TUESDAY, Nov. 30, 2004 (HealthDayNews) -- People who were exposed to radioactive gas released by a nuclear weapons facility in Washington state during the Cold War have not, as many suspect, experienced higher rates of thyroid cancer, according to a new study.
Government documents made public in 1986 revealed that, between 1944 and 1957, operators of the Hanford Nuclear Site in the southeastern part of the state intentionally discharged significant amounts of gas containing iodine 131 -- a radioactive form of the element and a carcinogen linked to thyroid cancer -- into the skies around the plant.
Residents who lived in the greater Hanford area during that time period, now known collectively as "downwinders," have pushed hard since then to determine the potential health risks, if any, of their exposure to this toxin.
The final draft publication of data, first released six years ago, appears in the Dec. 1 issue of the Journal of the American Medical Association. The findings may help ease the concerns of some downwinders, but they are unlikely to convince everyone who grew up there.
Hanford was the largest of several facilities the U.S. government built to help develop and produce nuclear weapons and materials in the 1940s and 1950s, beginning with the Manhattan Project. Iodine 131 is produced during a nuclear explosion.
The study, involving 3,440 Hanford-area residents, found no evidence linking exposure to airborne iodine 131 in childhood or youth to a heightened lifetime risk for thyroid cancer, or other thyroid disorders. The study compared lifetime rates for thyroid disease in people born and raised in the Hanford area and exposed to relatively high or low levels of the contaminant during those years.
"This is certainly one of the most comprehensive investigations of exposure of this type ever conducted," said study lead researcher Scott Davis, a professor of epidemiology at the Fred Hutchinson Cancer Research Center and the University of Washington, both in Seattle.
He stressed that no epidemiological study can guarantee "absolute proof" of a lack of carcinogenic effect. But he added, "In our estimation, this study had sufficient statistical power to detect effects of a magnitude that one would expect to see with this level of radiation dose, had there been an effect."
Others remain somewhat more cautious. Jude Van Buren, an epidemiologist with the Washington State Department of Health, was born in 1953 in Pasco, Wash., close to the Hanford site, and spent the first 20 years of her life in the area. She also served as a longtime member of the Hanford Health Effects Subcommittee, a panel convened by special federal charter to represent citizens potentially affected by the Hanford emissions. That committee was officially disbanded last fall.
Van Buren concurred that Davis' $18 million study "uses the best tools we have available to us in science right now." But she said that, even though the study group is large by most standards, "it's still very difficult to get an epidemiological study big enough to really understand very subtle changes in exposed vs. unexposed individuals."
Further complicating matters, in Van Buren's opinion, is that fact that the study doesn't include a true control group: individuals totally unexposed to iodine 131.
"In the study, the 'exposed' group were in counties [around Hanford] that were heavily exposed," she explained. "And what they called the 'non-exposed' were actually in counties where people still got exposure, but just not so much. So you're not comparing no exposure to a lot of exposure."
Van Buren also noted that certain thyroid conditions, including a dysfunction called autoimmune thyroiditis, are notoriously difficult to diagnose, even by thyroid specialists.
"I think that it was felt at the time when this study was done that this was the study that decided [the Hanford release] was not a health problem," she said. "But I think there's a lot of downwinders -- people who live in eastern Washington or who lived there when they were growing up -- that probably don't believe this. I myself am not sure there wasn't an effect."
A legacy of public suspicion hasn't helped matters, either. Documents reveal that during and after World War II, the public had little information on activities at the Hanford site, which was used to reprocess nuclear fuel to gain plutonium for use in atomic weapons.
"The whole Hanford project was a secret," Van Buren said. "In 1949, after the war, there was an intentional release of iodine 131 -- this was called the 'Green Run.' They released it into the environment, knowingly exposing people, just so they could see how far it would spread. They knew it was dangerous, but they felt it was so minimal it wasn't going to be a problem."
"Those records weren't released until 1986, so it's hard to trust the government if you've grown up in an area where you've never been told the truth," she said.
Davis acknowledged that the findings, while strong, will still leave many Hanford residents with lingering doubts. "Some people were reassured by these results and felt more at ease knowing there was no large, demonstrable effect from the Hanford release," he said, "while others weren't convinced at all."
Van Buren -- whose opinions do not reflect those of the Washington State Department of Health -- believes that exposed individuals should remain cautiously optimistic and pay attention to their health.
"I think one of the real benefits that's been gotten out of all this looking, searching and contacting people is to make people more aware of the fact there are things they need to monitor, such as their thyroid," she said. "You need to take responsibility for your health, making sure you're getting the checkups that you need."
To learn more about the Hanford site release, go to the Washington State Department of Health.