Assessment of Heavy Metal Concentration from a Lead-Zinc Mined Pit at Ebonyi State, Nigeria

Abstract

This study assessed the concentrations of heavy metals in soil and surface water from a Lead-Zinc mined pit at Enyigba, Ikwo Local Government Area in Ebonyi State, Nigeria. Soil samples were collected and analysed from different soil depths (0 – 15 cm) and (15 – 30 cm) at a tailing down (marked as TD) and refuse dumpsite (marked as RD) and a vegetation site 50 km away which was used as the control site. Surface water samples were collected from the Enyigba River from three (3) points (marked as point A, B, and C) and were analysed using routine laboratory procedures. The following parameters were analysed for soil: particle size distribution, pH, available phosphorus, total nitrogen, organic carbon, organic matter content, calcium, magnesium, potassium, sodium, exchangeable acidity, and effective cation exchange capacity. The results for mean values of soil samples obtained at both depths were 58.86% (sand), 11.73% (silt) and 34.04% (clay). Mean values obtained for heavy metals from the soil for Iron (Fe) ranged from 3.31 to 2.24 mg/kg: Zinc (Zn) 0.70 to 0.62 mg/kg and Lead (Pb) 0.01 to 0.01 mg/kg). Results obtained for surface water around the mined pit showed mean values for Iron (Fe) 0.57 mg/L, Magnesium (Mg) 151.6 mg/L, Calcium (Ca) 76.62 mg/L, Chlorine (Cl2) 416.6 mg/L and Lead (Pb) 0.01 mg/L. The high concentrations of chlorine make the water unsuitable to be discharged on any agricultural land as plants could accumulate these metals and when consumed could pose serious threat to humans. The discharge from the mining site increased the already slightly high turbidity of the water to a much higher and undesirable level. The mining activity at Enyigba Ikwo LGA, Ebonyi State has negatively impacted the environment through the introduction of heavy metals in soil and surface water, thereby causing an increase in the pollution of the environment. It is recommended that further studies and monitoring should be carried out in the study location for possible remediation.