Heavy metal contamination of road-deposited sediments in a medium size city of China

Road-deposited sediment (RDS) is an important environmental medium that affects the characteristics of heavy metals in stormwater runoff. 62 RDS samples were collected from four different land use types ( commercial, residential, intense traffic and riverside park) in the Zhenjiang city of China. The samples were analysed for concentrations of five metals (Zn, Pb, Cu, Cr and Ni). The maximum mean concentrations of Zn, Pb, Cu, Cr and Ni from different land use types were 686, 589, 158, 129 and 125 mg/kg, respectively. The intense traffic area displayed the highest metal concentrations, whilst Zn, Cr, Ni and Cu did not show any discernible variations among the other three areas. Seven particle sizes were analysed separately for the heavy metal concentrations. In all studied areas, particles < 63 mu m have the highest metal concentrations: 926-1,188 mg/kg of Zn, 270-928 mg/kg of Pb, 150-220 mg/kg of Cu, 99-172 mg/kg of Cr and 96 147 mg/kg of Ni. The fine particle fraction (< 63 mu m) of the samples accounted for about 25-60% of the total metal loading; in contrast, the coarsest fraction ( 1,000 2,000 mu m) only contributed 1-5%. The calculated ecological risk index shows that considerably high potential risks exist in the intense traffic area particularly due to high concentrations of Pb. These findings provide invaluable information for the development of appropriate management strategies to decrease non-point source contamination loading to the water environment in urban areas.