The aim of this study is to identify and investigate levels of toxic heavy metals in PM_2.5 fractioned road dust to better understand the associated inhalation risk and potential health impacts. To achieve this aim, concentrations of seven traffic generated heavy metals (Cu, Pb, Zn, Cd, Ni, Sb, and Cr) were determined in the PM_2.5 fraction of road dust samples from four different locations (offices, residential, hospital, and school) in two cities (Karachi and Shikarpur) of Pakistan using ICP-MS. The average concentration values of heavy metals in Karachi were as follows: 332.9 mg/kg Cu, 426.6 mg/kg Pb, 4254.4 mg/kg Zn, 62.3 mg/kg Cd, 389.7 mg/kg Ni, 70.4 mg/kg Sb, 148.1 mg/kg Cr, whereas the average concentration values of heavy metals in Shikarpur were 245.8 mg/kg Cu, 538.4 mg/kg Pb, 8351.0 mg/kg Zn, 57.6 mg/kg Cd, 131.7 mg/kg Ni, 314.5 mg/kg Sb, 346.6 mg/kg Cr. The pollution level was assessed through two pollution indices enrichment factor (EF) and geoaccumulation index (I_geo). These indices showed moderate to extreme level pollution in studied areas of both cities. The health risk assessment through inhalation contact was conducted according to the United States Environmental Protection Agency’s (USEPA) model for children and adults. Both non-cancerous and cancerous risks were characterised in the road dust samples for each location. As yet, there is not a single study on the concentrations of heavy metals in PM_2.5 fractions of road dust in Karachi and Shikarpur, findings of this research will facilitate researchers for further investigations in current field.

Inadvertent oral ingestion is an important exposure pathway of arsenic (As) containing soil and dust. Previous researches evidenced health risk of bioaccessible As from soil and dust, but it is unclear about As mobilization mechanisms in health implications from As exposure. In this study, we investigated As release behaviors and the solid–liquid interface reactions toward As(V)-containing iron minerals in simulated gastrointestinal bio-fluids. The maximum As release amount was 0.57 mg/L from As-containing goethite and 0.82 mg/L from As-containing hematite at 9 h, and the As bioaccessibility was 10.8% and 21.6%, respectively. The higher exposure risk from hematite-sorbed As in gastrointestinal fluid was found even though goethite initially contained more arsenate than hematite. Mechanism analysis revealed that As release was mainly coupled with acid dissolution and reductive dissolution of iron minerals. Proteases enhanced As mobilization and thus increased As bioaccessibility. The As(V) released and simultaneously transformed to high toxic As(III) by gastric pepsin, while As(V) reduction in intestine was triggered by pancreatin and freshly formed Fe(II) in gastric digests. CaCl₂ reduced As bioaccessibility, indicating that calcium-rich food or drugs may be effective dietary strategies to reduce As toxicity. The results deepened our understanding of the As release mechanisms associated with iron minerals in the simulated gastrointestinal tract and supplied a dietary strategy to alleviate the health risk of incidental As intake.