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PHILADELPHIA, MAY 26 -- Cancer rates went up among residents living closest to the Three Mile Island nuclear power plant several years after the near-meltdown of one of its reactors in 1979, but a new study says stress, not radiation, may have caused the increase.
Researchers report in the June issue of the American Journal of Public Health that stress resulting from the accident may have triggered "a small wave of excess cancers" in 1982 among people living within about 3 1/2 miles of the south-central Pennsylvania plant.
"We observed a modest post-accident increase in cancer near TMI that is unlikely to be explained by radiation emissions," concluded the researchers from Columbia University and the National Audubon Society. "Such a pattern might reflect the impact of accident stress on cancer progression."
A study last year by the same research team found no convincing evidence to link an increase in some forms of cancer among area residents to low-level radiation emissions from the plant during the accident.
Although the theory that stress could somehow trigger the growth of cancer has never been proved, the researchers reported in the journal that they decided to explore the possibility because of "growing interest in the effects of stress on cancer promotion and progression."
Past studies had shown that mental distress was a major consequence of the TMI accident, the worst in the history of commercial nuclear power in the United States. Women and children living within five miles of the plant at Middletown, Pa., 10 miles southeast of Harrisburg, the state capital, were told to evacuate after the accident. Thousands of others left the area on their own in fear of being exposed to radiation.
By searching medical records from 1975 to 1985 at hospitals within 30 miles of TMI, the researchers identified about 5,500 cancer cases involving people who lived within 10 miles of the plant. They found that cancer rates of those nearest TMI rose in 1982, remained elevated for a year and then declined.
The rate of cancer among residents within about 3 1/2 miles of the plant peaked in 1982 at just over 525 cases per 100,000 people -- up from about 300 cases per 100,000 in 1978, the researchers report.
The researchers found that people living closest to the reactor were 40 percent more likely to have been diagnosed with cancer after the accident than those people living farther away.
Even before the accident, the cancer risk was 20 percent higher for those living near the plant than for those farther away. The study did not address that earlier difference.
Jan Beyea, senior scientist at the Audubon Society, said the higher rates of cancer among people living nearest to TMI could not be attributed to radiation exposure. "This increase has occurred both in areas where there was radiation exposure and where there was not," he said.
The researchers said those closest to the plant tended to suffer the greatest stress from the accident and that stress could have promoted the growth of pre-existing cancers in people, thus bringing them to the point of being diagnosed.
"We can't say it's definitely stress, but it's suggestive of stress," Mervyn Susser, a Columbia University epidemiologist who was the principal investigator for the study, said in an interview.
The researchers also theorized that health concerns after the accident might have prompted doctors and people living in the area to check more vigilantly for cancer. But Susser said the medical records did not show an increase in early-stage cancers, something that would have suggested that people were being more attentive to screening for problems.
The researchers said the link between stress and cancer could be indirect. "The stress of the accident could have increased exposure to behavioral risk factors, such as cigarette smoking, but we have no data with which to evaluate this possibility," they wrote.
A representative of GPU Nuclear Corp., which operates TMI, said Friday that the company would not comment because company officials had not had a chance to review the report.