The carcinogenicity of chrysotile asbestos--a review

Our plain-English summary of The carcinogenicity of chrysotile asbestos--a review, by W.J. Nicholson (Industrial Health, 2001).

The study

• Author: W.J. Nicholson
• Journal: Industrial Health
• Published: 2001;39(2):57-64
• Type of article: Review
• Cited by: 40 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The world production of asbestos has been declining dramatically in recent years, particularly in Europe and the United States. However, increases have occurred in Asian nations and chrysotile is the dominant fiber used. Important uses are in cement products, wallboards, friction products and textiles. From studies in the United States and Great Britain, chrysotile has been shown to increase the risk of lung cancer and to produce mesothelioma in exposed workers.

In plain English

This article reviewed published research on chrysotile asbestos and cancer. About 99% of new asbestos use involved chrysotile. For lung cancer, the author compiled estimates from earlier worker studies. Excluding mining and milling, the geometric mean lung cancer increase was 1.0% per year of exposure to 1 fiber per ml. The figure for chrysotile mining and milling was about ten-fold lower. For mesothelioma, across more than 40 studies with little or no exposure information, the ratio of mesotheliomas to excess lung cancers, adjusted to a common underlying lung cancer risk, was the same within statistical uncertainty for chrysotile, amosite and mixed exposures. An earlier analysis of 632 New York and New Jersey insulators found that amosite alone predicted less than one-fifth of the 56 observed mesotheliomas. Calculated per-fiber risk was virtually the same for mainly chrysotile, chrysotile-amosite and amosite exposures. The author concluded that chrysotile is a potent cause of mesothelioma, similar to amosite per fiber, with crocidolite appearing four to ten times more potent. The author noted that uncertain early exposures and small numbers made these figures uncertain.

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 (single author) of published epidemiological studies and earlier analyses of chrysotile asbestos and cancer, including production and use data
• Who was studied: Workers in earlier published studies of asbestos exposure, chiefly in the United States, Canada, Great Britain and Australia. These included textile, insulation, asbestos products, cement and friction products workers, and chrysotile and crocidolite miners. The review also covered an earlier analysis of 632 New York and New Jersey insulation union members followed from 1943.
• Exposure: Chrysotile asbestos, compared with the amphiboles amosite and crocidolite (one table also includes anthophyllite and talc containing tremolite). The jobs covered included textile manufacturing, insulation work, cement products, friction products, and mining and milling.
• Main results:
  • About 99% of all new asbestos use involved chrysotile at the time of writing
  • Lung cancer: across the compiled studies, excluding mining and milling, the geometric mean percentage increase in lung cancer for a 1-year exposure to 1 fiber/ml was 1.0
  • Lung cancer: the value for chrysotile mining and milling was about ten-fold lower
  • Mesothelioma: the comparison of mesothelioma to excess lung cancer covered more than 40 studies for which little or no exposure information was available (table from Nicholson and Raffn)
  • In this comparison, the excess numbers of lung cancer were adjusted to the same underlying lung cancer risk (the table notes adjustment to U S male cancer rates in 1970)
  • Mesothelioma, more than 40 studies: the ratio of mesothelioma to adjusted excess lung cancer was the same, within statistical uncertainty, for 100% chrysotile, 97%+ chrysotile, 100% amosite and mixed exposures
  • Mesothelioma, same comparison: only 100% crocidolite exposures had a greater ratio, about two to four times that of predominantly chrysotile exposures
  • Mesothelioma, 632 New York and New Jersey insulators with 56 mesothelioma deaths (earlier analysis by Nicholson and Landrigan): the estimate of mesotheliomas from amosite exposure alone was less than one-fifth of the number observed
  • Mesothelioma risk per fiber exposure was virtually the same for three exposure groups: 97% chrysotile plus 3% crocidolite (textile production, 1.0 × 10 to the minus 8), 60% chrysotile plus 40% amosite (insulation application, 1.5 × 10 to the minus 8) and 100% amosite (factory workers, 3.2 × 10 to the minus 8)
  • Mesothelioma risk per fiber exposure for pure crocidolite exposure in the Australian mining population was about ten times greater
  • At the Rochdale, England textile plant, 2.6% of the asbestos fiber purchased from 1932 to 1968 was crocidolite; the author estimated that chrysotile contributed 66% of the total mesothelioma risk there
• The authors' conclusion: The author concluded that the case for chrysotile being a potent cause of mesothelioma is strong and that its per-fiber mesothelioma risk is similar to amosite's. The author also concluded that crocidolite appeared to have a four to ten times greater potential to produce mesothelioma for equal exposure.
• Limitations the authors state:
  • The compiled lung cancer studies varied substantially in statistical quality; some, such as the brake products studies, had low exposures and large uncertainties
  • All studies relied on a relatively limited number of exposure estimates made from particle counts in earlier years
  • The reason for the lower lung cancer risk in chrysotile mining and milling than in textile production is not fully understood
  • Mesothelioma risk coefficients are uncertain because exposures in the early years are uncertain and numbers are small
  • In the insulator analysis, the relative amounts of amosite and chrysotile after 1935 were uncertain, so the expected cases were adjusted to match the 56 observed mesotheliomas
  • The South Carolina textile workers had only two mesotheliomas, and misdiagnosis on death certificates must be considered

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Friction Products, Lung Cancer, Mesothelioma.

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