Lung asbestos content in long-term residents of a chrysotile mining town

Our plain-English summary of Lung asbestos content in long-term residents of a chrysotile mining town, by A. Churg (The American Review of Respiratory Disease, 1986).

The study

• Author: A. Churg
• Journal: The American Review of Respiratory Disease
• Published: 1986;134(1):125-7
• Cited by: 18 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. 000383).

Abstract

The effects of long-term exposure to very small amounts of chrysotile asbestos are controversial. To examine this problem, the lung asbestos content from 7 long-term (25 yr and greater) residents of Thetford Mines, Quebec, who were never employed in the chrysotile mining and milling industry, was analyzed. Thetford Mines is a chrysotile mining town with a demonstrated ambient atmospheric concentration of chrysotile asbestos approximately 200 to 500 times that in urban areas of North America. Data on the residents' lungs were compared with those obtained from 20 long-term (25 yr and greater) chrysotile industry workers from Thetford Mines and 20 members of the general population of Vancouver. The median concentrations of chrysotile and tremolite in the Thetford residents were only about one fiftieth of those of the chrysotile workers, but about 10 times that of the population of Vancouver. Because long fibers of asbestos are generally thought to be more dangerous than short ones are, the sizes of fibers from these 3 groups were also examined. The fiber size distribution of the asbestos from the Thetford residents was significantly longer than that of the Vancouver population, and resembled that of the chrysotile workers. Because epidemiologic studies have consistently failed to find an increased respiratory disease incidence in lifelong residents of Quebec chrysotile mining towns who were never employed in the chrysotile industry, these findings imply that even asbestos burdens much higher, and fiber size distributions much longer, than those of the general population of most North American cities, are not associated with demonstrable pathologic effects.

In plain English

This study measured asbestos fibers in autopsy lung tissue linked to Thetford Mines, Quebec, a chrysotile mining town. The author examined the lungs of 7 people who had lived there at least 25 years but had never worked in asbestos mining or milling. These were compared with lungs from 20 Thetford miners and millers employed at least 25 years, and from 20 Vancouver men over 50 with no occupational dust exposure. Fibers were counted and identified by electron microscopy. Tremolite and actinolite were grouped together as "tremolite". Chrysotile and tremolite concentrations were significantly higher in the Thetford residents than in the Vancouver group, and higher still in the workers. The residents' median burden was about 10 times Vancouver's and roughly one fiftieth of the workers'. The residents' fibers were significantly longer than the Vancouver fibers and similar to the workers' fibers. None of the 7 residents had died of an asbestos-related disease. Relying on earlier epidemiologic studies by others, the author concluded that such burdens are not associated with demonstrable harm. The author noted that only 7 residents were available and that the groups were not matched.

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: Comparative study of asbestos fiber content in autopsy lung tissue from three groups, using electron microscopy (not a case-control study, as the author notes)
• Who was studied: Three groups. (1) 7 long-term (at least 25 years) residents of Thetford Mines, Quebec, who were never employed in the asbestos mining or milling industry: 5 men and 2 women, all the non-industry cases among about 130 autopsy lungs collected at the Hôpital de la Région de l'Amiante between 1980 and 1985. (2) 20 chrysotile miners and millers from the same series, employed in Thetford Mines for at least 25 years. (3) 20 male autopsy cases from Vancouver, all older than 50, chosen at random from about 40 University of British Columbia autopsy cases with non-asbestos-related diseases; people with occupational dust exposure were excluded. Mean ages were 65 for the Vancouver group, 59 for the Thetford residents and 65 for the workers.
• Exposure: Non-occupational (environmental) exposure to chrysotile from living in a chrysotile mining town, compared with occupational chrysotile exposure in miners and millers and with ordinary urban background exposure in Vancouver. Lung burdens of chrysotile and of tremolite were measured; tremolite here includes actinolite, both described as natural contaminants of the chrysotile ore.
• Main results:
  • Chrysotile and tremolite fiber concentrations were significantly greater in the Thetford residents than in the Vancouver residents (p less than 0.004 for chrysotile, p less than 0.03 for tremolite).
  • The Thetford residents' median asbestos burden was about 10 times that of the Vancouver population.
  • The Thetford residents' median burden was roughly one fiftieth of that of the chrysotile workers, whose concentrations were significantly greater than the residents' (p less than 0.0001 for each comparison).
  • Mean chrysotile and tremolite fiber lengths were significantly greater in the Thetford residents than in the Vancouver residents (p less than 0.0001 for each comparison).
  • The workers had slightly longer chrysotile fibers than the Thetford residents (p less than 0.01), but not longer tremolite fibers.
  • Chrysotile fibers longer than 20 microns and tremolite fibers longer than 10 microns were seen only in the Thetford residents and the workers.
  • The widest chrysotile and tremolite fibers were in the Vancouver residents and the narrowest in the Thetford residents (all comparisons p less than 0.001). Aspect ratios (length relative to width) were lowest in the Vancouver residents and highest in the Thetford residents.
  • In the Vancouver group, fibers were scanty: no chrysotile fibers were found in 5 cases and no tremolite fibers in 2 cases.
  • None of the 7 Thetford residents had died of an asbestos-related disease. Table 1 lists the causes of death as myocardial infarct (four of the seven cases), sepsis, cirrhosis, and carcinoma, most likely colonic.
• The authors' conclusion: The author concluded that the Thetford residents inhale and retain more, and potentially more dangerous, fibers than Vancouver residents. Because earlier epidemiologic studies by others had failed to find increased respiratory disease in Quebec mining-town residents never employed in the industry, the author concluded that burdens much higher, and fibers much longer, than those of the general population of most North American cities are not associated with demonstrable pathologic effects.
• Limitations the authors state:
  • Lung tissue was available for only 7 Thetford resident cases.
  • Ideally the study would have been a case-control design, comparing the Thetford residents with residents of a nearby area without asbestos air pollution.
  • The groups were not matched for age, smoking or sex. The author had no autopsy material from women miners or millers. The author argued that the higher smoking in the Vancouver group should work against finding differences, and that an exact match was unlikely to have changed the results.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Thetford Mines, Tremolite, Quebec Chrysotile.

Related studies

• Environmental pleural plaques in residents of a Quebec chrysotile mining town — A. Churg, L. DePaoli (1988)
• Respiratory cancer in chrysotile textile and mining industries: exposure inferences from lung analysis — P. Sebastien, J.C. McDonald, et al. (1989)
• Fiber burden and patterns of asbestos-related disease in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1993)
• Exposures estimates of the Wittenoom mining workforce and town residents - Implications associated with risk estimation for persons exposed to asbestiform riebeckite — A.J. Rogers (2018)
• Fiber size and number in workers exposed to processed chrysotile asbestos, chrysotile miners, and the general population — A. Churg, B. Wiggs (1986)
• Mineralogic correlates of fibrosis in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1989)

Browse more research in The American Review of Respiratory Disease, or return to medical research.