Radioactive iodines (radioiodines, such as 131I) are produced during the operation of nuclear power plants (NPPs) and during the detonation of nuclear weapons. In the event of a radiation incident involving a disruption of the integrity of the fuel assembly and the containment structures of a nuclear power plant or a detonated nuclear device, radio—iodine is one of the contaminants that could be released into the environment. The major historical environmental releases of radioiodine were from the Hanford nuclear processing plant in the 1940s; from the Mayak processing plant in Russia in the 1940s and early 1950s; from the atmospheric nuclear-weapons tests conducted in the 1950s and 1960s; and from the nuclear reactor accidents at Windscale, UK, in 1957, and the Chornobyl Power Plant in Ukraine (in the former Soviet Union) in 1986. The Chornobyl accident caused the most serious consequences: it exposed many people to thyroid radiation from radioactive iodine and consequently induced thyroid cancer in a large number of children.
Because iodine concentrates in the thyroid gland (it is essential for the synthesis of thyroid hormones), exposure to radioiodine by inhalation of contaminated air or ingestion of contaminated food or milk can lead to radiation injury to the thyroid, including increased risk of thyroid cancer and other thyroid disorders.
Radiation to the thyroid from radioiodine can be limited by taking nonradioactive iodine (stable iodine) such as potassium iodide (KI).1 Fetuses, infants, children, and pregnant and lactating women are most in need of protection from radioiodine exposure and most likely to benefit from KI. To be most effective, KI must be taken within a few hours before or after exposure to radioiodine. KI does not protect other organs or tissues from external exposure to radiation or from internal exposure to other radioactive isotopes, such as strontium, cesium, or cobalt.
To ensure that KI will be available in the event of an incident at a nuclear power plant that causes release of radioiodine, the US Nuclear Regulatory Commission has supplied participating states with KI sufficient for two dosages for every person who lives or works within 10 miles of a nuclear power plant. In addition, the US Department of Health and Human Services has purchased KI tablets for the national pharmaceutical stockpile. Some local agencies have developed their own plans for stockpiling and distributing KI (see Chapter 6 and Appendix C for details).
To establish a coordinated program based on the latest scientific advice, Public Law 107-188, the Public Health Security and Bioterrorism Preparedness and Response Act of 2002, Section 127 (see Appendix A), requested that the president—in consultation with representatives of appropriate federal, state, and local agencies—establish guidelines for the stockpiling of KI tablets and for their distribution and use in the event of a nuclear incident. Before establishing the guidelines, the president was requested to enter into an agreement with the National Academy of Sciences to conduct a study to recommend the most effective and safest way to distribute
and administer KI tablets on a mass scale in the event of a nuclear incident, taking into account projected benefits and harms and the populations that should be included in such a program.
In response to the congressional mandate, the Centers for Disease Control and Prevention (CDC) asked the National Research Council’s Board on Radiation Effects Research to convene a Committee to Assess the Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident, taking into account projected benefit and harms and the populations that should be included in such a program, and to recommend studies that will improve the base of knowledge on which to make related public-health decisions. The committee was asked to consider the issues and make recommendations on the basis of scientific knowledge and principles. The study began on March 27, 2003.
The task set before the committee is described in the following scope of work:
The Board on Radiation Effects Research proposed to put together a slate of individuals to assess the distribution of the potassium iodide (KI) issue. On the basis of this assessment, the committee will make recommendations to the President and Congress within 9 months after the start of the study regarding:
the projected benefits and harms of a KI distribution program as part of a nuclear incident preparedness program;
the most effective and safe way to distribute and administer KI on a mass scale to prevent radiation effects;
the populations that should be included in the program;
the appropriate roles for local, state and federal agencies in such a preparedness program;
any additional issues that need to be researched, resolved, or addressed.
The committee made several important distinctions early in its deliberations. First, it was determined that in the United States, the inhalation pathway (breathing in contaminated air) is the primary
initial concern after a radiological incident. Radiation exposure can also result from ingestion of contaminated milk or other foods, but in the United States this is unlikely because of the wide-spread regulations and procedures in place for food testing and interdiction in the event of a radiological incident, particularly one involving radioiodine. In circumstances where food interdiction is not feasible, KI does provide protection to the thyroid from radioiodine ingestion. Second, the committee noted that the term “distribution”, in the context of KI, includes predistribution, local stockpiling outside of the emergency planning zone (EPZ), and national capacities to rapidly mobilize and deliver large inventories of KI as needed in the event of a radiological incident. Finally, the committee recognized the tremendous variability in the geographical, demographic, and political characteristics of areas where nuclear power plants are located. This variability makes comparisons with specific international experiences difficult and emphasizes the need for flexibility and a high degree of independence for state and local agencies to decide the most effective and efficient means to protect the public in the event of a radiological incident involving radioiodine. Within the context of this independence, however, the committee concluded that for many geopolitical regions, a KI predistribution program may provide the best assurance of timely KI availability to appropriate populations in the event of a radiological incident involving radioiodine.
To understand the context of the statement of task presented above, the committee believed that it was important to provide background information on the effects of radioactive iodine and KI on the thyroid gland, explore various options for using KI to protect the thyroid, explain how nuclear fallout that contains radioactive iodine can endanger the thyroid gland and how KI can protect it (such as sources and types of radiation affecting the thyroid after a nuclear incident), discuss current and pending federal policies on KI, and consider how European and US governments stockpile and distribute KI. The committee was not charged to do any quantitative analysis; it is beyond the committee’s scope. However, the committee has proposed a method in Chapter 7 and Appendix D that could be used for site-specific planning. For each nuclear power plant, there is specific information on population size, ages, and location,
geographical and meteorological conditions, evacuation routes, and resources available. This information can be used for quantitative analysis to aid planning in a specific region.
This report constitutes the results of the committee’s assessment and its recommendations. It is organized into eight chapters. Chapter 2 discusses thyroid physiology, Chapter 3 discusses potential exposure to radioactive iodine, Chapter 4 discusses previous radiation incidents and their potential health effects, Chapter 5 discusses protective measures, Chapter 6 discusses existing distribution plans for distribution of KI, Chapter 7 provides a scheme for evaluating KI distribution programs and options for KI distribution, and Chapter 8 contains the concluding remarks and recommendations for KI administration and distribution.
To fulfill its charge, the committee met five times in 2003: on May 29-30 in Washington, DC; on June 23-24 in Washington, DC; on July 25-26 in Irvine, CA; on August 21-22 in Washington, DC; and on September 29-30 in Woods Hole, MA. Three of the meetings included public information-gathering sessions, and the committee also received and considered other public comments and communications. The committee interacted with various federal agency representatives and other interested parties, and it benefited from the information provided by states’ authorities about the past, current, and future state plans to distribute KI. The committee appreciated and was impressed by the efforts of various speakers and other interested parties to work with us during the project; it has been important to the committee’s efforts.
Consistent with the policies of the National Academies, the committee conducted fact-finding activities involving outside parties in public information-gathering meetings and met in closed session only to develop committee procedures, review documents, and consider findings and recommendations. The information-gathering meetings were structured to solicit information from technical experts and the study sponsor on topics related to the study. All the information gathered at the open meetings is part of the National Research Council’s public-access file and is available on request.