Significance of fibre length in the clearance of asbestos fibres from the lung

Our plain-English summary of Significance of fibre length in the clearance of asbestos fibres from the lung, by A. Morgan, R.J. Talbot, A. Holmes (British Journal of Industrial Medicine, 1978).

The study

• Authors: A. Morgan, R.J. Talbot, A. Holmes
• Journal: British Journal of Industrial Medicine
• Published: 1978;35(2):146-53
• Cited by: 61 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Rats were exposed by inhalation to radioactive anthophyllite asbestos. Animals were then killed serially over a period of 205 days and the fibre content of the lungs measured radiometrically. The lungs were subjected to selective bronchopulmonary lavage and the mean fibre content determined of free cells recovered from the alveolar spaces. The length distributions of fibres recovered from the lungs by lavage, and of those remaining in the lungs following lavage, were measured. Short (less than 5 micrometer) fibres are cleared from the lung via the conducting airways more efficiently than longer fibres and fibres exceeding 50 micrometer in length are not removed from the lungs by this route. Although fibres of about 200 micrometer in length were present in all the lungs examined, the longest which could be recovered by lavage, once fibre deposited in the airways had been cleared, was only about 100 micrometer decreasing to 60-70 micrometer after 205 days. It is suggested that long fibres are more liable than short to penetrate the alveolar wall as they tend to bridge the alveolar ducts and alveoli.

In plain English

In this animal experiment, the authors exposed 14 male albino rats by inhalation to radioactive anthophyllite asbestos on three consecutive days. They killed the rats at intervals up to 205 days. They washed out the lungs (lavage) and measured fibre in the lungs, in scavenger cells (alveolar macrophages), and fibre lengths. Lung fibre fell from about 190 micrograms after exposure to 30 micrograms at 205 days. A fitted single-exponential curve gave a half-time of 76 days, but the authors noted clearance slowed, so one constant rate did not accurately describe it over several months. Over time, fibres shorter than 5 micrometres made up a smaller share in the macrophage washes and the washed lung, and longer fibres a larger share. After a few weeks, no fibre over 50 micrometres was recovered in the first, gentler washes. Yet fibres of at least 180 micrometres were seen in every washed lung. The authors concluded that short fibres are cleared via the airways more efficiently than long ones. They suggested long fibres are more likely to penetrate the alveolar wall. They could not tell whether very long fibres stay intact.

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 with serial killing of rats and lung lavage
• Who was studied: 14 male albino rats (Wistar strain), about five months old, studied at the Atomic Energy Research Establishment, Harwell, Oxfordshire; killed from immediately after exposure up to 205 days later
• Exposure: UICC standard reference sample of anthophyllite asbestos, made radioactive by neutron irradiation, inhaled at an airborne concentration of 35 mg per cubic metre on three consecutive days
• Main results:
  • Immediately after the final exposure, the rats' lungs contained about 190 micrograms of anthophyllite, mainly in the alveolar region.
  • Lung content declined to 30 micrograms after 205 days. A least-squares single-exponential fit gave a half-time of 76 days. The authors noted from faecal measurements that elimination slowed, so a single exponential does not accurately describe it over several months.
  • Alveolar macrophages recovered by physiological saline lavage initially contained on average about 8 picograms of anthophyllite each, falling to 2 picograms after 90 days.
  • In the physiological saline washes, the proportion of fibres shorter than 5 micrometres fell steadily (78% at day 0 to 63% at day 205 in the Table), with fibres over 40 micrometres always under 0.5%.
  • In the lavaged lung lobe, the share of fibres shorter than 5 micrometres fell over time (69% at day 0 to 56% at day 205 in the Table), while the share longer than 10 micrometres rose.
  • After a few weeks, no fibre longer than 50 micrometres was recovered in the balanced salt solution washes. The authors took this to mean such fibres are not removed via the conducting airways.
  • The longest fibre recovered in physiological saline washes decreased from a little over 100 micrometres initially to 60-70 micrometres after several months.
  • In the lavaged lung, fibres of at least 180 micrometres were observed in all samples, with the median length of the longest fibres about 125 micrometres.
• The authors' conclusion: The authors suggested that long fibres are more liable than short ones to penetrate the alveolar wall, because they tend to bridge the alveolar ducts and alveoli.
• Limitations the authors state:
  • The study could not show whether very long fibres in the lung stay intact or eventually break down.
  • Because of low radioactivity in the washings, cell fibre loadings could not be accurately determined after 90 days.
  • Based on faecal measurements, the authors noted that fibre elimination over several months cannot be accurately described by a single exponential.

Topics

Medical terms in this study, explained in our Lexicon: Anthophyllite, Alveoli.

Related studies

• A comparative study of the clearance of respirable para-aramid, chrysotile and glass fibres from rat lungs — A. Searl (1997)
• Clearance of anthophyllite fibers from the rat lung and the formation of asbestos bodies — A. Holmes, A. Morgan (1980)
• An overload hypothesis for pulmonary clearance of UICC amosite fibres inhaled by rats — R.E. Bolton, J.H. Vincent, et al. (1983)
• A study of the length and diameter of fibres, in lung and in broncho-alveolar lavage fluid, following exposure of rats to chrysotile asbestos — E. Kauffer, J.C. Vigneron, et al. (1987)
• Studies on the deposition of inhaled fibrous material in the respiratory tract of the rat and its subsequent clearance using radioactive tracer techniques. 1. UICC crocidolite asbestos — J.C. Evans, R.J. Evans, et al. (1973)
• Effects of cigarette smoke on the clearance of short asbestos fibres from the lung and a comparison with the clearance of long asbestos fibres — A. Churg, J.L. Wright, et al. (1992)

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