Speciation of heavy metals in airborne particles, road dusts, and soils along expressways in China

This study analyzed the concentrations and chemical forms of Zn, Cu, Pb, Sb, Cd and Mn in airborne particles, road dusts and soils collected along three expressways in Jiangxi Province, China, with different traffic densities, and identified the levels and sources of heavy metal contamination. The concentrations of Zn, Cu, Pb, Sb, and Cd except Mn in airborne particles, road dusts and soils were all in direct proportion to traffic volume. Cd concentrations were low compared with other metals. For instance, the concentrations of Zn, Cu, Pb, Sb, Mn and Cd were 6.6, 0.7, 2.2, 0.1, 0.1 and 0.1 μg·m^?3 in PM₁₀ along the Changjiu Expressway, 792.8, 241.4, 248.3, 9.6, 340.5 and 8.0 mg·kg^?1 in road dusts, and 201.1, 143.2, 59.5, 9.5, 338.9 and 2.3 mg·kg^?1 in soils, respectively, but in the case of the ratio of concentration to the environmental background value, most serious contamination was caused by Cd. The sources of the heavy metals were judged by comparisons of the chemical forms of the heavy metals in different environmental media. Pb and Mn in airborne particles were both derived from traffic; Pb in road dusts and soils resulted mainly from the use of leaded gasoline in the past; and Mn in road dusts and soils was derived from parent rocks. Zn, Cu, Sb and Cd in airborne particles, road dusts and soils were derived primarily from traffic, and differences in chemical forms of the heavy metals in different media were due to the interaction between heavy metals in airborne particles and organic matter and other surfaces in road dusts and soils. We also discussed the change of chemical forms of heavy metals in particles of different sizes and under different weather conditions. Bioavailability of heavy metals in airborne particles was much higher than that in road dusts and soils, especially Pb (0.676 in airborne particles, 0.159 in road dusts and 0.095 in soils).