Impacts of dumpsites on heavy metal concentration in soil and vegetation in four dumpsites in Akure North, Ondo State

Abstract

This research studied the physicochemical composition and concentration of heavy metals in both soil and vegetations in four different dumpsite locations in Akure North Local Government and compared the concentrations to those of the WHO and the National Environmental Standard and Regulation Enforcement Agency (NESREA). Four models were used to examine soil pollution levels and transfer coefficient was used to assess the heavy metal bioaccumulation in plant. Two soil samples (0-15cm and 15-30cm) and two plant samples were collected from each dumpsite. Control samples were taken 1km away. Metals (Zn, Fe, Cu, Cd, Pb) were analyzed using Atomic Absorption Spectrophotometer (AAS) with Aqua regia digestion.The physicochemical properties of the four dumpsite locations, such as electrical conductivity and organic matter, were higher than the control, reflected in the acidic pH (5.50-6.47) of the dumpsites compared to the control (6.37-8.17). This contributes significantly to heavy metal pollution. Soil samples from all locations showed a sandy-silt- clay composition, leading to heavy metal leaching. Heavy metal concentrations in soil and plant samples from dumpsites exceeded those in control sites. The geoaccumulation index ranged from -0.05 to 10.55, indicating contamination levels from uncontaminated to extremely contaminated. The enrichment factor, from 0.21 to 4914.44, and the contamination factor, from 86.83 to 21718251.81, and the pollution index ranges from 2.44 to 29.33. This further confirms that heavy metal pollution is present in all the dumpsites. Iron had the highest concentration in soil and plants, likely due to erosion, but its transfer coefficient was the lowest, indicating limited plant absorption. Cadmium had the highest transfer coefficient, binding with carbonates and transporters in the soil, facilitating plant uptake. This suggests that the dumping of wastes and metals are progressively impacting soil and plant quality through heavy metal leaching.