Changes in numbers and dimensions of chrysotile asbestos fibers in lungs of rats following short-term exposure.

Previous studies from this laboratory have demonstrated that in rats exposed briefly to aerosolized chrysotile asbestos, fibers initially deposited in the distal lung impact primarily at bifurcations of alveolar ducts. Subsequently, there is a progressive decrease in the numbers of fibers seen by scanning electron microscopy at the bifurcations with increasing time from initial exposure. The purpose of the present study was to assess the number and dimensions of fibers deposited in the lungs of these rats and to determine how these parameters changed at various intervals after the termination of exposure. This was accomplished using a sodium hypochlorite digestion-concentration technique to recover the fibers on a membrane filter. The numbers and dimensions of the fibers were then assessed using scanning electron microscopy. Utilizing these data, the mass of asbestos retained in the lung was calculated with a newly developed formula. Twenty-three percent of the respirable fraction was deposited in the lungs, and 19% of this amount was still present 31 days after exposure. Over the 31 days, there was a progressive increase (p less than 0.05) in mean fiber length and a significant decrease (p less than 0.05) in the diameter of the population of fibers retained in the lung. Such data should prove useful in attempting to understand the progressive pathogenesis of asbestos-induced interstitial lung disease, which seems to be related, at least in part, to the dimensions of the inhaled fibers.