Date: Feb. 11, 2003
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For Immediate ReleaseStudy Competently Estimates Cancer Risk From Radioactive Fallout; Reanalysis of Iodine-131 Needed, But Larger Study not Justified
WASHINGTON -- The authors of a congressionally mandated draft report on the increased risk of cancer for Americans who were exposed to fallout from nuclear-weapons tests did a good job estimating the amount of radiation exposure and the potential health risks associated with it, says a new report from the National Academies' National Research Council. But there are some weaknesses in the draft report, and its authors should reanalyze the public's exposure to iodine-131 -- a radionuclide that causes thyroid cancer -- in light of new information gleaned from the Chernobyl incident. However, a substantially expanded study of all the radionuclides found in the fallout is unnecessary.
"Apart from iodine-131, the draft report indicates that the health risk associated with other radionuclides released in weapons testing is small, so developing more precise estimates of radiation dose and cancer risk will probably be of little added value," said William J. Schull, chair of the committee that wrote the Research Council report, and professor emeritus, University of Texas, Houston. "The recommended reanalysis of iodine-131 exposure is unlikely to make large changes in the key results, but it will make the risk estimates current, and hence more credible."
The draft report was issued by the Centers for Disease Control and Prevention and the National Cancer Institute, which were asked by Congress in 1998 to study the health consequences for Americans exposed to radioactive fallout from above-ground nuclear-weapons tests conducted around the world. The purpose of the CDC-NCI study was to determine if a broader, more precise study was feasible. CDC and NCI focused on the period between 1951 and 1962, when most above-ground tests were carried out. A limited test-ban treaty was signed in 1963, but some above-ground testing continued until 1980. Americans were exposed primarily to fallout from tests conducted in the Nevada desert.
Radioactive materials from a nuclear detonation eventually fall to Earth, thus the term "fallout." Although it is possible to inhale those materials, the main threat to people comes from exposure to radiation emitted by the radioactive materials on the ground and consumption of meat or milk from animals that have ingested the radioactive materials. Children who drank such milk were particularly at risk; they are more sensitive to iodine-131 because their smaller thyroids absorb more of the radioactive isotope. The wind carried radioactive materials from the Nevada tests to the north and east for the most part, so a child born in 1951, for example, was exposed to the most radiation if he or she lived in Nevada or in the Midwest, although similar concentrations could be found as far away as Maine, and other distant states where wind patterns and rainfall caused more fallout.
The lifetime risk of death by cancer is about 20 percent for Americans, absent any exposure to radioactive fallout. The CDC-NCI study said fallout raised this risk to about 20.03 percent, which might have led to approximately 11,000 additional deaths -- most caused by thyroid cancer linked to exposure to iodine-131 -- among Americans who were exposed to fallout from tests conducted between 1951 and 1962. There were approximately 40 million cancer deaths total among this same population.
The methods used by CDC and NCI to estimate radiation doses and health effects are reasonable for a feasibility study, the committee said. There are some limitations, however. Although CDC and NCI used the best available data to estimate exposure, that data will probably always be limited because measurements of fallout were made at fewer than 100 sites around the country, the committee noted. It recommended that CDC urge Congress to prohibit the destruction of all remaining records relevant to fallout. In addition, the number of scientists with firsthand knowledge of the nuclear-weapons tests and fallout patterns is dwindling; these researchers should be interviewed and the information they provide should be archived.
As to the health risks posed by fallout, the authors of the draft report assumed that a cancer risk exists at very low doses of radiation, which the committee said is scientifically contentious, but appropriate in this instance because it guards against the underestimation of risk. The committee also noted that, except for children born in 1951, the draft report treated the U.S. population as a whole, without specific attention to more susceptible subgroups or people at risk of higher exposure. The authors of the draft report also should have better explained how they determined the credibility of their results in some instances.
In addition, the draft report should have presented the total number of excess cancer deaths in the exposed population with more context, the committee said. For example, it should have allowed readers to compare excess cancer deaths attributed to fallout with cancer risks posed by natural background radiation, smoking, or natural causes. In addition, the number of excess cancer deaths for the overall population is not readily translatable into an individual's excess risk in the draft report. This is important for public health purposes because individual risk, not population risk, is what determines whether cancer-screening programs are needed. A person's age, food sources, eating habits, and geographic location at particular times are all factors in determining individual risk. The authors of the draft report should translate population risks into individual risks for iodine-131 only.
Despite these limitations in the draft report, its results should be published promptly, the committee said. This should be followed by a reanalysis of the iodine-131 fallout data and related thyroid-cancer risk, including individual risk. A comprehensive and understandable public summary should be written and made part of the final report, which should be disseminated widely and posted on the CDC and NCI Web sites. The public summary should be produced as soon as possible, because many stakeholders were frustrated by delays in the release of the draft report and previous studies on fallout.
The Research Council study was sponsored by the Centers for Disease Control and Prevention. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides science and technology advice under a congressional charter. A committee roster follows.
Copies of Exposure of the American Population to Radioactive Fallout from Nuclear Weapons Tests
will be available from the National Academies Press; tel. (202) 334-3313 or 1-800-624-6242 or on the Internet at http://www.nap.edu
. Reporters may obtain a pre-publication copy from the Office of News and Public Information (contacts listed above).
NATIONAL RESEARCH COUNCIL
Division on Earth and Life Studies
Board on Radiation Effects ResearchCommittee to Review the CDC-NCI Feasibility Study of the Health Consequences from Nuclear Weapons Tests William J. Schull, Ph.D.(chair)
Ashbel Smith Professor Emeritus
School of Public Health
University of Texas
HoustonBruce B. Boecker, Ph.D.
Lovelace Respiratory Research Institute
Albuquerque, N.M.A. Bertrand Brill, M.D., Ph.D.
Department of Radiology and Physics
School of Medicine
Nashville, Tenn.Melvin W. Carter, Ph.D.*
International Radiation-Protection Consultant, and
Neely Professor Emeritus
Georgia Institute of Technology
AtlantaSue B. Clark, Ph.D.
Westinghouse Distinguished Professor of Chemistry
Washington State University
PullmanEdmund A.C. Crouch, Ph.D.
Cambridge Environmental Inc.
Cambridge, Mass.Sharon M. Friedman, M.A.
Professor and Director
Science and Environmental Writing Program
Bethlehem, Pa.Kathryn A. Higley, Ph.D.
Department of Nuclear Engineering
Oregon State University
CorvallisSusan E. Lederer, Ph.D.
Department of History and
School of Medicine
New Haven, Conn.Milton Levenson, B.Ch.E.*
Menlo Park, Calif.Herwig G. Paretzke, Ph.D.
Institute of Radiation Protection
German National Research Center for Environmental and Health Research
Neuherberg, GermanyBobby R. Scott, Ph.D.
Lovelace Respiratory Research Institute
Albuquerque, N.M.Roy E. Shore, Ph.D., Dr.P.H.
Professor of Environmental Medicine, and
School of Medicine
New York University
New York CityDaniel O. Stram, Ph.D.
Department of Preventive Medicine
University of Southern California
STAFFIsaf Al-Nabulsi, Ph.D.
Member, National Academy of Engineering