Nonoccupational exposure to chrysotile asbestos and the risk of lung cancer

Our plain-English summary of Nonoccupational exposure to chrysotile asbestos and the risk of lung cancer, by M. Camus, J. Siemiatycki, B. Meek (The New England Journal of Medicine, 1998).

The study

• Authors: M. Camus, J. Siemiatycki, B. Meek
• Journal: The New England Journal of Medicine
• Published: 1998;338(22):1565-71
• Cited by: 109 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Heavy industrial exposure to asbestos causes lung cancer and mesothelioma, but it remains unknown whether much lower environmental exposure to asbestos also causes these cancers. Nevertheless, regulatory agencies, including the Environmental Protection Agency (EPA), have assessed the risk of lung cancer by extrapolating known risks from past industrial exposure to asbestos to today's much lower environmental asbestos levels (roughly 100,000 times lower). We also tested the EPA's model for predicting the risk of asbestos-induced lung cancer in a population of women with relatively high levels of nonoccupational exposure to asbestos.

Methods: Mortality among women in 2 chrysotile-asbestos-mining areas of the province of Quebec was compared with mortality among women in 60 control areas, and age-standardized mortality ratios were derived. With the help of an expert panel, we estimated past exposure to asbestos among women in the mining areas and used these data with the EPA's model to predict the relative risk of lung cancer. We then compared this prediction with the observed mortality ratios.

Results: On the basis of the estimated exposure in the asbestos-mining areas, a relative risk of death due to lung cancer of 2.1 was predicted by the EPA's model, amounting to about 75 excess deaths from lung cancer in this population. By contrast, we calculated a standardized mortality ratio of 1.0 and a standardized proportionate mortality ratio of 1.1 (P> 0.05), suggesting that there were between 0 and 6.5 excess deaths from lung cancer among the women with nonoccupational exposure to asbestos. Seven deaths from pleural cancer were observed (relative risk=7.63; P<0.05).

Conclusions: We found no measurable excess risk of death due to lung cancer among women in two chrysotile-asbestos-mining regions. The EPA's model overestimated the risk of asbestos-induced lung cancer by at least a factor of 10.

In plain English

This study compared deaths from 1970 through 1989 among women aged 30 or older in two chrysotile-asbestos mining areas of Quebec (Thetford Mines and Asbestos) with deaths among women in 60 reference areas of the province. With help from an expert panel, the authors estimated the women's average lifetime exposure from asbestos in town air, dust brought home by asbestos workers, and work in the industry at 25 fiber-years per milliliter. They then applied the U.S. Environmental Protection Agency (EPA) model, which predicted a relative risk of lung cancer of 2.05. There were 71 lung cancer deaths among the exposed women. Their standardized mortality ratio for lung cancer was 0.99 (95 percent confidence interval 0.78 to 1.25). The model predicted 68 to 75 excess lung cancer deaths, but the authors observed 0 to 6.5. Deaths from pleural cancer (seven) and asbestosis (two) were significantly raised. Comparing predicted with observed excess deaths, the authors concluded that the EPA model overestimated the risk of asbestos-induced lung cancer in these women by at least a factor of 10. They noted that death certificates are adequate for studying lung cancer but not mesothelioma.

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: Mortality study comparing geographic areas (clusters of towns, not individuals), combined with a historical exposure assessment and a risk assessment using the EPA's dose-response model
• Who was studied: Women 30 years of age or older who died from 1970 through 1989 in two chrysotile-asbestos mining areas of Quebec (Thetford Mines and Asbestos), compared with women in 60 reference areas of Quebec; 221,375 person-years in the mining areas and 8,629,630 person-years in the reference areas
• Exposure: Nonoccupational (and some occupational) exposure to airborne asbestos that was mostly chrysotile. It came from neighborhood air (about 65 percent of exposure), household dust brought home by asbestos workers (about 30 percent) and work in the asbestos industry (about 5 percent). Estimated average cumulative exposure was 25 fiber-years per milliliter, with a subjective plausible range of 5 to 125.
• Main results:
  • Based on the estimated exposure, the EPA model predicted a relative risk of lung cancer of 2.05 (plausible range 1.21 to 6.25) for women in the mining areas
  • Among women in the two mining areas combined, the standardized mortality ratio was 0.91 for all causes (2242 deaths) and 0.92 for all cancers (595 deaths)
  • There were 71 lung cancer deaths among the exposed women. Their standardized mortality ratio for lung cancer was 0.99 (95 percent confidence interval 0.78 to 1.25), and the standardized proportionate mortality ratio was 1.10 (95 percent confidence interval 0.88 to 1.38).
  • The EPA model predicted between 68 and 75 excess lung cancer deaths in the mining-area women, whereas 0 to 6.5 excess deaths were observed
  • By the authors' calculation, the EPA model overestimated the lung cancer deaths attributable to asbestos by a factor of at least 10 (68 divided by 6.5)
  • There were significant excesses of deaths from pleural cancer (seven deaths) and asbestosis (two deaths) among women in the mining areas
  • The standardized mortality ratio for pleural cancer in the mining-area women was 7.63 (95 percent confidence interval 3.06 to 15.73). All seven pleural cancer deaths occurred in the Thetford Mines area.
  • The standardized mortality ratio for asbestosis in the mining-area women was 23.49 (95 percent confidence interval 2.64 to 84.83)
• The authors' conclusion: The authors concluded that, in this study, the EPA's model overestimated the risk of asbestos-induced lung cancer among women living in chrysotile-asbestos mining areas from 1970 to 1989 by at least a factor of 10
• Limitations the authors state:
  • The units of observation were clusters of towns, not individual residents
  • The study populations changed over time because people moved in and out of the areas. The authors concluded that migration could not have distorted the relative risk substantially.
  • Women in the mining areas may have smoked slightly less than women in the reference areas. The authors estimated this should not have distorted the lung cancer relative risk by more than 7 percent.
  • The retrospective exposure assessment relied on incomplete data and subjective, imprecise estimates. The authors addressed this by assigning a wide plausible range.
  • Death certificate data are adequate to study lung cancer but not mesothelioma, which is being investigated in a separate study

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Jeffrey mine, Asbestos, Quebec

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Lung Cancer, Mesothelioma, Environmental Exposure, standardized mortality ratio (SMR), Relative Risk.

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• Asbestos--still a carcinogen — P.J. Landrigan (1998)
• Human evidence: lung cancer mortality risk from chrysotile exposure — J.M. Hughes (1994)
• Mortality from cancer and other causes among Italian chrysotile asbestos miners — E. Pira, C. Romano, et al. (2017)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: development from 1904 and mortality to 1992 — F.D. Liddell, A.D. McDonald, et al. (1997)
• Pulmonary mineral fibers after occupational and environmental exposure to asbestos in the Russian chrysotile industry — A. Tossavainen, E. Kovalevsky, et al. (2000)

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