Nonasbestos pulmonary mineral fibers in the general population

Our plain-English summary of Nonasbestos pulmonary mineral fibers in the general population, by A. Churg (Environmental Research, 1983).

The study

• Author: A. Churg
• Journal: Environmental Research
• Published: 1983;31(1):189-200
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Total pulmonary nonasbestos mineral content was determined for a series of 20 patients who had no occupational dust exposure. To extract mineral fibers, lung tissue was dissolved in bleach and the treated sediment transferred to the electron microscope grid. Mineral fibers were identified using electron diffraction and energy dispersive x-ray spectroscopy. The mean number of nonasbestos fibers, 106 X 10(3)/g wet lung, was almost identical to the mean number of asbestos fibers, 102 X 10(3)/g. Thirteen different species or groups of nonasbestos minerals were found: apatite accounted for 18% of the total and talc for 16%. All other forms accounted for less than 8% each. Silica was found in every lung, and talc in 19 of 20 lungs. Of the fibers, 86% were shorter than 5 microns, and most of the fibers had aspect ratios less than 15. No correlations were seen between numbers or types of fibers and age, sex, or smoking. It is concluded that (1) substantial numbers of nonasbestos fibers are present in lungs of the general population. Most of these fibers are short and of low aspect ratio; and (2) by phase microscopy one is as likely to observe nonasbestos as asbestos fibers in these preparations, indicating that light microscopic methods are not suitable for this type of analysis. These data provide a baseline for comparison with patients believed to have a mineral fiber-related disease.

In plain English

This study counted mineral fibers other than asbestos in autopsy lung tissue from 20 people (11 men, 9 women) aged 40 or older. They were chosen for having no occupational asbestos exposure by history and fewer than 100 asbestos bodies per gram of wet lung. Fibers were extracted by dissolving tissue in bleach and identified by electron microscopy. The average was 106 x 10^3 nonasbestos fibers per gram of wet lung, roughly equal to the 102 x 10^3 asbestos fibers per gram in the same lungs. Thirteen mineral types were found; apatite made up 18% and talc 16%. Silica was in every lung and talc in 19 of 20. Of the fibers, 86% were 1 to 4.9 micrometers long. Fiber numbers showed no statistically significant link with sex, smoking or age. The author estimated that a light microscope would show about as many nonasbestos as asbestos fibers. The author concluded that the group could serve as a baseline for comparison with people who had definite occupational exposure and disease. The author noted that the number of cases was small.

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 lung-tissue study (case series) using electron microscopy, electron diffraction and energy dispersive x-ray spectroscopy to identify and count nonasbestos mineral fibers
• Who was studied: 20 patients (11 men, 9 women) from a general autopsy service, all 40 or older at death. They were selected for no occupational asbestos exposure by history and a light microscopic asbestos body count under 100 bodies per gram of wet lung. Place and dates of autopsy are not stated.
• Exposure: Background (non-occupational) exposure to nonasbestos mineral fibers. Exposure histories were obtained from relatives by standardized questionnaire, and no patient appeared to have occupational mineral fiber exposure.
• Main results:
  • Across the 20 lungs, the mean was 106 x 10^3 nonasbestos fibers per gram of wet lung (standard deviation 87 x 10^3). This is roughly equal to the mean of 102 x 10^3 asbestos fibers per gram.
  • Thirteen nonasbestos mineral groups or species were identified. Apatite made up 18% and talc 16% of total nonasbestos fibers.
  • Silica fibers were found in all 20 lungs and talc in 19 of 20 lungs.
  • Of the nonasbestos fibers, 86% were 1 to 4.9 micrometers long, 11% were 5 to 9.9 micrometers, and 3.0% were 10 micrometers or longer.
  • Fiber numbers did not differ significantly between the 11 men and 9 women, or between the 15 smokers and 5 nonsmokers. They did not correlate with smoking amount or age (correlation with age 0.026, not statistically significant).
  • The aspect ratios (length to width) of the nonasbestos fibers were, on the whole, much lower than those of asbestos fibers.
  • Fibers near the lung surface (subpleural, 67.5 x 10^3 per gram) outnumbered those in central samples (39 x 10^3 per gram). The text says this difference approached statistical significance.
  • The author estimated that about 10 x 10^3 asbestos fibers per gram would be visible by phase (light) microscope, compared with about 11 x 10^3 nonasbestos fibers per gram. One is therefore as likely to see a nonasbestos as an asbestos fiber with that method.
  • No patient had interstitial fibrosis that could not be explained by treatment or old infection. Fiber numbers in the three patients with lung cancer and three with gastrointestinal cancer did not appear different from the group as a whole.
• The authors' conclusion: The author concluded that occupational exposure in this group, if any occurred, appears small, so the group can serve as a baseline for comparing fiber numbers and types in people with definite occupational exposure and disease.
• Limitations the authors state:
  • The number of cases examined was small (for example, only 5 nonsmokers).
  • Some patients may have had occupational fiber exposure, although the author judged any such exposure to be small.

Topics

Medical terms in this study, explained in our Lexicon: Mineral Fiber, energy dispersive X-ray spectroscopy (EDS), Talc, Aspect Ratio (Length-to-diameter ratio).

Related studies

• Pulmonary mineral dust. A study of ninety patients by electron microscopy, electron microanalysis, and electron microdiffraction — J.P. Berry, P. Henoc, et al. (1976)
• 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)
• Quantitative x ray microanalysis of pulmonary mineral particles in a patient with pneumoconiosis and two primary lung tumours — S. Anttila, S. Sutinen, et al. (1984)
• Electron microscopy analysis of mineral fibers in human lung tissue — K.H. Friedrichs, M. Brockmann, et al. (1992)
• Small-airway lesions in patients exposed to nonasbestos mineral dusts — A. Churg, J.L. Wright (1983)
• Fiber size and number in workers exposed to processed chrysotile asbestos, chrysotile miners, and the general population — A. Churg, B. Wiggs (1986)

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