Determination of Heavy Metal Concentrations in Roadside Soils Along the Lagos-Ibadan Expressway, South West Nigeria

Vehicular emissions and tyre wear along high-traffic corridors are recognised sources of heavy metal pollution in roadside soils, posing ecological and human health risks in densely populated urban regions. This study determines the concentration of selected heavy metals, specifically lead, cadmium, zinc, copper, and nickel, in roadside soil samples collected at designated intervals along the Lagos-Ibadan Expressway in South West Nigeria. Soil samples are obtained at distances of 5, 10, and 25 metres from the road edge at five sampling stations using stainless steel corers and analysed by atomic absorption spectrophotometry following standard acid digestion procedures. The study assesses how distance from the road and traffic density influence metal accumulation patterns. A control site located 500 metres from active traffic corridors is included for baseline comparison. Statistical analysis employs one-way analysis of variance and Pearson correlation to examine relationships between metal concentrations and physicochemical soil parameters including pH, organic matter content, and particle size distribution. Preliminary literature suggests lead and cadmium are the most consistently elevated metals in Nigerian highway soils due to leaded fuel residues and brake lining wear. The findings are expected to inform urban land use planning, contribute to environmental impact assessment frameworks, and support national soil quality monitoring efforts. Results are mapped spatially to visualise contamination gradients across the expressway corridor. Keywords: heavy metals, roadside soils, Lagos-Ibadan Expressway, atomic absorption spectrophotometry, vehicular pollution