Hanford Releases and Dose Reconstruction

From 1944 through 1972, Hanford released many radioactive materials into the air. The Hanford Environmental Dose Reconstruction (HEDR) Project was established decades later. HEDR estimated how much radioactive material was released from Hanford, how that material may have reached and exposed people, and what radiation dose people living in the HEDR study area (see map) may have received from Hanford's releases.

HEDR reported that the major releases into the air occurred from 1944 to 1957 and included an estimated 740,000 curies of iodine-131.² The HEDR estimated that over this period, iodine-131 was the major contributor to radiation dose from the air releases. HEDR calculated dose estimates for 12 representative (typical) individuals for six of the radioactive materials released. These were: iodine-131, cerium-144, ruthenium-103, ruthenium-106, strontium-90 and plutonium-239.

From 1944 to 1971, Hanford released many radioactive substances into the Columbia River through water used to cool the reactors. The largest river releases occurred between the late 1950s and mid-1960s.³ According to HEDR, major contributers to dose from the river releases were sodium-24, phosphorus-32, zinc-65, arsenic-76 and neptunium-239. The Centers for Disease Control and Prevention (CDC) is now working to complete estimates of representative doses from the Columbia River and for people who worked on-site at hanford.

Potential Health Effects of Iodine-131

In January 1999, the CDC released the Draft Final Report from the Hanford Thyroid Disease Study (HTDS). The Fred Hutchinson Cancer Research Center conducted the study for the CDC. The study evaluated whether thyroid disease was related to the levels of estimated radiation doses among persons exposed as children in the 1940s and 1950s to Hanford's air releases of iodine-131.

The initial HTDS results were released in a draft report. While the study found thyroid diseases among HTDS participants, the initial results did not show a link between the estimated thyroid dose from iodine-131 and the amount of thyroid disease among participants. Those with higher estimated doses appeared to be no more likely to have thyroid diseases than were those with very low doses.

A National Academy of Sciences review panel wrote that the HTDS investigators "probably overstated the strength of their findings that there was no radiation effect." The panel found that the study methods were of high quality. However, that panel said that additional analyses are needed to explain what the study data mean about the full range of possible risk th the thyroid. A revised HTDS report is expected by December 2000.

The HTDS findings need to be viewed in light of other studies that suggest there is a link between iodine-131 and both benign and malignant thyroid tumors. A study was done of people who lived downwind from the Nevada Test Site and were exposed to nuclear fallout that included iodine-131. Study participants with higher doses were more likely to have thyroid nodules than were those with lower doses.⁴

Since 1992, scientists studying possible effects from the 1986 Chernobyl accident have reported that the rates of thyroid cancer were significantly increased among young people.⁵ Some recent data suggest a connection between radionuclide exposure and the thyroid cancers. Most of the exposure was from iodine-131. However, scientists cannot yet clearly describe the roles of iodine-131 and other factors in contributing to this increase. These other factors include exposure to additional radionuclides and a deficiency of nonradioactrive iodine in the diet (iodine deficiency disorder).

The National Research Council recently began a study to review the last 10 years of studies on the health effects of low-level ionizing radiation. Over the next three years, this study (called BEIR VII) will develop principles for quantifying the risk from this exposure.

When using information from dose reconstruction and health studies, readers should keep in mind that the strength of a study's findings is affected by a number of factors, such as the quality of the information available about doses or health outcomes, and the study's design.

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