Cancer risk from asbestos in drinking water: summary of a case-control study in western Washington

Our plain-English summary of Cancer risk from asbestos in drinking water: summary of a case-control study in western Washington, by L. Polissar, R.K. Severson, E.S. Boatman (Environmental Health Perspectives, 1983).

The study

• Authors: L. Polissar, R.K. Severson, E.S. Boatman
• Journal: Environmental Health Perspectives
• Published: 1983;53:57-60
• Cited by: 11 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. 000638).

Abstract

We conducted a case-control, interview-based study of the risk of developing cancer from asbestos in drinking water. An area that included Everett, Washington, was selected for the study because of the unusually high concentration of chrysotile asbestos in drinking water from the Sultan River. Through a population-based tumor registry, 382 individuals with cancer of the buccal cavity, pharynx, respiratory system, digestive system, bladder, or kidneys, diagnosed between 1977 and 1980, were identified, and they or their next of kin were interviewed. We conducted validation checks of our interviews, including a comparison with secondary sources. Data on asbestos exposure were collected based on residence and workplace history, and on individual water consumption. Logistic regression was used to estimate cancer risk. We found no convincing evidence for increased cancer risk from imbibed asbestos. Confidence intervals for relative risks for almost all sites included unity. There were significantly elevated risks only for male stomach and male pharyngeal cancer, but these sex-inconsistent results, based on small numbers of cases, are probably due to other factors.

In plain English

This paper summarized a population-based case-control study. The study area around Everett, Washington, drew tap water from the Sultan River, which contained chrysotile asbestos at around 200 million fibers per liter. The authors interviewed 382 people aged 40 to 79 with cancers of the mouth (buccal cavity), pharynx, respiratory system, digestive system, bladder or kidney diagnosed from 1977 to 1980 (or their next of kin) and 462 population controls. Exposure was estimated from residence, workplace and water-drinking histories, and it was very similar in cases and controls. No cancer site showed raised risk in both sexes. Comparing 20 years of Sultan River water use with none, the only statistically significant raised risks were for male pharyngeal cancer (relative risk 2.99, lower 95% confidence bound 1.43; four cases) and male stomach cancer (1.71, lower bound 1.06; eight cases). Women's values were 0.26 and 0.65. The authors judged these few results unsurprising given the many comparisons. They concluded there was no convincing evidence of increased cancer risk from swallowed asbestos. They noted too few cases for rarer sites and possible bias from next-of-kin interviews.

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: Population-based case-control study using in-person interviews, analyzed by logistic regression; this paper is a summary of a study described more fully elsewhere
• Who was studied: 382 white cases aged 40 to 79 with invasive or in situ cancer of the buccal cavity (excluding the lip), pharynx, respiratory system, digestive system, bladder or kidney, diagnosed November 1977 to December 1980 and identified through the Cancer Surveillance System tumor registry, plus 462 unmatched population controls aged 40 to 79 from the same 25 census tracts in the Everett, Washington, area. Interviews were with the subjects or their next of kin.
• Exposure: Chrysotile asbestos in Sultan River tap water (around 200 million fibers/L, used as a drinking-water source since 1918). Four cumulative exposure variables were built from residence and workplace history, with and without total water intake, and with and without a presumed 10-year latent period.
• Main results:
  • Exposure to Sultan River drinking water was very similar in the two groups: 23% of cases and 21% of controls had 30 years or more of exposure.
  • No cancer site, under any of the four exposure variables, showed raised risk in both males and females.
  • The only statistically significant (p less than 0.05) raised risks were for male pharyngeal cancer and male stomach cancer. The authors said this number of significant results was not surprising given the number of comparisons.
  • For 20 years of cumulative Sultan River tap water use versus no exposure, the relative risk for male pharyngeal cancer was 2.99 (lower 95% confidence bound 1.43). For females it was 0.26.
  • On the same basis, the relative risk for male stomach cancer was 1.71 (lower 95% confidence bound 1.06). For females it was 0.65.
  • The male risks rested on small numbers: eight stomach cancer cases and four pharyngeal cancer cases.
  • For pancreatic cancer, the risk was negative for males and positive for females. None of these risks was statistically significant at the 5% level.
  • The authors compared people with 30 years or more of Sultan River exposure against people with 5 years or fewer. This was done for the digestive system and for all study sites combined. The resulting risks were not statistically significant and were similar to those based on all exposure.
• The authors' conclusion: The authors concluded that they found no convincing evidence of increased cancer risk from swallowed (imbibed) asbestos. In their view, the risk is unlikely to be large for any of the sites studied.
• Limitations the authors state:
  • There were too few cases to judge risk solidly for rarer sites such as the kidneys and gallbladder.
  • A possible long latent period may have reduced the study's power. Migration also tends to reduce exposure to fixed sources such as a water supply.
  • Using next of kin for deceased cases, and a few proxies for controls, may have introduced unknown bias despite verification checks.

Topics

Medical terms in this study, explained in our Lexicon: Case-Control Study, Chrysotile, Cancer Registry, Asbestos Exposure, confidence interval, Relative Risk, Pharyngeal Cancer.

Related studies

• Additional notes on the case-control study in western Washington on the cancer risk from asbestos in drinking water — L. Polissar, R.K. Severson, et al. (1983)
• A case-control study of asbestos in drinking water and cancer risk — L. Polissar, R.K. Severson, et al. (1984)
• Cancer incidence in relation to asbestos in drinking water in the Puget Sound region — L. Polissar, R.K. Severson, et al. (1982)
• Assessment of studies on cancer risks from asbestos in Connecticut drinking water — J.W. Meigs (1983)
• The control of potential health risks related to drinking water in the UK — T.A. Dick (1981)
• Use of quantitative analysis of urine to assess exposure to asbestos fibers in drinking water in the Puget Sound region — E.S. Boatman, T. Merrill, et al. (1983)

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