Asbestos in drinking water and cancer incidence in the San Francisco Bay area

Our plain-English summary of Asbestos in drinking water and cancer incidence in the San Francisco Bay area, by M.S. Kanarek, P.M. Conforti, L.A. Jackson, et al (American Journal of Epidemiology, 1980).

The study

• Authors: M.S. Kanarek, P.M. Conforti, L.A. Jackson, R.C. Cooper, J.C. Murchio
• Journal: American Journal of Epidemiology
• Published: 1980;112(1):54-72
• Cited by: 59 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. 000821).

Abstract

Age-adjusted, sex- and race-specific 1969-1971 cancer incidence ratios for the 722 census tracts of the San Francisco-Oakland Standard Metropolitan Statistical Area were compared with measured chysotile asbestos counts in tract drinking waters. The water supplies serving the area have varying contact with naturally occurring serpentine. The t test for multiple regression coefficients and the t test for correlation coefficients showed significant (p less than 0.01) relationships between chrysotile asbestos content of tract drinking water and white male lung, white female gall bladder and pancreas, and peritoneal cancers in both sexes. Of weaker significance (0.01 less than or equal to 0.05) were female esophagus, pleura and kidney, as well as stomach cancers in both sexes. These associations appeared to be independent of income, education, asbestos occupation, marital status, country of origin and mobility.

In plain English

This geographic correlation study covered the 722 census tracts of the San Francisco-Oakland metropolitan area, where some water supplies contact serpentine rock. The authors measured chrysotile asbestos in 353 water samples, assigned counts to 705 tracts, and compared them with age-adjusted ratios of observed to expected cancer cases diagnosed in 1969-1971. Analyses accounted for income, education, marital status, asbestos-industry workers and country of origin. Among whites, higher chrysotile counts were associated with peritoneal cancer in both sexes, male lung cancer (p less than 0.001), and female gall bladder (p = 0.001) and pancreatic (p = 0.005) cancer. Weaker associations appeared for stomach cancer in both sexes and female esophageal, pleural and kidney cancer. For sites with the strongest dose-response results, the authors reported that the apparent asbestos effect held across income and education levels. The authors reported male lung and female gall bladder and peritoneum as consistently significant. They cautioned that regression models explained little variation and many tests were run. They lacked smoking, alcohol and diet data, and assumed water measured in 1977-1978 reflected past decades.

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: Geographic correlation (ecological) study comparing census tracts by chrysotile asbestos count in drinking water and cancer incidence
• Who was studied: The 722 census tracts of the San Francisco-Oakland Standard Metropolitan Statistical Area (Alameda, Contra Costa, Marin, San Francisco and San Mateo counties), with a 1970 population of slightly over 3 million. Newly diagnosed cancers for 1969-1971 came from the Third National Cancer Survey. Asbestos values were assigned to 705 tracts, and the main analyses were for white males and white females. The outcome was the Standard Incidence Ratio (observed to expected cases), indirectly age-adjusted.
• Exposure: Chrysotile asbestos fibers in tract drinking water from supplies with varying contact with naturally occurring serpentine. There were 353 water samples, mostly from household taps, counted by transmission electron microscopy and taken in 1977-1978. Tract groupings ranged from 16,000-290,000 up to 16,000,000-36,000,000 fibers per liter.
• Main results:
  • In the regression analysis, peritoneal cancer was the only site with a strong relationship to asbestos (p less than 0.01) in both sexes. The p values were 0.002 for white males and 0.009 for white females.
  • White males: lung cancer (trachea, bronchus, lung) was significantly related to asbestos (p less than 0.001).
  • White females: gall bladder cancer (p = 0.001) and pancreatic cancer (p = 0.005) were significantly related to asbestos.
  • The asbestos variable was of marginal significance (p from 0.01 to less than 0.05) for stomach cancer in both sexes and for esophageal, pleural and kidney cancer in females.
  • For the sites with significant (p less than 0.01) chi-square slope results, tracts were cross-classified by asbestos level and by education or income level. The authors reported that the apparent effect of asbestos was maintained irrespective of socioeconomic status, although individual ratios did not rise with asbestos in every stratum.
  • Corpus uteri cancer in white females showed a negative gradient with asbestos.
  • In 385 high-stability tracts (of 705), peritoneal cancer in both sexes and gall bladder cancer in females remained statistically significant.
• The authors' conclusion: The authors concluded that several cancer sites were statistically associated with chrysotile asbestos in drinking water. Male lung cancer and female gall bladder and peritoneal cancers were consistently significant across their analyses.
• Limitations the authors state:
  • The study assumed that asbestos levels measured in 1977-1978 reflected levels over the past 30 or 40 years. A drought during the sampling period also had to be considered.
  • The regression models explained only a small proportion of the variation in cancer incidence. R squared was always less than 0.10, usually 0.005 to 0.05, so the regression data must be viewed with caution.
  • Up to 210 regression equations were computed, so by a conservative standard p values would need to be considerably smaller than 0.05 or 0.01 to be considered significant.
  • No data were available on cigarette smoking, alcohol consumption or other dietary factors.
  • For some sites, such as peritoneum, case numbers were insufficient for definitive study.
  • Exposure was based on place of residence and did not account for daily mobility, such as place of work.

Topics

Medical terms in this study, explained in our Lexicon: Serpentine Group, Chrysotile, Pleura, Stomach Cancer.

Related studies

• "Asbestos in drinking water and cancer incidence in the San Francisco Bay area" — I.T. Higgins (1981)
• The San Francisco Bay epidemiology studies on asbestos in drinking water and cancer incidence: relationship to studies in other locations and pointers for further research — M.S. Kanarek (1983)
• "Asbestos in drinking water and cancer incidence in the San Francisco Bay area" — K. Browne (1982)
• Cancer incidence in relation to asbestos in drinking water in the Puget Sound region — L. Polissar, R.K. Severson, et al. (1982)
• Cancer incidence and asbestos in drinking water, Town of Woodstock, New York, 1980-1998 — M.L. Browne, D. Varadarajulu, et al. (2005)
• Cancer incidence following exposure to drinking water with asbestos leachate — H.L. Howe, P.E. Wolfgang, et al. (1989)

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