Introduction

During the Cold War, national security policies prevented government authorities from disclosing the health hazards associated with living near or working at weapon production facilities. These facilities released harmful levels of radiation into the environment.

On January 27, 1951, the United States launched a program of atmospheric testing of nuclear bombs in Nevada. This program continued for over a decade until August 5, 1963, with the passage and signing of Limited Test Ban Treaty. For over fifty years now, the impact and effects of fallout from those tests have generated much political debate and culminated in numerous scientific investigations. In October of 1997, the findings of one Congressionally mandated investigation were reported and brought to the public’s attention when the National Cancer Institute (NCI) published the two-volume report Estimated Exposures and Thyroid Doses Received by the American People from Iodine-131 in Fallout Following Nevada Atmospheric Nuclear Bomb Tests.

As the NCI began preparing the final stages of the report for publication, the Secretary of the Department of Health and Human Services (DHHS) asked the Institute of Medicine (IOM) and the National Research Council (NRC) to initiate an independent evaluation of the public health and medical implications of the iodine-131 doses received by the American people and to identify steps that might be taken in response. In 1997, the IOM and the NRC agreed to establish an expert panel to undertake this assessment in order to investigate the medical affects of the iodine-131 on behalf of the people of Nevada. This report found that long-term or chronic exposure to radioactive iodine could result in radiogenic thyroid cancer, non-cancerous growths and nodules and thyroiditis.

Iodine- 131 in the Environment

Iodine-131 is a radioisotope of iodine. It is typically present at low levels in hospital nuclear medicine departments, in patients administered radioactive iodine, and in releases from nuclear power plants. Iodine-131 is produced during nuclear fission, which occurs during the operation of nuclear reactors or detonation of a nuclear bomb.

Since 1944, when the first production atomic reactor was created, large amounts of Iodine-131have been intermittently released into the atmosphere. From 1945-to the early 1980′s, iodine-131 was released to the atmosphere as a gas during nuclear weapons. From 1951-1962, it was released in aboveground nuclear tests, medical isotope production, medical administrations to patients, and unintentional releases.

Exposure to Iodine-131 in Nevada

Iodine-131 released by the atomic bomb tests was carried thousands of miles away from the test areas on the winds, falling over parts of Utah, Colorado, Idaho, and Montana, as well as other states.  The majority of iodine-131 fell on pastures and on grasses. It was then digested by livestock, namely cows and goats. Once consumed by the animals, iodine-131 accumulated in the animals’ milk. Much of the health risk associated with iodine-131 occurred among milk drinkers, namely young children.

Health Risks

The major health risks associated with exposure to iodine-131 involve the thyroid gland which concentrates this radionuclide. Health risks include thyroid cancer and an increased frequency rate of the development of malignant as well as benign thyroid nodules.  Concern about the carcinogenic effects of exposure to radioiodine on the thyroid gland is motivated by three major factors. First, scientific evidence has demonstrated that the thyroid gland is uniquely sensitive to the effects of radiation developing even when exposed to extremely low levels of radiation. Second, the cow-milk-man pathway discussed in Chapter 2 of this report provides a vehicle by which radioiodines in the environment can be greatly coagulated in the human food chain. Finally, because most of the radiation dose is from ingested or inhaled radioiodine, the actual radiation dose to the thyroid is 500-1,000 times greater than is the largest radiation dose to other organs in the body.

Individuals exposed to I-131 as children are particularly at risk for carcinogenic effects. Children consume greater amounts of milk relative to their body size than do adults. Additionally, the same amount or a higher fraction of internalized iodine is concentrated in the smaller thyroid glands of children, thus the radiation dose to the thyroid in children is significantly higher than it is in adults. For individuals exposed to iodine-131 over the age of 15, little increase in thyroid cancers has been observed. However, under the age of 15, thyroid cancer increased by a factor of approximately two for every five years’ decrease in age. In addition to the formation of malignant tumors, benign nodules also occur with greater than usual frequency after exposure.

Additional Resources

Iodine
This resource provides an introduction to iodine as well as information on the health risks associated with iodine-131.

Nuclear Testing
George Mason University provides information on nuclear testing as well as the Nevada Test Site.

Native American Exposure to Iodine-131 from Nuclear Weapons Testing in Nevada
This resource explores the exposure of iodine-131 on behalf of the Native American people.

Short Term and Long Term Health Risks of Nuclear Power Plant Accidents
From the New England Journal of Medicine, this article analyzes the health risks of nuclear power plant accidents, beginning with the incident in Japan in 2011.

Radiation and Health
This guide provides an introduction to radiation and its effects on the health of men, women, and children.