Asbestos fibers in the general population

Our plain-English summary of Asbestos fibers in the general population, by A. Churg, M.L. Warnock (The American Review of Respiratory Disease, 1980).

The study

• Authors: A. Churg, M.L. Warnock
• Journal: The American Review of Respiratory Disease
• Published: 1980;122(5):669-78
• Cited by: 123 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000793).

In plain English

This study examined lung tissue taken at autopsy at the University of California, San Francisco, from 21 urban residents (11 men and 10 women). Each had fewer than 100 asbestos bodies per gram of lung, a level the authors had earlier linked to environmental rather than occupational exposure. The authors used electron microscopy to count, measure and identify uncoated asbestos fibers. Chrysotile and amphibole fibers were found in all 21 people. Chrysotile made up about 80% of fibers, with a mean of 130 x 10^3 fibers per gram of wet lung. Most amphiboles were noncommercial types such as tremolite. Amosite/crocidolite appeared in only 11 of the 21. About 90% of chrysotile fibers were shorter than 5 micrometres, while 20.6% of amosite/crocidolite fibers were longer than 10 micrometres. Short chrysotile was more concentrated just under the pleura. Counts did not differ significantly by sex or smoking. The authors concluded that substantial asbestos, mostly too small to form asbestos bodies, is present in the average urban lung and probably reflects general environmental contamination.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Descriptive autopsy study: electron microscopic counting and identification of uncoated asbestos fibers in lung tissue, with no comparison group of exposed workers
• Who was studied: 21 people from the autopsy service of the University of California, San Francisco: 11 men and 10 women. All were aged 40 or older at death (actual range 43 to 95, mean 64), and each had fewer than 100 asbestos bodies per gram of wet lung. The article does not state when the autopsies took place.
• Exposure: Background, presumed environmental exposure. Lack of an occupational history was confirmed in 20 of the 21. One woman (subject 78-242) had spent 6 weeks making sheetrock for shipyards during World War II; the opening summary calls this probable exposure and the results call it definite occupational exposure. Fibers measured were chrysotile, antigorite, tremolite, actinolite, anthophyllite, glaucophane and amosite/crocidolite (counted together).
• Main results:
  • In the 21 subjects, chrysotile ranged from 12 x 10^3 to 680 x 10^3 fibers per gram of wet lung (mean 130 x 10^3).
  • In the 21 subjects, total amphiboles ranged from 1.3 x 10^3 to 75 x 10^3 fibers per gram of wet lung (mean 25 x 10^3).
  • About 80% of fibers were chrysotile. Chrysotile outnumbered amphibole fibers in 19 of the 21 subjects.
  • Tremolite was the most frequent amphibole and was present in all cases. The commercial amphiboles amosite/crocidolite were seen in only 11 of the 21 subjects, at the lowest average concentration of any amphibole (1,100 fibers per gram).
  • Almost 90% of chrysotile fibers were shorter than 5 micrometres. Fibers longer than 10 micrometres made up 1.9% of chrysotile, 7.4% of noncommercial amphiboles, 20.6% of commercial amphiboles and 22% of anthophyllite.
  • Mean ratios of uncoated fibers to asbestos bodies ranged from 170 for anthophyllite to 9,700 for chrysotile.
  • Short chrysotile fibers (under 5 micrometres) were more numerous in subpleural than central samples, with an overall ratio of 2.9. This was statistically significant (p less than 0.03 in the upper lobe, p less than 0.02 in the lower lobe). For longer chrysotile, and for amphiboles of either length, the peripheral excess was not significant.
  • Short amphibole fibers were concentrated in the upper lobe (upper to lower ratio 2.3, p less than 0.02). Chrysotile showed no upper versus lower lobe difference.
  • Neither chrysotile nor amphibole counts differed significantly between women and men (amphiboles 36 x 10^3 in women versus 14 x 10^3 in men) or between 5 nonsmokers and 16 smokers. Total fibers did not correlate with age.
  • Subject 78-242, with the 6-week sheetrock exposure, had the highest chrysotile and amphibole counts and had pleural plaques at autopsy. For the other subjects, suggestive histories could not be correlated with fiber numbers.
  • All but 3 subjects had no or very minimal interstitial fibrosis. The 3 with marked fibrosis had clinical reasons for it, such as old tuberculosis.
• The authors' conclusion: The authors concluded four things. Substantial amounts of asbestos, mainly chrysotile and noncommercial amphiboles, are present in the average urban lung. Most of these fibers are too small to form asbestos bodies or to be seen by light microscopy. Asbestos bodies may give some indication of exposure to long amphiboles but say nothing about the bulk of fibers. Most of these fibers probably reflect general environmental contamination, which the authors believed represented background inhaled from urban ambient air.
• Limitations the authors state:
  • The authors stated that their view that these fibers represent urban background must await comparison with people of known modest and high exposure.
  • Amosite and crocidolite were not counted separately.
  • Tremolite and anthophyllite were separated by an arbitrary cutoff of 4% calcium, because the fibers showed a continuous range of calcium content.
  • Small amounts of short chrysotile fibers were sometimes found in the blank (no-tissue) preparations. Counts from the blanks were subtracted from the test values.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis.

Related studies

• Fiber size and number in workers exposed to processed chrysotile asbestos, chrysotile miners, and the general population — A. Churg, B. Wiggs (1986)
• Nonasbestos pulmonary mineral fibers in the general population — A. Churg (1983)
• Analysis of the cores of asbestos bodies from members of the general population: patients with probable low-degree exposure to asbestos — A. Churg, M.L. Warnock (1979)
• Asbestos fibers and pleural plaques in a general autopsy population — A. Churg (1982)
• Chrysotile biopersistence in the lungs of persons in the general population and exposed workers — A.M. Langer, R.P. Nolan (1994)
• Prevalence of pleural calcification in persons exposed to asbestos dust, and in the general population in the same district — M. Navrátil, F. Trippé (1972)

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