Three Mile Island: cancer risk ambiguous.

Three Mile Island: Cancer risk ambiguous

A court-ordered study finds no "convincing evidence" of inceased cancer risk among people exposed to radiation from the Three Mile Island nuclear power plant. But the long-awaited findings fall short of settling the issue.

The study looked for cancers possibly linked to the Pennsylvania facility, either from routine radioactive emissions since 1975 or from the 1979 accident there. The results remain statistically ambiguous: The authors don't rule out a cancer correlation, nor do they find a significant rise in the cancers most likely to appear soon after radiation exposure.

Antinuclear activists, as well as many of the more than 2,000 lawsuit-filing area residents who claim the accident damaged their health, maintain the study has serious flaws. Some suspect that many radiation-lined cancers have yet to develop. But the researchers claim the data strongly suggest that belated increases, if any, will be very small.

The findings are "consistent with all the medical and scientific evidence we have so far," says physicist Jacob I. Fabrikant of the University of California, Berkeley, who sered on the staff of the 1979 presidential commission that investigated the accident. That panel concluded that the amount of radiation released during the mishap was a fraction of the region's normal annual background radation from cosmic and geologic sources, and it predicted a maximum of one excess cancer death from the accident.

The new study, financed by a court-appointed fund created in the accident's aftermath, was led by Maureen C. Hatch of the Columbia University School of Public Health in New York City. Her team used a mathematical model and dosimeter readings to estimate neighborhood radiation exposures for the nearly 160,000 people living within a 10-mile radius of the plant. They also obtained regional hospital records documenting 5,493 cancer diagnoses between 1975 and 1985.

High-exposure areas did not show significant increases, in adult leukemias or in any childhood cancers. But because of the small numbers of people with some cancers, the true risk remains "indeterminate," the researchers say. Indeed, because of statistical uncertainties, the study's cancer risk estimates "are compatible with no association as well as with quite strong associations" in some categories, they write September AMERICAN JOURNAL OF EPIDEMIOLOGY.

Unexpectedly, the study reveals that high-exposure areas show significant increases in non-Hodgkins lymphoma, a cancer not generally associated with radiation exposure. It also reveals higher-than-expected rates of lung caner -- which, unlike leukemia and childhood cancers, usually takes many years to develop. The researchers suggest both increases are probably due to statistical flukes or to unrelated factors such as radon exposure or occupations hazards.

Activists and some scientists note that because the study relied on data from area hospitals, it may have missed substantial numbers of people who became ill after moving away from the region or who sought care in distant cancer centers. Critics also say that by lumping as many as 9,500 people in some exposure categories, the study may have diluted evidence of small cancer "hotspots".

So far, no funds have been allocated for a more detailed analysis or longer follow-up, Hatch says.