Geo-environmental Hazards Associated with Lead-Zinc Mining in Ishiagu Ebonyi State Nigeria

Abstract

Discharge of mine waste to farm lands and consequent drainage to nearby stream cause geo-environmental hazards (Geo-hazards). In this study, geo-hazards due to lead-zinc mining in Ishiagu (Lower Benue Trough Nigeria), were assessed using direct field and laboratory techniques. Field techniques comprised interaction with local farmers, mapping using vertical electric sounding (VES), GPS and photographic tools. Laboratory techniques involved analysis of soil, water and cassava (Manihot esculenta) samples obtained from the mine sites and from the local background (control). Atomic Absorption Spectrophotometer (AAS) was used to measure concentration of heavy metals, while physicochemical parameters were tested using standard procedure. Results show anomalous concentration of Pb, Cd, Mn, Zn, Ca, K, Na, Mg, and pH in the mine site samples against the background. Soil within the mine site have lead pollution index (Pi) of 2.5, downstream Ivo River with lead Pi of 4.0, while cassava had lead Pi of 0.08 indicating toxicity. Downstream Ivo River had pH enrichment factor of 1.25 indicating high level of acidity. Mine pit depth of 5 m was estimated against water table depth of 6 m, indicating groundwater vulnerability.  Drainage analysis showed about 74 acres of arable land with contaminated topsoil. This land area should be declared brown field, "No Farm Area” for 2-3 years of phytoremediation using local plants.