Clearance and dimensional changes of crocidolite asbestos fibers isolated from lungs of rats following short-term exposure

Our plain-English summary of Clearance and dimensional changes of crocidolite asbestos fibers isolated from lungs of rats following short-term exposure, by V.L. Roggli, M.H. George, A.R. Brody (Environmental Research, 1987).

The study

• Authors: V.L. Roggli, M.H. George, A.R. Brody
• Journal: Environmental Research
• Published: 1987;42(1):94-105
• Cited by: 41 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. 002491).

Abstract

Previous studies in this laboratory have demonstrated fiber clearance and dimensional changes in chrysotile asbestos using a rat inhalational model of short-term exposure. The purpose of the present study was to determine whether or not similar changes occurred in crocidolite asbestos fibers isolated from the lungs of rats at various intervals after termination of exposure. Fibers were recovered on a membrane filter using a sodium hypochlorite digestion-concentration technique, and the numbers and dimensions of the fibers assessed using scanning electron microscopy. The mass of crocidolite asbestos retained in the lung was then calculated. Of the respirable fraction, 19% was deposited in the lungs, and 25% of this amount was still present 1 month after exposure. These values are similar to the 23% deposition and 19% retention rates for chrysotile determined in our previous study. There was a progressive increase in mean fiber length with time postexposure (P less than 0.05), but no significant changes in the diameter of the population of crocidolite fibers retained in the lung. Thus it appears that the tendency for longer fibers to be retained within lung tissue is a characteristic shared by serpentine and amphibole asbestos fibers, whereas longitudinal splitting with progressive decrease in mean fiber diameter in vivo occurs primarily with the serpentine fibers.

In plain English

This was an animal experiment. The authors exposed CD-1 rats, through the nose only, to an aerosol of crocidolite asbestos (a UICC reference sample) for one hour. The respirable concentrations in two separate exposures were 3.55 and 4.54 mg/m3. Rats were killed immediately afterward and at 2 days, 8 days, 4 weeks, 2 months and 3 months, usually three or four per time point. Sham-exposed rats served as controls. Fibers were recovered from lung tissue by bleach digestion, then counted and measured by scanning electron microscopy. Of the respirable mass, 19% was deposited in the lungs, and 25% of that deposited amount remained at 4 weeks. Fiber mass in the lungs fell over time. The average length of retained fibers rose from 5.04 micrometers right after exposure to 7.32 micrometers at 3 months, while average diameter did not change. Comparing these results with their earlier chrysotile study, the authors concluded that retention of longer fibers is shared by serpentine and amphibole asbestos fibers, but that splitting into thinner fibers occurs mainly with serpentine fibers.

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, single nose-only exposure, with rats killed in sequence afterward)
• Who was studied: 8-week-old CD-1 rats (Charles River Breeding Laboratories). Three or four animals were examined at each time point (0 hr, 2 days, 8 days, 4 weeks, 2 months, 3 months after exposure), except two animals at 4 weeks. Two sham-exposed rats were killed at 4 weeks.
• Exposure: UICC reference standard crocidolite asbestos, inhaled nose-only for 1 hour. Respirable mass concentrations were 3.55 and 4.54 mg/m3 in two separate exposures.
• Main results:
  • In rats killed immediately after the 1-hour exposure, 19% of the respirable mass was deposited in the lungs (3.92 micrograms, out of a total respirable mass of 21 micrograms).
  • At 4 weeks after exposure, 25% of the deposited asbestos was still present in the rats' lungs.
  • Fiber mass in both lungs decreased progressively over the period studied, and fiber numbers per gram of lung also fell.
  • Mean fiber length of retained fibers increased with time: 5.04 micrometers at 0 hr and 7.32 micrometers at 3 months. The 3-month group was significantly longer than the 0 hr, 2-day, 8-day and 2-month groups (P less than 0.01).
  • Mean fiber diameter did not change over time (0.20 micrometers at 0 hr, 0.17 micrometers at 3 months).
  • Immediately after exposure, crocidolite fibers were deposited mainly at alveolar duct bifurcations. Within 48 hours, uptake by the alveolar epithelium and transport to the interstitium could be shown.
  • Sham-exposed rats had significantly fewer fibers and less asbestos mass than every crocidolite-exposed group. The authors suggested reagent contamination as the source of those fibers.
• The authors' conclusion: The authors concluded that retention of longer fibers in lung tissue is shared by serpentine and amphibole asbestos fibers, while longitudinal splitting with a progressive decrease in fiber diameter occurs mainly with serpentine fibers. They also concluded that deposition and clearance of crocidolite were similar to what they had previously reported for chrysotile.
• Limitations the authors state:
  • The 2-month and 3-month groups received a higher exposure (4.54 mg/m3) than the earlier groups (3.55 mg/m3), so fiber numbers and mass are not strictly comparable across these groups.
  • The digestion technique had a marginally significant effect on fibers per filter (P = 0.06), suggesting some fibers were lost during processing.
  • The authors stated that the findings do not explain the preferential retention of amphiboles compared with chrysotile seen with chronic inhalation in animals or humans.

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Short-Term Exposure, Fiber Clearance, Chrysotile, Sodium Hypochlorite Digestion, Scanning Electron Microscopy (SEM), Respirable Fraction, Deposition.

Related studies

• Changes in numbers and dimensions of chrysotile asbestos fibers in lungs of rats following short-term exposure — V.L. Roggli, A.R. Brody (1984)
• Biopersistences of man-made vitreous fibers and crocidolite fibers in rat lungs following short-term exposures — R.P. Musselman, W.C. Miiller, et al. (1994)
• 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)
• 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)
• Rat lung reactivity to natural and man-made fibrous silicates following short-term exposure — I. Lemaire, P.G. Dionne, et al. (1989)

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