On the occurrence of fibres of calcium sulphate resembling amphibole asbestos in samples taken for the evaluation of airborne asbestos

Our plain-English summary of On the occurrence of fibres of calcium sulphate resembling amphibole asbestos in samples taken for the evaluation of airborne asbestos, by A.P. Middleton (The Annals of Occupational Hygiene, 1978).

The study

• Author: A.P. Middleton
• Journal: The Annals of Occupational Hygiene
• Published: 1978;21(1):91-4
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

The author reported an observation made while measuring airborne asbestos with the membrane filter method, in which fibres on cleared filters are counted by phase contrast microscopy. Some laboratories reported total fibre counts and others reported asbestos fibres only, although no guidance was given on how to tell asbestos from other fibres. In a survey of airborne asbestos during the removal of asbestos lagging from steel roof panels in a prefabricated building, airborne dust was collected on membrane filters. The lagging was mostly chrysotile with a trace of crocidolite. Side-by-side samples were taken on Nuclepore filters for scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDXA). Phase contrast counts indicated significant concentrations of airborne asbestos, and almost all fibres had the needle-like shape typical of amphibole asbestos. In the SEM, many fibres still resembled amphibole asbestos. However, EDXA showed that their major elements were calcium and sulphur rather than silicon and iron, so they were presumably calcium sulphate, probably from plaster board disturbed during the work. The author concluded that mistaking non-asbestos fibres for asbestos in routine counting can considerably overestimate airborne asbestos, and suggested taking side-by-side samples for evaluation by another method such as SEM/EDXA. The author also noted that if fibre size rather than chemistry governs disease risk, all fine fibres might be counted, and expensive electron microscopy might not necessarily be justified.

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In plain English

This short report from the Institute of Occupational Medicine, Edinburgh, described air samples from one survey during the removal of asbestos lagging from steel roof panels in a prefabricated building. Analysis had shown the lagging was mostly chrysotile with a trace of crocidolite. Airborne dust was collected on membrane filters for routine counting with a phase contrast light microscope. Side-by-side samples were examined by scanning electron microscopy and X-ray chemical analysis. The light-microscope counts indicated significant concentrations of airborne asbestos, and almost all fibres looked needle-like, typical of amphibole asbestos. Under the electron microscope many fibres still resembled amphibole asbestos. However, they contained calcium and sulphur rather than silicon and iron, and were presumably calcium sulphate, probably from plaster board disturbed during the work. The report did not give the number of samples or the measured concentrations. The author concluded that mistaking non-asbestos for asbestos fibres in routine counting can considerably overestimate airborne asbestos. Noting increasing evidence that the physical character of fibres, rather than their chemical composition, controls their ability to cause disease, especially mesothelioma, the author suggested it may be that all fine fibres should be counted.

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: short report of laboratory observations from a single workplace air-sampling survey, comparing phase contrast microscopy with scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDXA)
• Who was studied: airborne dust samples taken during removal of asbestos lagging from steel roof panels in a prefabricated building; number of samples, location and dates not stated
• Exposure: asbestos lagging that was mostly chrysotile with a trace of crocidolite; plaster board was also disturbed during the de-lagging work
• Main results:
  • Phase contrast microscopy counts indicated significant concentrations of airborne asbestos, and almost all fibres had the needle-like shape typical of amphibole asbestos
  • Even under the scanning electron microscope, many fibres had a lath-like shape similar to amphibole asbestos
  • Chemical analysis showed these fibres contained calcium and sulphur as major elements, not the silicon and iron of amphibole asbestos, and they were presumably calcium sulphate
  • The author judged that the calcium sulphate fibres probably came from aggregates derived from plaster board disturbed during the de-lagging
  • In discussion, the author noted increasing evidence that the physical character of fibres, rather than their chemical composition, controls their ability to cause disease, especially mesothelioma
  • The author suggested that it may be that all fine fibres should be counted when assessing airborne dust, so expensive electron microscope methods may not necessarily be justified
• The authors' conclusion: The author concluded that confusing non-asbestos fibres with asbestos fibres during routine phase contrast counting can lead to a considerable overestimate of airborne asbestos concentration

Topics

Medical terms in this study, explained in our Lexicon: Amphibole Asbestos, Membrane Filter Method, phase contrast microscopy (PCM), Chrysotile, Crocidolite, Scanning Electron Microscopy (SEM).

Related studies

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• A routine for the control of the performance of microscopists evaluating airborne asbestos fibre samples on membrane filters by phase contrast microscopy — J.R. Hoyes, R. Clayton (1980)
• Relationships between simultaneous airborne dust samples taken with five types of instruments at South African asbestos mines and mills — R.S. Du Toit, L.W. Isserow, et al. (1983)
• Analysis of airborne dust samples for chrysotile by X-ray diffraction: interference by non-asbestiform serpentine — A.P. Middleton (1982)
• A study of the size distributions of airborne amosite fibres in the manufacture of asbestos insulation boards — S.T. Beckett, J.L. Jarvis (1979)
• Simultaneous airborne dust samples with konimeter, thermal precipitator and dosimeter in asbestos mines — R.S. du Toit, T.C. Gilfillan (1977)

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