Heavy metals in the finest size fractions of road-deposited sediments

摘要

The concentration of heavy metals in urban road-deposited sediments (RDS) can be used as an indicator for environmental pollution. Thus, their occurrence has been studied in whole road dust samples as well as in size fractions obtained by sieving. Because of the limitations of size separation by sieving little information is available about heavy metal concentrations in the road dust size fractions 20 mu m. In this study air classification was applied for separation of dust size fractions smaller than 20 mu m from RDS collected at different times during the year. The results showed only small seasonal variations in the heavy metals concentrations and size distribution. According to the Geoaccumulation Index the pollution of the road dust samples deceased in the following order: Sb As Cu approximate to Zn Cr Cd approximate to Pb approximate to Mn Ni Co approximate to V. For all heavy metals the concentration was higher in the fine size fractions compared to the coarse size fractions, while the concentration of Sr was size-independent. The enrichment of the heavy metals in the finest size fraction compared to the whole RDS 200 mu m was up to 4.5-fold. The size dependence of the concentration decreased in the following order: Co approximate to Cd Sb (Cu) approximate to Zn approximate to Pb As approximate to V Mn. The approximation of the size dependence of the concentration as a function of the particle size by power functions worked very well. The correlation between particle size and concentration was high for all heavy metals. The increased heavy metals concentrations in the finest size fractions should be considered in the evaluation of the contribution of road dust re-suspension to the heavy metal contamination of atmospheric dust. Thereby, power functions can be used to describe the size dependence of the concentration. (C) 2018 Elsevier Ltd. All rights reserved.