Comparison of Calidria chrysotile asbestos to pure tremolite: inhalation biopersistence and histopathology following short-term exposure

Our plain-English summary of Comparison of Calidria chrysotile asbestos to pure tremolite: inhalation biopersistence and histopathology following short-term exposure, by D.M. Bernstein, J. Chevalier, P. Smith (Inhalation Toxicology, 2003).

The study

• Authors: D.M. Bernstein, J. Chevalier, P. Smith
• Journal: Inhalation Toxicology
• Published: 2003;15(14):1387-419
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The differences between chrysotile asbestos, a serpentine mineral, and amphibole asbestos have been debated extensively. Many studies have shown that chrysotile is cleared from the lung more rapidly than amphibole. In order to quantify the comparative clearance of chrysotile and the amphibole asbestos tremolite, both fibers were evaluated in an inhalation biopersistence study that followed the European Commission recommended guidelines. In addition, the histopathological response in the lung was evaluated following the short-term exposure. This article presents the results of this study through 90 days after cessation of exposure. Following the termination of the study, a subsequent article will provide the complete results through 12 mo after cessation of exposure. In order to quantify the dynamics and rate by which these fibers are removed from the lung, the biopersistence of a sample of commercial grade chrysotile from the Coalinga mine in New Idria, CA, of the type Calidria RG144 and of a long-fiber tremolite were studied. For synthetic vitreous fibers, the biopersistence of the fibers longer than 20 microm has been found to be directly related to their potential to cause disease. This study was designed to determine lung clearance (biopersistence) and the histopathological response. As the long fibers have been shown to have the greatest potential for pathogenicity, the aerosol generation technique was designed to maximize the number of long respirable fibers. The chrysotile samples were specifically chosen to have 200 fibers/cm3 longer than 20 microm in length present in the exposure aerosol. These longer fibers were found to be largely composed of multiple shorter fibrils. The tremolite samples were chosen to have 100 fibers/cm3 longer than 20 microm in length present in the exposure aerosol. Calidria chrysotile fibers clear from the lung more rapidly (T1/2, fibers L > 20 microm = 7 h) than any other commercial fiber tested including synthetic vitreous fibers. With such rapidly clearing fibers, the 5-day exposure would not be expected to result in any pathological change in the lung, and the lungs of animals that inhaled Calidria chrysotile showed no sign of inflammation or pathology and were no different than the lungs of those animals that breathed filtered air. Following this 5-day exposure to tremolite, the tremolite fibers once deposited in the lung parenchyma do not clear and almost immediately result in inflammation and a pathological response in the lung. At the first time point examined, 1 day after cessation of exposure, inflammation was observed and granulomas were already formed. By 14 days postexposure these microgranulomas had turned fibrotic, and by 90 days postexposure the severity of the collagen deposits had increased and interstitial fibrosis was observed in one of the rats. These findings provide an important basis for substantiating both kinetically and pathologically the differences between chrysotile and the amphibole tremolite. As Calidria chrysotile has been certified to have no tremolite fiber, the results of the current study together with the results from toxicological and epidemiological studies indicate that this fiber is not associated with lung disease.

In plain English

In this animal experiment, male rats breathed Calidria chrysotile asbestos (type RG144, from the Coalinga mine in New Idria, California), tremolite asbestos, or filtered air through the nose for 6 hours a day on 5 consecutive days. The article reported results through 90 days after exposure. Results at 6 and 12 months were still to be completed. Chrysotile fibers longer than 20 µm cleared from the lungs with a half-time of 0.3 days (7 hours), and chrysotile fibers 5 to 20 µm long with a half-time of 7 days. Long tremolite fibers stopped clearing after about the first week, and about 0.6 million remained in the lung through 90 days. Chrysotile-exposed lungs showed no exposure-related microscopic findings and no statistically significant weight difference from air controls. Tremolite-exposed rats had statistically significantly heavier lungs, granulomas by day 1, collagen deposits in granulomas by day 14, and interstitial fibrosis in one rat at 90 days. The authors concluded that their results, together with other toxicological and epidemiological studies, indicate Calidria chrysotile is not associated with lung disease.

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: short-term (5-day) inhalation biopersistence and lung histopathology study in rats, with results reported through 90 days after exposure
• Who was studied: Groups of 56 male Wistar rats about 8 weeks old for each fiber, plus a control group that breathed filtered air. Subgroups were examined at set times: 5 rats per group per time point for lung fiber counts, and 3 to 5 rats per group for histopathology.
• Exposure: Calidria RG144 chrysotile from the Coalinga mine, New Idria, CA, at a target of 200 fibers longer than 20 µm per cm3, and tremolite at a target of 100 fibers longer than 20 µm per cm3. Exposure was nose-only, 6 h/day for 5 consecutive days. The mean total fiber counts were 48,343 fibers/cm3 for chrysotile and 3128 fibers/cm3 for tremolite.
• Main results:
  • In chrysotile-exposed rats, fibers longer than 20 µm cleared from the lung with a half-time of 0.3 days (7 h).
  • In chrysotile-exposed rats, fibers 5 to 20 µm long cleared with a half-time of 7 days. Objects shorter than 5 µm cleared with a half-time of 59 days.
  • In tremolite-exposed rats, long fibers (longer than 20 µm) showed early clearance that appeared finished by 7 days. After that there was no further clearance, with approximately 0.6 million fibers longer than 20 µm remaining in the lung through 90 days.
  • Lung weights showed no statistically significant differences between the air control and Calidria chrysotile groups at any time point. Tremolite-exposed rats had a statistically significant increase in mean lung weight compared with both the air control and chrysotile groups from day 1 through 90 days.
  • No microscopic findings related to Calidria chrysotile exposure were observed at any time point. Foam-cell aggregation seen in a few chrysotile rats was considered common in control rats and not exposure related.
  • In tremolite-exposed rats, a granulomatous response was present at 1 day after exposure (granulomas in 5 of 5 rats examined).
  • In tremolite-exposed rats, collagen deposition (fibrosis) in microgranulomas was found at 14 days (4 of 5 rats) and at 90 days (4 of 4 rats, with severity up to grade 3).
  • At 90 days, interstitial fibrosis (interstitial collagen deposition) was seen in 1 of the 4 tremolite-exposed rats examined.
• The authors' conclusion: The authors concluded that, because Calidria chrysotile has been certified to contain no tremolite fiber, the results of this study together with results from other toxicological and epidemiological studies indicate that this fiber is not associated with lung disease.
• Limitations the authors state:
  • The 6-month and 12-month time points had not yet been completed and were to be reported later.
  • Because the whole lung was digested, the authors could not tell in which parts of the body (for example, the lymphatics) the shorter chrysotile objects remained.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Santa Rita mine, Joaquin Ridge near Coalinga, California

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Calidria, Chrysotile, Tremolite, biopersistence, Histopathology, Short-Term Exposure, Serpentine Group, Amphibole Asbestos.

Related studies

• 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)
• 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)
• 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: interim results — D.M. Bernstein, R.A. Rogers, et al. (2010)
• The biopersistence of Canadian chrysotile asbestos following inhalation — D.M. Bernstein, R. Rogers, et al. (2003)
• The biopersistence of Canadian chrysotile asbestos following inhalation: final results through 1 year after cessation of exposure — D. Bernstein, R. Rogers, et al. (2005)

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