Mesothelioma after crocidolite exposure during gas mask manufacture

Our plain-English summary of Mesothelioma after crocidolite exposure during gas mask manufacture, by A.D. McDonald, J.C. McDonald (Environmental Research, 1978).

The study

• Authors: A.D. McDonald, J.C. McDonald
• Journal: Environmental Research
• Published: 1978;17(3):340-6
• Cited by: 92 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001089).

Abstract

Of 199 persons employed in the manufacture and handling of Canadian military gas mask canisters containing pure crocidolite, 1939 to 1942, by the end of 1975, 56 had died, 120 were still alive, and 23 could not be traced. Nine (16%) of the deaths were probably due to malignant mesothelioma, six involving the peritoneum. The risk of mesothelioma after crocidolite exposure appears to be many times greater than that after chrysotile.

In plain English

This cohort study followed 199 people who worked between 1939 and 1942 making or handling filters for Canadian military gas mask canisters that contained pure crocidolite asbestos. Filter pads were made at two factories in Quebec, one in the town of Asbestos and one in Montreal. They were packed into canisters at an assembly plant in Ottawa. By the end of 1975, 56 had died, 120 were alive and 23 could not be traced. Malignant mesothelioma was judged the probable cause of 9 (16%) of the 56 deaths, and six of these involved the peritoneum. In 6 of the 9 cases, total asbestos exposure was not more than 3 years. The authors compared proportions of deaths with a cohort of Quebec chrysotile miners and millers. Mesothelioma was some 60 times more frequent in the gas mask workers, and lung cancer over twice as frequent. The authors concluded that mesothelioma risk after crocidolite appears many times greater than after chrysotile. They cautioned that the numbers were small and exposure levels were unknown. Workers at two of the factories were also exposed to chrysotile, and the industrial process, rather than fiber type, might explain the difference.

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: Cohort mortality study, with proportional mortality compared against a cohort of Quebec chrysotile miners and millers
• Who was studied: 199 persons employed 1939 to 1942 in three Canadian factories: filter pad manufacture in Asbestos, Quebec and in Montreal, and gas mask assembly in Ottawa. They were traced to the end of 1975: 56 dead, 120 alive, 23 untraced.
• Exposure: Crocidolite in gas mask filter pads. The pads were made in two plants and packed into canisters in a third. Crocidolite was used only until spring 1942, and in Ottawa it was the only type of asbestos used.
• Main results:
  • Among the 56 deaths, 23 were from malignant disease, including 9 from mesothelioma and 8 from lung cancer.
  • Malignant mesothelioma was the probable cause of 9 (16%) of the 56 deaths in the gas mask cohort.
  • Six of the 9 mesothelioma cases in the gas mask cohort involved the peritoneum, compared with 1 of 11 in the chrysotile cohort.
  • The intervals between working with gas mask filters and death in the 9 cases ranged from 24 years after last exposure to 36 years after first exposure.
  • Compared with the chrysotile miners and millers, mesothelioma was some 60 times more frequent in the crocidolite cohort, and lung cancer over twice as frequent.
  • Proportional mortality from mesothelioma was 20% in Ottawa, 20% in Montreal and 15% in Asbestos.
  • Total exposure to asbestos was not more than 3 years in 6 of the 9 mesothelioma cases, and only 4 and 6 months in two cases.
  • Two additional cases of pleural mesothelioma, not counted among the 9, were reported by a national survey in men who had worked at the Montreal factory.
  • Pneumoconiosis was the certified cause of death in four long-term employees: two with asbestosis at Montreal, and one with silicosis and one with silicotuberculosis at Asbestos.
• The authors' conclusion: The authors concluded that the risk of mesothelioma after crocidolite exposure appears to be many times greater than after chrysotile.
• Limitations the authors state:
  • Comparisons of proportional mortality may be biased by differences in age, other causes of death and length of observation.
  • The numbers are small.
  • Only the Ottawa workers were exposed solely to crocidolite. Workers at Montreal and Asbestos also had chrysotile exposure.
  • Information on exposure levels is lacking.
  • The difference may relate to the industrial process rather than fiber type, since fiber concentration and size may differ between factories and mines or mills.
  • Relatively few of the workers had yet died, so the proportions of lung cancer and mesothelioma deaths may increase.
  • No employment records existed for civilian employees of the Ottawa plant, so workers there were identified from names people remembered.
  • At Asbestos, gas mask filter workers could not be distinguished, so everyone in the textile department during 1939 through 1941 was assumed to be exposed.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Crocidolite, Malignant Mesothelioma, Peritoneum, Chrysotile.

Related studies

• Mortality of two groups of women who manufactured gas masks from chrysotile and crocidolite asbestos: a 40-year follow-up — E.D. Acheson, M.J. Gardner, et al. (1982)
• Dust exposure and mortality in an American factory using chrysotile, amosite, and crocidolite in mainly textile manufacture — A.D. McDonald, J.S. Fry, et al. (1983)
• Sixty years on: the price of assembling military gas masks in 1940 — J.C. McDonald, J.M. Harris, et al. (2006)
• Lung fiber burden in the Nottingham gas mask cohort — G. Berry, F. Pooley, et al. (2009)
• Modelling mesothelioma risk for workers assembling military gas masks — J.W. Cherrie, H.A. Cowie, et al. (2007)
• Age and sex differences in malignant mesothelioma after residential exposure to blue asbestos (crocidolite) — A. Reid, G. Berry, et al. (2007)

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