Ecological Risk Assessment of Potentially Toxic Metals in Arable Soils around Adudu Lead – Zinc Mine, North-Central Nigeria

Mining is a major source of toxic heavy metals into the soil when mine wastes are discharged into the nearby farmlands used for the cultivation of food crops. This study investigated the influence of Pb–Zn mining on the quality and ecological risk of arable soils around active mining sites in Adudu, Nasarawa State, Nigeria. Composite soil samples were collected at 0–20 cm depth, pulverized, and analyzed for heavy metal (Al, As, Cr, Cu, Fe, Mn, Pb, and Zn) concentration using X–ray fluorescence technique. Enrichment factor, geo–accumulation index, improved Nemerow index (IIN), contamination factor (CF), degree of contamination (Cd), pollution load index (PLI), and ecological risk assessment (ERA) were used to evaluate the effect of the mining activities on the environment. Results showed elevated levels of Pb, Zn, Cu, Fe, Mn, and Cr in arable soils around the mine and lower levels of these metals in the control soil. IIN, Cd, and PLI showed that the mine and the nearby arable soils were the most deteriorated, and soil quality improved away from the mining vicinity. ERA revealed that the mine and the closest arable soils (sites F1 and F4) have significant to high ecological risk index as a result of the dominant presence of Pb, Zn, and Cu at the sites. Thus, arable soils which are disposal channels for mine wastes are not good for growing food crops. This study clearly shows that Pb–Zn mining activities introduced heavy metals into the arable soils surrounding the mine.