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

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.