The dimensions of airborne asbestos fibres--I. Crocidolite from Kuruman area, Cape Province, South Africa

Our plain-English summary of The dimensions of airborne asbestos fibres--I. Crocidolite from Kuruman area, Cape Province, South Africa, by C.Y. Hwang, G.W. Gibbs (The Annals of Occupational Hygiene, 1981).

The study

• Authors: C.Y. Hwang, G.W. Gibbs
• Journal: The Annals of Occupational Hygiene
• Published: 1981;24(1):23-41
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The dimensions of airborne fibres collected at an underground mine and two mills producing crocidolite in the Kuruman area of Cape Province, South Africa, and of those collected at a plant manufacturing pipes in South Africa using Cape crocidolite and chrysotile asbestos are reported. The measurements were made using a transmission electron microscope, a scanning electron microscope and a light optical microscope. There was no apparent change in diameter with stage of processing although in certain processes, such as cutting asbestos cement pipe, the presence of chrysotile fibres altered the size distribution markedly. However, there was some change in length with stage of processing. The finding that the observed diameter distributions in airborne samples in this study are similar to those previously reported in the lungs of workers exposed to Cape crocidolite may indicate that, if diameter is the important parameter in relation to health effects, the hazard associated with exposure to Cape crocidolite should, dose for dose, be similar for all stages of processing. The proportion of long fibres in the air has been found to be very small and observations on very large numbers of fibres are necessary to confirm their presence.

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

In plain English

This study measured the size of airborne asbestos fibres in South African workplaces. The authors collected 52 air samples (26 on each of two filter types) at an underground mine and two mills producing crocidolite near Kuruman, Cape Province, and at a pipe-making plant using Cape crocidolite and chrysotile. Fibres were measured by transmission and scanning electron microscopy and by light optical microscopy, and results were grouped into seven processes from mining to pipe cutting. Median crocidolite fibre diameters were 0.07 to 0.10 micrometres. During pipe cutting the median was 0.04 micrometres, which the authors attributed to chrysotile in the air. Leaving cutting aside, diameter distributions did not differ significantly between processes, but length distributions did. Fewer than 1.6% of fibres seen by transmission electron microscopy were longer than 10 micrometres. Fibres longer than 10 micrometres and thinner than 0.5 micrometres made up 0.1 to 1.3% of airborne fibres, depending on the process. The authors inferred that, if diameter matters most for health effects, the hazard of Cape crocidolite should, dose for dose, be similar at all stages of handling. They noted that more data on long fibres are still needed.

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: Workplace air-sampling study measuring the dimensions of airborne fibres by electron and light optical microscopy (no health outcomes studied)
• Who was studied: 52 airborne dust samples (26 on Millipore and 26 on Nuclepore filters) from an underground mine and two crocidolite mills near Kuruman, Cape Province, South Africa, and a South African pipe manufacturing plant. Three membrane filters were too heavily loaded for transmission electron microscopy, and 23 samples were grouped by process. Sampling dates are not given.
• Exposure: Airborne Cape crocidolite at seven process stages: mining, ore storage, crushing, bagging, dumping, mixing and cutting. The cutting samples came from pipes containing both crocidolite and chrysotile.
• Main results:
  • Median diameters of airborne crocidolite fibres ranged from 0.07 to 0.10 micrometres, depending on sampling location. During pipe cutting the median diameter was 0.04 micrometres, attributed to chrysotile contamination.
  • Diameter distributions for all processes except cutting were not significantly different (p = 0.59 for median diameters).
  • Fewer than 1.5% of fibres had diameters greater than 0.4 micrometres.
  • Length distributions at the processing stages, excluding cutting, were significantly different (p = 0.02 for median lengths).
  • Fewer than 1.6% of fibres observed by transmission electron microscopy were longer than 10 micrometres. Fibres longer than 20 micrometres only appeared after more than 2500 fibres had been measured.
  • For mining samples, 21.2% of fibres seen by phase contrast microscopy were shorter than 5 micrometres, compared with 96.0% seen by transmission electron microscopy.
  • The minimum diameter of fibres visible by optical microscopy was estimated at 0.21 micrometres.
  • Fibres longer than 5 micrometres and thicker than 0.5 micrometres were about 0.1 to 0.6% of all airborne fibres. On that assumption, an optical count of 2 fibres per cubic centimetre would correspond to 333 to 2000 total fibres per cubic centimetre.
  • Fibres longer than 10 micrometres and thinner than 0.5 micrometres made up 0.1 to 1.3% of airborne fibres, depending on process, with no consistent pattern.
• The authors' conclusion: The authors noted that the airborne diameter distributions resembled those found in the lungs of Cape crocidolite workers in an earlier study by Timbrell et al. They inferred that, if diameter is the key factor for health effects, the hazard of Cape crocidolite should be similar, dose for dose, at all stages of handling. Because length varied more between processes, any differences in health risk between stages are likely influenced at least partly by fibre length.
• Limitations the authors state:
  • Because of the grid mesh size, straight fibres longer than 65 micrometres could not be measured by transmission electron microscopy.
  • Very narrow fibres (diameter about 0.01 micrometres) could not be identified as crocidolite with certainty by energy dispersive analysis.
  • The aerodynamic behaviour of fibres with adhering particles has not been investigated.
  • Additional data on long fibres are still needed.
  • The fibre selection rule introduced a length bias, with fibres around 24 micrometres overestimated by about 6%.

Topics

Medical terms in this study, explained in our Lexicon: Crocidolite, Cape Province, Chrysotile, Asbestos-Cement.

Related studies

• Collaborative research, participatory solutions: research on asbestos in Kuruman, South Africa — N. Jacobs, S. Kisting, et al. (2004)
• A study of the size distributions of airborne amosite fibres in the manufacture of asbestos insulation boards — S.T. Beckett, J.L. Jarvis (1979)
• Lung cancer, tobacco, and environmental factors in the African population of the Northern Province, South Africa — O. Mzileni, F. Sitas, et al. (1999)
• The influence of external aerodymanic factors on the measurement of the airborne concentration of asbestos fibres by the membrane filter method — A.M. Johnston, A.D. Jones, et al. (1982)
• A study of personal and area airborne asbestos concentrations during asbestos abatement: a statistical evaluation of fibre concentration data — J.H. Lange, P.R. Lange, et al. (1996)
• Excess mortality from stomach cancer, lung cancer, and asbestosis and/or mesothelioma in crocidolite mining districts in South Africa — J.L. Botha, L.M. Irwig, et al. (1986)

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