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A major independent review of disease rates around the Three Mile Island nuclear power plant has found no evidence that radioactivity released during the 1979 accident caused any increase in cancer incidence during the six-year period immediately afterward.
The report did find that people living in the path of the radioactive plume emanating from the damaged plant were slightly more likely to develop lung cancer or a blood cancer called non-Hodgkin's lymphoma than were people living nearby in areas away from the plume. However, the authors said there are reasons why neither of these diseases is necessarily linked to the accident.
The increases "are curious and we can't explain it," said Maureen Hatch, a Columbia University epidemiologist who was the report's chief author. "It would be hard to make an argument that this is convincing evidence, but it certainly raises questions."
The study, released yesterday, is the largest yet to look at cancer incidence, rather than deaths from cancer, among people living near the plant. Previous studies looked at cancer deaths or at cancer incidence over a shorter period of time. Many experts say incidence figures give a better measure of cancer risk after exposure to radiation, because it can be many more years before stricken people die.
The report appears in this month's issue of the American Journal of Epidemiology. It was commissioned by the Three Mile Island Public Health Fund, which was established in 1981 as a result of a class-action suit against General Public Utilities Corp., which owns the plant, and other companies involved with the power plant.
Some local citizens and lawyers for people seeking damages from TMI's owners said they do not think the study was well done, and some charged the utility company was involved in pressuring the scientists to produce a favorable report.
"It's as if the tobacco industry was issuing a report on whether cigarettes are good for you," said Arnold Levin, a Philadelphia lawyer who represents several people seeking personal damages from the utility company.
The study focused on leukemias and childhood cancer, which Hatch said are the types of cancer most likely to occur after exposure to low doses of radiation. It found that people living in areas that received the most radiation from the plant were no more likely to develop either disease than were people living in areas exposed to the least amount of radiation from the plant.
The incidence of childhood cancer in the heavy radiation areas was 1.06 times that in the low radiation areas, and that of leukemia in people under the age of 24 living in the high exposure area was 2.81 times that of the people in the low exposure area. But the researchers said these differences were not statistically significant because the number of cases was very low. Between 1980 and 1985, for example, there were only three cases of leukemia for that age group in the two highest radiation exposure areas and one case in the lowest exposure area.
The researchers gave several reasons why the increase in lung cancer and non-Hodgkin's lymphoma could not be blamed on emissions from the plant. One is that studies of people exposed to radiation, such as survivors of the nuclear bombings in Japan, indicate that lung cancer usually takes at least 10 years to develop after a radiation exposure (the study only went to six years after the Three Mile Island accident) and also that non-Hodgkin's lymphoma is not caused by radiation.
The average dose of radiation received by local residents ranged from 0.01 rem in the low exposure areas to 0.025 rem in the high exposure areas, the researchers said. The highest dose was about one-third to one-fourth that of the average annual "background" dose that Americans receive from natural radioactivity.
The researchers said the low incidence of cancers found in their study indicates official estimates of radiation released by the plant were correct. Many nearby residents have been skeptical about these estimates and said the plant had released more radioactivity.