| Traffic is one of the main source of heavy metal pollution, which has been an important issue in the field of environmental geochemistry. Due to vehicle emissions and other factors, heavy metals of atmospheric particulates near the surface in the microsystem along the urban road migrate, accumulate and transformate in the atmospheric near the ground, road dust, roadside soil, vegetables and the green belt with the atmospheric circulation. It has become a potential threat in the road ecological environment, and has become an important factor in the deterioration of the earth atmospheric environment. The pollution from heavy metals in the atmospheric, soil and water directly or indirectly endanger human health.This study identified the levels and sources of heavy metal contamination in airborne particles, road dusts and soils collected along three highways in Jiangxi Province with different traffic densities, and discuss the influence of traffic volume, driving conditions, weather and distance. A modified BCR three-step sequential extraction procedure in this article was adopted to study the possible chemical forms and the relative mobility and bioavailability of the heavy metals. The main conclusions of this study can be summed up as follows:1. Heavy metal concentrations in airborne particles, road dusts and soils presented similar rules:Zn>Cuã€Pb>Sbã€Cd. Manganese concentrations in road dusts and soils were in the range of the natural background value of soils in the Jiangxi area, and that in airborne particles was under zinc and lead, which suggested that airborne Mn came from traffic, and that Mn in road dusts and soils from background soil.2. Traffic-related Zn mainly come from the wear of tyre, and temperature was one of the main factors that influence the wear of tyres; although leaded petrol was banned, lead was still released from traffic to the environment; enrichment factors (EFs) of copper and antimony in road dusts and in soils were similar, which accounted further that copper and antimony had same source; although Cd concentrations in road dusts and soils were not very high, Cd pollution was very serious compared with background value. 3. Significant positive correlation between Pb and Zn, Cd, Cu and Sb concentrations in airborne particles, road dusts and soils suggested that those airborne metals mainly derived from traffic. Correlations between atmospheric Mn and Cu, Pb, Zn, Cd and Sb concentrations were far better than that between Mn and Cu, Pb, Zn, Cd and Sb concentrations in road dusts and soils, which suggested that airborne Mn came from traffic, and that Mn in road dusts and soils from background soil.4. There was no linear relationship between Mn concentrations and traffic volume, while there were strong linear relationships between Zn, Cu, Pb, Sb and Cd concentrations and traffic volume, which reflected that traffic was not the main source of Mn in road dusts and soils, and was the main source of Zn, Cu, Pb, Sb and Cd.5. Stop-start driving conditions injunctions were thought to be a major factor in the relationship of traffic to metal pollution levels.6. There was just a little decline of Pb, Mn, Cu, Cd and Sb concentrations when raining. It was likely because automotive exhaust or metal wear/corrosion were the main sources of these metals, which were hardly subject to weather. When raining atmospheric Zn concentration in PM10increased regardless of rain wash, which can be explained by the fact that the particles from tyre wear will become smaller due to the decreased frictional force when raining, and rain wash had a little effect on PM10.7. Heavy metal concentrations showed a little decreasing trend with increasing distance from the road, which can be explained by the fact that heavy metals mainly existed in PM10moving more easily.8. The values of the contamination factor of the road dust decreased in the following order:Cd>>Cu, Sb, Zn>Pb, while the results of soils reflected similar patterns. Ecological risks of road dusts and soils were in order Cd>>Cu>Pb>Zn. These results show extreme high ecological risks of Cd except of soils near WH highway which corresponded to very high ecological risk, and low ecological risks of Cu, Pb, Zn.9. The chemical association of Cu within airborne particles, road dusts and soils was dominated by the the organic and residual fraction. The chemical association of Pb in airborne particles was dominated by the acid soluble/exchangeable, and that in road dusts and soils was dominated by the residual. The chemical association of Zn within airborne particles, road dusts and soils were all dominated by the acid soluble/exchangeable phase. The chemical fraction of Cd in airborne particles, road dusts and soils were all dominated by the acid soluble. The chemical fraction of Sb in road dusts and soils were both dominated by the organic. Considering the acid soluble phase, the order of bioavailability in airborne particles decreased in the following order:Zn>Pb>Mn>Cd>Cu, in road dusts:Zn>Cd>Mn>Pb>Sb>Cu, and in soils: Zn>Cd>Mn>Pb>Cu>Sb. |
