Assessment of Heavy Metal Concentration and Fractionation in Selected Dumpsite Soils within Ibadan Metropolis, Nigeria

Abstract

Dumpsites are gradually turning into farm land with the belief that they must have accumulated necessary nutrient element required for plant growth and thus making some farmers to use refuse dumpsite material for composting not minding the type of waste that are involved and what they are actually made up off. This study therefore investigated the concentrations of heavy metals in selected dumpsite soils and various forms to determine their mobility with the view to crystallize their extent of contamination to the soil when used for farming activities. Two dumpsites (Bodija dumpsite (BD) and  Olukunle dumpsite (OD) were purposively selected from Ibadan South Western Nigeria based or different waste distributions at the depth of 0-20 cm. The metals investigated include: Cd, Pb, Cu, Zn, As, Cr and Ni. Sequential extraction method was used to assess the redistribution of heavy metals from which total heavy metals were earlier determined by acid digestion with aqua regia solution. Treatments were laid out in a completely randomized design with four replicates. Data collected were analyzed using descriptive statistics and T-test. The mean concentrations (mg/kg) of total HM were 100.9, 48.9, 57.8, 16.6, 49,022.0 and 3,627.3 for As, Cr, Cu, Ni, Pb and Zn respectively with coefficient of variance ranging from 1.31% for Ni to 141.2% for Pb. There was no significant difference (t=1.70; p>0.05) in metal concentration in both BD and OLD soil. The residual fraction was the most predominant in the soils with the exception of Pb and Zn.  The average metal concentration over soil samples were 307.6, 2,390.8, 1,666.8 and 4,448.8 for the exchangeable, reducible, oxidizable and residual fractions respectively. Only Zn had an appreciable amount (54.3%) associated with the exchangeable fractions while the oxidizable fraction was highest for Pb (79.1%) in soil BD and Zn (78.4%) in soil OD. It is therefore paramount to create awareness on the health hazard inherent in planting on refuse dumpsite soil without ascertaining its heavy metal status because of the possibility of metal uptake in the edible parts of crops. This could be detrimental to human health and the ecosystem at large.