PITTSBURGH, Nov. 1 – In a 20-year follow-up study of mortality data on residents living within a five-mile radius of Three Mile Island (TMI), researchers at the University of Pittsburgh's Graduate School of Public Health (GSPH) found no significant increase overall in deaths from cancer. The findings were published Friday, Nov. 1, on the Web site of Environmental Health Perspectives, http://ehis.niehs.nih.gov, a journal of the National Institutes of Health's National Institute of Environmental Health Sciences. The paper will appear in the March 2003 issue of the journal.
"This survey of data, which covers the normal latency period for most cancers, confirms our earlier analysis that radioactivity released during the nuclear accident at TMI does not appear to have caused an overall increase in cancer deaths among residents of that area over the follow-up period, l979 to l998," said Evelyn Talbott, Dr.P.H., professor of epidemiology at GSPH and principal investigator on the study. Dr. Talbott's previous study, published in the June 2000 issue of Environmental Health Perspectives, analyzed 13 years of mortality data.
The TMI incident occurred at a nuclear power plant near Harrisburg, Pa., on March 29, 1979, when a reactor leaked small amounts of radioactive gases. Scientists have calculated that the average person present in the area during the 10 days following the incident was exposed to considerably less radiation than the annual dose an individual receives from the everyday environment in the United States. However, little is known about the long-term health effects of low-level radiation.
The current University of Pittsburgh study examined causes of death that included heart disease and malignancies as well as specific cancers known to be sensitive to radioactivity: bronchus, trachea and lung; breast (women only); lymphatic and hematopoietic tissue (blood-forming organs), excluding chronic lymphocytic leukemia and Hodgkin's disease; and the central nervous system. Thyroid cancer was considered, but only one death was reported during the study period.
Researchers used information collected by the Pennsylvania Department of Health in interviews conducted with 32,135 TMI residents within two months of the accident. Information included education, occupation, smoking status, residential history, medical history, previous radiation exposure and daily travel into and out of the area during the 10 days following the accident. This exposure data was combined with mortality data from the Pennsylvania Department of Health.
The ratio of the number of observed deaths in the TMI "exposed" population was compared with the expected number of deaths in the general population. The overall number of cancer deaths among men and women in the TMI population was not significantly different from the general population, but there was a slight increase in the number of deaths from lymphatic and hematopoietic cancers in women in the TMI population.
Comparisons of mortality risks also were performed to assess the impact of the radiation related exposures on the cancer rates in the cohort. After adjusting for background radiation, educational level and smoking, no significant differences were noted. There was however, a slight increase in the risk of lymphatic and hematopoietic cancers among males, which was related to radiation exposure from the accident, and an increased risk of mortality from lymphatic and hematopoietic cancers in women, which was related to everyday background radiation exposure.
"While these findings overall convey good news for TMI residents, the slight increased risk of death from lymphatic and hematopoietic cancers may warrant further investigation. Also, while our 13-year follow-up indicated a significant upward trend in breast cancer risk related to radiation exposure the day of the accident, this relationship was no longer significant in our current study."
This research was supported by a grant from the Three Mile Island Public Health Fund.
Materials provided by University Of Pittsburgh Medical Center. Note: Content may be edited for style and length.
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