Health effects of amosite mining and milling in South Africa

Our plain-English summary of Health effects of amosite mining and milling in South Africa, by J. Murray, G. Nelson (Regulatory Toxicology and Pharmacology, 2008).

The study

• Authors: J. Murray, G. Nelson
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2008;52(1 Suppl):S75-81
• Type of article: Historical article
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This study focuses on the amosite mining region in South Africa and associated health effects, compared to other mined asbestos fiber types. Historically, dust and fiber levels were high in the amosite mills and mines, and many miners and members of the surrounding communities were exposed to the fibers. Research has shown that amosite produces both benign and malignant disease. Nevertheless, the mesotheliomagenic potential of amosite is several fold lower than crocidolite. The risk of disease associated with amosite exposure is difficult to quantify. Reasons for this include the scarcity of available information, including fiber measurements, and case ascertainment, as well as the juxtaposition of the amosite and crocidolite asbestos seams in South Africa.

In plain English

This was a review by authors from South Africa's National Institute for Occupational Health and the University of the Witwatersrand. It drew on published studies and unpublished institute work on health effects of amosite mining in the Pietersburg asbestos field. Most of it concerned the Penge mine, which produced amosite from 1914 to 1992. They compared these with crocidolite mining in the Northern Cape. They described historical fiber levels around Penge as exceptionally high. The reviewed studies reported high rates of pleural abnormalities and asbestosis among amosite-exposed workers. A community study found pleural changes in 34% of residents with only environmental exposure. Another survey found pleural and/or parenchymal asbestosis in 96% of 770 women who had worked on the area's asbestos mines. A 1992 study of white miners found mesothelioma incidence of 44.6 per 100,000 person-years with Cape crocidolite exposure and 7.8 with amosite. The authors concluded that amosite causes benign asbestos disease and mesothelioma, though crocidolite carries a higher mesothelioma risk. They noted that overlapping amosite and crocidolite seams, sparse fiber measurements and missing employment records made amosite's risk hard to quantify.

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: Narrative review of published studies, plus some unpublished institute (PRU/NIOH) work, on amosite mining and health in South Africa
• Who was studied: Miners, mill workers and community residents of the Pietersburg asbestos field (Limpopo Province), mainly the Penge amosite mine, compared with the Northern Cape (Cape crocidolite) asbestos field; the studies reviewed cover roughly the 1940s to the 1990s
• Exposure: Amosite, with crocidolite exposure overlapping in the same field, from mining, milling, hand cobbing and environmental contamination. Reported measurements at Penge: 162 to 720 p/ml in the mills in 1947; up to 327 f/ml in the mills in personal samples (Rendall, 1971); 0.1 to 6.5 f/ml in the mills in the 1980s. In the Mafefe district in 1988, children had a mean of 0.02 f/ml.
• Main results:
  • In an autopsy series of black miners who died while employed (Sluis-Cremer, 1965), asbestosis was found in 80% of Penge miners and 72% of Cape crocidolite miners
  • Irwig et al. (1979) found a significantly higher prevalence of pleural abnormalities among amosite-exposed workers with more than 15 years of service than among crocidolite miners (34% vs. 17%)
  • In a community-based study in Mafefe (Felix, 1997), pleural changes were found in 52% of occupationally exposed subjects and 34% of subjects with only environmental exposure
  • Among 770 women who had worked on asbestos mines in the Pietersburg asbestos field, 80% of them cobbers (Davies et al., 2001), pleural and/or parenchymal asbestosis was diagnosed in 96%
  • In the 1992 cohort study of white amphibole miners (Sluis-Cremer et al.), mesothelioma incidence per 100,000 person-years was 44.6 for Cape crocidolite exposure and 7.8 for amosite. Of 30 mesotheliomas, 4 had exposure to pure amosite, 6 to both fibers and 20 to Cape crocidolite only.
  • In the same 1992 study, the proportional mortality ratio (PMR) for mesothelioma was 4.7 for crocidolite exposure and 0.6 for amosite
  • Of the first 375 mesothelioma cases sent to the Asbestos Tumour Reference Panel, only 4 (1%) had worked at amosite mines, and those 4 had also been exposed to crocidolite elsewhere
  • In a case-control study of 123 mesotheliomas (Rees et al., 1999), 3 cases had mined amosite and 3 had mined both fibers. Of 22 environmental mesotheliomas, 20 (91%) had exposure to Cape crocidolite and 2 to both amosite and crocidolite. No cases were associated with chrysotile.
  • In the 1992 study, the standardized mortality ratio (SMR) for lung cancer was 2.03 for crocidolite exposure and 1.38 for amosite (relative toxicity 1.85)
• The authors' conclusion: The authors concluded that there is solid evidence of high rates of benign asbestos disease from amosite and that amosite causes mesothelioma (and lung cancer). They also concluded that the South African evidence supports a fiber gradient for mesothelioma: crocidolite highest, then amosite, with chrysotile not implicated in South Africa.
• Limitations the authors state:
  • Amosite and crocidolite seams overlapped, so people exposed only to amosite cannot be identified with certainty
  • Fiber measurements were few, inconsistently defined and often averaged across sites or over time
  • Scarce hygiene data and incomplete employment records, especially for black workers, meant the studies generally could not do dose-response analyses
  • Some mesotheliomas in Limpopo Province may not have been included in published studies (under-ascertainment)
  • Lung cancer studies in asbestos workers are confounded by smoking; only the 1992 study controlled for it

Topics

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

Medical terms in this study, explained in our Lexicon: Amosite, Crocidolite.

Related studies

• Rapporteur's Report Session 3: exposure to grunerite (amosite) asbestos: historical perspectives of the health effects — G.W. Gibbs (2008)
• 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)
• Re: "Excess mortality from stomach cancer, lung cancer, and asbestosis and/or mesothelioma in crocidolite mining districts in South Africa" — H.P. Hart (1987)
• Risk of asbestosis in crocidolite and amosite mines in South Africa — L.M. Irwig, R.S. du Toit, et al. (1979)
• Asbestos-related disease in South Africa: the social production of an invisible epidemic — L. Braun, S. Kisting (2006)
• Risk of asbestosis in crocidolite and amosite mines in South Africa: an erratum — L.M. Irwig, R.S. du Toit, et al. (1984)

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