Solubility of rockwool fibres in vivo and the formation of pseudo-asbestos bodies

Our plain-English summary of Solubility of rockwool fibres in vivo and the formation of pseudo-asbestos bodies, by A. Morgan, A. Holmes (The Annals of Occupational Hygiene, 1984).

The study

• Authors: A. Morgan, A. Holmes
• Journal: The Annals of Occupational Hygiene
• Published: 1984;28(3):307-14
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Sized rockwool fibres were administered to rats by intratracheal instillation to study their solubility in the lung, and also to hamsters to study the formation of pseudo-asbestos bodies. Rats were killed serially and the fibres recovered by digesting lungs with hypochlorite solution. Count median diameters (CMDs) of the recovered fibres were measured at their centres with the light microscope and, after 18 months, there was no significant change in CMD. Even after six months, however, it was apparent that fibres were becoming thinner at their ends than in the middle so that slow dissolution does occur. The formation of pseudo-asbestos bodies on rockwool fibres in the hamster lung followed a similar time course to that for anthophyllite asbestos and glass fibres.

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

In plain English

In this animal experiment, the authors tested whether rockwool, a man-made mineral fibre used for thermal insulation, dissolves in the lung and becomes coated to form "pseudo-asbestos bodies". Sized rockwool fibres were instilled into the windpipes of rats (0.5 mg) and Syrian golden hamsters (0.4 mg). Rats were killed at intervals up to 18 months, and fibres recovered from their lungs were measured at their centres. With one exception, median diameters stayed between 1.0 and 1.2 micrometres, with no trend over time. From about 6 months, however, fibres became visibly thinner at their ends than in their middles, and by 18 months the thinner fibres had pointed ends. Rat lung weights showed no increase suggesting a disease response, although the study had no parallel control series. Very few coated fibres were seen in rats. In hamsters, coating appeared after 2 months, mainly on thinner fibres. Fibres thicker than 2 micrometres did not appear to become coated within 12 months. The authors concluded that rockwool dissolves relatively slowly in the lung, faster at the fibre ends than in the middle.

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 (intratracheal instillation in rats and hamsters, with serial sacrifice)
• Who was studied: HMT strain rats and Syrian golden hamsters, about 3 months old at dosing, at the Atomic Energy Research Establishment, Harwell, UK. The number of animals is not stated.
• Exposure: Sized rockwool fibres (a man-made mineral fibre) supplied by Rockwool International, with count median length about 27 micrometres and count median diameter about 1.1 micrometres. Rats received 0.5 mg and hamsters 0.4 mg by intratracheal instillation.
• Main results:
  • In a check of the extraction method, only about 2% of the radioactive sodium-24 and iron-59 dissolved from rockwool fibres after 16 hours in hypochlorite at room temperature. At 4°C a similar fraction of sodium-24 dissolved but only about 0.5% of iron-59, so digestion was judged unlikely to affect fibre diameter.
  • In rats, count median diameters of fibres recovered up to 18 months after dosing were, with one exception, within 1.0 to 1.2 micrometres, with no apparent trend over time.
  • In rats, after about 6 months fibres became thinner at their ends than in their middles, indicating dissolution. By 18 months the thinner fibres all had pointed ends.
  • In a subsidiary study in rats, small amounts of iron-59 from radioactive rockwool were detected in liver and blood over 6 months. This indicated that a small fraction of the iron had dissolved.
  • In dosed rats, lung weight as a percentage of body weight declined slightly with age. It did not show the later increase that a disease response might have produced.
  • In rats, very few coated rockwool fibres were observed.
  • In hamsters, coating was first seen at 2 months, and by 6 months a relatively high proportion of the thinner fibres were coated. Fibres thicker than 2 micrometres did not appear to become coated over 12 months.
• The authors' conclusion: The authors concluded that rockwool fibres dissolve relatively slowly in the lung, and faster at the ends than in the middle, where the diameter was essentially unchanged after 18 months. They stated that pseudo-asbestos body formation in hamsters followed a time course similar to that for glass fibres and anthophyllite asbestos in their earlier work.
• Limitations the authors state:
  • The study had no parallel control series. Only two control rats given saline were included.
  • Only a small fraction of the dose consisted of long fibres thinner than 0.5 micrometres, the fibres the authors considered most likely to cause disease.
  • Diameters were measured at fibre centres, so the thinning at the fibre ends did not show up in the diameter measurements.
  • The half-life of iron-59 limited the radioactive tracer study to 6 months.
  • The sized rockwool fibres used were thinner than commercial rockwool.

Topics

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

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

Related studies

• Formation of pseudo-asbestos bodies on sized glass fibres in the hamster lung — A. Holmes, A. Morgan, et al. (1983)
• Solubility of asbestos and man-made mineral fibers in vitro and in vivo: its significance in lung disease — A. Morgan, A. Holmes (1986)
• Clearance of anthophyllite fibers from the rat lung and the formation of asbestos bodies — A. Holmes, A. Morgan (1980)
• The enigmatic asbestos body: its formation and significance in asbestos-related disease — A. Morgan, A. Holmes (1985)
• Iron associated with asbestos bodies is responsible for the formation of single strand breaks in phi X174 RFI DNA — L.G. Lund, M.G. Williams, et al. (1994)
• The mechanism of formation of asbestos bodies — S.K. Botham, P.F. Holt (1968)

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