Health effects of tremolite. Now and in the future

Our plain-English summary of Health effects of tremolite. Now and in the future, by B.W. Case (Annals of the New York Academy of Sciences, 1991).

The study

• Author: B.W. Case
• Journal: Annals of the New York Academy of Sciences
• Published: 1991;643:491-504
• Type of article: Review
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Although tremolite asbestos has been well characterized since 1916, appreciation of its role in disease induction is relatively recent. It has always been understood that the morphology of tremolite is complex, and part of the slowness in recognizing it as a hazard has been definitional in nature. Reduced to simple terms the questions are, when is tremolite "asbestos-like," when is it an innocuous amorphous particle, do these forms occur together, with what confidence can they be separated for regulatory purposes, and what is the spectrum of disease potential for varying exposure? A brake on regulation is partially due to a convergence of opinion of unlikely and unintentional allies: industries producing tremolite-containing materials and some epidemiologists resisting attribution of risk to tremolite on the grounds that its known effects--pleural plaques, asbestosis, lung cancer and mesothelioma--are principally due to chrysotile, which is often contaminated with fibrous tremolite. The latter group concentrate their skepticism on internal-dose biomarker studies associating lung tremolite content with mesothelioma (but not so clearly with lung cancer or asbestosis). They ignore the basic carcinogenic quality of fibrous tremolite, shown in both animal and epidemiological studies. Evidence from the Quebec chrysotile/tremolite mining districts suggests that very low concentrations of tremolite in ambient air can be translated into high concentrations in lung, even in those without occupational exposure. Disease incidence, especially for mesothelioma, seems also to be associated with tremolite air and lung content. The risk associated with tremolite has been demonstrated in Corsica, Cyprus, the United States, and Canada. Of particular importance is an apparent increase in the proportion of mesothelioma risk attributable to tremolite, since the fibers heretofore most responsible for that disease--commercial amphiboles--have been or are being severely regulated or completely eliminated in production and use. Further, amosite and crocidolite, while still a concern, form a small fraction of "asbestos-in-place": most of this material is chrysotile and we do not really know to what degree it is contaminated with tremolite. The available evidence suggests that bulk analysis or airborne fiber analysis will not answer this question, and perhaps only animal bioaccumulation assay is sufficient. Until we know more, it seems prudent for public health to avoid dispersing chrysotile/tremolite into the environment, and, where we can, to regulate all tremolite "fibers" conservatively.

In plain English

This paper reviewed and commented on the health effects of tremolite, a mineral that contaminates chrysotile. It covered regulation, human and animal studies, and the author's own lung-tissue studies in the Quebec chrysotile mining region. In a prospective autopsy study, 19 environmentally exposed Thetford-area residents were compared with environmentally exposed Asbestos-area residents studied earlier. The Thetford group's lungs held more asbestos bodies (median 1880 versus 480 per gram of dry lung) and more tremolite (geometric mean 0.33 versus 0.08 fibers per microgram), while chrysotile levels were about equal. Four of the 19 had pleural plaques, which the author attributed to tremolite. No plaques were seen in 29 non-occupationally exposed Asbestos-area residents. In a retrospective study of 74 autopsies, published only as an abstract, possible household contact appeared to add little lung fiber, but people with definite household exposure (a father or husband in the mines or mills at least 15 years) had about an order of magnitude more lung chrysotile and tremolite. The author noted small numbers and possible autopsy selection bias. The author concluded that the tremolite component of Quebec chrysotile causes 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: Review and commentary on tremolite health effects (regulation, epidemiology, animal studies), including the author's own autopsy lung-content (internal dose) studies in Quebec. One retrospective Thetford study is reported here and was otherwise unpublished except as an abstract.
• Who was studied: Residents and chrysotile miners and millers autopsied in the Quebec chrysotile mining region. The retrospective Thetford study used lung paraffin blocks from 74 area residents autopsied at one small regional hospital: 20 referents, 14 neighborhood, 8 possible domestic, 10 definite domestic, and 22 miners and millers. Earlier studies covered 19 environmentally exposed Thetford-area residents (10 neighborhood, 9 domestic) and, in Asbestos, 29 non-occupationally exposed residents plus 23 miners and millers.
• Exposure: Environmental exposure (living near the mines, or household contact with a mine or mill worker) and occupational exposure to chrysotile and its contaminant tremolite in the Quebec mining region. Exposure was measured as asbestos bodies and fibers in lung tissue.
• Main results:
  • The 19 environmentally exposed Thetford-area residents had more lung asbestos bodies than environmentally exposed residents of the Asbestos area (median 1880 versus 480 per gram of dry lung, p less than .01).
  • The same 19 Thetford-area residents had more lung tremolite than the Asbestos-area group (geometric mean 0.33 versus 0.08 fibers per microgram of dry lung, p less than .05).
  • Lung chrysotile was about equal in the two groups (geometric mean 0.33 in Thetford versus 0.28 fibers per microgram in Asbestos; not significant).
  • Four of the 19 environmentally exposed Thetford-area residents had pleural plaques (two domestic, two neighborhood).
  • Because chrysotile exposure was similar to that in the Asbestos area, where no plaques were seen, the author attributed these plaques to tremolite.
  • In the Asbestos-area study, none of the 29 non-occupationally exposed individuals had asbestos-related disease or pleural plaques.
  • In the retrospective Thetford study, possible household contact (siblings or offspring who worked a year or more in the asbestos industry) appeared to add little lung fiber content.
  • In the retrospective Thetford study, people with definite household exposure (father or husband who worked in mines or mills at least 15 years) had about an order of magnitude excess of lung chrysotile and tremolite. Miners and millers had a further order of magnitude more.
  • In the retrospective Thetford study, lung tremolite rose with years lived in the region (Spearman R = .62) and fell with distance lived from the mines (R = -.75).
  • In the retrospective Thetford study, respiratory cancer was found in 4 of 30 autopsies of those living nearest the mines and in none of the 20 referents living more than 10 km away without domestic exposure.
• The authors' conclusion: The author concluded that the tremolite component of Quebec chrysotile is what causes mesothelioma.
• Limitations the authors state:
  • The author's own studies had very small numbers of subjects and may be affected by autopsy selection bias.
  • The Asbestos-area study did not separate neighborhood exposure from household exposure.
  • No proper analytical epidemiological study of environmental exposure alone had yet been done in the area.
  • The author cautioned against applying animal results directly to human exposure.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Jeffrey mine, Asbestos, Quebec

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Tremolite, Attribution, Pleural Plaques, Lung Cancer, Mesothelioma, Chrysotile, Biomarker, Carcinogenic.

Related studies

• Health of vermiculite miners exposed to trace amounts of fibrous tremolite — J.C. McDonald, A.D. McDonald, et al. (1988)
• Variations in the carcinogenicity of tremolite dust samples of differing morphology — J.M. Davis, J. Addison, et al. (1991)
• Cohort study of mortality of vermiculite miners exposed to tremolite — J.C. McDonald, A.D. McDonald, et al. (1986)
• Health effects of tremolite. This official statement of the American Thoracic Society was adopted by the ATS Board of Directors, June 1990 — (1990)
• Chrysotile, tremolite, and malignant mesothelioma in man — A. Churg (1988)
• Biological effects of tremolite — J.C. Wagner, M. Chamberlain, et al. (1982)

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