Cancer risk from asbestos in drinking water: summary of a case-control study in western Washington.

We conducted a case-control, interview-based study of the risk of developing cancer from asbestos in drinking water. An area that included Everett, Washington, was selected for the study because of the unusually high concentration of chrysotile asbestos in drinking water from the Sultan River. Through a population-based tumor registry, 382 individuals with cancer of the buccal cavity, pharynx, respiratory system, digestive system, bladder, or kidneys, diagnosed between 1977 and 1980, were identified, and they or their next of kin were interviewed. We conducted validation checks of our interviews, including a comparison with secondary sources. Data on asbestos exposure were collected based on residence and workplace history, and on individual water consumption. Logistic regression was used to estimate cancer risk. We found no convincing evidence for increased cancer risk from imbibed asbestos. Confidence intervals for relative risks for almost all sites included unity. There were significantly elevated risks only for male stomach and male pharyngeal cancer, but these sex-inconsistent results, based on small numbers of cases, are probably due to other factors.