Purpose

Intensive urbanization decreases the self-regulation of urban ecosystems, leading to accumulation of persistent pollutants such as trace metals and metalloids in urban environments. Road-deposited sediments (RDS) are important carriers of trace metals and metalloid contaminants that could contribute to urban runoff pollution. This study aims to investigate the concentration and speciation systemically and assess the risks of trace metals and metalloids from RDS comprehensively.

Materials and methods

Road-deposited sediments (RDS) were analyzed for As, Cd, Cr, Cu, Mn, Pb, and Zn, in terms of total concentrations, speciation, release, and risks at 23 sites across six land types (the rural-urban fringe, commercial, residential, industrial, traffic, and the natural areas) in Daxing District of Beijing, China, in April 2018. Risk factors evaluating different aspects included contamination levels and ecological risk, I_geo, and RI; source of metal (natural or anthropogenic), EF; bioavailability, RAC. Six particle sizes vs. metal concentrations were also analyzed for trace metals and metalloids from rural-urban fringe samples.

Results and discussion

Obvious variations were found for the concentrations of Cr, As, and Cd in rural-urban area, especially for Cr. Industrial sites exhibited highest average values for all trace metals and metalloids except for As and Cu. Cr, Cd, and Pb in particular posed more risk. Traffic area showed signs of contamination for Cu, Pb, and Zn. Commercial and residential areas presented low ecological risk. However, there were signs of As and Cu contaminations in both areas, and of Pb in the residential area as well. No research sites were contaminated by Mn, despite the high concentration values. Although high contamination levels of Cr were found in many sites, the risk level of Cr was low. Generally, RDS with smaller particle size (< 80, 80–150, and 150–300 μm) possessed higher concentrations of trace metals and metalloids compared to larger size (300–500 and 500–1000 μm).

Conclusion

The study showed that metals of high concentration do not always pose high risk. More attention should be paid to the systematical risk assessment of trace metals and metalloids than the concentration.

Graphical abstract