Mesotheliomas and chrysotile

Our plain-English summary of Mesotheliomas and chrysotile, by P. Elmes (The Annals of Occupational Hygiene, 1994).

The study

• Author: P. Elmes
• Journal: The Annals of Occupational Hygiene
• Published: 1994;38(4):547-53, 415
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Mesotheliomas are rare. While most are reported to be associated with exposure to durable fibres, a proportion are not caused by the inhalation of fibres at all. Reports of individual cases and studies of small groups are unreliable as evidence of cause because: (a) diagnosis is often unreliable; (b) even if chrysotile fibres are found in lung tissues, the mesothelioma may still be spontaneous. Present knowledge has not progressed much since 1964 when the absence of cases of mesothelioma in amosite and chrysotile miners in South Africa and the very low incidence in Canadian mines was known but not believed. Now we know this information was correct. The significance of low-level amphibole exposures in predominantly chrysotile mixes was not appreciated until studies of fibres in lungs using electron microscopy showed the high lung burden of amphibole fibres in the 1970s and 1980s. The effect of these findings is to make most European and U.S.A. factory cohorts inappropriate for the evaluation of chrysotile mesothelioma risk. Reviewing the current evidence published and unpublished, it seems likely that chrysotile uncontaminated by tremolite may not have caused any mesotheliomas even at high cumulative life-time exposures. Information on the mesothelioma risk among chrysotile user populations using fibres not containing tremolite is badly needed.

In plain English

This article was a review, read as a paper at a 1993 workshop on health risks of chrysotile asbestos. It assessed evidence since 1964 on whether chrysotile causes mesothelioma, and reported no new data. The author reviewed mines, user industries and environmental exposures, such as tremolite-contaminated soil, in Southern Africa, Australia, China, Russia, Turkey, the Mediterranean area, Finland, Canada, the United States, Europe and Japan, plus animal studies. Many case reports lacked lung fibre analysis. Some cohorts once thought exposed only to chrysotile, such as a Lancashire factory cohort, later showed crocidolite in workers' lungs. Southern African chrysotile miners had very few cases of lung cancer, let alone mesothelioma, though studies there were incomplete. Studies of Canadian and US mines had confirmed a low level of mesothelioma risk. The author stated that the evidence was not yet conclusive. The author nonetheless concluded that risk would be negligible if mines and mine mills were kept within present-day safety limits, and that it may be possible to mine chrysotile ore containing less than a certain amount of fibrous tremolite without any risk of mesothelioma.

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 presented as a workshop paper; no new data collected
• Who was studied: Evidence since 1964 on mesothelioma in chrysotile and amphibole mines, user industries and environmentally exposed populations in many countries, plus animal studies
• Exposure: Chrysotile, including chrysotile contaminated with tremolite, compared with amphibole fibres (crocidolite, amosite, anthophyllite, tremolite) and erionite; occupational and environmental (soil and rock) exposures
• Main results:
  • The author put the latent interval between first exposure and mesothelioma at somewhere between 40 and 50 years
  • Among miners and mine mill workers at Southern African chrysotile mines, the author reported very few cases of lung cancer, let alone mesothelioma, while noting that formal studies were incomplete
  • In the Lancashire factory cohort once treated as a 'pure' chrysotile exposure, later lung fibre analysis showed crocidolite levels consistent with crocidolite being the cause of the mesotheliomas
  • Studies of the mines in Eastern Canada and the United States confirmed a low level of mesothelioma risk, which seemed to vary from mine to mine
  • In the one study the author knew of pure chrysotile exposure in civilian gas-mask making, there was probably no mesothelioma risk, but the study had no lung fibre analysis
  • In south-east Turkey, where early reports implicated chrysotile, closer study found the fibre to be tremolite
  • Where tremolite in the rock contaminates the soil in Eastern Europe and the Mediterranean basin, in most areas the only risk was pleural plaques in agricultural workers
  • Animal studies showed that chrysotile changes and is cleared from lung tissue, whereas amphiboles remain unchanged
• The authors' conclusion: The author concluded that the evidence was not yet conclusive. The author also concluded that the risk would be negligible if the mines and mine mills were kept within present-day safety limits, and that it may be possible to mine chrysotile ore containing less than a certain amount of fibrous tremolite without any risk of mesothelioma.
• Limitations the authors state:
  • The author stated that the evidence on human experience was not yet conclusive
  • The author stated that only a few studies are relevant to the risk from pure chrysotile exposure
  • The author stated that many case reports and survey series had no lung fibre analysis
  • The author stated that formal studies of Southern African chrysotile mines were incomplete because of social and political difficulties

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Chrysotile, Amosite, Amphibole Group, Tremolite.

Related studies

• Human evidence: lung cancer mortality risk from chrysotile exposure — J.M. Hughes (1994)
• Deposition and clearance of chrysotile asbestos — A. Churg (1994)
• Chrysotile, tremolite, and mesothelioma — J.C. McDonald, A.D. McDonald (1995)
• Chrysotile asbestos is the main cause of pleural mesothelioma — A.H. Smith, C.C. Wright (1996)
• Inferences on the kinetics of asbestos deposition and clearance among chrysotile miners and millers — M.M. Finkelstein, A. Dufresne (1999)
• Pulmonary mineral fibers after occupational and environmental exposure to asbestos in the Russian chrysotile industry — A. Tossavainen, E. Kovalevsky, et al. (2000)

Browse more research in The Annals of Occupational Hygiene, or return to medical research.