PR-100 ACNW Report on Health Effects of Low Levels of

["Wesley M. Dunn" <WDUNN@brc1.tdh.state.tx.us>]

I think this might be of interest.  NOTE: This is from the NRC, not
Texas.  I am merely forwarding this on.  - Wes

------------------- 96-100.txt follows --------------------
           United States Nuclear Regulatory Commission
                     Office of Public Affairs
                       Washington, DC 20555
              Phone 301-415-8200   Fax 301-415-2234
                       Internet:opa@nrc.gov

No. 96-100                              FOR IMMEDIATE RELEASE
                                      (Thursday, July 11, 1996)

NOTE TO EDITORS:

     The Nuclear Regulatory Commission has received the attached
report from its Advisory Committee on Nuclear Waste.  The report,
in the form of a letter, provides comments on the health effects
of low levels of ionizing radiation.

                                #


Attachment:
As stated

                                        July 10, 1996





The Honorable Shirley Ann Jackson
Chairman
U.S. Nuclear Regulatory Commission
Washington DC  20555-0001

Dear Chairman Jackson:

SUBJECT:   HEALTH EFFECTS OF LOW LEVELS OF IONIZING RADIATION

The health effects of ionizing radiation are central to many of
the regulations that are promulgated by the Nuclear Regulatory
Commission (NRC).  The validity of the linear- no threshold (LNT)
dose-response relationships in the area of low doses and low dose
rates has been questioned.  This letter supports the Commission's
present course of action of a review and analysis by the National
Council on Radiation Protection and Measurements (NCRP) leading
to an evaluation of this important issue.

Our discussion and recommendations concerning this subject derive
from the first meeting of the Joint Subcommittee of the Advisory
Committee on Reactor Safeguards (ACRS) and the Advisory Committee
on Nuclear Waste (ACNW) held on March 26, 1996.  Presentations
were made by members of the NRC staff, including the visiting
medical fellow, and representatives from institutions and agen-
cies such as the NCRP, the Health Physics Society, and the Massa-
chusetts Emergency Management Agency.  Written comments were also
received from the public.

Most national and international scientific committees dealing
with the subject take the view that the safest approach to
regulation is one that relies on the LNT model of response to
doses of ionizing radiation.  This model holds that the ill
health effects observed at high doses and high dose rates (mainly
among atomic bomb survivors) can be extrapolated linearly to low
doses and low dose rates, down to the smallest doses.  The NRC
staff prepares regulations on the basis of this model.  One of
the basic questions in this field is whether the LNT model
is valid at the low doses and rates normally encountered in many
of the regulatory domains.  The increasing emphasis placed by the
Commission on risk-informed regulation makes it imperative that
the actual health risk of low levels of ionizing radiation be
assessed accurately.

The NRC is currently funding a contract with the NCRP to make a
critical evaluation of the LNT assumption.  The ACNW has not
reached conclusions on the validity of the LNT model, and will
continue to study the matter.  We see the NCRP study as an
opportunity to obtain an independent review of the data and their
quality.

The presence of unavoidable background radiation and the need for
very large samples have made it difficult in the past to obtain
definitive data on the validity of the LNT model.  As with all
small-effects phenomena, the quality of the data and the statis-
tical interpretation of the results govern the ability of any
study to contribute to the testing of the model.  However,
investigators in the field have recently been able to account for
the effect of such confounding factors such as variation in back-
ground radiation.  Some studies in the United States, as well as
in China, Sweden, Poland, and Canada, have arrived at conclusions
that do not support the LNT model.  Other research concludes that
it is likely that at least a threshold or perhaps a corresponding
zero equivalent point with beneficial risk decrements (hormesis)
exists at lower doses.

A notable example of the latter is a ten-year study by Johns
Hopkins University of U.S. nuclear shipyard workers which, we
were told, showed lower mortality, no increase in malignancies
among workers exposed to radiation when compared to those who
were not exposed, and no "healthy worker effect."  This study may
be particularly significant since the investigators were looking
for evidence to support the LNT model.  Another study, of Canadi-
an women patients in tuberculosis sanitariums who underwent re-
peated fluoroscopy to monitor response to therapy, is used fre-
quently to show the validity of the LNT model, but examination of
data at lower doses shows significant beneficial effects.  The
1994 report of the United Nations Scientific Committee on the
Effects of Atomic Radiation (UNSCEAR) contains an extensive
appendix detailing cellular repair mechanisms (called "adaptive
response mechanisms") that could contribute to an explanation of
a threshold, or, if such cellular responses were stimulated by
low doses of radiation, to an explanation of beneficial effects.
In contrast, some of the public comments received by the Subcom-
mittee suggested that the LNT model underestimates the harmful
effects of low doses of radiation.  Also NCRP Report No. 121,
"Principles and Application of Collective Dose in Radiation
Protection," issued November 1995 and discussed with the Joint
Subcommittee at its March 26, 1996 meeting, finds that "from the
point of view of the scientific bases of collective doses for
radiation protection purposes, it is prudent to assume the effect
per unit dose in the low-dose region following single acute
exposures or low-dose fractions is a linear response."

In the face of conflicting views, the general belief of the
national and international committees dealing with the matter has
been that using the LNT model for regulatory purposes is a safe
and conservative approach and, if there is error, it is on the
side of enhanced protection.  However, if there is a health
benefit at low doses, this logic is incorrect.  Even if there is
no evident health benefit, there are significant societal costs
associated with this conservatism that could be avoided or
reduced if a threshold level could be established below which no
harm occurs.  A basic principle of risk-informed regulation is to
prevent a situation in which scarce resources are misspent
to avoid negligible risks, while significant risks remain
unattended for want of resources to deal with them.  Owing to the
potentially significant costs of the present conservatism, we
conclude that a reexamination of the regulatory model is
appropriate.

It is obvious that agreement on an appropriate dose-response
model is made more difficult by the differing voices on this
subject within the scientific community and those outside of this
community, including regulators, policy makers, and members of
the public.  The first task required to reach such an agreement
is an impartial review of the data and their quality in the face
of the extensive application of the LNT model in regulations and
scientific opinion.

We recommend that the need for special attention be conveyed to
the NCRP regarding its study.  Such attention should include:
(1) assurance that the study includes scientists other than those
who are "recognized experts" with a reputation built on the LNT
model, (2) an evaluation of the data by an entity with expertise
in statistics or information science, but no prior position on
LNT - such as the National Institute of Standards and Technology
(NIST) as well as the NCRP study committee, and (3) consideration
of essentially all studies that could relate to the LNT.

The Committee strongly believes in the NCRP goal of critically
evaluating data related to low dose health effects.  We will
follow the program through interaction with NRC's Office of
Research and will report to the Commission on the study and its
implications.

                               Sincerely,

                                 /S/

                               Paul W. Pomeroy
                               Chairman, ACNW



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Wesley M. Dunn, C.H.P.                     512-834-6688
Deputy Director, Licensing                 512-834-6690 (fax)
(Texas) Bureau of Radiation Control        wdunn@brc1.tdh.state.tx.us
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