Cancer incidence in relation to asbestos in drinking water in the Puget Sound region

Our plain-English summary of Cancer incidence in relation to asbestos in drinking water in the Puget Sound region, by L. Polissar, R.K. Severson, E.S. Boatman, et al (American Journal of Epidemiology, 1982).

The study

• Authors: L. Polissar, R.K. Severson, E.S. Boatman, D.B. Thomas
• Journal: American Journal of Epidemiology
• Published: 1982;116(2):314-28
• Cited by: 29 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Population-based and proportional odds ratios for various cancers, based on incidence data from 1974-1977 and mortality data from 1965-1975 for western Washington State, were calculated in relation to three measures of exposure to asbestos in community water supplies. Six odds ratios were calculated for each neoplasm that occurred in sufficient numbers in each sex. About half of the 332 odds ratios calculated were above unity and half were below unity, and no more of them differed significantly from unity at the 5% level than would be expected by chance. Odds ratios for tumors of the small intestine were consistently elevated in both sexes, as were those for neoplasms of the thyroid, eye, testis, and prostate in males; however, odds ratios for brain tumors and leukemia were consistently less than one in both sexes. Chance is the most likely explanation for these findings. Results of this study and prior studies of cancer in relation to waterborne asbestos are inconsistent, and provide little evidence that asbestos in community water supplies has altered the risk of any cancer. However, all investigations conducted to date are correlational studies which have an inherently higher probability of failing to detect actual increased risks associated with imbibed asbestos, and additional studies of individual exposures are warranted. Neoplasms of the pancreas and small intestine should be included in such studies.

In plain English

This correlational study compared cancer rates across Puget Sound areas of western Washington with different tap-water asbestos levels. High-exposure census tracts were served by the Sultan River (around Everett); low-exposure tracts by the Cedar, Tolt and Green Rivers and Lakewood Wells. The authors used cancers diagnosed in 1974-1977 and, for people aged 35-79 at death, cancer deaths in 1955-1975. In 95 tap water samples the asbestos was chrysotile; only one amphibole fiber was found. Mean chrysotile concentration was more than 25 times higher in the Sultan River area. Of 332 odds ratios, 30 were statistically significant, and only six of those were above one. Small intestine cancers were consistently elevated in both sexes, but not in low-migration tracts. Brain and central nervous system cancers and leukemia were inversely related to asbestos levels in both sexes; the authors considered these probably chance. Pleural and peritoneal tumors were too few to analyze. The authors concluded that cancer risk from drinking-water asbestos in the Sultan River area was, at most, very low, although some anatomic sites showed suggestive evidence.

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: Correlational (geographic) study using a case-control style analysis of cancer incidence and mortality. Six Mantel-Haenszel pooled odds ratios were calculated for each cancer site and sex.
• Who was studied: Residents of census tracts in the Seattle-Everett-Tacoma area of western Washington. Tracts served by the Sultan River were the high-asbestos group, and tracts served by the Cedar River, Tolt River, Green River or Lakewood Wells were the low-asbestos group. The study used cancer cases diagnosed 1974-1977 from a population-based cancer registry. It also used cancer deaths 1955-1975, limited to residents aged 35-79 at death.
• Exposure: Asbestos in community drinking water, measured by electron microscopy in 95 tap water grab samples. Only one amphibole fiber was found in all the samples, so exposure was characterized by chrysotile concentration alone. In some analyses within the Sultan River area, duration of exposure was estimated as 30 or more years versus under 30 years.
• Main results:
  • Mean chrysotile fiber concentration in the Sultan River area (22 samples, mean 206.5) was more than 25 times that in the other areas (73 samples, mean 7.3). The unit's exponent is garbled in the scan.
  • Of 332 odds ratios, about half were above one and half below. About 16.6 would be expected to be significant by chance and 30 were, but only six of the 30 significant odds ratios were greater than one.
  • Cancers of the small intestine (small bowel) showed the most consistent positive association with the high-asbestos area, in both males and females.
  • The small intestine association was not seen when analyses were limited to census tracts with relatively low migration rates. There were no small intestine cases in the low-migration tracts with high asbestos levels.
  • Cancers of the brain and central nervous system, and leukemia, were inversely related to asbestos levels in water in both sexes. The authors considered these probably chance observations.
  • In males, odds ratios tended to be elevated for cancers of the prostate, testis, eye and orbit, and thyroid, but most of these were not statistically significant.
  • Results for pancreatic cancer were inconsistent, with some odds ratios above and some below one.
  • There were too few pleural and peritoneal tumors for analysis.
• The authors' conclusion: The authors concluded that the cancer risk from asbestos in drinking water in the Sultan River area is, at most, very low, although there is suggestive evidence for some anatomic sites.
• Limitations the authors state:
  • Exposure was assigned to whole geographic areas rather than measured for individuals, which allows confounding by other factors that vary by area.
  • Exposure may be misclassified because of recent in-migration into the study area.
  • Errors in estimated population counts may bias the population-based odds ratios.
  • Because so many comparisons were made, some results are likely significant by chance alone.

Topics

Medical terms in this study, explained in our Lexicon: Odds Ratio, Neoplasm.

Related studies

• 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)
• A case-control study of asbestos in drinking water and cancer risk — L. Polissar, R.K. Severson, et al. (1984)
• 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 in drinking water and cancer incidence in the San Francisco Bay area — M.S. Kanarek, P.M. Conforti, et al. (1980)

Browse more research in American Journal of Epidemiology, or return to medical research.