J^tB^ % UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
r WASHINGTON, D.C. 20460
SAB-RAC-88^041
September 9, 1988
OFFICE OF
THE ADMINISTRATOR
Honorable Lee M. Thomas
Administrator
U. a. Environmental Protection Agency
401 M Street SW
Washington, DC 20460
Dear Mr. Thomas:
The Dose and Risk Subcommittee of the Science Advisory
Board's Radiation Advisory Committee has completed its review of
the Office of Radiation Programs' Low-LET Risk Estimate for
Regulatory Purposes. This review was requested on February 25,
1988 by the Director of the Office of Radiation Programs and was
conducted on June 20, 1988, at an open meeting in Washington, DC,
at which Dr. Douglas Chambers of SENES Consultants and
Dr. Leonard Hamilton of Brookhaven National Laboratory presented
public comment. Because the Office of Radiation Programs is
considering using its new estimate of risk as part of the
technical basis for the revised raOlonuelides NESHAP, the Science
Advisory Board was asked to respond as early as possible.
The 1980 report of the National Academy of Sciences
Committee on the Biological Effects of Ionizing Radiation (BEIR-
UT} , for a linear-quadratic dose-response model and the absolute
as well as the relative risk projection models, estimated a range
of 77 to 226^ additional fatal cancers in a population of one
million individuals exposed to a single, whole-body absorbed dose
of 1 rad of low-LST radiation (see page 209 of the BEIR-IH
Report). The lower value corresponds to the absolute risk
projection model, and the higher one, the relative risk
projection model, currently thought to be the most generally
appropriate method for predicting lifetime radiation risks to a
population. For a linear dose-response model and a relative risk
projection, the Committee estimated about 400 fatal cancers.
BEIR-IXi attributes risk to individual organs by a mixture of
roethods, the specific one in a given instance depending upon the
organ in question. Although published in 1980 and based on data
through 1974, this report still represents the most current
national technical consensus on low-LET radiation risks.
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Several important reports on radiation risks are expected
within the next year which could alter our perceptions of their
magnitude. Based, in part, on new information from Japan on the
survivors of the atomic bombing of Hiroshima and Nagasaki, and
representing months of work and debate by distinguished panels of
internationally recognized scientists, these reports will
undoubtedly advance significantly the scientific understanding of
the cancer risk presented by low-LET radiation. These technical
consensus documents include a report of the National Academy of
Sciences' Committee on the Biological Effects of Ionizing
Radiation (BEIR-V), a report of the United Nation's Scientific
Committee on the Effects of Atomic Radiation (0NSCEAR), and
reports of the International Commission on Radiological
Protection (ICRp) and the National Council on Radiation
Protection and Measurements (NCRP). The Subcommittee urges the
Environmental Protection Agency to take the findings and
conclusions of such reports into account in the development of
final regulations on radionuclides in the environment.
Generally speaking, the Subcommittee believes the effect of
the new information and new analyses will be to raise the level
of risk understood to be associated with low-LET radiation
exposure. The sources of this change are: the recalculation of
doses for individuals exposed to the atomic bombs in Japan which
shows the doses to have been generally lower than previously
thought, and the risks correspondingly higher; increased follow-
up, particularly among those who were children at the time of the
bombing, which has detected more cancer cases; and changes in the
statistical models used to predict lifetime risk from the
absolute or additive projection model to the currently more
widely accepted relative or multiplicative projection method.
The technical consensus evaluations of the new information from
Japan and its implications for radiation risks which will be
available in the near future will provide the Agency a much
sounder basis for estimating risks from low-LET radiation.
Under these circumstances, we do not believe that an intensive
Agency effort this summer to create an interim model for low-LET
radiation risks is likely to be of lasting value to the Agency.
The Office of Radiation Programs', recognising many of the
above changes, has now proposed, based on the BEIR-III linear
relative risk model, a nominal central estimate of 400 fatal
cancers and a range of 120-1200 additional fatal cancers per
million persons exposed to one rad of low-LET radiation. The
risk to individual organs are essentially those given in BEIR-III
prorated over the new range.
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For th_e. interim, until the reports alluded to above become
_available, the Subcommittee finds acceptable the Agency's
proposed central estimate, and range.
The Subcommittee recognizes that techniques to evaluate the
uncertainty inherent in risk projections lag behind understanding
of their importance. It must be borne in mind, however, that
these^uncertainty estimates address only the uncertainties in the
existing human data and models, and not those in estimating
environmental sources, transport and future human exposures.
In summary, the Dose and Risk Subcommittee advises the
Agency to rely on the model in the BEIR-III report, suitably
scaled up to the proposed interim values, during the brief period
until the national and international technical consensus
documents become available within the next six to twelve months.
This should allow the Agency to incorporate the scientific
community's best understanding of the risks presented by low-LET
radiation in its Background Information Document and final
regulations.
The Subcommittee•looks forward to the opportunity to review
the Background Information Document on which the final
regulations will be based.
We appreciated the opportunity to share our views with you
and look forward to a written response from the Agency.
Sincerely,
h
Norton Nelson
Chairman, Executive Committee
Science Adviscarv Bdard
William J, Scl
Chairman, Radiation Advisory Committee
and Dose and Risk Subcommitte
Attachment: Roster
cc; R. Guimond
J, Cotruvo
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