Heavy metal contamination and assessment of roadside and foliar dust along the outer-ring highway of Shanghai, China

Foliar and roadside dust samples were collected from five sites alongthe outer-ring highway of Shanghai, one of the biggest metropolitanareas of China, to assess heavy/toxic metal contamination.Concentrations of Zn, Cu, Ni, As, and Hg in foliar dust werehigher than in roadside dust, whereas concentrations of Pb andCd were higher in roadside dust. In the roadside dust, averageconcentrations of all metals except As in foliar and roadsidedust samples were significantly above the background values ofsoil in Shanghai: the ratios between the average of samples andbackground values of Shanghai were in the order: Cd (25.1) >Zn (12.2) > Cu (6.16) > Pb (5.74) > Ni (5.50) > Hg (5.18) > As(1.05). By using the geo-accumulation index, the pollution grades ofseven heavy metals at five sampling sites were calculated. Roadsidedust was heavily to extremely contaminated with Cd; moderatelyto heavily contaminated with Zn; and moderately contaminatedwith Cu, Hg, Pb, and Ni. Foliar dust was heavily contaminatedwith Cd; moderately to heavily contaminated with Zn and Cu; andmoderately contaminated with Hg, Pb, and Ni. The contaminationlevel of heavy metals in the Puxi area was greater than that in thePudong area, which might be related to the industrial distributionand land use. Combined with correlation analysis, hierarchicalcluster analysis indicated that atmospheric deposition is the mainsource of Cd, Hg, As, and Pb in dust and that Cu and Zn in dust aremainly from heavy traffic on the highway. A portion of Ni in dustalso comes from the parent soil.