Figure 1.

Clearance of asbestos from the lower respiratory tract. Exposure to longer amphibole fibers can result in “frustrated phagocytosis” and failure of clearance pathways, while shorter fibers and fragments can be successfully phagocytosed and removed via the mucociliary pathway. Phagosomal degradation of amphibole with release of metals does not occur (A). In contrast, longer chrysotile fibers are phagocytosed and the brucite layer is destroyed in an acidic environment with release of metal (e.g., magnesium) constituents. This results in fragments that can eliminated from the lower respiratory tract via the mucociliary clearance pathway (B).