NANOPARTICLES IN ROAD DUST FROM IMPERVIOUS URBAN SURFACES: DISTRIBUTION, IDENTIFICATION, AND ENVIRONMENTAL IMPLICATIONS IN A FIRST STUDY OF ITS TYPE

Air pollution is one of the most important global environmental issues, and particulate matter with an aerodynamic diameter smaller than 2.5 μm (PM2.5), in particular, is known to cause significant damage to the environment and to human health. Outdoor air pollution, mostly PM2.5, has been linked to cardiovascular and respiratory effects, and has been estimated to lead to 3.3 million premature deaths per year worldwide. Recently more attention has been paid to ultrafine PM (the smallest PM2.5 which is below 0.1 μm, or <100 nm), because these nanoscale particles can penetrate through the alveolar regions of the lungs and translocate via blood to other organs, including the heart and brain. What is most often missing from these considerations is that NPs typically show dramatically different properties relative to the corresponding bulk material.

The objective of this study was to investigate the heavy metal and nanoparticle content of PM2.5 generated in the laboratory using a novel aerosolization technique, simulating the atmospheric dispersion of dust blown off a surface by wind, of 66 road dust samples collected throughout the mega-city of Shanghai (China). We characterized the samples using an array of techniques including inductively-coupled plasma mass spectrometry, aerosol size distribution measurements, and scanning and transmission electron microscopy coupled with elemental characterization and electron diffraction. Principal metal concentrations were plotted geospatially. Fe-, Pb-, Zn-, and Ba containing NPs were identified using electron microscopy, spectroscopy, and diffraction, and we tentatively identified most of them as either engineered, incidental, or naturally occurring. For example, dangerous Pb sulfide and sulfate NPs likely have an incidental origin and are also sometimes associated with Sn; we believe that these materials originated from an e-waste plant. Nanoparticles identified as most liking to be naturally occurring included hematite, ferrihydrite, schwertmannite, calcite, hydroxyapatite, and amorphous silica. Size distributions of most aerosolized samples presented a peak in the ultrafine range (<100 nm), with the smallest grain size down to below 20 nm. We estimate that 3.2 ± 0.7 μg mg⁻¹ (or 3 ppt) of Shanghai road dust may become re-suspended in the form of PM2.5.