Asbestosis in South African asbestos miners

Our plain-English summary of Asbestosis in South African asbestos miners, by G.K. Sluis-Cremer (Environmental Research, 1970).

The study

• Author: G.K. Sluis-Cremer
• Journal: Environmental Research
• Published: 1970;3(4):310-9
• Cited by: 23 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. 001411).

Summary of the article

This study examined how long after first exposure asbestosis appeared, and at what rate it was being produced, in South African crocidolite (North West Cape) and amosite (Northern Transvaal) asbestos mines. The author followed white miners employed in these mines between 1954 and 1958, as far as the mine records, which were incomplete, allowed. The groups numbered 391 in the North West Cape and 147 in the Transvaal. Each man's last X-ray at the Miners' Medical Bureau was read. Vital capacity and carbon monoxide diffusion (DCO) were measured in white North West Cape miners without radiological asbestosis. Autopsy findings in Bantu labourers who died between 1965 and 1969 were also reviewed.

Radiological diagnoses of asbestosis increased with length of service. One case in each area was diagnosed after less than 5 years' service and 15-19 years of follow-up. Calcified pleural plaques generally did not appear within 20 years of first exposure. No man who started work in 1954-1958 developed bronchial carcinoma or mesothelioma. Two bronchial carcinomas and one pleural mesothelioma occurred in men who started earlier.

At autopsy, asbestosis, mainly slight, was common in Bantu labourers after relatively short recorded service. It was less frequent than in a 1959-1964 series (71.5% and 79.7%). DCO showed no significant fall with service. Vital capacity fell with service only in men aged 40-49, and no result was definitely abnormal. The author concluded that both length of exposure and time since exposure matter, and that the disease may progress after exposure stops.

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 radiological study followed white miners employed 1954-1958 on South African crocidolite mines (North West Cape) and amosite mines (Northern Transvaal), using their last chest X-rays. The author also reviewed autopsies of Bantu labourers from 1965 to 1969 and measured lung function in some North West Cape white miners without X-ray asbestosis. X-ray diagnoses of asbestosis, which here included calcified pleural plaques alone, increased with service. One man per area was diagnosed after under 5 years' service and 15-19 years' follow-up. No one who started work in 1954-1958 had developed bronchial carcinoma or pleural mesothelioma. Vital capacity fell significantly with service only in men aged 40 to 49, and no lung function result was definitely abnormal. Autopsies showed a high incidence of mostly slight asbestosis after relatively short recorded service, but the author warned these service records were very unreliable and often underestimates. The author concluded that both length of exposure and time asbestos stays in the lungs appear to matter. Records were incomplete, and men who left asbestos work tended to be lost to follow-up.

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: Radiological follow-up study of white miners based on mine and Miners' Medical Bureau records, with a review of autopsy findings in Bantu labourers and lung function measurements in a subgroup of white miners
• Who was studied: White miners employed 1954-1958 on crocidolite mines (North West Cape) and amosite mines (Northern Transvaal, mainly Penge), South Africa. The article refers to 147 people in the Transvaal group and 391 in the North West Cape group. Also studied: Bantu labourers whose lungs were examined at autopsy from Jan. 1, 1965 to Dec. 31, 1969, and 179 North West Cape white miners in lung function tests (64, 68, 41 and 6 men in the age groups 20-29, 30-39, 40-49 and 50-59).
• Exposure: Mining and surface work on crocidolite and amosite mines. Both fibers occur in banded ironstone, and the mine dust was described as about 30% fibre and 36% free silica, the rest iron oxides and other minerals. Exposure was measured as years of service and years since first exposure.
• Main results:
  • Among the white miners, X-ray diagnoses of asbestosis increased with length of service. One case in the North West Cape and one in the Transvaal were diagnosed after less than 5 years of service, following 15-19 years of follow-up.
  • Calcified pleural plaques generally did not appear less than 20 years after starting service. In one case, plaques appeared 15 years after first mining exposure, with no evidence of earlier exposure.
  • In five cases in the North West Cape and five in the Northern Transvaal, calcified pleural plaques were the only X-ray sign counted as asbestosis.
  • No person who started work during 1954-1958 had developed bronchial carcinoma or pleural mesothelioma.
  • Among men with earlier service, one North West Cape miner who started work in 1928 and had developed asbestosis developed carcinoma of the bronchus in 1965. A Transvaal miner, whose start year is unreadable in the text (194-), developed the tumour in 1963, and slight asbestosis was found at autopsy.
  • One North West Cape miner whose service started in 1937 developed a mesothelioma of the pleura. He had no X-ray evidence of asbestosis.
  • In the lung function subgroup (North West Cape white miners with no X-ray asbestosis), carbon monoxide diffusion showed no statistically significant fall with service in any age group.
  • Vital capacity fell significantly with service only in the 40-49 age group, where vital capacity as percent of predicted normal was negatively correlated with asbestos service (printed as p less than .01). None of these observations was definitely abnormal.
  • At autopsy, Bantu labourers showed a high incidence of asbestosis, mainly of slight degree, after relatively short recorded service. The author warned that service details for Bantu labourers were very unreliable and often underestimated. The table with the numbers is not legible in the text.
  • The author reported that asbestosis at autopsy in Bantu labourers was appreciably lower than in an earlier study of Bantu who died between July 1, 1959 and June 30, 1964. That earlier study, not this one, found asbestosis in 71.5% of North West Cape cases and 79.7% of Transvaal cases. The author attributed the improvement to efforts to improve dust conditions.
• The authors' conclusion: The author concluded that both length of exposure and the length of time asbestos remains in the lungs appear to be significant in determining the onset of asbestosis. The author also suggested that in some cases the disease progresses after exposure stops, and that the tests used could not identify people with minimal asbestosis during life.
• Limitations the authors state:
  • Mine records were imperfect, so the North West Cape and Penge populations are incomplete.
  • Many men had less than 10 years of follow-up and short service.
  • Men who stopped asbestos work were not required to have medical examinations and tended to be lost to the study.
  • The study was purely radiological: cases with asbestosis found at autopsy but normal X-rays were not counted.
  • Some long-service men had substantial service before 1954, before dust conditions were measured.
  • Service details for Bantu labourers were very unreliable and often underestimated.
  • Counting calcified pleural plaques as diagnostic of asbestosis is considered controversial by some.

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Amosite, Transvaal, Autopsy, Bantu, Pleural Plaques, Carcinoma, Mesothelioma.

Related studies

• Evidence for an amphibole asbestos threshold exposure for asbestosis assessed by autopsy in South African asbestos miners — G.K. Sluis-Cremer, E. Hnizdo, et al. (1990)
• Effects of commodity on the risk of emphysema in South African miners — S.L. Mabila, K.S. Almberg, et al. (2020)
• 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)
• 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)
• Some investigations into the nature and cause of massive fibrosis (MF) in the lungs of South African gold, coal, and asbestos mine workers — M.C. Leibowitz, B. Goldstein (1987)
• Radiologic abnormalities in South African mica millers: a survey of a mica milling plant in the Limpopo Province — E. Venter, B. Nyantumbu, et al. (2004)

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