An introduction to the short-term toxicology of respirable industrial fibres

Our plain-English summary of An introduction to the short-term toxicology of respirable industrial fibres, by K. Donaldson, C.L. Tran (Mutation Research, 2004).

The study

• Authors: K. Donaldson, C.L. Tran
• Journal: Mutation Research
• Published: 2004;553(1-2):5-9
• Type of article: Review
• Cited by: 82 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Fibrous materials, exemplified by asbestos, that release respirable fibres are in common use and there is considerable knowledge regarding the toxicology of these common fibres. Newer materials or those that are under development, such as synthetic organic fibres and carbon nanotubes may have a different toxicology paradigms. The existing paradigm for silicate fibres suggests that respirable fibre types vary in their ability to cause lung disease and that this can be understood on the basis of the length of the fibres and their biopersistence in the lungs. Because fibres are regulated on a fibre number basis and the hazard is understood on the basis of the number of long fibres, in fibre testing the dose should always be expressed as fibre number, not mass and the length and diameter distribution need to be known. Short-term biological tests are likely to produce false positives in the case of long non-biopersistent fibres, because whilst they may have effects in vitro, they do not persist long enough in the lungs for sufficient dose to build up and produce effects in vivo. The biopersistence of fibres is therefore a key factor that needs to be known in order to interpret short-term tests that may claim to predict fibre pathogenicity.

In plain English

This article was a short review, not a new study. The authors described how scientists understood the short-term toxicology of breathable industrial fibres, mainly asbestos and silicate-based synthetic vitreous fibres such as glass wool, rock wool, slag wool and refractory ceramic fibres. Drawing on earlier research, they explained that fibre types differ in their ability to cause lung disease. In their account, long, thin fibres that persist in the lungs, such as amphibole asbestos, were highly harmful. Fibres that dissolve and break up, such as Rockwool, were low in harmfulness even when long. They cited earlier work suggesting that chrysotile's lower persistence may explain its lower cancer-causing effect, with the effects seen in chrysotile miners suggested to be due to tremolite. The authors concluded that fibre doses in testing should be expressed as fibre number, not mass. They also concluded that short laboratory tests may give false positive results for long fibres that do not persist in the lungs. They stated that this framework referred only to silicate fibres, and that it was not known whether it applies to newer fibres such as carbon nanotubes.

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: Narrative review of existing research (no new data)
• Who was studied: Published research on respirable industrial fibres, mainly asbestos and silicate-based synthetic vitreous fibres. Newer fibres (synthetic organic fibres, carbon nanotubes) were mentioned as not well understood.
• Exposure: The review covered asbestos (amphiboles, chrysotile, tremolite), synthetic vitreous fibres (glass wool, rock wool, slag wool), refractory ceramic fibres, silicon carbide, erionite, and code 100 fibres. It focused on fibre length and biopersistence.
• Main results:
  • The review reported IARC judgements. Asbestos was Group 1 (carcinogenic to humans). Refractory ceramic fibres were Group 2B (possibly carcinogenic). Glass wool, rock wool and slag wool were Group 3 (not classifiable).
  • Citing earlier studies, the authors stated that biosoluble fibres such as Rockwool, which do not persist in the lungs, are low in pathogenic potential even if long. Amphibole asbestos and other biopersistent fibres are highly pathogenic if long and thin.
  • Citing earlier work, the authors noted that the cancer-causing effects seen in chrysotile miners had been suggested to be due to tremolite. Tremolite is a more biopersistent amphibole present in chrysotile-bearing ore.
  • The authors explained that long fibres cannot be fully engulfed by lung cells (frustrated phagocytosis), which stimulates release of inflammatory mediators. Short fibres are cleared.
  • Citing earlier work, the authors stated that fibres cleared quickly from the lung (short retention halftime) are generally of low pathogenicity, while those with a long halftime are pathogenic.
  • As an example, code 100 fibres (long but non-biopersistent) caused no pathology in chronic rat studies. Yet in earlier short-term tests their long fibres stimulated more TNF production and caused cell transformation.
• The authors' conclusion: The authors concluded that fibre toxicology is understood on the basis of the number of long fibres, modified by biopersistence. Dose in fibre testing should therefore be expressed as fibre number, not mass. Short-term tests are likely to give false positives for long non-biopersistent fibres.
• Limitations the authors state:
  • The authors stated that it is not known whether the silicate-fibre framework is relevant to newer fibres such as carbon nanotubes and organic fibres. The toxicology of those fibres is not yet understood and may follow different paradigms.
  • The authors stated that the nature of the especially reactive surface of fibres such as erionite and silicon carbide is unknown.

Topics

Medical terms in this study, explained in our Lexicon: Silicate, biopersistence.

Related studies

• Superoxide anion release by alveolar macrophages exposed to respirable industrial fibres: modifying effect of fibre opsonisation — K. Donaldson, I.M. Hill, et al. (1995)
• An in vitro/in vivo study into the short term effects of exposure to mineral fibres — A. Clouter, C.E. Houghton, et al. (1996)
• Testing of fibrous particles: short-term assays and strategies — D. Bernstein, V. Castranova, et al. (2005)
• Short-term inhalation and in vitro tests as predictors of fiber pathogenicity — R.T. Cullen, B.G. Miller, et al. (1997)
• Detection of surface free radical activity of respirable industrial fibres using supercoiled phi X174 RF1 plasmid DNA — P.S. Gilmour, P.H. Beswick, et al. (1995)
• New perspectives on basic mechanisms in lung disease. 5. Respirable industrial fibres: mechanisms of pathogenicity — K. Donaldson, R.C. Brown, et al. (1993)

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