Fiber exposure reassessed with the new indices

Our plain-English summary of Fiber exposure reassessed with the new indices, by T. Schneider, J. Skotte (Environmental Research, 1990).

The study

• Authors: T. Schneider, J. Skotte
• Journal: Environmental Research
• Published: 1990;51(1):108-16
• Cited by: 11 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. 000038).

Abstract

The concentration of airborne fibers longer than 5 microns, thinner than 3 microns, and with an aspect ratio exceeding 3 as counted by phase contrast optical microscopy is the most widely used fiber exposure index. Recently, more adequate, specific exposure indices for asbestosis, lung cancer, and mesothelioma risk have been suggested by Lippmann (1988, Environ. Res., 46, 86-106). The consequences of using these indices are examined on the basis of calculations for a broad range of theoretical and published size distributions. Optical microscopy appears to be a good predictor of the exposure indices for asbestosis and for lung cancer after scaling. Only fibers longer than about 3 microns need to be counted in a transmission electron microscope. The lung cancer index still cannot explain the large differences of risk among chrysotile exposures. Both the mesothelioma exposure index and the ratio mesothelioma to lung cancer index ranks in order of increasing risk: wollastonite, glass and mineral wool, amosite, glass microfibers, chrysotile, and crocidolite. Amosite is thus not ranked according to epidemiological evidence. Detailed size information should be made available so that the size criteria can be adjusted. It may still prove necessary to use fiber type specific concentration limits.

In plain English

This was a calculation study, not a study of people. The authors examined Lippmann's 1988 fiber-size indices for asbestosis, lung cancer and mesothelioma. They compared these with the standard optical-microscope count of 'regulated fibers,' using theoretical and published fiber size distributions. The asbestosis index ran about 1 to 4 times the regulated count, with exceptions for very thick or very thin fibers with narrow size distributions. The lung cancer index could be estimated as 0.6 times the regulated count, within half to twice that estimate, except for narrow size distributions with extreme length-to-diameter ratios. It did not explain differing lung cancer risks among chrysotile exposures. The mesothelioma index varied over 4 orders of magnitude for the same regulated count. It ranked mesothelioma risk, lowest to highest: wollastonite, conventional mineral wool, amosite, glass microfibers, chrysotile, crocidolite. The authors noted that amosite came out too low compared with epidemiological evidence. Short tremolite fibers scored low for lung cancer and higher for mesothelioma. The authors concluded that, for assessing health risk, only fibers longer than about 3 micrometers need transmission electron microscope counting.

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: Theoretical calculation (modeling) study of fiber size distributions; no human or animal subjects
• Who was studied: No people were studied. The authors used modeled (bivariate log-normal) fiber size distributions, with median diameter varied from 0.0313 to 2 micrometers and median length from 1.25 to 20 micrometers. They also used size distributions published in the literature for specific fiber types.
• Exposure: Airborne fiber size categories: the standard regulated fiber count, Stanton fibers, Pott fibers, and Lippmann's asbestosis, lung cancer and mesothelioma indices. Fiber types in the published examples included wollastonite, conventional mineral wool, glass microfibers, amosite, chrysotile, crocidolite and short tremolite fibers.
• Main results:
  • Across realistic theoretical size distributions, the asbestosis index was about 1 to 4 times the regulated fiber count.
  • For the prediction of the asbestosis index from regulated fibers, the authors named exceptions: very thick or very thin fibers with narrow size distributions.
  • The lung cancer index could be predicted as 0.6 times the regulated fiber count, with the true value within 0.5 and 2 times the prediction.
  • For the lung cancer prediction, the authors named exceptions: narrow size distributions with extreme median aspect ratios (length to diameter).
  • The lung cancer index did not predict differences in relative lung cancer risk within chrysotile exposure.
  • For the same regulated fiber count, the mesothelioma index varied over 4 orders of magnitude. The authors wrote that mesothelioma risk cannot be assessed by optical microscopy.
  • The mesothelioma index ranked relative risk, in increasing order: wollastonite, conventional mineral wool, amosite, glass microfibers, chrysotile, crocidolite.
  • Compared with epidemiological evidence, amosite came out with too low a mesothelioma risk. The ratio of mesothelioma to lung cancer was also not ranked correctly.
  • Short tremolite fibers showed low relative lung cancer risk and higher relative mesothelioma risk.
  • The regulated fiber count was not a good predictor of Pott fibers.
• The authors' conclusion: The authors concluded that the optical-microscope regulated fiber count is a good predictor of the asbestosis and lung cancer indices after scaling. They concluded that, for assessing fiber-related health risk, only fibers longer than about 3 micrometers need to be evaluated by transmission electron microscope. They also concluded that, with more detailed size data, the size criteria might be adjusted to better match epidemiology.
• Limitations the authors state:
  • The mesothelioma-to-regulated-fiber ratio comes from the tails of the size distributions, where the fit may be poor.
  • The fiber-type-specific examples were based on a limited number of size distributions.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite, Chrysotile, Crocidolite.

Medical terms in this study, explained in our Lexicon: Aspect Ratio (Length-to-diameter ratio), Lung Cancer, Mesothelioma, Chrysotile, Wollastonite, Amosite, Crocidolite.

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