Clearance of anthophyllite fibers from the rat lung and the formation of asbestos bodies

Our plain-English summary of Clearance of anthophyllite fibers from the rat lung and the formation of asbestos bodies, by A. Holmes, A. Morgan (Environmental Research, 1980).

The study

• Authors: A. Holmes, A. Morgan
• Journal: Environmental Research
• Published: 1980;22(1):13-21
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The length distributions of both uncoated and coated fibers in the rat lung were measured at various times up to ? years following exposure to anthophyllite asbestos by inhalation. Fibers were measured by optical microscopy using a membrane filter technique which enables fibers with diameters down to about 0.2 μm to be detected. The frequency of uncoated fibers less than 5 μm in length decreased from 5% at 100 days after exposure to 19% after 2 years. These findings confirm and extend earlier investigations which showed that fibers in this length range are cleared more efficiently from the lung than longer fibers. The length distributions of uncoated and coated fibers were dissimilar. No coated fiber <10 μm in length was detected at any time and the greatest frequency invariably occurred in the 40- to 80-μm range. All fibers longer than 80 μm appeared to be coated. Although the appearance of coated fibers in the rat lung differs from those in human lung, there are similarities in the length distributions of uncoated and coated fibers.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This was an animal experiment. The authors exposed rats by nose-only inhalation to the UICC standard reference sample of anthophyllite asbestos. They examined lung fibers from one rat killed at each of 100 days, 247 days, 332 days and 2 years after exposure. The first three were exposed for 30 minutes, the last for 3 hours on each of 5 consecutive days. Using optical microscopy, the authors measured uncoated and coated fibers (asbestos bodies). Among uncoated fibers, the share shorter than 5 micrometers fell from 52% at 100 days to 19% at 2 years. The authors took this as confirming that short fibers are cleared more efficiently. No coated fiber shorter than 10 micrometers was found. Coated fibers were most common at 40 to 80 micrometers, and all fibers longer than 80 micrometers appeared coated. Most bodies appeared to form during the first year. Rat coatings looked different from human ones. The authors noted shared length features. For example, no coated fibers under 10 micrometers were found in these rats, and the authors cited reports that such bodies are rarely found in human lung. In human lung, they wrote, coated amphibole fibers generally peak at 20 to 40 micrometers.

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 (inhalation exposure of rats, with fibers recovered from lung tissue and measured by optical microscopy)
• Who was studied: Rats of an inbred strain from the Medical Research Council Radiobiology Unit, Harwell, 5 months old and about 350 g at exposure. The results table lists four rats (Rat No. 1 to 4), killed at 100 days, 247 days, 332 days and 2 years.
• Exposure: UICC standard reference sample of anthophyllite asbestos, given by nose-only inhalation. The first three rats killed were exposed for 30 minutes, estimated to deposit about 20 micrograms in the alveolar region. The rat killed at 2 years was exposed for 3 hours on each of 5 consecutive days, estimated to deposit about 300 micrograms.
• Main results:
  • Among uncoated fibers in the rat lungs, the frequency of fibers shorter than 5 micrometers was 52% after 100 days and 19% after 2 years. The article reports 79% in the dust cloud the animals breathed, a figure taken from the authors' earlier study.
  • The count median length of uncoated fibers increased from about 5 micrometers at 100 days to 11 micrometers at 2 years. The table values were 4.7, 6.0, 6.5 and 11.0 micrometers.
  • The frequency of uncoated fibers 5 to 10 micrometers long stayed relatively constant, while all longer length categories increased in frequency. No uncoated fibers longer than 80 micrometers were found in any animal.
  • No coated fiber shorter than 10 micrometers was found. Coated fibers were most frequent in the 40 to 80 micrometer range, with count median lengths between 50 and 60 micrometers. About 20% of coated fibers were longer than 80 micrometers.
  • After 2 years in the rat lung, the probability of a fiber being coated was 100% for fibers longer than 80 micrometers, 7% for fibers 40 to 80 micrometers long, and less than 1% for shorter categories.
  • The ratio of uncoated fibers longer than 5 micrometers to coated fibers indicated that most asbestos bodies formed during the first year after exposure.
  • Coatings on anthophyllite fibers in rat lungs were discontinuous, often in globules, and very pale yellow (almost white). They differed from the golden yellow-brown asbestos bodies seen in human lung. Bodies from rats exposed to crocidolite, amosite and a synthetic nickel chromium fluoramphibole looked similar to those on anthophyllite.
• The authors' conclusion: The authors concluded that fibers shorter than 5 micrometers are cleared relatively efficiently from the rat lung, and that the probability of a fiber becoming coated increases with its length. Coated fibers in rats look different from those in human lung. Even so, the authors reported similarities in the length distributions and listed specific features. No coated fibers under 10 micrometers were found in the rats, and such bodies are rarely found in human lung. No uncoated fibers longer than 80 micrometers were found in the rats, and such fibers are rarely encountered in human lung. They also noted a difference in the peak: 40 to 80 micrometers for coated fibers in these rats, and generally 20 to 40 micrometers for coated amphibole fibers in human lung.
• Limitations the authors state:
  • Fibers shorter than 2 micrometers could not be reliably detected by optical microscopy, so they were not counted.
  • The data do not rule out that fibers longer than 10 micrometers are also cleared from the lung, though less effectively.

Topics

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

Medical terms in this study, explained in our Lexicon: Anthophyllite, Asbestos Bodies, Membrane Filter Method.

Related studies

• Formation of pseudo-asbestos bodies on sized glass fibres in the hamster lung — A. Holmes, A. Morgan, et al. (1983)
• Solubility of rockwool fibres in vivo and the formation of pseudo-asbestos bodies — A. Morgan, A. Holmes (1984)
• Asbestos-body formation in the lungs of rats and guinea-pigs after inhalation of anthophyllite — S.K. Botham, P.F. Holt (1972)
• The distribution and characteristics of asbestos fibers in the lungs of Finnish anthophyllite mine-workers — A. Morgan, A. Holmes (1984)
• Significance of fibre length in the clearance of asbestos fibres from the lung — A. Morgan, R.J. Talbot, et al. (1978)
• Clearance of asbestos bodies from the lung: a personal view — K.J. Arul, P.F. Holt (1980)

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