Tracing source and distribution of heavy metals in road dust, soil and soakaway sediment through speciation and isotopic fingerprinting

• Soakaway sediment and residential road dust exhibit high metal content and mobility.
• Exchangeable fraction showed the least 206Pb/207Pb and 208Pb/207Pb ratios.
• Heterogeneity of isotopic signature has originated from mixing of multiple sources.
• Speciation and isotopic signatures showed close resemblance for road dust samples.

Soakaway sediment trapped in urban infiltration facilities exhibits high heavy metal content that makes it an important diffuse pollution source of groundwater contamination. In this study, heavy metal (Cu, Zn, Cd and Pb) content, speciation and stable isotopic variation of Pb in soakaway sediments were coupled and compared with soils (surface and underlying), and road dusts (residential and highway) to trace their contamination characteristics, mobility and source. Soakaway sediment and residential road dust were found to exhibit higher metallic content of anthropogenic origin with high mobility. Isotopic ratios in exchangeable fraction showed the least 206Pb/207Pb and 208Pb/207Pb ratios. Although there were significant differences in total metal content and speciation between two road dust samples, their isotopic signatures exhibited close resemblance and aligned with anthropogenic markers such as paint, petrol and aerosols. Heterogeneity of isotopic signature in different fractions of soakaway sediments seems to have originated from the mixing of multiple sources of heavy metals. Study concludes that mobility, source and contamination characteristics of metals in soakaway sediment were different from urban soil and road dust samples due to their complex environment and regular metal supply by road runoff.