Metal accumulation in roadside soil in Melbourne, Australia: Effect of road age, traffic density and vehicular speed.

Concentrations of vehicular emitted heavy metals in roadside soils result in long term environmental damage. This study assessed the relationships between traffic characteristics (traffic density, road age and vehicular speed) and roadside soil heavy metals. Significant levels were recorded for Cd (0.06-0.59 mg/kg), Cr (18-29 mg/kg), Cu (4-12 mg/kg), Ni (7-20 mg/kg), Mn (92-599 mg/kg), Pb (16-144 mg/kg) and Zn (10.36-88.75 mg/kg), with Mn concentrations exceeding the Ecological Investigation Level. Significant correlations were found between roadside soil metal concentration and vehicular speed (R = 0.90), road age (R = 0.82) and traffic density (R = 0.68). Recently introduced metals in automotive technology (e.g. Mn and Sb) were higher in younger roads, while the metals present for many years (e.g. Cd, Cu, Pb, Zn) were higher in medium and old age roads confirming the risk of significant metal deposition and soil metal retention in roadside soils.