HTDS Guide - Hanford History

Iodine-131 was carried by winds to surrounding areas and deposited on vegetation. It was then absorbed in the milk of cows and goats that grazed on the contaminated vegetation. Drinking contaminated milk caused most of the radiation dose for most of the exposed people.

People were also exposed by eating contaminated fruits and vegetables, and by breathing contaminated air.

The main reason why the HTDS was conducted is that the public, health officials and scientists were concerned about the possible health effects of Hanford's radiation.

Thyroid disease was a particular concern because iodine concentrates in the thyroid gland and the DOE documents showed that large amounts of iodine-131 were released from Hanford. In response to public concerns, Congress directed CDC to conduct a study of the effects of Hanford's iodine-131 on thyroid disease.

Many people ask, "Didn't we already know that Hanford radiation causes thyroid disease?" Over the years, many studies of other populations have provided compelling reasons to suspect that the risk of thyroid disease might have increased in people who were exposed to Hanford's iodine-131.

Nevertheless, the published literature left room for doubt, since none of the studies examined circumstances quite like those of the Hanford experience. The following are ways other radiation studies are different from the Hanford situation:

Type of radiation exposure – External irradiation by gamma rays (such as the atomic bombings in World War II) or x-rays used in medical treatments may have different effects than iodine-131.

The people who were exposed – People who received iodine-131 for treatment or diagnosis already had, or were likely to have, thyroid diseases, while people exposed to Hanford's iodine-131 were a general population, including some people with good health and some with poor health.

How big the doses were – Doses of iodine-131 used for medical treatments are much higher than anyone is likely to have received from Hanford's iodine-131. Doses from Chernobyl's fallout were higher as well.

How long people were exposed – External irradiation typically occurs within a few seconds or minutes. Medical exposures of iodine-131 typically occur over days to weeks. Exposure to Chernobyl's fallout occurred from weeks to months. In contrast, many of those exposed to Hanford's iodine-131 were exposed over a period of several years.

Because other studies have addressed situations different from Hanford in important ways, it was necessary to study people who were actually exposed to Hanford's iodine-131 in order to get the most reliable answer to the question of whether thyroid disease had been increased by Hanford's iodine-131.

No study can determine the cause of an individual case of thyroid disease. However, an epidemiological study, such as the HTDS, provides the best way to determine whether disease has increased in a population exposed to a potentially harmful agent such as radiation.