Heavy metals concentration and distribution in soils around Oshiri and Ishiagu lead – zinc mining areas, southeastern Nigeria

The study area is characterized by ubiquitous ore deposits within the underlying Asu River Group of the southern Benue Trough of Nigeria. The extensive mineralization resulted in widespread artisan and unlawful mining activities, necessitating the need for the assessment of the effects on soils in the area. Careful evaluation of the soils was undertaken to give account of heavy metals concentrations and distribution, and pollution level in soils across the lead – zinc mines. The soil samples were digested and chemically analysed using Atomic Absorption Spectrophotometer (AAS). Results showed concentrations of heavy metals of the soil samples in the order trend Zn>Pb>Mn>Cd>Cu>Fe> Ni>Co>Cr and Pb>Zn>Mn>Fe>Cu>Cd>Ni>Cr>Co in both Oshiri and Ishiagu areas. Cd showed high contamination in the soils with higher amount of contamination occurring in Oshiri. Findings also revealed Co, Fe Cu, Mn, Zn, Pb and Ni whose Igeo’s values indicated uncontaminated to moderate contamination have an insignificant contribution to the pollution in the study area while Cd showed highest Igeo with moderate contamination. Co, Cr, Ni, Pb and Zn show deficiency to minimal enrichment while Cd recorded very high enrichment 23.95 – 37.48 and 25.66 – 34.21 mk/kg in the Oshiri and Ishiagu areas respectively. Cd showed high index of contamination ranging from 7.21 – 13.89, while other metals showed no index of contamination in the area. Pollution load index indicates that only few sites in Oshiri area require urgent rectification measures. The food chain in the area is not safe due to possible biomagnifications; hence arable soil around the mines is not suitable for production of food crops