The hazards of chrysotile asbestos: a critical review

Our plain-English summary of The hazards of chrysotile asbestos: a critical review, by P.J. Landrigan, W.J. Nicholson, Y. Suzuki, et al (Industrial Health, 1999).

The study

• Authors: P.J. Landrigan, W.J. Nicholson, Y. Suzuki, J. Ladou
• Journal: Industrial Health
• Published: 1999;37(3):271-80
• Type of article: Review
• Cited by: 61 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Chrysotile, or "white", asbestos is the dominant form of asbestos in international commerce today. It accounts for 99% of current world asbestos production of 2 million tonnes. Chrysotile is an extremely hazardous material. Clinical and epidemiologic studies have established incontrovertibly that chrysotile causes cancer of the lung, malignant mesothelioma of the pleura and peritoneum, cancer of the larynx and certain gastrointestinal cancers. Chrysotile also causes asbestosis, a progressive fibrous disease of the lungs. Risk of these diseases increases with cumulative lifetime exposure to chrysotile and rises also with increasing time interval (latency) since first exposure. Comparative analyses have established that chrysotile is 2 to 4 times less potent than crocidolite asbestos in its ability to cause malignant mesothelioma, but of equal potency of causation of lung cancer. The International Agency for Research on Cancer of the World Health Organization has declared chrysotile asbestos a proven human carcinogen. Sales of chrysotile asbestos have virtually ended in Western Europe and North America, because of widespread recognition of its health hazards. However, asbestos sales remain strong in Japan, across Asia and in developing nations worldwide. The claim has been made that chrysotile asbestos can be used "safely" under "certain conditions" in those nations. That claim is not accurate. The Collegium Ramazzini, an international learned society in environmental and occupational medicine, has called for an immediate worldwide ban on all sales and uses of all forms of asbestos, including chrysotile. The rationale for this ban is threefold: (1) that safer substitute materials are readily available, (2) that "controlled" use of asbestos is not possible, and (3) that the health risks of asbestos are not acceptable in either the industrialized or the newly industrializing nations.

In plain English

This article was a review. The authors examined published studies of workers exposed to chrysotile alone or mixed with other asbestos. A cited study of 17,800 insulation workers attributed nearly 24% of deaths to bronchogenic (lung) carcinoma and 9% to mesothelioma. In three chrysotile textile studies, lung cancer risk rose 1% to 2.6% per year of exposure to 1 fiber/ml. Chrysotile miners and millers still had excess lung cancer, but their risk per unit of exposure was over 10 times lower than chrysotile production workers'. Across more than 40 studies, the mesothelioma-to-excess-lung-cancer ratio was the same, within statistical uncertainty, for chrysotile, amosite and mixtures. Only 100% crocidolite appeared to have a higher ratio, about two to four times that of predominantly chrysotile exposures. In 632 New York and New Jersey insulators, mesothelioma timing was reported incompatible with amosite as the sole cause, barring undiscovered amphibole exposures before 1935. The authors noted uncertain early exposure data and small numbers. They concluded that chrysotile's role as a potent cause of lung cancer and malignant mesothelioma is incontrovertible, and called for a worldwide ban.

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 published epidemiologic studies (not a new study)
• Who was studied: Asbestos-exposed worker populations from previously published studies, including insulation workers, textile, friction-product and cement workers, and chrysotile miners and millers. More than 40 studies were included in the mesothelioma ratio analysis.
• Exposure: Commercial chrysotile asbestos alone or mixed with other asbestos types (amosite, crocidolite), compared with pure amosite and pure crocidolite exposures. Exposure was expressed as years of exposure at a given fiber/ml level.
• Main results:
  • In a cited study of 17,800 heavily exposed asbestos insulation workers (Selikoff and Seidman), nearly 24% of deaths were due to bronchogenic carcinoma and 9% to mesothelioma.
  • In three chrysotile textile manufacturing studies, lung cancer risk ranged from 1% to 2.6% per 1-year exposure to 1 fiber/ml.
  • Lung cancer risk per cumulative fiber exposure was very similar for all exposure circumstances except chrysotile mining and milling.
  • Chrysotile mining and milling studies showed an excess risk of lung cancer. The risk per unit of exposure was more than 10 times lower than in production workers exposed only to chrysotile or to 97% to 98% pure chrysotile.
  • The authors' best estimate for workers in industries using chrysotile (as opposed to mining and milling) was a 1% increase in lung cancer risk for each year of exposure to 1 fiber/ml (KL = 0.01).
  • The ratio of mesothelioma to excess lung cancer was the same, within statistical uncertainty, for 100% chrysotile, 97%+ chrysotile, 100% amosite, and mixtures of chrysotile, amosite and crocidolite.
  • Only 100% crocidolite exposures appeared to have a greater ratio of mesothelioma to excess lung cancer, about two to four times above that of predominantly chrysotile exposures.
  • The authors described an analysis of 632 members of the New York and New Jersey locals of the Insulator's Union who were members on January 1, 1943.
  • In those 632 insulators, the time course of mesothelioma deaths was reported as totally incompatible with an exposure pattern beginning only in the late 1930s, when amosite came into use.
  • Barring undiscovered amphibole exposures before 1935, the authors described these data as strong evidence that chrysotile was the dominant contributor to mesothelioma risk in this group of insulators.
  • The authors cited an estimate that the strictest exposure limit in the world for chrysotile (0.1 f/ml) is associated with a lifetime lung cancer risk of 2.3 per 1,000.
• The authors' conclusion: The authors concluded that the evidence that chrysotile asbestos is a potent cause of both lung cancer and malignant mesothelioma is incontrovertible. They supported an immediate worldwide ban on asbestos.
• Limitations the authors state:
  • Only limited data exist on workplace asbestos exposures before the mid-1960s, which makes the lung cancer risk estimates uncertain.
  • Early exposure data were usually particle counts, and the relationship between particle and fiber counts is highly uncertain.
  • Mesothelioma risk estimates (KM) are not definite because of uncertain early exposures and small numbers.
  • The reason for the lower lung cancer risk in chrysotile miners and millers is not fully understood.
  • The insulator analysis assumes there were no undiscovered amphibole exposures before 1935.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Malignant Mesothelioma, Pleura, Peritoneum, Laryngeal Cancer, Latency, Crocidolite, Causation.

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