A retention model of man-made vitreous fibers (MMVFs) inhaled by rats

A general model has been developed to describe the deposition and clearance processes of man-made vitreous fibers (MMVFs) in the rat lung at chronic exposure. Fiber removal from the lung by macrophage-mediated mechanical clearance, fiber dissolution, and breakage were considered in the model, and the rates for these mechanisms were determined from the experimental data. It was found that the breakage of long fibers (lf > 20 mm) into short segments and subsequent removal of short segments by macrophages is principally responsible for the fast clearance of long fibers as observed in the experiment. The breakage rate was found to increase with the fiber solubility and decrease with lung burden. An expression for the breakage rate as a function of the fiber in-vitro dissolution rate and lung burden is proposed.