Observations of cancer incidence surveillance in Duluth, Minnesota

In 1973, amphibole asbestos fibers were discovered in the municipal water supply of Duluth, Minnesota. The entire city population of approximately 100,000 was exposed from the late 1950s through 1976 at levels of 1-65 million fibers per liter of water. Because of previous epidemiologic studies that linked mesothelioma, lung and gastrointestinal cancers to occupational exposure to asbestos, surveillance of cancer incidence in residents of Duluth was initiated to determine the health effect from ingestion of asbestos. The methodology of the Third National Cancer Survey (TNCS) and SEER Program was used. Duluth 1969-1971 rates were compared with TNCS rates for the cities of Minneapolis and St. Paul during 1969-1971; Duluth rates during 1974-1976 are compared with Duluth 1969-1971; Duluth rates during 1979-1980 are compared with Duluth 1969-1971 and with Iowa SEER; and a table of the occurrence of malignant mesothelioma is presented. Statistically significant excesses are observed in several primary sites in Duluth residents. However, lung cancer in Duluth females is the only primary site considered also of biological significance. The mesothelioma incidence rate is no more than expected. This paper also describes the problems of long-term surveillance of exposed populations considered at risk of environment cancer, the need for improved study methodologies and the use of federal records for follow up of exposed individuals.