Evaluation of Lead and Cadmium Contamination in Roadside Soils Along the Ibadan-Lagos Expressway, Oyo State

Vehicular traffic emissions constitute a significant source of heavy metal contamination in roadside environments, with lead and cadmium posing particular toxicological concern owing to their persistence, bioaccumulative nature, and well-documented health effects. This study evaluated lead and cadmium concentrations in roadside soils collected along a 30-kilometre stretch of the Ibadan-Lagos Expressway in Oyo State, South West Nigeria. Samples were collected from four positions relative to the road edge at 0, 2, 5, and 10 metres from the carriageway at ten sampling stations. Digestion was performed using aqua regia, and metal analysis was carried out by atomic absorption spectrophotometry. Geo-accumulation index, contamination factor, and pollution load index were calculated to assess contamination severity. Lead concentrations at 0 m ranged from 64 to 312 mg/kg, substantially exceeding the Dutch intervention value of 85 mg/kg at several stations. Cadmium values ranged from 1.2 to 8.4 mg/kg, with the highest levels recorded near fuel stations and repair workshops. Contamination decreased significantly with distance from the road edge. Geo-accumulation indices indicated moderate to heavy contamination for lead and moderate contamination for cadmium at stations with high traffic density. Pollution load indices greater than unity were recorded at all zero-metre positions. These findings indicate significant ecological and human health risks, particularly for communities and agricultural lands adjacent to this high-traffic corridor, and emphasise the need for continuous environmental monitoring along major Nigerian highways.

Keywords: lead, cadmium, roadside soils, heavy metal contamination, Ibadan-Lagos Expressway