Incidence of cancer among lighthouse keepers exposed to asbestos in drinking water.

The study population comprises 690 Norwegian male lighthouse keepers whose water supply came from cisterns that received rain water off asbestos-cement-tiled roofs. The asbestos-cement tiles were installed in the late 1950s, and two decades later the fiber content in the tap water was analyzed. The fiber content ranged from 1,760 to 71,350 million fibers per liter, which is significantly higher than measured in any other Norwegian public water supply. During the follow-up period, 1960-1991, no statistically significant excess risk was found for any type of cancer in the group with a latency period of 20 years or more, except for stomach cancer (11 observed cases vs. 4.57 expected, standardized incidence ratio = 241, 95% confidence interval 120-431). No cases of malignant mesothelioma were found. The study is limited by lack of knowledge as to when the tiles began to deteriorate and, thus, the magnitude of total exposure as well as by the inability to control for such potential confounding factors as diet.