Settled iron-based road dust and its characteristics and possible association with detection in human tissues.

Settled road dust was examined to detect the presence of non-airborne submicron and nano-sized iron-based particles and to characterize these particles. Samples were collected from a road surface near a busy road junction in the city of Ostrava, Czech Republic, once a month from March to October. The eight collected samples were subjected to a combination of experimental techniques including elemental analysis, Raman microspectroscopy, scanning electron microscopy (SEM) analysis, and magnetometry. The data thereby obtained confirmed the presence of non-agglomerated spherical nano-sized iron-based particles, with average sizes ranging from 2 down to 490 nm. There are several sources in road traffic which generate road dust particles, including exhaust and non-exhaust processes. Some of them (e.g., brake wear) produce iron as the dominant metallic element. Raman microspectroscopy revealed forms of iron (mainly as oxides, Fe2O3, and mixtures of Fe2O3 and Fe3O4). Moreover, Fe3O4 was also detected in samples of human tissues from the upper and lower respiratory tract. In view of the fact that no agglomeration of those particles was found by SEM, it is supposed that these particles may be easily resuspended and represent a risk to human health due to inhalation exposure, as proved by the detection of particles with similar morphology and phase composition in human tissues.