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1
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‘Tlowest practicable" concep asures to reduce both annual and
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longer term exposure
Risk Considerations
the \
i sors have reviewed '
3
technii cal advi
k Group and its
e
anee
from ICRP, UNSCEAR,
Theable sformation
us
t cou
Committee tha
Academy of Science BEIR
ey
estimate the health risk that may be associated with long-term
exposures at-the level of the radiation dose and soil removal
- criteria being recormmended.
It is clear from this review that
kpowlecgs of the relationship between radiation dose and effects
_of that
on man as characterized in dose-effect curves
incomplete even for external radiation exposures. For internal
e
érs and particularly for plutonium, the sitwationis even
less satisfactory. UNSCEAR has summarized their findings
by stating that one should not extrapolate ina linear fashion
from effects seen at high doses and dose rates to effects at
low doses and dose rates since there is strong likelihood of
recovery and repair.
The BEIR Committee, using only human
data, concluded that since the low dose data were incomplete,
one should conservatively assure a linear no-threshold dose-effect
curve drawn through data obtained at high doses‘and dose rates.
The committee further suggested that if this linear no-threshold
curve is assumed to be correct, it follows that 6, 000cases of
cancer would be produced each year in a population of 200, 000, 000
people exposed at a rate of 0.17 Rem/yr. (This is the FRC RPG
for population groups - see Table I.) For the Enewetak population
of less than 500 exposed at the same level, one can make the
following estimate:
6 X 10° cases/yr X 500 people = 1.5 X 107” cases of cancer/yr
2X 10° people
Using a linear dose-~effect curve, exposure at the level of the
recommended criterion of 0.25 Rem/yr would give 2.2 X 1072
cases per year.
The Task Group vieys this as a pessimistic
upper limit of risk.
It could be inferred that there may be
between zero and three cases of cancer in 100 years if the
entire Enewetak population were continuously exposed to
0.25 Rem/yr over that time period,
exposurewhole body,at Enewetak, and in fact,
to all organs will come from inter
jitters. The shape of the .
dose-effect curve for exposures from internal emitters is most
uncertain because of lack of experience and lack of confidence
in extrapolation of high dose and dose rate effects into the very
low dose and low dose rate situation.
oo
MmEereT AVA ADIL FrABY
A lack of confidence in
A
(7,