Particle Loading in the Human Lung—Human Experience and Implications for Exposure Limits

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Abstract
Timbrell's analyses of fiber burdens in the post-mortem lungs of workers with long-term inhalation exposures to a variety of amphiboles have shown that the clearance of fibers is strongly dependent on lung burden and its associated lung fibrosis, with a small percentage of very heavily exposed workers having little, if any clearance from parts of the lung. The extent of lung fibrosis is proportional to the total surface of retained mineral particles for both fibers and more compact particles. The human data base from the asbestos workers can provide a sound basis for the development of more generic models describing the influence of lung burden of mineral dust on particle deposition in, and clearance from, human lungs. The implications of the results obtained to the pathogenesis of chronic lung diseases and the evaluation and/or establishment of exposure limits are also discussed, along with some research needs to facilitate interspecies extrapolation of fiber toxicity data.