The carcinogenicity of chrysotile asbestos

Our plain-English summary of The carcinogenicity of chrysotile asbestos, by J.S. Harington (Annals of the New York Academy of Sciences, 1991).

The study

• Author: J.S. Harington
• Journal: Annals of the New York Academy of Sciences
• Published: 1991;643:465-72
• Type of article: Review
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In in vitro test systems, chrysotile is markedly toxic, causes chromosomal aberrations, and is capable of inducing morphological and preneoplastic transformation. In carefully designed animal experiments, chrysotile produces lung cancer and mesothelioma as effectively as do the amphiboles tested. Human population studies do not refute these experimental results. Chrysotile asbestos is carcinogenic to humans, especially for the induction of lung cancer and mesothelioma in exposed populations. For cancers of other sites, with the exception of laryngeal and possibly gastrointestinal cancer, the evidence for association with exposure to all forms of asbestos, including chrysotile, is not yet adequate for evaluation.

In plain English

This article was a review, not a new study. The author gathered published cell, animal and human research on chrysotile asbestos and cancer. In the reviewed laboratory work, chrysotile damaged chromosomes and transformed cells. In rat inoculation experiments it was as carcinogenic as crocidolite or amosite. The author examined eight human studies with dose-response data, covering mining and milling, textile manufacture and brake manufacture in Quebec, northern Italy, South Carolina and England. In these eight studies, reported lung cancer standardized mortality ratios ranged from 106 for the whole Italian mining cohort to 315 for South Carolina textile workers. Four other studies were also reviewed. In Rochdale, England, 14 men died of mesothelioma, of whom three were excluded for record purposes. Small amounts of crocidolite (approximately 5%) may have contributed, perhaps substantially, to that risk. The author stated that chrysotile causes fewer mesotheliomas than crocidolite or amosite under the exposure conditions studied. The author concluded that chrysotile is carcinogenic to humans, especially for lung cancer and mesothelioma. The author noted that the dose-response evidence was weak and that few studies involved exposure ostensibly to chrysotile and no other commercial asbestos.

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 of published cell and tissue studies, animal experiments and human epidemiological studies
• Who was studied: Published studies. The human studies included eight with dose-response data from three occupational categories: chrysotile mining and milling in Quebec and northern Italy, textile production in South Carolina and Rochdale (England), and friction-product manufacture at the Ferodo brake plant (England). Four further studies were reviewed: retired US asbestos maintenance employees aged 65 or over, two studies of British World War II gas mask assemblers, and Connecticut friction-product workers. Lung-content data from mesothelioma patients in Osaka, Japan, were also discussed.
• Exposure: Chrysotile asbestos, compared with the amphiboles crocidolite and amosite, with discussion of tremolite contamination of commercial chrysotile
• Main results:
  • In the reviewed cell studies on Syrian hamster embryo cells, chrysotile was nearly twice as potent as crocidolite in inducing cell transformation
  • In the reviewed rat inoculation experiments, chrysotile was as carcinogenic as crocidolite or amosite
  • South Carolina chrysotile textile plant: one study (Dement et al., 1983) found a lung cancer SMR of 315. A second study (McDonald et al., 1983) found an SMR of 199.5 in men 20 or more years after first exposure, with an exposure-response relationship some 50-fold steeper than for Quebec miners and millers.
  • Quebec miners and millers: 11 mesotheliomas were found, rising to 18 by 1978. The exact number is uncertain because there was no pathology review.
  • Northern Italy mining and milling: the lung cancer SMR was 106 for the total cohort and rose to 206 during the last 5 years of observation as latency increased
  • Rochdale textile factory: the lung cancer SMR was 131. Fourteen men died of mesothelioma, of whom three were excluded for record purposes. Small amounts of crocidolite (approximately 5%) may have contributed, perhaps substantially, to the risk.
  • Ferodo brake factory: there was no increase in lung cancer risk with duration or cumulative exposure (SMR = 108 and 122). There were 11 deaths from pleural mesothelioma, and eight of these workers might have been exposed to crocidolite.
  • Retired US maintenance employees: men exposed only to chrysotile had lung cancer mortality 2.4 times the expected (SMR = 236.4), compared with 5.3 times the expected (SMR = 526.3) for men exposed to chrysotile and crocidolite
  • British gas mask workers (Acheson et al.): 570 women exposed to chrysotile had an SMR of 145 for cancer of the lung and pleura, compared with 241 for the crocidolite group. Five of the six mesotheliomas were in the crocidolite-exposed group.
  • Connecticut friction-product workers exposed only to chrysotile: lung cancer SMR of 148.7. No mesothelioma deaths were reported in the study, although other sources identified three.
  • Osaka lung-content data: asbestos fibers were found in 19 of 23 mesothelioma patients. In six of these cases (five pleural and one peritoneal mesothelioma), only chrysotile was found, with no tremolite or other amphiboles.
• The authors' conclusion: The author concluded that chrysotile asbestos is carcinogenic to humans, especially for lung cancer and mesothelioma, while causing fewer mesotheliomas than crocidolite or amosite under the exposure conditions studied. The author considered the question of tremolite contamination to be of academic rather than practical concern.
• Limitations the authors state:
  • The dose-response evidence in the human studies is weak, even if it is the best available
  • Few occupational studies involved exposure ostensibly to chrysotile and to no other commercial form of asbestos
  • Other minerals mixed with chrysotile may have contributed to the effects seen
  • Fibers found in lung burden studies may not reflect past exposure
  • In the gas mask studies the populations were small and chrysotile exposure lasted less than five months, so the two exposure types could not be compared

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Lung Cancer, Mesothelioma, Amphibole Group, Carcinogenic.

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