A national-scale assessment of heavy metal contamination in urban road dust across China: a synthesis of data from 82 cities.

Urban road dust acts as a significant sink and secondary source of heavy metal (HM) pollution, with direct implications for environmental quality and public health. This study provided a comprehensive, national-scale assessment of HM contamination in road dust across 82 major Chinese cities. We established an urban-agglomeration analytical framework, integrating a large dataset of 13269 samples from 169 studies to analyze spatial distributions, quantify anthropogenic enrichment via the geo-accumulation index (Igeo), and evaluate ecological risks using the potential ecological risk index (RI). Multivariate statistics were employed to decipher pollution sources and regional signatures. Results demonstrated that Cd and Hg are the priority pollutants of nationwide concern, exhibiting severe anthropogenic enrichment and jointly contributing over 85% to the total ecological risk in all agglomerations, despite their relatively lower concentrations compared to high-load elements like Mn and Zn. Furthermore, this study proposed the Cd/Hg Igeo ratio as a diagnostic fingerprint for source differentiation. Diagnostic Cd/Hg ratios and correlation patterns revealed distinct regional pollution fingerprints, which were mechanistically linked to dominant socio-economic pathways. The findings advocated for a paradigm shift in environmental management from a load-based to a risk-prioritized strategy, emphasizing the necessity of regionally differentiated, source-specific control measures. This work offered a transferable methodology for precise pollution mitigation in rapidly urbanizing regions globally.