[Pollution Characteristics and Potential Ecological Risks of Heavy Metals in Road Dust in Beijing]

Based on the concentrations of 21 inorganic elements in particulate matter with diameters less than 10 μm (PM₁₀) in 2004, and PM_2.5 in 2004 and 2013 of representative road dust in Beijing, the pollution characteristics and potential ecological risks of heavy metals in this dust were analyzed and discussed. The results showed that the six main elements in road dust in Beijing were Si, Ca, Al, Fe, Mg, and K, and the proportions of the total content of the six elements in PM₁₀ in 2004, PM_2.5 in 2004, and PM_2.5 in 2013 accounted for 96.51%, 96.42%, and 96.53% of the total content of all elements tested, respectively. The elemental enrichment level and the pollution degree and the potential ecological risk of heavy metal in road dust in Beijing in 2004 were PM_2.5>PM₁₀. Se, a characteristic element of coal dust, was highly enriched in PM_2.5 in 2004, and Cd was high in PM₁₀ and PM_2.5 in 2004 with enrichment factors of 1024.03, 68.15, and 871.55, respectively. Co, Zn, Ca, and Cu were significantly enriched in PM₁₀ and PM_2.5 in 2004 with enrichment factors of 12.93, 12.33, 8.30, and 8.07 in PM₁₀ and 17.41, 21.80, 12.83, and 19.73 in PM_2.5, respectively; Na and Si were not enriched in the road dust. The pollution load index (PLI) of heavy metals was 3.95 in PM₁₀ and 7.71 in PM_2.5 in 2004. Owing to the implementation of dust, motor vehicles, and combustion source control measures in Beijing and the relocation of the Shougang corporation, the elemental enrichment level, pollution degree, and potential ecological risk of heavy metals in road dust PM_2.5 in 2013 were significantly lower than those in 2004. The enrichment factors of Cd and Se in PM_2.5 in 2013 decreased to 98.47 and 0.95, respectively; those of Cu, Ca, and Zn decreased to 11.90, 8.84, and 8.20, respectively; and PLI decreased to 2.56. The results showed that the total potential ecological risk of heavy metals in road dust in Beijing was extremely strong. Heavy metal Cd was the most significant pollution factor and the main potential ecological risk source; its potential ecological risk index (RI) contribution to the total RI of heavy metals was more than 85%. In 2004, the pollution degree of heavy metals in road dust of main roads was significantly higher than that for other road types. The pollution degree of heavy metals in PM₁₀ was main road > expressway entrance to Beijing > secondary main road > ring road; that for PM_2.5 was main road > ring road > expressway entrance to Beijing > secondary main road. For PM_2.5 in 2013, however, the order was expressway entrance to Beijing > main road > ring road > secondary main road. The pollution degree of heavy metals in road dust of secondary main roads was significantly lower than that for other road types. In 2013, for road dust PM_2.5 in Beijing, the correlation of heavy metals Ti, Zn, V, Cr, Cu, Pb, and Ni was significant owing mainly to traffic-related emissions.