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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.

Recently there has been a confusing and somewhat frustrating difference of opinion in epidemiology concerning the relative merit and utility of descriptive versus mechanistic knowledge in approaching the comprehension and control of human cancer. This distinction has both historical and evolutionary rationale; it generally being necessary to know something of WHAT is happening before one can be legitimately concerned with HOW it is happening. As outlined below, however, there is little justification for making value judgements based on this distinction, and the situation is more one in which descriptive approaches and mechanistic approaches are equally essential in the development of a systematic viewpoint, a viewpoint providing guidance to meaningful intervention.

The association between gastrointestinal, urinary tract, brain, lung, and breast cancer mortality and drinking water trihalomethane exposure, as estimated by average daily chlorine dosage of water source 20 years past, was investigated for Wisconsin white females by use of a death certificate-based case-control study design. A total of 8,029 cancer deaths and 8,029 controls (noncancer deaths) matched on county of residence, year of death, and age were taken from mortality records of 28 counties for the years 1972-77. Data on characteristics and treatment of municipal water supplied to the residences of cases and controls were obtained from questionnaires sent to the water superintendents of the 202 waterworks associated with the sample. By the use of logistic regression analysis, odds ratios for site-specific cancer death associated with high, medium, and low chlorine-dosed water as compared to unchlorinated water exposure were determined; the control variables were urbanicity, marital status, and occupation. With the exception of cancer of the colon, no anatomic cancer site was significantly associated with any chlorine dose exposure category. For colon cancer, odds ratios of 1.51 [95% confidence interval (Cl) = 1.06-2.14], 1.53 (95% Cl=1.08-2.00, and 1.53 (95% Cl-1.11-2.11) were obtained for high-, medium-, and low-dose chlorination, respectively (P less than or equal to 0.02). For colon cancer cases and controls exposed to water sources affected by rural runoff, odds ratios of 3.30 (95% Cl=1.45-7.47), 3.60 (95% Cl=1.57-8.26), and 2.74 (95% Cl=1.10-6.88) were observed for high, medium, and low chlorine dosages 20 years past (P less than or equal to 0.025).

A case control study of drinking water treatment practices and female cancer mortality was conducted in Wisconsin. Cancer deaths for 1972-1977 from 28 Wisconsin counties and noncancer deaths matched to cancer deaths on age, year of death and county of residence, were compared for characteristics of drinking water supplied to their places of residence. Using logistic regression, estimates of relative risk associated with chlorinated water were examined allowing for the influence of indicators of water organics and the potential confounders of occupation, marital status and urbanicity. Only colon cancer appeared to be related significantly to chlorination in all models explored. A dose-response relationship was found between crude indicators of trihalomethane level (chlorination X organic contamination) and colon cancer death. The odds ratio for chlorinated surface water for colon cancer was 2.81 (p less than 0.01); approximately half this risk was found for chlorinated ground water. Consequently, a case control study of colon cancer and drinking water quality utilizing newly diagnosed patients is being conducted in Wisconsin.

The epidemiological studies of ingested asbestos fibres conducted world-wide are reviewed and evaluated. Most of the studies have been done in the United States and Canada and have involved community exposures via natural contamination of drinking-water supplies. One or more studies found associations between asbestos fibres in drinking-water supplies and cancer incidence or mortality associated with many body sites, including oesophagus, stomach, small intestine, colon, rectum, gall-bladder, lungs, pancreas, peritoneum, pleura, prostate, kidneys, brain and thyroid. Each study has methodological limitations or weaknesses that limit the ability to assess risk from ingested asbestos. There is no agreement between the results of the various studies, but an association between ingested asbestos fibres and cancer of the stomach and pancreas has been found with some degree of consistency.