Comments on the California studies

Our plain-English summary of Comments on the California studies, by R.C. Cooper (Environmental Health Perspectives, 1983).

The study

• Author: R.C. Cooper
• Journal: Environmental Health Perspectives
• Published: 1983;53:109-10
• Cited by: 2 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. 000600).

In plain English

In this short commentary, the author described earlier work by the author's research group in the San Francisco Bay Area and a later reanalysis. That work began in 1973, when the group noted that several reservoirs sat on serpentine rock, known to contain asbestos, and found asbestiform fibers in raw drinking water. The group's 1980 epidemiologic study compared drinking-water fiber levels with tumor registry data. The author wrote that it found a statistically significant correlation between fiber concentration and cancer incidence, especially of the digestive tract, and that the group claimed only a statistical relationship, not cause and effect. A reanalysis generally reconfirmed this. It judged a negative correlation with uterine cancer most likely a statistical artifact. It found population density had no impact on the correlation, but data from San Francisco City and County had a major effect on it. The author listed problems with the original study and concluded that if the relationship proved independent of this "San Francisco phenomenon," more work would be needed to estimate whether asbestos in drinking water causes cancer, a well-conceived case-control study being the most logical next step.

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: Commentary describing the author's group's earlier drinking-water and cancer studies and a later reanalysis of their data; no new data are presented in full
• Who was studied: Residents of the San Francisco Bay Area counties, analysed by 1970 census tracts, using tumor registry data from the San Francisco Bay Area Resource for Tumor Epidemiology; the study was funded in 1976
• Exposure: Asbestiform fibers in drinking water from reservoirs located on asbestos-containing geologic formations (serpentine rock), rather than from mining or industry
• Main results:
  • The 1980 study found a statistically significant correlation between asbestos fiber concentration in drinking water and cancer incidence, particularly in organs of the digestive tract
  • A later reanalysis of all the data generally reconfirmed the earlier observations
  • The original study also found a statistically significant negative correlation between uterine cancer and fiber concentration. The reanalysis judged this most likely a statistical artifact of the original residual analysis method
  • Population density showed no impact on the correlation between asbestos concentration and tumor incidence
  • Data from San Francisco City and County had a major effect on the correlation that was not related to population density (called the 'San Francisco phenomenon'). Whether it is independent of asbestos dose was still being studied
• The authors' conclusion: The authors claimed only a statistical relationship, not cause and effect. The author concluded that if the relationship proves independent of the San Francisco phenomenon, more work is needed to estimate whether asbestos in drinking water causes cancer, with a well-conceived case-control study as the most logical next step
• Limitations the authors state:
  • Insensitivity of the asbestos assay method
  • Incomplete employment history available from the tumor registry
  • No smoking or alcohol consumption data
  • Population mobility
  • Uncertainty whether the water supply information reflected 20 to 30 years of past history

Related studies

• Additional comments on the study of the effect of population density on the results of the California Bay area study — P.M. Conforti (1983)
• Effect of population density on the results of the study of water supplies in five California counties — P.M. Conforti (1983)
• Chemical contamination of California drinking water — H.H. Russell, R.J. Jackson, et al. (1987)
• Asbestos in drinking water and cancer incidence in the San Francisco Bay area — M.S. Kanarek, P.M. Conforti, et al. (1980)
• 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" — I.T. Higgins (1981)

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