A biopersistence study following exposure to chrysotile asbestos alone or in combination with fine particles

Our plain-English summary of A biopersistence study following exposure to chrysotile asbestos alone or in combination with fine particles, by D.M. Bernstein, K. Donaldson, U. Decker, et al (Inhalation Toxicology, 2008).

The study

• Authors: D.M. Bernstein, K. Donaldson, U. Decker, S. Gaering, P. Kunzendorf, J. Chevalier, S.E. Holm
• Journal: Inhalation Toxicology
• Published: 2008;20(11):1009-28
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

In designing a study to evaluate the inhalation biopersistence of a chrysotile asbestos that was used as a component of a joint-compound, a feasibility study was initiated to evaluate the short-term biopersistence of the chrysotile alone and of the chrysotile in combination with the sanded reformulated joint-compound. Two groups of Wistar rats were exposed to either 7RF3 chrysotile (Group 2) or to 7RF3 chrysotile combined with aerosolized sanded joint-compound (Group 3). In addition, a control group was exposed to filtered-air. The chrysotile used in the Ready Mix joint compound is rapidly removed from the lung. The chrysotile alone exposure group had a clearance half-time of fibers L > 20 microm of 2.2 days; in the chrysotile plus sanded exposure group the clearance half-time of fibers L > 20 microm was 2.8 days. However, across all size ranges there was approximately an order of magnitude decrease in the mean number of fibers remaining in the lungs of Group 3 as compared to Group 2 despite similiar aerosol exposures. Histopathological examination showed that the chrysotile exposed lungs had the same appearance as the filtered-air controls. This study uniquely illustrates that additional concurrent exposure to an aerosol of the sanded joint-compound, with large numbers of fine-particles depositing in the lungs, accelerates the recruitment of macrophages, resulting in a tenfold decrease in the number of fibers remaining in the lung. The increased number of macrophages in the chrysotile/sanded joint exposure group was confirmed histologically, with this being the only exposure-related histological finding reported.

In plain English

This was a feasibility study in rats, preparing for a larger study of chrysotile asbestos in wallboard joint compound. Because the original grade's mine had closed, it used grade 7RF3, judged most similar, as a substitute. Male rats breathed through the nose only, 6 hours a day for 5 days: filtered air, 7RF3 chrysotile, or chrysotile mixed with dust from a sanded, reformulated joint compound. Chrysotile in the two groups' air did not differ significantly. Right after exposure, rats given chrysotile alone had a mean of 27.2 million WHO fibers in their lungs, versus 2.3 million with sanded dust added. For fibers longer than 20 µm, the clearance half-time was 2.2 days with chrysotile alone and 2.8 days with the mixture; these rested on two time points and were not statistically different. On microscopic examination, chrysotile-alone lungs showed no exposure-related findings; in the mixed group, minimal alveolar macrophages appeared in 2 of 3 rats. The authors concluded that more macrophages, and potentially more acidic conditions inside them, could explain faster shortening and clearance of chrysotile during the ongoing mixed exposure.

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: Short-term inhalation biopersistence feasibility study in rats (animal experiment)
• Who was studied: Male weanling rats aged 8 to 10 weeks, in groups of 14, in three exposure groups (filtered-air controls, chrysotile alone, chrysotile plus sanded joint compound)
• Exposure: Nose-only inhalation for 6 hours a day for 5 days of filtered air (group 1), chrysotile 7RF3 (group 2), or chrysotile 7RF3 mixed with sanded reformulated joint compound powder (M971/974) (group 3). Mean fibers longer than 20 µm in the air were 1055 fibers/cm3 (group 2) and 912 fibers/cm3 (group 3).
• Main results:
  • The original joint compound used chrysotile grade 7RF9 from a mine no longer in operation. Johns Manville 7RF3 was used instead, because it was considered most similar in fiber length and diameter to the historical 7RF9.
  • The chrysotile in the air breathed by group 2 and group 3 did not differ significantly in fiber number or size
  • Immediately after exposure (day 0), the mean was 27.2 million WHO fibers per lung in group 2 (chrysotile alone) and 2.3 million in group 3 (chrysotile plus sanded powder)
  • At day 0, the mean number of fibers longer than 20 µm was 0.44 million in group 2 and 0.037 million in group 3
  • At 3 days after exposure, the mean number of fibers longer than 20 µm was 0.17 million in group 2 and 0.018 million in group 3
  • The clearance half-time of fibers longer than 20 µm was 2.2 days in group 2 and 2.8 days in group 3. The authors stated these two values were not statistically different.
  • The clearance half-time of fibers 5 to 20 µm long was 4.9 days in group 2 and 10.7 days in group 3, also not statistically different
  • On histopathological (microscopic) examination at the end of exposure, group 2 (chrysotile alone) had no exposure-related findings
  • In group 3 (chrysotile plus sanded powder), minimal alveolar macrophages were noted in 2 of the 3 rats examined
  • At 3 days after exposure, no exposure-related histopathological findings were seen in either exposed group
• The authors' conclusion: The authors concluded that the lower fiber numbers in group 3 at the end of exposure reflected more efficient clearance during the ongoing combined exposure. They proposed that greater numbers of macrophages, and potentially a more acidic environment inside them, could explain the faster shortening and clearance of chrysotile during that exposure.
• Limitations the authors state:
  • The clearance half-times were calculated from only two time points
  • The lung digestion method counts all fibers in the lung and cannot tell which fibers would have been cleared to the lymphatics or airways
  • Sample preparation dissolved the limestone particles that made up most of the joint compound filler, so these particles could not be counted in the air or lung samples
  • Fiber recovery was not validated within this study; the authors said a comparison with a noninvasive technique is planned for the main study

Topics

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

Medical terms in this study, explained in our Lexicon: biopersistence, Chrysotile, Joint Compound, Macrophage.

Related studies

• 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)
• 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)
• Comparison of Calidria chrysotile asbestos to pure tremolite: inhalation biopersistence and histopathology following short-term exposure — D.M. Bernstein, J. Chevalier, 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)

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