NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competencies and with regard for appropriate balance.
This report was prepared under EPA Assist ID No. X825133-01-0 between the National Academy of Sciences and the US Environmental Protection Agency.
ISBN: 0-309-06176-8
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COMMITTEE ON HEALTH EFFECTS OF EXPOSURE TO LOW LEVELS OF IONIZING RADIATIONS (BEIR VII) PHASE I
RICHARD B. SETLOW (Chair),
Brookhaven National Laboratory, Upton, New York
KENNETH H. CHADWICK,
Radiation Protection Research Unit, European Commission, Brussels, Belgium
PHILIP C. HANAWALT,
Stanford University, Stanford, California
GEOFFREY R. HOWE,
Columbia University, New York, New York
ALBRECHT M. KELLERER,
Strahlenbiologisches Institut der Ludwig-Maximilians-Universität, Munich, Germany
CHARLES E. LAND,
National Cancer Institute, Rockville, Maryland
NANCY L. OLEINICK,
Case Western Reserve University, Cleveland, Ohio
ROBERT L. ULLRICH,
The University of Texas Medical Branch at Galveston, Texas
CLS ADVISER
CHARLES F. STEVENS,
The Salk Institute for Biological Studies, La Jolla, California
NATIONAL RESEARCH COUNCIL STAFF
EVAN B. DOUPLE, Study Director and Director,
Board on Radiation Effects Research (effective March 1997)
RICK JOSTES, Senior Program Officer (effective August 1997)
STEVEN L. SIMON, Senior Program Officer (effective January 1997)
PEGGY Y. JOHNSON, Project Assistant (effective December, 1997)
DORIS E. TAYLOR, Staff Assistant
NORMAN GROSSBLATT, Editor
SPONSOR'S PROJECT OFFICER
Jerome Puskin,
US Environmental Protection Agency
BOARD ON RADIATION EFFECTS RESEARCH
JOHN B. LITTLE (Chair),
Harvard School of Public Health, Boston, Massachusetts
VALERIE BERAL,
University of Oxford, United Kingdom*
MERRIL EISENBUD,
Chapel Hill, North Carolina (deceased September 1997)
MAURICE S. FOX,
Massachusetts Institute of Technology, Cambridge, Massachusetts
R.J. MICHAEL FRY,
Oak Ridge, Tennessee
PHILIP C. HANAWALT,
Stanford University, Stanford, California
LYNN W. JELINSKI,
Cornell University, Ithaca, New York*
WILLIAM J. SCHULL,
The University of Texas Health Science Center at Houston, Texas
DANIEL O. STRAM,
University of Southern California, Los Angeles, California*
SUSAN W. WALLACE,
University of Vermont, Burlington, Vermont
H. RODNEY WITHERS,
UCLA Medical Center, Los Angeles, California
NATIONAL RESEARCH COUNCIL STAFF
EVAN B. DOUPLE, Director,
Board on Radiation Effects Research (effective March 1997)
RICK JOSTLES, Senior Program Officer (effective August 1997)
STEVEN L. SIMON, Senior Program Officer (effective January 1997)
CATHERINE S. BERKLEY, Administrative Associate
KAREN BRYANT, Project Assistant (effective February 1997)
PEGGY JOHNSON, Project Assistant (effective December 1997)
DORIS E. TAYLOR, Staff Assistant
COMMISSION ON LIFE SCIENCES
THOMAS D. POLLARD (Chair),
The Salk Institute for Biological Studies, La Jolla, California
FREDERICK R. ANDERSON,
Cadwalader, Wickersham & Taft, Washington, DC
JOHN C. BAILAR III,
University of Chicago, Chicago, Illinois
PAUL BERG,
Stanford University School of Medicine, Stanford, California
JOANNA BURGER,
Rutgers University, Piscataway, New Jersey
JOHN L. EMERSON,
Indianapolis, Indiana
NEAL L. FIRST,
University of Wisconsin, Madison, Wisconsin
SHARON L. DUNWOODY,
University of Wisconsin, Madison, Wisconsin
URSULA W. GOODENOUGH,
Washington University, St. Louis, Missouri
HENRY W. HEIKKINEN,
University of Northern Colorado, Greeley, Colorado
HANS J. KENDE,
Michigan State University, East Lansing, Michigan
CYNTHIA J. KENYON,
University of California, San Francisco, California
DAVID M. LIVINGSTON,
Dana-Father Cancer Institute, Boston, Massachusetts
THOMAS E. LOVEJOY,
Smithsonian Institution, Washington, DC
DONALD R. MATTISON,
University of Pittsburgh, Pittsburgh, Pennsylvania
JOSEPH E. MURRAY,
Wellesley Hills, Massachusetts
EDWARD E. PENHOET,
Chiron Corporation, Emeryville, California
MALCOLM C. PIKE,
Norris/USC Comprehensive Cancer Center, Los Angeles, California
JONATHAN M. SAMET,
The Johns Hopkins University, Baltimore, Maryland
CHARLES F. STEVENS,
The Salk Institute for Biological Studies, La Jolla, California
JOHN L. VANDEBERG,
Southwest Foundation for Biomedical Research, San Antonio, Texas
NATIONAL RESEARCH COUNCIL STAFF
PAUL GILMAN, Executive Director
ALVIN G. LAZEN, Associate Executive Director
BARBARA SMITH, Administrative Officer
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Preface
Humans have always lived in the presence of low levels of ionizing radiation arising from cosmic rays and emissions from radioisotopes in the air, in water, and on the land. Relatively small populations receive a range, usually small amounts, of occupational exposures, or are exposed to larger doses from diagnostic or therapeutic medical procedures. Other groups have received exposures from radioactive fallout from bomb tests, or from radiation accidents such as Chernobyl. New information has become available in recent years on large exposures of workers in nuclear facilities in the former Soviet Union and on populations affected by their hazardous wastes. In the latter case, precise doses are often difficult to establish, but the data are of particular relevance to radiation protection because they relate to long term low dose-rate exposures. However, the observations on the atomic-bomb survivors in Hiroshima and Nagasaki continue to be the main source of information.
The health effects of acute or chronic ionizing-radiation exposure, such as cancer, are superimposed on the effects that arise from endogenous chemical reactions or exogenous exposures to carcinogens in the environment. Radiation is different from other carcinogens in that in principle it is possible, even if often difficult, to estimate radiation doses whereas, although the mechanisms of action of many chemical carcinogens have been elucidated, environmental- or occupational-exposure doses are poorly known if at all.
The ability to measure radiation doses implies that it is possible to quantify the hazard so as to estimate the mortality arising from low doses of radiation. Low-dose radiation effects cannot be estimated by direct observation, because of the large numbers of background cancers arising from other causes, which usually are not known. For high acute exposures, as in Japan, or for some medical procedures, sufficiently precise data can be obtained to permit extrapolation to lower acute exposures or to lower chronic exposures, assuming a knowledge of the relation between effect and dose and the effect of dose rate. However, extrapolation to low exposures is attended by large uncertainties because the shape of dose-response curves is not well known, especially at the lower doses, and because of uncertainty in background levels (zero added dose). Often, in the absence of reliable data, it is assumed that extrapolation to low doses should be linear and without a threshold, a straight line connecting high dose with zero radiation dose (and zero excess cancers). That point of view is controversial. Some investigators believe that there is a threshold dose—a dose below which radiation has no deleterious effect. Others cite data indicating that the shape of a dose-response curve close to the zero dose has a slope much greater than that of the straight-line that represents interpolation between zero dose and high doses.
The uncertainties in the magnitude of low-dose effects led to a request from the US Environmental Protection Agency (EPA) to the National Research Council that a committee be formed to consider recent data derived from molecular, cellular, animal, and human epidemiologic studies and to evaluate whether it would be feasible to improve the estimated risks to humans posed by exposures to low levels of ionizing radiation. As a result, the Research Council's Commission on Life Sciences authorized the Board on Radiation Effects Research (BRER) to form the Committee on Health Effects of Exposure to Low Levels of Ionizing Radiations (referred to as BEIR VII because it is the seventh committee
in a series that began with the Committee on Biological Effects of Ionizing Radiations). The Committee was to carry out a preliminary scoping (phase-1 study) to review and evaluate the scientific literature pertinent to the biologic and health effects of low-level ionizing radiation and make a concerted effort to learn about the status of all relevant research in progress. The committee was charged to determine, on the basis of those data, whether sufficient information had become available since the 1990 BEIR V report to warrant a comprehensive reassessment of health risks in a phase-2 study by an enlarged BEIR VII committee.
The phase-1 committee, organized in January 1997, had 8 members with expertise in molecular, cellular and animal radiation biology and in human epidemiology and radiation dosimetry. The committee met first in March to summarize what it knew about relevant advances since the 1990 BEIR V report and to organize 2 workshops. The workshops were to encompass invited speakers and position papers at publicized meetings on epidemiology and on the impact of new biologic knowledge on risk assessment. A 2-day committee meeting in June included a half-day workshop devoted to epidemiology and a 2-1/2 day committee meeting in July included 2 days devoted to the impact of new biologic knowledge on risk assessment. A 2-day meeting in August, overlapping a BRER meeting, was devoted to summarizing the committee's conclusions derived from the members' own reading, discussion, and the workshops and to begin the writing of the committee's report.
This BEIR VII phase-1 report includes an executive summary recommending a full, BEER VII phase-2 study, and describes the general structure of the phase-2 study. Chapters on epidemiology, cellular and molecular considerations, animal studies, and mechanistic cancer modeling provide the background information for a phase-2 study and the committee's rationale for endorsing such a study.
Richard B. Setlow, Chairman