Distribution and potential source evaluation of heavy metals in prominent soils of Accra Plains, Ghana

Abstract

Environmental contamination by heavy metals remains a major threat to health and agricultural productivity, particularly in developing countries. This study evaluated the distribution, controlling variables, and potential sources of heavy metals in the soils of the Legon hill catena, prominent soils of Accra Plains, Ghana, West Africa. Soil samples were collected from the profiles of five dominant soil series, comprising four Alfisols and one Vertisol, developed on different physiographic positions. Samples were characterized for various soil properties including total elemental analysis. Variations in major physical and chemical characteristics among the soils were chiefly attributed to physiographic position and parent materials. Dominant heavy metals and concentration ranges observed were Co (22.0-260 mg kg- 1), Cu (9.80-72.9 mg kg- 1), Ni (22.8-201 mg kg-1), Pb (9.30-45.0 mg kg- 1), and Zn (5.80-69.8 mg kg- 1), with averages of 76.8, 35.5, 66.3, 26.0, and 44.0 mg kg- 1, respectively. Except in a few occasions, the concentrations of these metals generally increased with depth. All the soils were dominated by SiO2, Al2O3, and Fe2O3. Copper and Zn were positively correlated with Fe2O3 (R2 ≥ 0.67, P < 0.001), but negatively correlated with SiO2 (R2 ≥ 0.71, P < 0.001). Principal component and correlation analyses suggested that Cu, Pb, and Zn contents of this region could be of similar lithogenic origin, while Co and Ni were attributed to a different geogenic source. Evidence gathered from this study further suggested that the metal contents of these soils were generally below the maximum allowable limits set by most countries.