Contamination levels, health risks and source apportionment of potentially toxic elements in road dusts of a densely populated African City

Potentially toxic elements (PTEs) are increasingly becoming a health and ecological concern, especially in cities with heavy traffic from rapid urbanization and industrialization. Contamination levels, sources and health risks of ten PTEs (Fe, Pb, Zn, As, Co, Cr, Cu, Cd, Mn and Ni) in twenty-five traffic hotspots (sites) of Ibadan -a densely populated African city were investigated during the rainy and dry seasons. The possible sources of PTEs were identified and quantified by combining positive matrix factorization (PMF) with existing and new contamination indices. PMF results identified six main sources (factors) each contributing to PTEs pollution during the rainy and dry seasons. The rainy season factors which include combustion of leaded gasoline, roadside smoke, mechanical abrasion in vehicles, lubrication oil leakages and tyre wears, vehicular body wears, as well as Brake and engine wears had percentage source contributions of 35.89%, 0.03%, 12.91%, 1.71%, 8.74% and 40.73%, respectively. The dry season factors were: Mechanical Abrasion in vehicles, vehicular exhausts, roadside smoke, roadside coal combustion, lubricating oil leakage and tyre wears as well as brake and engine wears in vehicles with percentage source contributions of 27.56%, 34.23%, 0.02%, 1.30%, 0.46% and 36.43%, respectively. A significant amount of PTEs in Ibadan road dust were contributed by traffic-related sources. The estimates of new contamination indices -Nemerov Integrated Risk Index (NIRI) were generally consistent with results of existing indices: Enrichment Factor (EF), Geo-accumulation (Igeo), Contamination factor (Cf) and ecological risk factor (E_rⁱ) during the two seasons. The contamination levels of Cd and Pb were more serious than that of other PTEs during the two seasons studied. Non-carcinogenic risks posed by PTEs during the two seasons were insignificant except Pb and Cd with significant risks in Children and Adults at few sampling sites (TIs). Carcinogenic risks of Cd were unacceptable at some sites during both seasons. Children were more prone to both non-carcinogenic and carcinogenic hazards. This study provides information to prevent and control sources and exposure to road dust PTE pollution.