Translocation and effects of ultrafine particles outside of the lung.

Ultrafine, or nano-, particles (< 100 nm) have been associated in epidemiological, human clinical, and animal studies with adverse cardiopulmonary outcomes. Deposition of inhaled ultrafine particles in the respiratory tract is mainly governed by diffusion and is most efficient for alveolar regions of the lung, although deposition occurs in other regions, too. The nose is also a very efficient filter for smaller ultrafine (< 5 nm, diffusion) particles. Solid poorly-soluble ultrafine particles are not efficiently cleared via mucociliary or macrophage-mediated mechanisms and are, thus, likely to be taken up by epithelial cells and translocate to extrapulmonary sites (interstitium, lymph and blood circulation, neurons). These translocation processes are explored here as well potential consequences that result from exposure of extrapulmonary organs to inhaled ultrafine particles.