Asbestos Fibers in the General Population ^1– ³

Abstract

We isolated uncoated asbestos fibers from the lungs of 21 urban dwellers who had fewer than 100 asbestos bodies/gram of lung, a level shown previously to be associated with environmental rather than occupational exposure to asbestos. Lack of occupational history was confirmed in 20 of the 21 patients; history of probable exposure was obtained for 1 patient. Fibers were counted, measured, and identified using a combination of electron optical morphology, diffraction, and energy dispersive x-ray spectroscopy. Eighty per cent of the fibers were chrysotile (mean 130 × 103, range 12 × 103 to 680 × 103 fibers/gram wet lung) and 90% of the chrysotile was less than 5 μ long. Total amphiboles had a mean of 25 × 103 and ranged from 1.3 × 103 to 75 × 103 fibers/g; 95% were noncommercial amphiboles and two thirds were less than 5 μ long. However, 20% of the commercial fibers, amosite/crocidolite, and 20% of the anthophyllite were longer than 10 μ, a finding in accord with the types of fibers seen in asbestos bodies in these patients. Short (<5 μ) chrysotile was preferentially deposited subpleurally; similar but not statistically significant accumulation was seen for the other types and lengths of asbestos fiber. We conclude that: (1) Substantial amounts of asbestos, mainly chrysotile and noncommercial amphiboles, are present in the average lung in an urban environment; (2) Most of these fibers are too small to form asbestos bodies or to be visible by light microscopy; (3) Asbestos bodies may serve as some indication of exposure to long amphiboles, but offer no information about the bulk of fibers present; and (4) It is probable that most of these fibers reflect general environmental contamination.