Abstract
BACKGROUND: There is indirect evidence that inhaled traffic-related particulate matter (PM) penetrates into the human circulation. Since nanoparticles readily adhere to red blood cells (RBCs) in vitro, we sought to determine whether a mechanism of systemic transport of translocated traffic-related particles is via adherence to RBCs in vivo. METHODS: Adult volunteers were exposed to traffic-related emissions from a main road for 1 h. Volunteers were also exposed to emissions wearing a FFP2 mask. Exposure to black carbon PM was assessed by portable aethalometer. The mean area (μm(2)) of adherent black PM per RBC was determined from unstained blood smears from 3000 cells by light microscopy. Particle composition was determined by scanning transmission electron microscopy and energy-dispersive X-ray analyses. The capacity of diesel exhaust particles to adhere to human RBCs in vitro was determined, and RBCs were examined after intratracheal instillation of diesel exhaust particles to a mouse model. RESULTS: Exposure to traffic-related emissions increased personal black carbon PM (n=12, p=0.001 versus baseline). Exposure increased the area of particles adherent to RBCs (p<0.001 versus baseline), and this was reduced by wearing a FFP2 mask (p=0.002 versus no mask). Traffic exposure increased the abundance of metal-bearing nanoparticles associated with RBCs. Diesel exhaust particles adhered to RBCs in vitro in a dose-dependent manner. Particles were found adherent to circulating RBCs after intratracheal instillation of diesel exhaust particles. CONCLUSION: Adhesion of traffic-related PM to RBCs is a systemic transport mechanism. Quantification of particles on RBCs is a putative practical biomarker of inhaled dose.