Evidence for an amphibole asbestos threshold exposure for asbestosis assessed by autopsy in South African asbestos miners

Our plain-English summary of Evidence for an amphibole asbestos threshold exposure for asbestosis assessed by autopsy in South African asbestos miners, by G.K. Sluis-Cremer, E. Hnizdo, R.S. du Toit (The Annals of Occupational Hygiene, 1990).

The study

• Authors: G.K. Sluis-Cremer, E. Hnizdo, R.S. du Toit
• Journal: The Annals of Occupational Hygiene
• Published: 1990;34(5):443-51
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 004063).

Abstract

In an attempt to determine whether there exists a threshold asbestos dose below which asbestosis does not occur, data on 807 men who had worked on amphibole asbestos mines and undergone autopsy were analysed. When exposure was expressed as fibre-years no asbestosis was found at autopsy when exposure was up to 2 fibre-years, even after 31-45 years of residence time. In the group exposed to greater than 2-5 fibre-years asbestosis was found. When exposure was expressed as average fibre concentration asbestosis occurred below 2 fibres per ml (f ml-1) and the prevalence increased with residence time. In conclusion, if a threshold dose for asbestosis does exist it is at approximately 2 fibre-years if off-shift exposure is ignored.

In plain English

This study analysed autopsy records of 807 white and mixed-race men who had worked on South African amphibole asbestos mines. The aim was to see whether there is an exposure level below which asbestosis does not occur. Black miners were excluded because their exposure records were not accurate enough. Each man's exposure was estimated from mine dust measurements as cumulative fibre-years and as average fibre concentration. No asbestosis was found in the 62 men exposed to up to 2 fibre-years, however long the time from first exposure to death. Asbestosis was found in the group exposed to more than 2 to 5 fibre-years. Its prevalence and severity rose with fibre-years and with time since first exposure. For average concentration, no threshold was seen: asbestosis occurred among men exposed to 2 fibres per ml or less. Men of mixed race had almost double the prevalence of white men. The authors concluded that if a threshold exists, it is approximately 2 fibre-years, if off-shift exposure is ignored. They noted that the low autopsy rate and unmeasured environmental exposure could affect the results.

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: Analysis of medico-legal autopsy records of former asbestos miners, using frequency tables and stepwise logistic regression
• Who was studied: 807 white or mixed-race men who had worked on amphibole asbestos mines in South Africa and whose heart and lungs were examined at the National Centre for Occupational Health. Autopsies were recorded on the PATHAUT system from 1974, and the examinations covered 1974-1987. Black miners, men with inadequate exposure records, and men who had mainly done chrysotile mining were excluded.
• Exposure: Amphibole asbestos mining. The article does not name specific amphibole fibre types. Exposure was estimated from mine dust measurements taken from about 1940 to 1987, weighted by occupation, and summed as cumulative fibre-years. Average fibre concentration in fibres per ml was cumulative fibre-years divided by years of exposure. Off-shift environmental exposure was not quantified.
• Main results:
  • No asbestosis was found at autopsy in the 62 men with exposure up to 2 fibre-years, regardless of residence time (time from first exposure to death).
  • Asbestosis was found in the group exposed to more than 2 to 5 fibre-years.
  • Slight asbestosis occurred in the more than 2 to 5 fibre-years category. Moderate asbestosis occurred in the more than 5 to 10 fibre-years category.
  • In general, the prevalence and severity of asbestosis increased with increasing fibre-years and with longer residence time.
  • In logistic regression, fibre-years were significantly related to asbestosis in all five year-of-birth groups and in the total group.
  • When exposure was expressed as average fibre concentration, no threshold was shown. Significant proportions of men exposed to an average of 2 fibres per ml or less had asbestosis.
  • At each residence time and each average fibre concentration, men of mixed race had almost double the prevalence of asbestosis seen in white men. The authors suggested that exposures for men of mixed race may have been underestimated.
• The authors' conclusion: The authors concluded that if a threshold dose for asbestosis exists, it is approximately 2 fibre-years, if off-shift exposure is ignored. They also concluded that any safe average fibre concentration is certainly less than 2 fibres at the workplace. They suggested that keeping cumulative exposure below 2 fibre-years may prevent slight asbestosis.
• Limitations the authors state:
  • The autopsy rate in asbestos miners was relatively low, which may bias the results. Cases of asbestosis with low exposure may have been lost.
  • Off-shift environmental exposure near mills, mine dumps and residential areas could not be quantified.
  • The tissue slides examined may not fully represent the total degree of asbestosis in the lungs.
  • The thermal precipitator used from 1965 to 1975 may have materially underestimated fibre concentrations compared with the membrane filter method.
  • Many of the men had also worked on gold mines, and there are no data on how gold mining dust and asbestos dust interact in causing asbestosis.
  • Exposures for men of mixed race may have been underestimated.

Topics

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

Medical terms in this study, explained in our Lexicon: Amphibole Asbestos, Autopsy.

Related studies

• Asbestosis in South African asbestos miners — G.K. Sluis-Cremer (1970)
• Effects of commodity on the risk of emphysema in South African miners — S.L. Mabila, K.S. Almberg, et al. (2020)
• The mortality of amphibole miners in South Africa, 1946-80 — G.K. Sluis-Cremer, F.D. Liddell, et al. (1992)
• Risk of mesothelioma from exposure to crocidolite asbestos: a 1995 update of a South African mortality study — D. Kielkowski, G. Nelson, et al. (2000)
• Factors influencing the reading of small irregular opacities in a radiological survey of asbestos miners in South Africa — G.K. Sluis-Cremer, P.A. Hessel, et al. (1989)
• Asbestosis in South Africa--certain geographical and environmental considerations — G.K. Sluis-Cremer (1965)

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