A COMPOSITIONAL COMPARISON OF URBAN ROAD DUST AND SOIL IN PHILADELPHIA, PENNSYLVANIA

Currently, over half of the world’s population is living in urban environments; this number is projected to grow as the 21^st century progresses due to rapid urbanization. As a result, soil and air pollution are expected to increase, creating human health hazards. The geochemical characterization of urban environments is vital, as potentially toxic elements can accumulate to high levels in environmental media such as road dust and soils. Urban road dust is an accumulation of both natural and anthropogenic particles on outdoor, impervious surfaces in metropolitan environments. To assess the compositional relationships between the road dust and soil, we collected paired samples at 20 sites in the Fishtown neighborhood of Philadelphia. Studies using X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), loss on ignition, and laser diffraction are underway to determine mineral phases present, elemental composition, organic content, and particle-size distributions, respectively. The XRD data revealed that three mineral phases were present at a majority of road dust sample sites: quartz (SiO₂), dolomite (CaMg(CO₃)₂), and anorthite (CaAl₂Si₂O₈); quartz was present in all 40 samples examined. The most common phases present in road dust were also identified in soil samples. More than 40 phases were detected in our sample set, but most only occurred in one individual sample. Organic content was higher within soil, but both media featured large variations. For ICP-OES analysis, we expect similar elements to be present at paired road dust and soil sites. However, the concentrations of heavy metals are expected to be higher within road dust sites, as has been reported by other studies. For minerals, the most common phases are likely related to local geologic formations, specifically the Wissahickon formation, consisting primarily of oligoclase-mica schist and hornblende gneiss. These results are akin to our first study of road dust in Philadelphia and highlight the importance of local geologic sources to the composition not only of topsoil, but also road dust. Future work will explore the spatial statistics of local source material.