South African experience with asbestos related environmental mesothelioma: is asbestos fiber type important?

Our plain-English summary of South African experience with asbestos related environmental mesothelioma: is asbestos fiber type important?, by N. White, G. Nelson, J. Murray (Regulatory Toxicology and Pharmacology, 2008).

The study

• Authors: N. White, G. Nelson, J. Murray
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2008;52(1 Suppl):S92-6
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

South Africa (SA), a country in which all three commercially important asbestos minerals have been mined and milled, has retained proven cases of mesothelioma linked with environmental exposure to asbestos. This study illustrates the importance of fiber type in the occurrence of environmental mesothelioma. Four studies have reviewed the source of occupational or environmental asbestos exposure in 504 histologically proven cases of mesothelioma in South Africa. One hundred and eighteen cases (23%) were thought to be related to environmental exposure to asbestos. In the vast majority of these cases, exposure was linked to crocidolite mining activities in the Northern Cape Province. Two cases were thought to have occurred in relation to amosite and Transvaal crocidolite exposure in the Limpopo Province. In the balance of cases there was some uncertainty. No cases were reported with exposure to South African chrysotile. Consequently, in the vast majority of cases of mesothelioma, environmental exposure to asbestos occurred in the Northern Cape Province, in proximity to mines, mills and dumps where crocidolite was processed. Crocidolite appears to be far more mesotheliomagenic than amosite, and chrysotile has not been implicated in the disease. This is true for both occupationally and environmentally exposed individuals.

In plain English

This article was a review. The authors pooled four earlier South African reports, published in 1973, 1978, 1984 and 1999, that recorded how 504 people with histologically proven mesothelioma had been exposed to asbestos. The first three were case series. The 1999 report, by Rees and colleagues, was a case-control study. Across the four, 118 of the 504 cases (23%) were classed as environmental exposure, meaning exposure outside work. Each study defined this differently. Fiber type was known for only 35 of these 118 cases. Of those, 33 (94%) involved Cape crocidolite. Two involved amosite, and both also involved crocidolite. No cases were linked to chrysotile. From the Rees study, the review reported relative risks for environmental exposure of 21.9 for Cape crocidolite and 7.1 for mixed amosite and Transvaal crocidolite compared with cancer controls. Compared with medical controls, the figures were 50.9 and 12.0. The authors concluded that fiber type is important and that crocidolite represents the greatest hazard at low doses. They noted that the earlier studies reported fiber types unevenly.

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: Review of four earlier South African studies (three case series and one case-control study) of mesothelioma cases and their asbestos exposure
• Who was studied: 504 histologically proven mesothelioma cases in South Africa, drawn from four published studies: Webster (1973), Cochrane and Webster (1978), Solomons (1984) and Rees et al. (1999)
• Exposure: Occupational (mining and non-mining) and environmental asbestos exposure, as each original study defined it. Fiber types considered were Cape crocidolite (Northern Cape Province), Transvaal crocidolite (Limpopo Province), amosite and chrysotile.
• Main results:
  • Across the four studies, 118 of 504 cases (23%) were attributed to environmental exposure to asbestos
  • Among the 118 environmentally exposed cases, fiber type was determined in 35. Of these 35, 33 (94%) had been exposed to Cape crocidolite.
  • Only two environmentally exposed cases involved amosite, and both had also been exposed to crocidolite. The article's table lists these as Transvaal crocidolite plus amosite.
  • No cases of mesothelioma in South Africa were reported in association with chrysotile
  • In the Rees et al. (1999) study, amosite exposure was reported in three miners (10% of the occupationally exposed cases) and in none of the environmentally exposed cases
  • Rees et al. (1999) reported relative risks for environmental exposure. Compared with cancer controls, the figures were 21.9 for Cape crocidolite and 7.1 for mixed amosite and Transvaal crocidolite. Compared with medical controls, they were 50.9 and 12.0. No confidence intervals were given.
• The authors' conclusion: The authors concluded that asbestos fiber type is important for environmental mesothelioma. They found that most such cases with known fiber type were related to crocidolite mining activities in the Northern Cape, and judged that crocidolite represents the greatest hazard to human health at low exposure doses.
• Limitations the authors state:
  • The original studies did not give the same detail on fiber types, especially for environmental exposure
  • Three of the four studies were case series. Only Rees et al. (1999) was an analytical study.
  • Except for Rees et al., the studies gave no information on the geographic regions the cases came from or lived in
  • Mesothelioma is under-reported to official data sources
  • There are few local epidemiological studies of mesothelioma in South Africa

Topics

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

Medical terms in this study, explained in our Lexicon: Environmental Mesothelioma, Asbestos, Mesothelioma, Environmental Exposure, Asbestos Exposure, Crocidolite, Northern Cape Province, Amosite.

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)
• Compensation for environmental asbestos-related diseases in South Africa: a neglected issue — N. Ndlovu, J.T. Naude, et al. (2013)
• Risk of mesothelioma from exposure to crocidolite asbestos: a 1995 update of a South African mortality study — D. Kielkowski, G. Nelson, et al. (2000)
• Cape Plc: South African mineworkers' quest for justice — R. Meeran (2003)
• 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)
• Health effects of amosite mining and milling in South Africa — J. Murray, G. Nelson (2008)

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