Radiation study shows no thyroid harm

UPI Science News

ATLANTA, Jan. 28 (UPI) -- A nine-year, $18 million investigation has found no increase in thyroid disease among people living near a federal nuclear plant in Washington state that released radioactive gases during the Cold War years.

The Centers for Disease Control and Prevention in Atlanta released a draft today of its report on thyroid disease among 3,441 adults born in the 1940s in the south central Washington counties surrounding the Hanford Nuclear Reservation, which produced plutonium for nuclear weapons.

The study was mandated by Congress in 1988, after the government declassified thousands of documents, revealing huge releases of radioactive gas from the plant in the 1940s and 1950s.

In the study, conducted by the Fred Hutchinson Cancer Research Center for the CDC, scientists estimated levels of exposure to one radioactive substance, iodine-131. The scientists then measured rates of thyroid diseases, such as cancer, non-cancerous tumors, hypothyroidism and hyperthyroidism in people who were children living in the area at the time.

Scott Davis, the study's lead investigator, says, ``We looked at all types of thyroid disease and found no evidence that the number of cases was significantly elevated among those with higher I-131 doses.''

He adds that this is ``a very powerful study because it included a large number of people estimated to have a wide range of exposures to I- 131.''

The scientists focused on I-131 because it was the biggest source of radiation for children in the area, who were most likely exposed to the substance by drinking contaminated milk, says Paul Garbe, the CDC's scientific adviser to the study. Iodine concentrates in the thyroid gland.

The researchers did find that people exposed to the highest doses of radiation had ``small abnormalities'' of the thyroid that could be detected only by ultrasound, and slightly lower levels of calcium in their blood. But the higher numbers were not statistically significant, says Garbe.

The death rate in the study population was higher than in the rest of the state, but much of this was attributed to infants and children who died before the plant opened, says Garbe. Another study looking at infant and fetal deaths in the area is under way and results are expected in the late spring.

The preliminary draft of the thyroid study is available through the CDC, and will be open to public comment until April 1, 1999.

Other studies, such as those looking at children after the atomic bombings of Hiroshima and Nagasaki have shown that short intense exposure to radiation causes thyroid cancer. Research from Chernobyl, the Marshall Islands and the Nevada Test Site supported that finding.

Garbe says that based on those reports, scientists thought they would find some rise in thyroid disease from Hanford radiation.

Garbe says, ``We were a little surprised.''

But the scientists say there are differences between the nuclear explosions and accidents and Hanford, mainly in the levels and kinds of radiation exposure experienced. The scientists say that children at Hanford got much lower doses of radiation over a long period of time.