Nanosized magnetite particles in urban road dust: distribution characteristics and their potential risk

Abstract

Urban road dust acts as a significant reservoir for nanosized magnetite particles (NMPs), which pose health risks through atmospheric resuspension. This study systematically investigated the characteristics of NMPs in Shanghai's road dust, using a cycle magnetic extraction system to isolate NMPs from bulk dust samples. Transmission electron microscopy (TEM) analyses revealed the aggregation of NMPs and Pd-nanoparticles, indicative of vehicular emissions. Number concentrations of NMPs in road dust were 1.4 × 10⁴–9.5 × 10⁶ particles per mg, with an average size of 102 nm. Seasonally, the number concentrations of NMPs in summer were 2.24-fold higher than in winter, which could be attributed to the enhanced wet deposition from PM_2.5 during rainy periods. Spatially, industrial and traffic areas exhibited NMP number concentrations averagely 2.1 times higher than other functional areas, accompanied by elevated mass fractions of toxic metals (including V, Mn, As, Ag, Sn, Sb, Tl, and Pb) in NMPs. The industrial land area was identified as the primary spatial determinant of NMP distribution, and the larger the industrial land area, the higher the number concentration of NMPs in road dust. Notably, traffic and commercial areas showed heightened exposure risks due to the combined effects of elevated NMP concentration and dense human activity. These findings highlight the necessity for targeted pollution control strategies in mega-cities, particularly addressing vehicular and industrial emission sources.