Pollution levels, distribution characteristics and risk assessment of heavy metals (HMs) in road dust in major cities of China

Trace metals in road dust are crucial risk factors for human health. However, comprehensive study on a large spatial scale is scarce, resulting in risk assessments that lack representativeness. This study conducts a comprehensive investigation on the pollution characteristics of 18 heavy metals (HMs) in road dust collected from 47 megacities in China. The average concentration of HMs in capital cities is higher than that in non-capital cities. Fe and Al are the dominant elements in road dust, and nine HMs exceeded the background values of Chinese soil, implying the impact of human activities. Enrichment factor, pollution index, and geo-accumulation Index revealed high pollution levels of Cd, Cu, Zn, and Pb. Severe pollution of HMs was observed in the eastern coastal and southwestern regions. The contribution rates of natural sources, industrial sources, and traffic sources to the accumulation of heavy metals in dust for capital cities and non-capital cities are 50%, 33%, and 17%, and 58%, 27%, and 15%, respectively. The ecological risk assessment underscored Cd as a metal of significant concern due to its toxicity and persistence. This study represents the first nationwide investigation on metals in road dust across China. The results of their levels, geographical distribution, and associated health risks provide a scientific basis for the formulation of relevant environmental policies.