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About Exposure to I-131

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Plutonium for nuclear weapons was produced at the Hanford Nuclear Reservation from 1944, when it opened, until 1972 when the last reactor was closed. The Hanford Environmental Dose Reconstruction Project (HEDR) estimated that 740,000 curies of radioactive iodine were released to the air from chemical separation facilities used to produce plutonium for atomic weapons and that the majority of releases of iodine-131 occurred between 1944 and 1951 - with 1945 being the year of the highest releases.

HEDR also estimated that children aged up to five years old who lived in the three counties of Adams, Benton, and Franklin received the highest doses of I-131. It was estimated that children who lived in several counties beyond the three high exposure counties received significant, but lower, doses of I-131.

The most important exposure to the Hanford releases of I-131 was the consumption of contaminated milk produced by cows (and goats) grazing on contaminated pasture downwind of Hanford. Iodine accumulates in the thyroid gland and some studies have shown that exposure to radioactive iodine is associated with an increased risk of developing thyroid cancer and other thyroid related diseases. Medical studies indicate that exposed children up to five years of age may be at greater risk than the general population for developing thyroid problems following exposure to radioactive iodine.

More information about the history of the Hanford releases can be found in many of the educational materials that are available on this Web site. The following Hanford Health Information Network publications (all accessible via links on this Web site) provide more detailed information about the history of Hanford releases of I-131:

  • An Overview of Hanford and Radiation Health Effects
  • Hot Spots: Weather and Hanford's Radioactive Releases to the Air
  • Timeline of Major Events Related to the Release of Radioactive Materials from Hanford
  • The Release of Radioactive Materials from Hanford: 1944-72

This page last updated on January 19, 2005
Questions? - Contact CDC: 800-232-4636 / TTY: 888-232-6348

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