A case-control study of asbestos in drinking water and cancer risk

Our plain-English summary of A case-control study of asbestos in drinking water and cancer risk, by L. Polissar, R.K. Severson, E.S. Boatman (American Journal of Epidemiology, 1984).

The study

• Authors: L. Polissar, R.K. Severson, E.S. Boatman
• Journal: American Journal of Epidemiology
• Published: 1984;119(3):456-71
• Cited by: 27 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. 000567).

Abstract

The authors conducted a case-control, interview-based study of the risk of developing cancer from asbestos in drinking water. The Everett, Washington area was selected for the study because of the unusually high concentration of chrysotile asbestos in the drinking water it draws from the Sultan River (200 X 10(6) fibers/liter). Through a population-based tumor registry, the authors identified 382 individuals with cancer of the buccal cavity, pharynx, respiratory system, digestive system, bladder, or kidney, diagnosed between 1977 and 1980, and then interviewed them or their next-of-kin. The authors conducted similar interviews of a control group of 462 individuals. Finally, interviews were validated in several ways, including comparing the collected data with that from secondary sources. Estimates of exposure to asbestos in drinking water were based on residence and workplace history, and on individual water consumption. Four different measures of exposure were used. Cancer risk was estimated by logistic regression and other methods. The authors found no convincing evidence for cancer risk from imbibed asbestos. Exposure was similar between cases and controls. Confidence intervals for relative odds for almost all sites included unity. Out of 84 dependent estimates of risk by sex, site, and exposure measure, 63 indicated a protective effect and 21 indicated an increased risk. In instances where relative odds differed appreciably from unity for both males and females, the effect was protective. The relative odds of cancer for 20 years of exposure to Sultan River drinking water varied from 0.92 to 0.99 for females and 0.82 to 1.01 for males for all study sites grouped. For cancer of the digestive system, the corresponding range was 1.03 and 1.08 for females and 0.85 to 1.00 for males. There were six statistically significant associations (p less than 0.05). All involved male stomach (eight cases) and male pharynx (four cases), and indicate elevated risk. This number of significant associations is close to that expected (for the number of comparisons made). The female risks for these two sites indicate a protective effect, and it is concluded that the male results are probably due to chance.

In plain English

This case-control study examined cancer and chrysotile asbestos in Sultan River drinking water (about 200 million fibers per liter) in the Everett, Washington area. The authors interviewed 382 white people aged 40 to 79 with cancers of the buccal cavity, pharynx, digestive or respiratory system, bladder or kidney (or their next-of-kin), and 462 controls from the same census tracts. Estimated four ways from home and work histories, exposure was extremely similar in cases and controls. Relative odds compared 20 equivalent years of Sultan River water with none; for all sites grouped they were near or slightly below one. Statistically significant raised relative odds (one-sided tests) appeared only for male stomach cancer (eight cases; 1.7 to 2.6 in all four measures; lower 95 per cent bounds 1.04 to 1.19) and male pharynx cancer (four cases; 3.0 and 3.2 in two water-intake measures; lower bounds 1.43 and 1.34). Female results for these sites were less than or very close to one. The authors found no convincing evidence of cancer risk, judging these results consistent with chance. They noted too few cases for rarer sites.

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
• Who was studied: 382 white cancer cases aged 40 to 79 and 462 controls from 25 low-migration census tracts in the Everett, Washington area. Cases were diagnosed between November 1977 and December 1980 and identified through a population-based tumor registry. Forty-seven per cent of case interviews were with next-of-kin.
• Exposure: Chrysotile asbestos in Sultan River drinking water (about 200 million fibers/liter; 207 x 10 to the 6th fibers/liter used as the reference). Exposure was measured as equivalent years of Sultan River water, from residence and work history. Two of the four measures added water intake, and two ignored the last 10 years (latent period). A value of 1.0 equals 20 years of exposure; for the intake measures, two quarts of Sultan River tap water per day over 20 years.
• Main results:
  • Exposure to asbestos in drinking water was extremely similar between cases and controls (for example, 23.0% of cases and 21.0% of controls had 30 or more equivalent years).
  • Relative odds compare the equivalent of 20 years of Sultan River water with no exposure. For all study sites grouped, they were close to or slightly less than unity, ranging from 0.92 to 0.99 for females and 0.82 to 1.01 for males across the four measures.
  • Across the four exposure measures, 63 of 84 site-sex estimates were below unity and 21 were above.
  • Male stomach cancer (8 cases), 20 equivalent years versus none: relative odds were statistically significant (one-sided) in all four models, from 1.7 to 2.6, with significance levels 0.02 to 0.04. Lower one-sided 95% confidence bounds in Table 7 were 1.04 to 1.19.
  • Male pharynx cancer (4 cases), 20 equivalent years versus none: relative odds were significant (one-sided) in the two models that included water intake, at 3.0 and 3.2 (significance level 0.01). Lower one-sided 95% confidence bounds in Table 7 were 1.43 and 1.34.
  • In each of these six significant instances, the relative odds for females at the same site were less than or very close to unity.
  • Comparing 30 or more equivalent years with five or fewer gave non-significant relative odds: 0.54 for male digestive cancer, 1.32 for female digestive cancer, and 0.78 for both sexes and all sites combined.
• The authors' conclusion: The authors concluded there was no convincing evidence of cancer risk for the sites studied. They judged the few significant results for male stomach and pharynx consistent with chance, given the number of comparisons and the lack of consistency between sexes.
• Limitations the authors state:
  • Exposure was estimated indirectly; the exact history of tap water drinking could not be determined.
  • Too few cases to judge risk for less frequent sites such as pharynx, stomach, kidney and gallbladder.
  • Low-exposure subjects had generally moved into the area more recently, so exposure was partly confounded with migration.
  • Only about 25 per cent of cases and controls had exposure beginning at least 40 years earlier, which limits study of a possible long latent period.
  • Using next-of-kin for deceased cases and some proxies for controls may have introduced unknown bias.

Topics

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

Related studies

• Cancer incidence in relation to asbestos in drinking water in the Puget Sound region — L. Polissar, R.K. Severson, et al. (1982)
• Cancer risk from asbestos in drinking water: summary of a case-control study in western Washington — L. Polissar, R.K. Severson, et al. (1983)
• 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)
• Asbestos in drinking water and cancer — K.D. MacRae (1988)
• Asbestos-contaminated drinking water: its impact on household air — J.S. Webber, S. Syrotynski, et al. (1988)
• Assessment of studies on cancer risks from asbestos in Connecticut drinking water — J.W. Meigs (1983)

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