineralized with Pb–Zn deposits, artisanal mining activities persist despite the decommissioning of major mines. Water flowing from the active or abandoned mining pits interacts with nearby water in streams and boreholes with negative impacts. In this study, twenty water samples from mine ponds, streams, and boreholes, in five locations were used to determine the physical, chemical, and heavy metal concentrations by on-site field measurements and spectrophotometry. The objective was to assess the magnitude and spatial distribution of pollution using the contamination factor (CF), the degree of contamination (Cd), the pollution load index (PLI), the enrichment factor (EF), and the index of geo-accumulation (Igeo). The suitability of the water for irrigation was assessed using sodium absorption ratio, Kelly’s index, and magnesium absorption ratio. The statistical analysis of the data included use of Spearman’s rank correlation coefficient, clustering analysis, and principal component analysis. The current result showed that pH values ranged between 4.32 and 8.5 with an average of 6.28 which was classified as weakly acidic to alkaline. Physicochemical parameters followed the trend of EC > TDS > Salinity, while major ionic abundance was dominated by Ca2+ and SO42−. The CCME WQI of 56 in ponds indicated that the water quality was threatened or impaired, while values of 88 in streams, and 82 in boreholes indicated good water quality with only a slight degree of threat or impairment. Moderate to very high contamination were identified with potentially harmful elements in the order Cd > Pb > As, but it decreased away from the ponds. Spearman’s rank correlation matrices revealed that Ca, Mg, Na, K, Cl, SO4, and NO3 exhibited very strong positive correlations with each other, with values ranging between 0.70 and 0.98. The heavy metals showed moderate to strong positive correlations with major ions which could suggest common mobilization pathways. Three distinct clusters were identified, reflecting variations in underlying geochemical conditions, ionic strength, and overall water quality influenced by metal enrichment. Aside from the potential salinity, water quality supports the suitability of the water for safe irrigation. The combined use of different approaches for assessing potential pollution has facilitated a comprehensive interpretation of water characteristics to help policy makers and farmers to make informed decisions and devise strategies in sustainable managing of mining sites and allocation of water resources.

Lead–zinc artisanal mining pollution footprints on surface and groundwater of an area in southeastern Nigeria

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2026年5月25日

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Akaha Tse,
Austine Uchenna Alo,
Taiwo Bolaji

摘要

In the Abakaliki area of Southern Benue Trough which is mineralized with Pb–Zn deposits, artisanal mining activities persist despite the decommissioning of major mines. Water flowing from the active or abandoned mining pits interacts with nearby water in streams and boreholes with negative impacts. In this study, twenty water samples from mine ponds, streams, and boreholes, in five locations were used to determine the physical, chemical, and heavy metal concentrations by on-site field measurements and spectrophotometry. The objective was to assess the magnitude and spatial distribution of pollution using the contamination factor (CF), the degree of contamination (C_d), the pollution load index (PLI), the enrichment factor (EF), and the index of geo-accumulation (I_geo). The suitability of the water for irrigation was assessed using sodium absorption ratio, Kelly’s index, and magnesium absorption ratio. The statistical analysis of the data included use of Spearman’s rank correlation coefficient, clustering analysis, and principal component analysis. The current result showed that pH values ranged between 4.32 and 8.5 with an average of 6.28 which was classified as weakly acidic to alkaline. Physicochemical parameters followed the trend of EC > TDS > Salinity, while major ionic abundance was dominated by Ca²⁺ and SO₄²⁻. The CCME WQI of 56 in ponds indicated that the water quality was threatened or impaired, while values of 88 in streams, and 82 in boreholes indicated good water quality with only a slight degree of threat or impairment. Moderate to very high contamination were identified with potentially harmful elements in the order Cd > Pb > As, but it decreased away from the ponds. Spearman’s rank correlation matrices revealed that Ca, Mg, Na, K, Cl, SO₄, and NO₃ exhibited very strong positive correlations with each other, with values ranging between 0.70 and 0.98. The heavy metals showed moderate to strong positive correlations with major ions which could suggest common mobilization pathways. Three distinct clusters were identified, reflecting variations in underlying geochemical conditions, ionic strength, and overall water quality influenced by metal enrichment. Aside from the potential salinity, water quality supports the suitability of the water for safe irrigation. The combined use of different approaches for assessing potential pollution has facilitated a comprehensive interpretation of water characteristics to help policy makers and farmers to make informed decisions and devise strategies in sustainable managing of mining sites and allocation of water resources.