Assessment of Heavy Metal Concentrations and Geochemical Speciation in Dumpsite Soils Derived from Coastal Plain Sands in Akwa Ibom State, Nigeria

Abstract

This study assessed the concentrations and geochemical speciation of Pb, Cd, Cr, Ni, and V in dumpsite soils derived from coastal plain sands in Akwa Ibom State, Nigeria. Automechanic, paint-processing, and abattoir dumpsites were investigated in Etinan, Uyo, and Ikot Ekpene, with uncontaminated soils serving as controls. Soil samples were collected from 0–20, 20–40, and 40–60 cm depths and analysed for physicochemical properties, total metal concentrations, and six operationally defined geochemical fractions using sequential extraction and atomic absorption spectrophotometry. Metal mobility and contamination indices were also evaluated. Waste deposition altered soil properties, with dumpsite soils generally showing higher pH, organic matter, exchangeable bases, and base saturation than control soils. Heavy metal concentrations were markedly elevated at all affected sites, particularly in automechanic and paint-processing soils. Lead and cadmium occurred in appreciable proportions in water-soluble, exchangeable, and carbonate-bound fractions, indicating comparatively greater potential mobility and bioavailability. Chromium, nickel, and vanadium were more strongly associated with reducible and residual fractions, although measurable proportions occurred in non-residual forms. The results demonstrate that waste type influenced both metal accumulation and geochemical partitioning. While stable fractions accounted for part of the metal burden, the occurrence of metals in labile fractions indicates potential for leaching, plant uptake, and broader environmental exposure. Improved waste segregation, controlled disposal, and periodic soil monitoring are therefore required in the study area.