Observations of cancer incidence surveillance in Duluth, Minnesota

Our plain-English summary of Observations of cancer incidence surveillance in Duluth, Minnesota, by E.E. Sigurdson (Environmental Health Perspectives, 1983).

The study

• Author: E.E. Sigurdson
• Journal: Environmental Health Perspectives
• Published: 1983;53:61-7
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000643).

Abstract

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.

In plain English

This report described cancer surveillance in Duluth, Minnesota, a city of about 100,000 people. From the late 1950s through 1976 its tap water contained amphibole fibers, from taconite mining wastes dumped into Lake Superior, at 1 to 65 million fibers per liter. Cancer cases were found through hospital, pathology, autopsy and death records. Duluth rates for 1969-1971 were compared with Minneapolis and St. Paul. Later Duluth rates were compared with earlier Duluth rates and with Iowa. Several cancer sites showed statistically significant differences, some based on very small numbers. In 1979-1980, lung cancer in Duluth women was significantly higher than in Duluth in 1969-1971 (standardized morbidity ratio 2.3) but not when compared with Iowa. Nine pleural and one peritoneal mesothelioma were recorded in 1969-1980. The pleural count was 3.75 times the expected 2.4 cases, which was statistically significant, though the author suggested heightened diagnostic attention may partly explain this. The author concluded that only the rise in lung cancer among women had clear biological significance and attributed it to cigarette smoking.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Population-based cancer incidence surveillance using Third National Cancer Survey and SEER methods, comparing age-adjusted rates and standardized morbidity ratios across cities and time periods
• Who was studied: Residents of Duluth, Minnesota (population approximately 100,000; 100,578 in the 1970 census), with cancer cases diagnosed 1969-1980. Comparisons were with Minneapolis and St. Paul (1969-1971) and with the Iowa SEER program (1973-1977, whites only).
• Exposure: Amphibole fibers (principally cummingtonite-grunerite) in the municipal drinking water, from taconite tailings dumped into Lake Superior, at 1 to 65 million fibers per liter from the late 1950s through 1976. A filtration plant began operating in January 1977.
• Main results:
  • 1969-1971, Duluth compared with Minneapolis and St. Paul: statistically significant excesses in Duluth for male peritoneum, retroperitoneum and intra-abdominal cancer (rate 4.3 per 100,000, 7 cases), male other peritoneum and digestive, female uterine corpus, and male prostate (90.4 per 100,000, 161 cases).
  • Duluth 1974-1976 compared with Duluth 1969-1971: statistically significant increases for female peritoneum, retroperitoneum and intra-abdominal cancer, female lung cancer (17.9 per 100,000, 34 cases, compared with 9.3, 18 cases), female uterine corpus, and female multiple myeloma. Male prostate cancer showed a statistically significant decrease. The author cautioned that some sites involved very small numbers.
  • Duluth 1979-1980, male stomach cancer: SMR 1.7 compared with Iowa SEER, statistically significant. It was not statistically significant compared with Duluth 1969-1971 (SMR 0.8).
  • Duluth 1979-1980, female lung cancer: SMR 2.3 compared with Duluth 1969-1971, statistically significant. It was not statistically significant compared with Iowa (SMR 1.5).
  • Duluth residents 1969-1980: 9 pleural malignant mesotheliomas (6 male, 3 female) and 1 peritoneal mesothelioma.
  • Pleural mesothelioma averaged 0.75 cases per 100,000 per year in Duluth, compared with 0.2 per 100,000 per year in the Minneapolis-St. Paul component of the Third National Cancer Survey. The SMR was 3.75 (9 observed, 2.4 expected), statistically significant at p = 0.01.
  • Six pleural mesothelioma cases were found in 1974-1976, a period of heightened community concern, against about three expected.
• The authors' conclusion: In the author's opinion, the only statistically significant result with clear biological significance was the increase in lung cancer among Duluth women, which the author attributed to increased cigarette smoking. The author stated the other variations could not be explained and that longer surveillance with follow-up of the exposed population is needed.
• Limitations the authors state:
  • Some statistically significant findings rest on very small numbers.
  • With many comparisons, some results are expected to be statistically significant by chance alone.
  • Increased diagnostic surveillance in the mid-1970s may partly account for the mesothelioma excess.
  • It is uncertain how far the incidence observed in Duluth reflects disease in the people who were actually exposed, because of migration.
  • Stomach cancer rates were high before asbestos exposure began, and the effect of the exposure beyond known risk factors cannot be determined.
  • Longer surveillance, with evaluation of residents' mobility and follow-up, is needed before the differences can be resolved.

Topics

Medical terms in this study, explained in our Lexicon: Amphibole Asbestos, Mesothelioma, Occupational Exposure, SEER, Malignant Mesothelioma, Lung Cancer, Incidence.

Related studies

• Investigating possible effects of abestos in city water: surveillance of gastrointestinal cancer incidence in Duluth, Minnesota — B.S. Levy, E. Sigurdson, et al. (1976)
• Cancer incidence in relation to asbestos in drinking water in the Puget Sound region — L. Polissar, R.K. Severson, et al. (1982)
• Cancer incidence among Minnesota taconite mining industry workers — E.M. Allen, B.H. Alexander, et al. (2015)
• Asbestos in drinking water and cancer incidence in the San Francisco Bay area — M.S. Kanarek, P.M. Conforti, et al. (1980)
• Cancer incidence following exposure to drinking water with asbestos leachate — H.L. Howe, P.E. Wolfgang, et al. (1989)
• Cancer incidence and asbestos in drinking water, Town of Woodstock, New York, 1980-1998 — M.L. Browne, D. Varadarajulu, et al. (2005)

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