Technical Report 122

UFP show a rapid translocation from the site of deposition

Oberdörster and colleagues (Oberdörster et al, 2002a) estimated that on average, two-thirds of the lung deposits are cleared between an initial 6-hour exposure and the subsequent 0.5 hour post-exposure measurement. Since no significant lung clearance was measured at the other post-exposure periods, it was implied that very rapid clearance of UF carbon particles from the lower respiratory tract occurred in the initial stages of exposure. This finding was considered consistent with previous observations (Oberdörster et al, 2000), where UF particles depositing in the lower respiratory tract escape AM clearance and have a rapid translocation to epithelial, interstitial and endothelial sites. Once uptake from interstitial sites in the respiratory tract has taken place, further translocation of UF particles to lymphatic channels (or directly via the endothelium) and then to the blood circulation could take place.