The biopersistence of Canadian chrysotile asbestos following inhalation: final results through 1 year after cessation of exposure

Our plain-English summary of The biopersistence of Canadian chrysotile asbestos following inhalation: final results through 1 year after cessation of exposure, by D. Bernstein, R. Rogers, P. Smith (Inhalation Toxicology, 2005).

The study

• Authors: D. Bernstein, R. Rogers, P. Smith
• Journal: Inhalation Toxicology
• Published: 2005;17(1):1-14
• Cited by: 43 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Chrysotile asbestos, a serpentine mineral, has been shown to be notably different from amphibole asbestos such as amosite, crocidolite, and tremolite in that chrysotile once inhaled is rapidly removed from the lung while the amphiboles persist. This has been demonstrated for three different chrysotile samples from Canada, the United States, and Brazil. The initial results of the inhalation biopersistence study on the Canadian chrysotile were reported earlier. This article presents the full results through 365 days after cessation of exposure. In order to fully understand the dynamics of the clearance of chrysotile from the lung, the study included a standardised inhalation biopersistence study following the recommendations of the European Commission (EC) Interim Protocol for the Inhalation Biopersistence of synthetic mineral fibers (Bernstein & Riego-Sintes, 1999) in which the lungs were digested to evaluate fiber content remaining. In addition, confocal microscopy was used to examine lungs in three dimensions to determine where and what size the remaining fibers were in the lung tissue. The results showed that Canadian chrysotile is cleared from the lung with a clearance half-time of 11.4 days for the fibers longer than 20 microm. Canadian chrysotile clears in a range similar to that of glass and stone wools. It remains less biopersistent than ceramic and special purpose glasses and considerably less biopersistent than amphibole asbestos. At 1 yr after cessation of exposure, no long (L>20 microm) chrysotile fibers remained in the lung. In contrast, with amosite asbestos there were 4 x 10 (5) long fibers (L>20 microm) remaining in the lungs at one year after cessation of exposure (Hesterberg et al., 1998). These results fully support the differentiation of chrysotile from amphiboles reported in recent evaluations of available epidemiological studies (Hodgson & Darnton, 2000; Berman & Crump, 2004).

In plain English

In this animal experiment, groups of 56 young male Wistar rats breathed textile-grade chrysotile asbestos from Québec, Canada, through the nose for 6 hours a day on 5 consecutive days; a control group breathed filtered air. The researchers measured fibers left in the lungs at time points up to 12 months afterward, and used confocal microscopy to locate fibers in lung tissue. Fibers longer than 20 micrometers (µm) cleared with a half-time of 11.4 days, fibers 5 to 20 µm in 29.7 days, and fibers shorter than 5 µm in 108.4 days. At 12 months no fibers longer than 20 µm were found; the longest was 15.5 µm. By microscopy, 92% of the fibers present at 1 day had cleared by 1 month, and neutrophils, a type of inflammatory cell, were not seen free in the air sacs. The authors concluded that this and other chrysotile studies clearly differentiate chrysotile from amphibole asbestos. They acknowledged that their results appear to contradict many other investigators, and that there is evidence humans develop lung cancer from high, long-lasting exposure to chrysotile.

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: Animal experiment: an inhalation biopersistence study in rats following European Commission guidelines. Whole lungs were digested and examined by transmission electron microscopy, and confocal microscopy was used to locate fibers in lung tissue.
• Who was studied: Groups of 56 weanling (about 9 weeks old) male Wistar rats, specific pathogen free, supplied by RCC Ltd, Füllinsdorf, Switzerland, plus a negative control group exposed to filtered air. Five lungs were analyzed at each time point for fiber counts. Study dates were not stated.
• Exposure: Commercial textile-grade Canadian chrysotile from the Eastern Townships of Québec, given by nose-only inhalation for 6 hours a day on 5 consecutive days. The target was 200 fibers longer than 20 µm per cubic centimeter, twice the EC protocol requirement. Total fibers in the exposure air were 14,805 per cubic centimeter.
• Main results:
  • Chrysotile fibers longer than 20 µm cleared from the rat lungs with a clearance half-time of 11.4 days.
  • Chrysotile fibers 5 to 20 µm long had a clearance half-time of 29.7 days.
  • Chrysotile fibers shorter than 5 µm had a clearance half-time of 108.4 days, which the authors described as similar to or faster than the clearance of insoluble nuisance dusts.
  • At 12 months (1 year) after exposure ended, no chrysotile fibers longer than 20 µm remained in the lungs. The longest fiber present was 15.5 µm.
  • By confocal microscopy, 92% of the fibers seen at 1 day after exposure had been cleared from the lungs by 1 month after exposure.
  • At 1 day after exposure, 68% of the fibers and particles seen by confocal microscopy were inside alveolar macrophages. The parenchyma held 99% of the total fiber load at all time points.
  • Neutrophils were not seen free in the alveolar spaces in any of the lung volumes examined by confocal microscopy.
• The authors' conclusion: The authors concluded that this and other chrysotile biopersistence studies clearly differentiate serpentine chrysotile from amphibole asbestos. They stated that Canadian chrysotile clears in a range similar to glass and stone wools and is considerably less biopersistent than amphibole asbestos.
• Limitations the authors state:
  • The authors acknowledged that their results appear to contradict those of many other investigators, and that there is evidence humans develop lung cancer from high, long-sustained chrysotile exposure.
  • The lung digestion method processes the whole lung, so it cannot show where in the lung the fibers were located.
  • Some fibers were too thin to be detected by the confocal microscope.
  • The slow clearance half-time for fibers shorter than 5 µm may be strongly influenced by longer fibers breaking apart into short ones.

Topics

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

Medical terms in this study, explained in our Lexicon: biopersistence, Chrysotile, Serpentine Group, Amphibole Asbestos, Amosite, Crocidolite, Tremolite, Amphibole Group.

Related studies

• The biopersistence of Canadian chrysotile asbestos following inhalation — D.M. Bernstein, R. Rogers, et al. (2003)
• The biopersistence of brazilian chrysotile asbestos following inhalation — D.M. Bernstein, R. Rogers, et al. (2004)
• Comparison of Calidria chrysotile asbestos to pure tremolite: final results of the inhalation biopersistence and histopathology examination following short-term exposure — D.M. Bernstein, J. Chevalier, et al. (2005)
• Comparison of Calidria chrysotile asbestos to pure tremolite: inhalation biopersistence and histopathology following short-term exposure — D.M. Bernstein, J. Chevalier, et al. (2003)
• Evaluation of the deposition, translocation and pathological response of brake dust with and without added chrysotile in comparison to crocidolite asbestos following short-term inhalation: interim results — D.M. Bernstein, R. Rogers, et al. (2014)
• Quantification of the pathological response and fate in the lung and pleura of chrysotile in combination with fine particles compared to amosite-asbestos following short-term inhalation exposure — D.M. Bernstein, R.A. Rogers, et al. (2011)

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