Interplay of chemical toxicants and urban microenvironments in the oxidative potential and comprehensive risk of road dust

The oxidative potential (OP) of urban road dust PM_2.5 poses major health implications, primarily driven by key toxicants including heavy metals and polycyclic aromatic compounds (PACs). This study systematically measured toxics components in road dust across commercial, traffic, and residential urban functional areas in the Guanzhong Plain. Interpretable machine learning (XGBoost-SHAP), land-use regression (LUR), and a sources-pathways-receptors (S-P-R) framework were applied together to quantify drivers of OP, linking contaminant patterns to urban functional area. All areas exhibited high ecological risks from PACs and metals. Spatially, heavy metal was universally driven by non-exhaust traffic emissions, while dense e-waste and electronic repair activities created extreme Co and Ni hotspots in commercial areas. For PACs, primary tailpipe exhaust dominated traffic areas, whereas commercial areas were more influenced by congested idling traffic and high-temperature catering. Machine learning revealed that specific PACs strongly drive OP, which synergistically coupled with co-occurring transition metals to amplify oxidative toxicity. LUR models further identified that high OP in traffic areas was primarily driven by estimated vehicle number and transportation facilities, and elevated OP in residential areas were closely associated with catering and residential activities. Using the S–P–R framework, this study found that sources (47.1%), pathways (21.2%) and receptors (31.8%) jointly determined road dust health risk. Commercial areas showed the highest mean comprehensive risk (CR = 0.257), but traffic areas exhibited more widespread high risk hotspots driven chiefly by OP and traffic-related exposure pathways, while residential areas were distinguished by concentrated sensitive receptors, e.g., kindergartens, schools, green spaces. This study provides a novel assessment system and highlights the interactions between urban functional areas and road dust toxicity, underscoring the need for targeted strategies to mitigate urban dust pollution.