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

Our plain-English summary of 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, by D.M. Bernstein, R. Rogers, R. Sepulveda, et al (Toxicology and Applied Pharmacology, 2014).

The study

• Authors: D.M. Bernstein, R. Rogers, R. Sepulveda, P. Kunzendorf, B. Bellmann, H. Ernst, J.I. Phillips
• Journal: Toxicology and Applied Pharmacology
• Published: 2014;276(1):28-46
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Chrysotile has been frequently used in the past in manufacturing brakes and continues to be used in brakes in many countries. This study was designed to provide an understanding of the biokinetics and potential toxicology following inhalation of brake dust following short term exposure in rats. The deposition, translocation and pathological response of brake dust derived from brake pads manufactured with chrysotile were evaluated in comparison to the amphibole, crocidolite asbestos. Rats were exposed by inhalation 6 h/day for 5 days to either brake dust obtained by sanding of brake-drums manufactured with chrysotile, a mixture of chrysotile and the brake dust or crocidolite asbestos. No significant pathological response was observed at any time point in either the brake dust or chrysotile/brake dust exposure groups. The long chrysotile fibers (>20 μm) cleared quickly with T(½) estimated as 30 and 33 days, respectively in the brake dust and the chrysotile/brake dust exposure groups. In contrast, the long crocidolite fibers had a T(½)>1000 days and initiated a rapid inflammatory response in the lung following exposure resulting in a 5-fold increase in fibrotic response within 91 days. These results provide support that brake dust derived from chrysotile containing brake drums would not initiate a pathological response in the lung following short term inhalation.

Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.

In plain English

This animal inhalation study in male Wistar rats reported interim lung results through 91 days after exposure. For 6 hours a day over 5 days, rats breathed filtered air, dust from grinding drum brake shoes whose friction material contained about 30% chrysotile by area, that brake dust with added chrysotile, or crocidolite asbestos. Chrysotile fibers longer than 20 micrometres had estimated lung clearance half-times of 33 days in the added-chrysotile group and 30 days in the brake-dust-alone group. Long crocidolite fibers had an estimated half-time greater than 1000 days. Both brake dust groups showed slight build-up of particle-laden macrophages and Wagner scores of 1 to 2. Confocal connective-tissue measurements in both brake dust groups showed no statistically significant trends versus air controls. In the crocidolite group, interstitial fibrosis was seen by day 32, the Wagner score reached 4, and mean connective tissue at 91 days was 5 times that of air controls. The authors concluded that brake dust from chrysotile-containing brake drums would not initiate a pathological response in the lung after short-term inhalation. Later time points and pleural results were to be published separately.

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 inhalation experiment (short-term exposure in rats); interim results on the lung through 91 days after exposure
• Who was studied: Male Wistar rats, 8 to 10 weeks old at exposure, in four groups, studied at the Fraunhofer Institute for Toxicology and Experimental Medicine, Hannover, Germany. The exposure system held 16 animals per level. The article does not state a clear total number of rats or the study dates.
• Exposure: Nose-only inhalation for 6 hours a day for 5 days. Group 1 breathed filtered air. Group 2 breathed brake dust mixed with grade 5R04 Canadian chrysotile (3.48 mg/m3; mean 189 fibers longer than 20 micrometres per cm3). Group 3 breathed brake dust alone (1.52 mg/m3; about 3 fibers longer than 20 micrometres per cm3). Group 4 breathed crocidolite asbestos from the Voorspoed mine, South Africa (6.34 mg/m3; mean 93 fibers longer than 20 micrometres per cm3). The brake dust came from grinding Bendix drum brake shoes whose friction material contained about 30% chrysotile by area.
• Main results:
  • Estimated lung clearance half-times for chrysotile fibers longer than 20 micrometres were 33 days in the brake dust with added chrysotile group and 30 days in the brake dust alone group.
  • In the crocidolite group, long fibers remaining in the lung parenchyma had an estimated clearance half-time greater than 1000 days.
  • In the brake dust with added chrysotile group and the brake dust alone group, slight accumulation of particle-laden macrophages was seen from 7 through 91 days. Very slight particle-laden microgranulomas were seen at 32 days, with no associated giant cells.
  • In the crocidolite group, interstitial fibrosis was observed by day 32.
  • The Wagner score was 1 to 2 in both brake dust groups through 91 days. In the crocidolite group it rose from 2 at day 0 to 4.
  • Connective tissue measured by confocal microscopy showed no statistically significant trends in either brake dust group compared with air controls.
  • In the crocidolite group, mean percent connective tissue was 4.4 (plus or minus 3.4) at day 0, 8.0 (plus or minus 4.4) at 32 days and 14.7 (plus or minus 12.8) at 91 days. At 91 days this was 5 times the air control mean.
  • The particle clearance half-time in the brake dust with added chrysotile group was 510 days. The authors suggested the combined exposure exceeded the lung's ability to clear the particles.
• The authors' conclusion: The authors concluded that the study provides in-vivo toxicological support that brake dust derived from chrysotile-containing brake drums would not initiate a pathological response in the lung following short-term inhalation, in contrast to crocidolite asbestos.
• Limitations the authors state:
  • These are interim lung results only. Results through 365 days, including pleural translocation and response, were to be published separately.
  • The study did not examine possible effects of co-exposures that may occur alongside brake dust exposure.
  • Whole-lung fiber counts from confocal microscopy are estimates, affected by fiber orientation and how inflated the lungs were.
  • The lung digestion method cannot show where in the lung the fibers are located.

Topics

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

Medical terms in this study, explained in our Lexicon: Deposition, Translocation, Chrysotile, Crocidolite, Brake Lining, Amphibole Group.

Related studies

• Evaluation of the fate and pathological response in the lung and pleura of brake dust alone and in combination with added chrysotile compared to crocidolite asbestos following short-term inhalation exposure — D.M. Bernstein, R.A. Rogers, et al. (2015)
• Evaluation of the exposure, dose-response and fate in the lung and pleura of chrysotile-containing brake dust compared to TiO2, chrysotile, crocidolite or amosite asbestos in a 90-day quantitative inhalation toxicology study - Interim results Part 1: Experimental design, aerosol exposure, lung burdens and BAL — D.M. Bernstein, B. Toth, et al. (2020)
• Evaluation of the dose-response and fate in the lung and pleura of chrysotile-containing brake dust compared to TiO2, chrysotile, crocidolite or amosite asbestos in a 90-day quantitative inhalation toxicology study - Interim results Part 2: Histopathological examination, Confocal microscopy and collagen quantification of the lung and pleural cavity — D.M. Bernstein, B. Toth, et al. (2020)
• 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)
• Evaluation of the dose-response and fate in the lung and pleura of chrysotile-containing brake dust compared to chrysotile or crocidolite asbestos in a 28-day quantitative inhalation toxicology study — D.M. Bernstein, B. Toth, et al. (2018)
• 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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