Geochemical Enrichment and Surface Contamination of Heavy Metals in Soils from the Ikole–Itapaji Area, Southwestern Nigeria

Heavy metal contamination in soils poses significant environmental concerns due to its persistence and potential ecological impacts. This study assessed the distribution, mobility, enrichment, and sources of selected heavy metals (Fe, Mn, Pb, Cu, Zn, Ni, Co, Cr, and Cd) in soils from the Ikole–Itapaji area, Southwestern Nigeria. Seventeen soil samples were collected and analyzed using a modified seven-step Tessier sequential extraction procedure, Atomic Absorption Spectrophotometry (AAS), Geo-accumulation Index (Igeo), and Enrichment Factor (EF). The results show that Fe and Mn dominate all geochemical fractions, with the highest concentrations occurring in the residual phase, indicating strong lithogenic control. Most metals were concentrated in the residual, Fe–Mn oxide, and organic matter-bound fractions, while the water-soluble and exchangeable fractions contained only minor amounts, reflecting low mobility and bioavailability. Igeo and EF results indicate that Mn, Cu, Zn, Ni, Co, and Cr are mainly derived from natural weathering of the basement rocks. In contrast, Cd and Pb exhibit moderate to strong enrichment at some locations, particularly SQ3, SQ4, SQ8, and SQ15, suggesting localized anthropogenic influence. Hheavy metal distribution in the Ikole–Itapaji area is controlled predominantly by geological factors, with limited anthropogenic contributions affecting Cd and Pb. The predominance of metals in stable geochemical fractions indicates generally low environmental risk, although continued monitoring of Cd- and Pb-enriched zones is recommended.