Concentration of heavy metals in street dust: an implication of using different geochemical background data in estimating the level of heavy metal pollution

Geochemical background data are used to distinguish between the sources of heavy metal (natural or anthropogenic) and to categorize the level of heavy metal pollution. In this study, we present the results of using different geochemical backgrounds (BG1-BG3) to establish the level of heavy metal pollution in street dust in Warsaw, Poland. We applied individual and collective indicators calculated with respect to the following backgrounds: (1) upper continental crust (UCC) (BG1), (2) the regional geochemical background established for Quaternary surface deposits of the Mazovian region (Poland) (parent geological material occurring in the studied area, Warsaw, Poland) (BG2), and (3) the minimal values of the concentration of heavy metals determined for the real street dust sample collectives from Warsaw (BG3). The assessment of the heavy metals pollution of street dust significantly depended on the background values used in the calculation of individual and collective indicators. Street dust was classified as unpolluted for almost all the heavy metals based on the values of indicators calculated for UCC data. The effect of traffic-related pollution was detected more precisely based on the values of indicators calculated for BG2 and BG3. The naturally elevated concentrations of heavy metals in UCC data can be responsible for the underestimation of pollution impact in street dust. When relatively low concentration of heavy metals is only observed, the application of BG2 or BG3 background data, which better correspond to the geogenic material in street dust, allows to realistically reflect the level of pollution from moving vehicles.