Cancer In Chrysotile Mines And Mills

Our plain-English summary of Cancer In Chrysotile Mines And Mills, by J.C. Mcdonald (1973).

The study

• Author: J.C. Mcdonald
• Published: Biological Effects Of Asbestos (J.C. Wagner, Editor), Lyon: Iarc Scientific Publications, Volume 8, Pp. 189-194 (1973)
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library, J-M no. 001308. The article is still under copyright, so we describe it here rather than post it.

In plain English

This 1973 article is the author's review of evidence on cancer among chrysotile asbestos miners and millers. It drew mainly on a Quebec mortality study of about 12,000 people employed for more than one month in the industry, along with a similar study in northern Italy and reports from other mining countries. In the Quebec cohort there were 134 respiratory cancers in men, including five pleural mesotheliomas. About 139 were expected from Quebec death rates, or about 93 from estimated rates for the mining region. Any excess was virtually confined to men with a dust index above 200 mppcf-years. A reanalysis by another method estimated 95 expected male respiratory cancer deaths against 136 observed. Across six producing countries, eleven mesothelioma cases (nine probable, two doubtful) came to light. For gastro-intestinal cancer there was only a suggestion of an increased rate above 400 mppcf-years. The author concluded that the evidence linking chrysotile mining and milling to cancer was not strong. It appeared to show a modest increase in respiratory and probably gastro-intestinal cancer, most serious in heavily exposed long-term workers, and the author called the link with mesothelioma weak.

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 epidemiological studies of cancer in chrysotile mining and milling, drawing mainly on the author's group's Quebec cohort mortality study (combined results of two earlier analyses plus a provisional reanalysis), a comparable Italian cohort and a survey of mesothelioma cases in producing countries
• Who was studied: A Quebec cohort of some 12,000 people who had ever worked in any part of the chrysotile mining and milling industry for more than one month, with 2457 deaths up to November 1966 and a further 813 deaths up to the end of 1969. Also covered: a cohort of 1,098 chrysotile mine and mill workers at Balangero, northern Italy (study by Viglani and colleagues), and mesothelioma cases from six chrysotile-producing countries.
• Exposure: Chrysotile dust in mines and mills. Exposure was measured by a dust index: dust level in millions of particles per cubic foot (mppcf) multiplied by years at that level, summed. The review also covered household and neighbourhood exposure for mesothelioma cases.
• Main results:
  • Quebec cohort: 135 respiratory cancers in all, 134 in men, including five pleural mesotheliomas. The number expected in men was 139 on Quebec death rates, or about 93 on estimated rates for the mining region.
  • The author stated that respiratory cancer mortality in chrysotile workers was at most about 45% above expectation. The scan prints '457', which matches 134 observed against about 93 expected.
  • Any respiratory cancer excess was virtually confined to people with a dust index above 200 mppcf-years, and was most evident above 400 mppcf-years.
  • Men in the highest exposure category who were employed 30 years or more had about five times the respiratory cancer mortality rate of men in the lowest exposure group employed less than one year. The author noted the numbers were very small.
  • A provisional reanalysis by another method estimated 95 expected male respiratory cancer deaths in the cohort, compared with 136 observed. The excess appeared somewhere between 100 and 400 mppcf-years.
  • Among X-rayed cohort members (785 deaths), most of the excess mortality was in men with radiographic parenchymal changes and was attributable to respiratory disease, including cancer.
  • In six countries producing 92% of the world's chrysotile, eleven mesothelioma cases (nine probable, two doubtful) were found. Almost all were in Canada.
  • Among the Quebec industry mesothelioma cases with dust data, the men tended to be long-term employees, but there was little or no relation to dust index.
  • The author stated that the eight definite mesothelioma cases were at least four times expectation. The author judged it unlikely that better ascertainment explained this completely.
  • Gastro-intestinal cancer: there was a suggestion of an increased rate in men with a dust index above 400 mppcf-years. The site distribution did not follow any consistent pattern.
• The authors' conclusion: The author concluded that the evidence linking cancer to work in chrysotile production was not strong. The results appeared to show a modest increase in respiratory and probably gastro-intestinal cancer, most serious in those heavily exposed over long periods. This hazard would probably not be detectable below about 200 mppcf-years. The link with malignant mesothelioma was also weak, with no evidence of an association with peritoneal tumours. Too few chrysotile-related tumours existed for firm conclusions on exposure-response.
• Limitations the authors state:
  • Diagnosis of respiratory and gastro-intestinal tumours depends heavily on autopsy, and whether an autopsy is performed is related to social influences often correlated with occupation.
  • The age-correction method used in the Quebec study did not allow for interaction between length of exposure and length of survival.
  • Mesothelioma cases may have been missed in Cyprus, South Africa and Rhodesia.
  • Industry-related mesothelioma cases were probably more likely to be diagnosed than cases in the general population.
  • The fibre-count equivalent of the 200 mppcf-years threshold had not been established.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Pleural Mesothelioma, Million Particles per Cubic Foot (mppcf), Mesothelioma.

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