Assessment of Potentially Toxic Metals in Soil and Sediment of the Keana Brinefield in the Middle Benue Trough, Northcentral Nigeria

Abstract

This research was conducted in the Keana area of the middle Benue trough endowed with abundant mineral deposits (brine/salt, lead-zinc sulfide ores, barite and limestone) and has a long history of mining activity. Small scale mining activity in the area is currently increasing in intensity causing immeasurable damage to the environment and to the surrounding communities. Potentially toxic metal releases and remobilization from the mining sites into the surrounding arable soils and stream sediments poses serious human health risks since the surrounding communities live and grow their food from such environment. This research assesses the accumulation and the extent of contamination of Potentially Toxic Metals (PTM) in the vicinity of the mining environment using standard pollution indices such as geo-accumulation index (Igeo), Enrichment Factor (EF), Contamination Factor (CF) and Pollution Load Index (PLI). A total of 40 samples were analyzed for As, Ba, Co, Cr, Cu, Mo, Ni, Pb, Sc, Sr and Zn, using ICP-OES geochemical technique. Analysis of geochemical data shows that the soil and stream sediments in the area are extremely polluted by Zn, Cr and Ni, having Igeo values of 4.9, 3.8 and 2.9 respectively. Igeo levels of Pb, Cr and Ba indicate moderate to no pollution. Zn and As with EF of 128.60 and 87.66 respectively, are severely enriched in the environment, while Pb, Ni and Cr with EF between 6 and 8, are moderately enriched. The calculated CF and PLI values for Cu, Sr and Sc in the soil and sediments remain very low, indicating these media are not contaminated by these elements. A pollution load index of < 1 as seen in most locations for those elements, indicate no pollution. The continued exposure of the populations living in this area particularly those in the mining locations who depend on the soil (for subsistence farming) and water from ponds, wells and boreholes (for drinking, cooking and other domestic uses), would result in various health risks and concerns, if not checked or abated. Lead, for example is known to be toxic even at very low exposure, with chronic lethal effects. This study recommends an immediate plan for analysis of the quality of drinking water and some staple crops grown in the area to determine the levels of these noxious metals and uptake by plants, to be followed by a comprehensive mitigation or remediation plan.