Pb-Zn artisanal mining pollution footprints on surface and groundwater of an area in southeastern Nigeria

Abstract

<title>Abstract</title> 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 from the active or abandoned mining pits interact 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 concentration by in-situ field measurements and spectrophotometry. The aim was to evaluate the magnitude and spatial distribution of pollution using contamination factor (Cf), degree of contamination (C _d ), pollution load index (PLI), enrichment factor (EF), index of geo-accumulation (Igeo). Water suitability for irrigation was evaluated using Sodium Absorption Ratio, Kelly’s Index and Magnesium Absorption Ratio. Statistical analysis of the data included use of Spearman’s Rank correlation, cluster analysis and Principal Component Analysis. The pH of 4.32 to 8.5 with a mean of 6.28 classified the water as weakly acidic to alkaline. The general trend of physiochemical parameters was EC &gt; TDS &gt; Temperature &gt; DO &gt; Salinity, while cations and anions were Ca ²⁺ &gt; K ⁺ &gt; Mg ²⁺ &gt; Na ⁺ and SO ₄ ²⁻ &gt; NO ₃ ⁻ _&gt; Cl ⁻ respectively. CCME WQI of 56 in ponds rate the water quality as threatened or impaired, and values of 88 in streams, and 82 in boreholes, indicate good water quality with only a minor degree of threat or impairment. Moderate to very high contamination with potential harmful elements in the order Cd &gt; Pb &gt; As was established, but it decreased away from the ponds. Spearman’s rank correlation matrices revealed that Ca, Mg, Na, K, Cl, SO ₄ , and NO ₃ show very strong positive correlations with each other, with values ranging between 0.7 to 0.98. The heavy metals show moderate to strong positive correlations with major ions which could suggest common mobilization pathways. Three distinct clusters were identified, reflecting variations in background geochemical conditions, ionic strength, and overall water quality influenced by metal enrichment. Apart from the potential salinity, water quality supports the suitability of the water for safe irrigation. The combined use of different approaches for evaluating pollution potential facilitated a comprehensive interpretation of the water characteristics to aid policy makers and farmers to make informed decisions and strategies in the management of mining sites, and allocation of water resources.