Comprehensive assessment of remarkable heavy metals contamination in road dust in Greater Cairo: Priority control factors based on source apportionment and risk assessment

Heavy metals (HMs) accumulation in road dust (RD) is a critical consequence of uncontrolled anthropogenic activities, posing a major challenge to the environment and human health. Greater Cairo, one of the world's most densely populated megacities, embodies this dilemma, driven by rapid urbanization, unchecked industrial expansion, traffic congestion, and weak environmental management. For managing HMs in the RD of Greater Cairo, this investigation assessed the pollution levels, sources, and related eco-health risks of 10 HMs (Cr, Mn, Ni, Fe, Cu, Zn, Cd, Pb, Hg, As). The result revealed that the mean concentrations (mg/kg) of Cd (0.43), Zn (184.2), Cu (69.5), and Pb (54.2) were three times higher than the Upper Continental Crust (UCC) background. The most serious contamination levels were those of Cd, Zn, Cu, and Pb, with more than 80 % of sites showing significant and very high enrichment of these metals. The integrated ecological risk for total HMs in 91.8 % of sites ranged between moderate and considerable risk. Absolute principal component analysis and multiple linear regression receptor model (APCS/MLR) identified three sources of contamination: mixed natural/traffic sources (70.7 %), industrial/construction sources (15.9 %), and traffic sources (13.4 %). The probabilistic health risk based on Monte Carlo simulation revealed acceptable non-carcinogenic risks for adult and children, while the probability of cancer risk for children was substantially higher in children (99.6 %) than in adults (71.4 %). Environmental and health risk control strategies prioritize natural and traffic sources, with an emphasis on Cd, Zn, Cu, and Pb in RD. This study provides a framework for governing HMs pollution in the RD of Greater Cairo.