Ecological risk assessment and spatial distribution of heavy metals in soils surrounding urban abattoir waste systems in southwestern Nigeria

Abstract

This study investigated the accumulation and ecological risk of heavy metals in soils surrounding a major open dumpsite adjacent to the New Abattoir in Akerebiata Harmony Estate, Ilorin, Southwestern Nigeria. Ten representative soil samples were collected at 9 m by 45 m intervals and analyzed using Atomic Absorption Spectroscopy (AAS) to determine concentrations of Copper (Cu), Zinc (Zn), Chromium (Cr), Iron (Fe), Cadmium (Cd), Cobalt (Co), Arsenic (As), Lead (Pb), Silver (Ag), and Mercury (Hg). Environmental impact was evaluated through the calculation of the Geo-accumulation Index (Igeo), Contamination Factor (CF), Pollution Index (PI), Enrichment Factor (EF), Hazard Quotient (HQ), Hazard Index (HI), and Cancer Risk (CR). Results indicated that while absolute concentrations remained below current regulatory limits, the site is moderately to strongly polluted (PI = 3.37) due to significant anthropogenic inputs. Igeo values showed that the area is uncontaminated regarding Cr, Hg, and Cd, but moderately contaminated with Co and As. The HQ and HI values for all metals were below 1.0 for both children (HI = 0.0016) and adults (HI = 0.0002), indicating no immediate non-carcinogenic risk via soil ingestion. Total cancer risk (CR = 2.08 × 10⁻ 8 for children) fell within the acceptable range (< 10⁻⁶). However, trends in As, Co, and Hg contamination factors warrant precautionary monitoring. Principal Component Analysis (PCA) attributed PC1 (34.73% variance) primarily to geogenic Fe–Cr inputs and PC2 (24.52%) to anthropogenic Cu-As loading. These findings suggest that the current open dumping system poses a growing risk to the local ecosystem and public health. The study recommends the implementation of engineered sanitary landfills, regular environmental monitoring, and remediation strategies to mitigate future heavy metal accumulation.