Asbestosis in South Africa--certain geographical and environmental considerations

Our plain-English summary of Asbestosis in South Africa--certain geographical and environmental considerations, by G.K. Sluis-Cremer (Annals of the New York Academy of Sciences, 1965).

The study

• Author: G.K. Sluis-Cremer
• Journal: Annals of the New York Academy of Sciences
• Published: 1965;132(1):215-34
• Cited by: 32 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. 001541).

Summary of the article

The author asked why pleural mesothelioma had been reported often from the North West Cape (N.W.C.) crocidolite mining area of South Africa but never from the Transvaal (TVL) asbestos field, where amosite and Transvaal crocidolite are mined. He compared the two areas on medical services, production history, dust counts, ore constituents, neighbourhood pollution, a field survey and post-mortem findings. In the field survey (1960 to 1962), the Pneumoconiosis Research Unit examined a random sample of households: 1904 persons aged 20 and over from the N.W.C. asbestos area, 485 from the TVL, and residents of a control N.W.C. town with no asbestos industry. The survey used questionnaires, clinical examination, chest X-rays read blind, and single sputum samples. Mines and mills in the N.W.C. were about twice as dusty as in the TVL during the 1940s and 1950s. Asbestos bodies were found in sputum in both asbestos areas, including in people with no occupational exposure, but not in the control town. Among exposed people, bodies were found in 35% of males in the N.W.C. versus 10% in the TVL, and in 20% versus 7% of females. Fibre prevalence was similar in the two areas. Post-mortem reports on 87 N.W.C. and 64 TVL Bantu miners (1959 to 1964) showed no significant difference in the frequency or severity of asbestosis. The author concluded that there appears to be a real difference between N.W.C. crocidolite and TVL amosite in producing mesothelioma, not explained by environmental differences.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This paper compared South Africa's two main asbestos mining areas. The North West Cape produces crocidolite (Cape blue). The Transvaal produces amosite and Transvaal blue crocidolite. Mesothelioma had been reported from the North West Cape, but no case had been reported from the Transvaal area. The author reviewed production and dust records, a 1960 to 1962 survey of residents (1904 in the North West Cape, 485 in the Transvaal, and a control town with no asbestos industry), and post-mortem reports on Bantu miners (87 from North West Cape mines and 64 from Transvaal mines). North West Cape mines and mills were approximately twice as dusty in the 1940s and 1950s. Among exposed males, sputum asbestos bodies were found in 35 per cent in the North West Cape and 10 per cent in the Transvaal. Fibers were found in 39 and 38 per cent of the same groups. Asbestosis at post-mortem did not differ significantly between the areas. The author concluded that the evidence appeared to indicate a real difference between North West Cape crocidolite and Transvaal amosite in producing mesothelioma, not explicable by the environmental differences examined.

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: Comparative study of two asbestos mining areas, using production and dust-count records, a population field survey (questionnaire, clinical examination, chest X-ray, single sputum sample) and a review of post-mortem lung reports
• Who was studied: Field survey (1960 to 1962): residents aged 20 and over in randomly sampled houses in three North West Cape towns and one Transvaal mining village, plus a control North West Cape town with no asbestos industry. Persons currently working in mining or milling were excluded, but past workers were included. Samples were 1904 persons from the North West Cape area and 485 from the Transvaal area. Post-mortem review: lungs of Bantu miners who died while working on asbestos mines, July 1, 1959 through June 1964, 87 from North West Cape mines and 64 from Transvaal mines.
• Exposure: Crocidolite (Cape blue) in the North West Cape; amosite and crocidolite (Transvaal blue) in the Transvaal. Exposure was occupational (mining, milling, handling, transport) and also neighborhood pollution from mills, dumps and tailings. Chrysotile mining was excluded from consideration.
• Main results:
  • No case of mesothelioma had been reported from the Transvaal asbestos area or its surroundings, or had come to the author's attention.
  • Mills and mines in the North West Cape were, on average, approximately twice as dusty as those in the Transvaal during the 1940s and 1950s.
  • Free silica content of the ore mined and milled showed negligible differences between the two areas.
  • No asbestos bodies were found in sputa from the control population.
  • Asbestos bodies were found in sputum in 35 per cent of exposed males in the North West Cape and 10 per cent in the Transvaal. For exposed females the figures were 20 per cent and 7 per cent. The author described this as a significant difference.
  • Asbestos fibers in sputum showed no difference between areas: 39 per cent (North West Cape) and 38 per cent (Transvaal) of exposed males, and 46 per cent and 47 per cent of exposed females.
  • Asbestos bodies were found in the nonexposed groups in both asbestos areas but not in the control area.
  • Fibers were found in just under five per cent of control-area sputa (13 out of 280). The author said this raised a suspicion that other fibrous materials indistinguishable from asbestos fibers may be responsible.
  • On X-ray, nonexposed males of all three races in the North West Cape appeared to show a clear excess of radiological abnormality compared with the control group. For North West Cape females and the Transvaal groups the figures were not significant at the ten per cent level.
  • At post-mortem, the incidence and severity of asbestosis among Bantu miners were not significantly different between the two areas.
  • Whites showed lower rates of radiological changes than the other racial groups, as they also did for asbestos bodies and fibers.
• The authors' conclusion: The author concluded that the available evidence appeared to indicate a real difference between North West Cape crocidolite and Transvaal amosite as far as the production of mesothelioma is concerned. The author also concluded that this difference is not explicable on any environmental differences between the two mining areas examined in the paper.
• Limitations the authors state:
  • No objective measurements of general neighborhood pollution had yet been completed in the two areas.
  • Only one sputum specimen was examined per person, so the observed rates must greatly underestimate the true situation.
  • Neither class of radiological change is pathognomonic of asbestosis. Parenchymal changes are hard to read consistently and show inter-observer variation.
  • Length-of-service data in the post-mortem series are almost invariably a gross underestimate, though probably to a similar degree in both areas.
  • Many sputum fibers may come from the mouth rather than the lung, reflecting recent pollution exposure.
  • Amosite may form asbestos bodies less readily than crocidolite, or such bodies may appear less readily in sputum.

Topics

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

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Crocidolite, Transvaal, Amosite, Pneumoconiosis, Chest X-Ray, Sputum, Asbestos Bodies.

Related studies

• Lung cancer, tobacco, and environmental factors in the African population of the Northern Province, South Africa — O. Mzileni, F. Sitas, et al. (1999)
• Radiological and pathological correlations in asbestosis in the Republic of South Africa and the United Kingdom. I. A proposed radiological classification of asbestosis — G.K. Sluis-Cremer, C.P. Theron (1965)
• 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)
• Asbestos-related disease in South Africa: the social production of an invisible epidemic — L. Braun, S. Kisting (2006)
• Radiological and pathological correlations in asbestosis in the Republic of South Africa and the United Kingdom. II. A preliminary study of observer variation in the classification of radiographs of asbestos-exposed workers and the relation of pathology and x-ray appearances — A. Caplan, J.C. Gilson, et al. (1965)
• Risk of asbestosis in crocidolite and amosite mines in South Africa — L.M. Irwig, R.S. du Toit, et al. (1979)

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