Priority Polycyclic Aromatic Hydrocarbons and Heavy Metals in Urban Roadside Soils of Heavy-Traffic Density Areas in Ibadan, Nigeria: Levels, Sources and Health Risk Assessment

Abstract

Priority polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) were investigated in heavy-traffic roadside soils in Ibadan, Nigeria to assess the level of contamination and human health risk. PAHs and HMs were analyzed using gas chromatography-mass spectrometry (GC-MS) and atomic absorption spectroscopy. The concentrations of ∑11PAHs were 263.2 ± 20.9 to 380.0 ± 23.8 µg kg–1, with a dominance of the higher molecular PAHs, and the soils can be classified as weakly contaminated. The most abundant PAH was fluoranthene. Also, five carcinogenic PAH were identified in the study. PAH diagnostic ratios suggested mixed pyrogenic and petrogenic sources. Roadside soil concentrations (mg kg−1) of Cd, Ni and Pb were 1.3 ± 1.2–5.3 ± 7.4, 15.0 ± 7.3–24.5 ± 4.8 and 41.6 ± 13.7–56.8 ± 8.3, respectively. Pollution indices revealed roadside soils were highly contaminated with Cd and Pb according to contamination factor and geoaccumulation index. Cd presented a considerable to high ecological risk. Health risk assessment for children and adults revealed soil ingestion was the main exposure pathway to metals. The hazard quotient (HQ) and health index (HI) were within the safe level (<1.0), although, HI values were higher for children. The cancer risk of exposure to Pb in roadside soils (1.18 E–06 to 1.61 E–06) was within safe limit (1.0 E–04 to 1.0 E–06). This study provides the basis for the reduction of anthropogenic emissions of PAHs and HMs.