Determination of Toxic Heavy Metals of a Selected Dumpsite (Asunle Dumpsite), Ibadan, Oyo State, Nigeria

Abstract

Levels of toxic heavy metals (Pb, As, Cd, Ni, Cr, and Hg) were determined in surface soils
from the Asunle dumpsite (Ibadan, Nigeria), adjacent receptor areas, and a background control
site using Inductively Coupled Plasma – Optical Emission Spectrometry (ICP-OES).
Concentrations for all metals were in the ppb (μg/kg) range and below established residential
soil limits. However, a consistent gradient was observed: receptor samples concentrations
greater than dumpsite sample concentrations greater than control sample concentrations,
indicating outward migration of contaminants from the waste body. Indices of contamination
(e.g., contamination factor, ecological risk factor, and geo-accumulation index) corroborated
anthropogenic enrichment, with receptor soils showing the strongest signals—particularly for
Pb, Cd, and Cr—despite absolute concentrations remaining low. Site activities such as informal
scavenging and dismantling of materials likely contribute to localized hotspots and
redistribution. Although current levels do not exceed guideline thresholds, the pattern of
enrichment at receptors highlights the potential for progressive accumulation and associated
ecological and health risks. Routine monitoring, improved leachate control, and targeted
remediation of receptor soils are recommended to prevent long-term deterioration of soil
quality and to protect nearby communities and ecosystems.