Exogenous Mineral Particles in the Human Bronchial Mucosa and Lung Parenchyma. I. Nonsmokers in the General Population

Abstract

We extracted mineral particles from 7 different regions of the bronchial tree and 4 regions of lung supplied by these airways from 11 morphologically normal adult autopsy right lungs. All patients were nonsmokers. Particles were identified, counted, and sized by analytical electron microscopy. Both particle concentration and particle size showed a significant negative correlation with airway diameter; detailed analysis showed that the correlation for concentration was only true of large particles. Distance from the carina (pathlength) showed a weaker correlation with particle concentration. The lowest particle concentration was found in the mainstem bronchi, and there was a consistent (case to case) increase in particle concentration with airway generation. Parenchyma supplied by the apical segmental bronchus had a higher particle concentration than that in other sample sites. Segmental bronchial particle size was consistently larger than particle size in the supplied lung tissue, and particles from both upper-lobe tissue sample sites were slightly larger than those from the two lower-lobe sample sites. Bronchial mucosa from all sites showed a predominance of silica, whereas tissue sites appeared to preferentially concentrate silicates, especially kaolin and mica. These observations suggest that in morphologically normal lungs from lifetime nonsmokers (1) in the noncarinal portions of the larger airways, airway diameter and, to a much lesser extent, pathlength are the major influences on long-term bronchial particle concentration and size; (2) tissue particle concentration does not appear to relate to pathlength; (3) the airways accumulate very specific sizes and types of particles compared to the parenchyma, an effect that may influence the location of specific pathologic lesions; and (4) the pattern of long-term particle concentration appears to be fairly similar to acute bronchial deposition patterns seen in experimental human systems, an observation that may imply that long-term burden is the result of translocation of a fraction of the locally deposited particles to the interstitial tissues.