UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, O.C. 20460
EPA-SAB-LTR-91-001
OFFICE OF
22, 1991 THE ADMINISTRATOR
Honorable William K. Reilly
Administrator
U.S. Environmental Protection Agency
401 M Street, SW
Washington, DC 20460
Re: Letter Report on Radon Risk Estimates for General
Population and Smokers, Non-Smokers, and Children
Dear Mr. Reilly:
The Radiation Advisory Committee of the Science Advisory Board
has reviewed the February 15, 1990 draft document "Estimation of
Risks from indoor ladon Exposure." In his memorandum of February
17, 1990, the Director of the Office of Radiation Programs
requested that the Science Advisory Board, "assess whether the
scientific radon risk assessment information is appropriately
summarized." Dr. Fuskin of the Office of Radiation Programs
briefed the Committee on the specifics of the risk estimates on
February 18 and was available to discuss the document with the
Committee at its public meeting May 17-18, 1990.
This document, prepared by office of Radiation Programs staff,
addresses risk to the general population as well as to the sub-
populations of smokers, non-smokers and children. For estimating
the risk of radon exposure to the general population, the Office
of Radiation Programs essentially followed the earlier (June 1988)
recommendation of the Radiation Advisory Committee that the average
of the projection values from the National Academy of Sciences'
model developed by.the Board on .the Effects of Ionizing Radiation
(BEIR IV) and the International Commission on Radiological
Protection's ICRP 50 Model be used (of, letter to Honorable Lee M.
Thomas of September 9, 1988? SAB-RAC-88-Q42), Since there has
been no new scientific data reported since 1988, the Committee sees
no reason to alter that recommendation.
The BEIR IV model in its projection assumes a decreased excess
relative risk with time since exposure, a decreased risk with age
of the individual, and a minimum latency period of 5 years.
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The ICRP 50 model uses a constant excess relative risk but
assigns a three-fold higher risk for exposure to children and young
adults below the age of 20 years. Although there is admittedly
limited evidence, the ICRP felt it prudent to assign a higher risk
coefficient to children and young adults than to more mature
individuals. The ICRP 50 model uses a minimum latency period of
10 years.
Both the BEIR V and ICRP 50 models are relative risk
projection models based on data from studies of underground mining
populations. Despite their differences, the two models project
quite similar estimates of cancer fatalities for a lifetime
exposure to a given concentration of radon.
The Office of Radiation Programs has introduced minor
modifications to the two models! In the case of the ICRP 50 model
ORP applied the same risk coefficient to adult members of the
general population as had been determined for the mining
populations from which the risk projection model was derived; the
original ICRP 50 had reduced this risk coefficient by 20% when
applied to the general population. In the BEIR IV model, the
Office of Radiation Programs corrected the risk coefficient for
the average background radon level. The results of these two
modifications of the models are to increase the lifetime risk
estimate by the former, and decrease the risk estimate by the
latter,* the average value of the two estimates remains essentially
the same, however.
The Committee does not object to the modifications that the
Office of Radiation Programs has introduced to the models. That the
BEIR IV did not adjust for the average background level of radon
might be viewed as a minor shortcoming of that model. The Office
of Radiation Programs adjustment of the risk coefficient in the
ICRP 50 model is based on the opinion that ICRP's 20% lowering of
the risk coefficient, to miners . .when,- applied to the general
population is not warranted. In this regard, the Office of
Radiation Programs is following the recommendation of the BEIR IV
report. The conversion of exposure to dose for the two populations
is fraught with great uncertainties and some of the known modifying
factors are likely to cancel each other.
Overall, the lifetime risk projections for any of the models
fall within the uncertainty range for those of the others and, as
already pointed out, the "fine-tuning H of the models done by the
Office of Radiation Programs did not change the average value of
the estimates.
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The average life-time risk projection value for the general
public derived and used by the Office of Radiation Programs is 360
excess lung cancers per 10 person-working level months (W1M). For
an average U.s, residential exposure of 0.2S WUt per year and for
a population of 240 million, this translates to 21,600 deaths per
year of 14% of all lung cancer deaths in the U.S.A. The Committee
finds this value acceptable and as good as can be achieved at the
present time. It would be highly desirable, however/ to present
this risk estimate with an uncertainty range/ such as the range
from the ICRP report as described in Section F of the document
being reviewed.
There is an important relationship in lung cancer causation
between cigarette smoking and exposure to radon. In order to
establish a perspective on the combined risk of exposure to radon
and smoking, the Office of Radiation Programs should qualify the
overall population risk from exposure to radon in terms of smoking
and indicate the comparative risks to smokers and non-smokers.
The Office of Radiation Programs should provide advice that there
is an increased risk of lung cancer from continuing exposure to
elevated concentrations of indoor radon, and also that this risk
is greatly increased by smoking because of the near-multiplicative
interaction between radon exposure and smoking. Such advice would
allow smokers to recognize that their overall risk may be greatly
reduced by the combination of cessation of smoking and radon
reduction.
In regard to the assumed greater risk for radon exposure in
children/ direct evidence is lacking. However/ follow-up data on
atomic bomb survivors in Japan indicate that individuals exposed
as children may be a higher relative risk for radiation-induced
cancer. In addition, dosimetric modeling suggests that for a
given exposure to radon and radon daughters, children will receive
a higher radiation dose to the bronchial epithelium than do adults.
One final comment is offered in regard to the present Office
of Radiation Programs' estimate for risk from radon exposure. The
office of Radiation Programs should continue to review its risk
estimate as new information is gained. The Committee understands
that the Office of Radiation Programs has commissioned a National
Academy of Sciences/National Research Council study of whether any
correction should be required when using epidemiological data from
underground uranium and iron miners for the estimation of radon
risk to the general U.S, population. When the results of the
National Academy of Sciences/National Research Council study become
available, they should be reviewed, as changes in the current risk
assessment may be warranted.
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in conclusion, the Committee believes the office of Radiation
Programs has adequately treated the available information on lung
cancer risk from radon and arrived at an estimate for lifetime rislc
for the general population which is as good as can be achieved at
the present time. The committee believes the Office of Radiation
Programs should qualify the overall population rislc from exposure
to radon in terms of smoking and indicate the comparative risks to
smokers and non-smokers. The Committee also believes it is prudent
to assign a higher risk coefficient to children and young adults
than to more mature individuals even if supportive evidence is
limited in regard to this point. The Office of Radiation Programs
should continue to review its risk estimate and risk assessment
methodology as additional data and technical consensus documents
become available.
We appreciate the opportunity to present our advice concerning
this radon document and would appreciate receiving a written
response which addresses our recommendations,
sincerely,
Ra.yftond--CTTjoehr, Chairman
Executive Committee
Science Advisory Board
• i ^i"_^ ^"s..
^^•^^^^^^^^^^^L.^^^
Oddvar P. Nygsar«, Chafrnian
Radiation Advisory Committee
Science Advisory Board
cc: ORP
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ADDENDUM TO LITTER REPORT NUMBERS EPA-SAB-LTR-91-Q01
Ret Letter Report on Radon Risk Estimates for General
Population and Smokers, Non-Smokers, and Children
The review by the Radiation Advisory Committee of the "Radon
Risk Estimates for the General Population and Smoker, Non-smokers
and Children" was conducted during the spring of 1990. The
letter report was essentially completed on May 18 and represents
the committee's recommendations based on material available to it
at that time. Although the Committee does not want to alter its
endorsement of the Agency's risk estimates, it wishes, at this
time, to expand on its comment in regard to the 3-fold greater
risk of lung cancer, assigned to individuals exposed as children
of young adults below the age of 20 years, since this current
risk estimate derives from the SAB 1988 recommendation that the
Agency should average the risks projected by the two radon risk
models proposed by the BEIR IV committee and the ICRP-50 report,
but use the ICRP-50 model for exposures to children and young
adults. As already pointed out, the only supportive evidence for
a higher relative risk for children derives from studies of
Japanese atomic bomb survivors exposed to external gamma and
neutron radiation. In a recent case control study of Chinese tin
miners, Lubin et al. (Cancer Res. 50, 174-180, 1990) report that
there is no evidence for a higher risk to workers who were first
exposed to radon under the age of 13 years. This study, although
not statistically significant by itself, is apparently the first
report of lung cancer in individuals exposed to radon at an early
age. Additionally, the recently published (1990) BEIR V report,
the consensus report of the National Research Council's committee
on the Biological Effects of Ionizing Radiation, states (p. 273)
that "The Committee's analysis of respiratory cancer in A-bomb
survivors showed little effect of age at exposure..,.." which
greatly weakens the rationale for the higher risk to children,
referred to above.
Another area of uncertainty is the conversion of radon
exposure to lung dose, the relationship of this conversion in
underground miners va. the general—population, and whether
children receive the same dose as do adults from a given radon
exposure. The National Research Council under contract to EPA
has recently completed a review of this particular issue, and the
report should be available to the Agency by the end of December
(1990).
In the opinion of the Radiation Advisory Committee, the
review by the National Research Council might be a significant
document for the assessment of radon risk to the general US
population, including children, and the committee emphatically
recommends that the Agency give high priority to reviewing this
report with a view to whether its conclusions warrant a re-
assessment of the currently recommended risk coefficients to the
general population based on radon exposures.
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