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UCRL- 3644
States per year (plus 2,000 cases of bone-tumor deaths, which may be similarly
affected by radiation), such a radiation burden is equivalent to an increase of
40 cases per year after fifty years' equilibration with this level of fallout. If
radiation fallout and uptake of Sr’
in human bones were to increase by a factor
of 10, one could estimate 400 additional cases of bone tumor and leukemia induced per year after a 50-year period, in comparison with 1,000,000 deaths
from all causes and 10,000 expected deaths from leukemia and bone tumors.
Both above numbers are small in comparison with over-all public health problems.
Although there are some sizable uncertainties regarding Sr? burdens
dug ing the next 10 to 20 years, it seems from the average human values that
Sr
rise
may increase and become a public heaith problem if levels shouid
to
50 ppc Sr99 fp Ca (equal to about 0.2r/yr to bone).
There is time--
but not much time--for a re-evaluation of many unsatisfactorily estimated
aspects of this problem, including the extent to which radiation exposure induces leukemia and bone tumors, and more precise estimation of the strontium
levels in humans.
—
At the reference level of 1 MPC of sr?0 burden, which is
_—
AY
G
4r/yr to bone, an estimated increase in bone tumors and leukemia is
4r/yr x 50 years
(,)
50 r per doubling of incidence of tumors ’
mj
or an approximately fourfold increase in natural expectancy of these neoplasms a
with respect to the radiation-related component of their origin. This level may/ »’/
be reached by humans as a result of sr 90 fallout.
At some such value,
reason
argues against further exposure. The 1-MPC value based on radium exposure
is consistent with a prediction of a fourfold increase in natural incidence of
tumors. It would be difficult to observe a fourfold increase above natural
incidence of bone tumors in animal-colony studies with radium, but not at all
difficult in large human populations.
In summarizing their
Mayneord and Mitchell write,
of radiostrontium absorbed by
tumour formation, the tumour
opinion for the British Report Cmd 9780,
"It appears however that each unit quantity
bone confers a certain probability of bonedevelopment time perhaps decreasing and the
tumour incidence increasing with the dose.
Onthe whole, the experiments
seem in favour of a proportionality between the frequency of tumoure produced
in a given length of time and the amount of radioactive material in the body
even at low dose levels."
The problem in the experimental animal is that the frequency of bone
tumor appearance is so slight that statistically significant increases in the
frequency are not to be expected as a result of irradiation. The human problem
is similar in that osteogenic sarcoma and leukemia are relatively unlikely
occurrences, together causing about 1% of adult deaths in the United States,
so that a small percentage change in incidence caused by radiation could not
be distinguished from random fluctuation, and a relatively large fractional
increase in the number of these cancers would not appreciably increase the
total death rate.
/