Heavy Metals Enrichment in Surface Soil from Abandoned Waste Disposal Sites in a Hot and Wet Tropical Area

Abstract

High levels of heavy metals in the environment pose threat to the ecosystem, due to their deleterious effects on humans, animals and plants. The present study aims at determining the extent of pollution of heavy metals such as Fe, Pb, Cr, Zn, Co, Cu and Al in surface soil from Aboabo and Santasi abandoned landfill sites and examining the quality of the soil using pollution indices. In all, 30 soil samples were collected from two study sites and a control sample was also taken from KNUST Botanic Gardens. Concentration of heavy metals were determined using Atomic Absorption Spectroscopy (AAS) after acid digestion. Analyses of the physicochemical parameters revealed that pH of soils from both study sites were slightly alkaline and the soils have a sandy loam texture. At such pH, precipitation of hydroxides and carbonate is induced, leading to limitation in metal mobility. Mean organic matter contents of soil samples were 8.67 ± 7.19 % at Aboabo site and 19.23 ± 4.80 % at Santasi site. High organic content can lead to cation adsorption and reduced metal bioavailability. The study further revealed that mean concentrations of all the heavy metals exceeded their respective levels in the control samples. Correlation analysis of metal concentrations indicated that Pb/Cu correlated at the Aboabo, whereas Cu/Zn, Fe/Pb and Cr/Co showed strong correlation in Santasi site. Heavy metals pollution was assessed using Igeo, contamination factor and PLI, and the results indicated elevated levels of all the metals in soil samples from both areas. Finally, the results indicate that pH and organic content are important barriers to metal distribution in the environment.