Health implications of environmental exposure to asbestos

Our plain-English summary of Health implications of environmental exposure to asbestos, by J.C. McDonald (Environmental Health Perspectives, 1985).

The study

• Author: J.C. McDonald
• Journal: Environmental Health Perspectives
• Published: 1985;62:319-28
• Cited by: 117 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000488).

Abstract

The health impact of environmental pollution resulting from the industrial use of asbestos can be assessed in three ways. First, there are the direct epidemiological surveys. These indicate that domestic exposure has been responsible for cases of mesothelioma and possibly lung cancer and radiological changes in family contacts of asbestos workers. Exposure in the neighborhood of crocidolite mines and factories has also resulted in cases of mesothelioma but no similar evidence exists for chrysotile or amosite. Neither air nor water pollution has been directly incriminated as a cause of either respiratory or digestive malignancies. Second, a few attempts have been made to extrapolate from exposure response findings in industrial cohorts. For several reasons, even for lung cancer, this approach is dubious: the observed gradients have a 100-fold range in slope; the equivalences of dust, fiber and gravimetric measures are largely guesswork; and the carcinogenic potential of mineral fibers, particularly for the pleura, varies enormously with fiber type and/or dimensions. No adequate exposure-response observations have been made for mesothelioma. A third approach makes use of the differing incidence of mesothelioma in men and women. Data from several countries indicate that, until the 1950s (i.e., 30-40 years after significant industrial use of asbestos began), the rates were similar in both sexes. Since then, the incidence in males has risen steeply--in the U.S. and U.K. at about 10% per annum. In females, on the other hand, there has been little or no convincing increase. These data suggest that the "background" level of mesothelioma in both sexes is and has been about 2 per million per annum and that--as at least some mesothelioma cases in females are directly or indirectly attributable to occupational exposure--there is little room left for any contribution from the general environment. It is recommended that mesothelioma surveillance, backed by appropriate epidemiological inquiries, offers an effective method of monitoring the health impact of asbestos air pollution.

In plain English

This 1985 article was a review by the author of evidence on the health effects of nonoccupational asbestos exposure, focusing on North America in the 1980s. It used three approaches. First, it reviewed direct epidemiological surveys. These indicated that household exposure among family contacts of asbestos workers had caused cases of mesothelioma, and possibly lung cancer and X-ray changes. Living near crocidolite mines and factories had also resulted in mesothelioma cases, with no similar evidence for chrysotile or amosite. Neither air nor water pollution had been directly incriminated as a cause of respiratory or digestive cancers. Second, it assessed estimates extrapolated from worker studies. It noted that lung cancer exposure-response gradients in industrial cohorts varied 100-fold. The author called extrapolation "pure guesswork" until this variation was explained and better evidence was obtained on how mass and fiber measurements correspond. Third, it compared mesothelioma trends by sex. In U.S. registry data the male rate rose nearly 10% per year, while any change in the female rate was doubtful. The author concluded that background mesothelioma had been about 2 per million per year in both sexes, leaving little room for any contribution from the general environment.

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 published epidemiological surveys, extrapolation-based risk estimates, and mesothelioma incidence and mortality trends by sex
• Who was studied: Nonoccupationally exposed populations, with the focus on North America (USA and Canada) in the 1980s. Evidence drew on studies of household contacts, neighborhood residents, drinking-water populations, industrial cohorts and cancer registries in several countries.
• Exposure: Nonoccupational asbestos exposure: domestic (household contacts of asbestos workers), neighborhood exposure near mines, plants and shipyards, general urban air pollution, and asbestos fibers in drinking water. Fiber types discussed included crocidolite, amosite and chrysotile.
• Main results:
  • Reviewed studies showed mesothelioma cases among people living near crocidolite mines and factories. No similar evidence was found for chrysotile or amosite.
  • One reviewed study examined household contacts of workers at the Patterson amosite asbestos plant: 679 household contacts who had never been exposed at work, and 325 controls. Small opacities and/or pleural abnormalities on X-ray were seen in 35% of household contacts and 5% of controls.
  • In the author's group's North American mesothelioma surveys, residence was compared for 146 female case-control pairs with no occupational, domestic or mining-neighborhood exposure. The author judged that the very small differences between cases and controls could easily be due to chance.
  • Neither air nor water pollution had been directly incriminated as a cause of respiratory or digestive cancers in the reviewed studies.
  • Lung cancer exposure-response gradients in industrial cohorts with individual exposure estimates varied about 100-fold in slope, making extrapolation to environmental levels dubious.
  • The author considered the equivalence of dust, fiber and mass (gravimetric) measurements largely guesswork. In the author's view, extrapolation would remain pure guesswork until the 100-fold difference in slopes was explained and better evidence on these equivalences was obtained.
  • In U.S. cancer registry (SEER) data for 1973-1980, the male mesothelioma rate was increasing by nearly 10% per year, while it was doubtful that the female rate had changed.
  • From the sex-difference data, the author concluded that the background mesothelioma level had been about 2 per million in men and women for many years.
• The authors' conclusion: The author concluded that, because at least some mesothelioma in women is attributable to occupational or domestic exposure, there is little room left for any contribution from the general environment. The author also concluded that linear extrapolation to very low fiber concentrations almost certainly overstates the true risk.
• Limitations the authors state:
  • The time trends in mesothelioma may be confounded by changes in levels of diagnosis and case ascertainment.
  • Direct epidemiological studies may not be sensitive enough to detect very low risks.
  • In comparing published risk estimates (Table 4), the author took liberties with the data, so the figures are approximate.

Topics

Medical terms in this study, explained in our Lexicon: Environmental Exposure, Mesothelioma, Lung Cancer, Crocidolite, Chrysotile, Amosite, Carcinogenic, Mineral Fiber.

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