RE: Asbestos in Drinking Water and Cancer Incidence in the San Francisco Bay Area + The Authors Reply

Our plain-English summary of RE: Asbestos in Drinking Water and Cancer Incidence in the San Francisco Bay Area + The Authors Reply, by I.T.T. Higgins, M.S. Kanarek (1981).

The study

• Authors: I.T.T. Higgins, M.S. Kanarek
• Published: Letters to the Editor Section p161-164 July (1981)
• Type of article: Letter
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This item is an exchange of letters, not a new study. Higgins criticized an earlier paper by Kanarek and colleagues on asbestos fibers in drinking water and cancer incidence in the San Francisco Bay Area. The letter argued that the paper ignored the known link between cancer and population density. High fiber counts were found in San Francisco and San Mateo counties, and digestive tract cancer death rates were higher in San Francisco than in California as a whole. But New York City, which has no high fiber counts, showed similar differences from New York State. The letter stated that the fiber/cancer association was confounded by population density. In reply, Kanarek and Conforti wrote that their study compared cancer incidence across 722 census tracts within the San Francisco-Oakland area, not counties against the state. They said the area had no rural counties and that asbestos counts did not vary with population density by tract. They added that Connecticut asbestos-cement pipe studies involved lower exposures and generally longer fibers than the Bay Area water, where fibers appeared to come from serpentine rock.

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: Letter to the editor criticizing a published study, followed by the original authors' reply; no new study data
• Who was studied: The study under discussion compared cancer incidence rates for the 722 census tracts (1970 census) of the San Francisco-Oakland Standard Metropolitan Statistical Area (SMSA)
• Exposure: Asbestos fibers in drinking water. The authors' reply stated that the Bay Area fibers appeared to come mainly from contact with naturally occurring serpentine rock, whereas the Connecticut exposures were presumably from fibers leaching out of asbestos-cement pipe.
• Main results:
  • Higgins stated that, according to Kanarek's doctoral thesis, high fiber concentrations were in San Francisco County and San Mateo County, with the highest in San Mateo County
  • Higgins stated that digestive tract cancer death rates were higher in San Francisco than in the State of California. Similar differences were seen between New York City and New York State, although New York City does not have high fiber counts in its drinking water.
  • Higgins stated that the fiber/cancer association was confounded by population density
  • Higgins noted that a similar study by Severson in the Puget Sound area reached negative conclusions
  • The reply stated that the study made no comparisons of metropolitan county cancer mortality rates with those of the rest of California
  • The reply stated that the San Francisco-Oakland SMSA consists of two urban and three suburban counties, with no rural counties
  • The reply stated that measured census tract asbestos counts did not vary with population density by census tract in the San Francisco-Oakland SMSA
  • The reply stated that high counts were also found in parts of Marin and San Mateo counties, which have low population density relative to the SMSA. High-density areas of Alameda County (Oakland and Berkeley) had relatively low asbestos.
  • The reply stated that exposures in the Connecticut asbestos-cement pipe studies were generally much lower than in the Bay Area, and that fibers released from pipe were generally longer than those in San Francisco Bay water supplies
  • The reply stated that the Puget Sound master's thesis was unavailable for the authors' review
• The authors' conclusion: Higgins concluded that all the evidence was against the conclusion that asbestos fibers in drinking water may be a cancer hazard. The original authors replied that population density as an issue is minimized in studies comparing census tracts within one metropolitan area.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos-Cement Pipe, Serpentine Group.

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