-4longer periods of observations. All that can be said at present is
that the milk values by the end of 1959 were roughly one-half the
maximum values observed in the middle of that year. From the yearly
averages already known it can be predicted that maxima of approximately
10 ye sr90 per gram of Ca may be found in selected samples of bones
of children in localities where milk content has been observed to reach
values exceeding 20 strontium units.
It may be useful to consider, however, that the variations in Sr90
concentrations measured thus far in foods available to man and in his
skeleton appear to be comparable to those observed for the case of
. naturally occurring Ra226; the latter has been shown to vary by more
than a factor of 1000 in foods and by a factor of about 15 in assays of
human and bovine skeletons selected from various geographical areas.
Strict comparison of the contribution of Sr99 to the biological dose in
bone accruing from natural radioactivity awalts a more exhaustive analysis
of the latter; however, some idea of the magnitudes involved can be had
from the following table:
Radioisotopes in the Human Skeleton
Radioisotope
K40
c14
Ra226
Ra? 28
Pb210
238 |). y235
5 S.uU. $r29
External Radiation
Skeletal Content
(Units of 10-10 curie)
50.0
40.0
0.4
0.2
1.0
0.05
50.0
Average Dose
mrad/yr
7.0
0.5
1.2
1.6
1.4
0.1
15.0
73-197
mrems/yr
7.0
0.5
4.8
6.4
5.6
0.4
15.0
73-197
These values refer to skeletal values in localities where the contribution
of Ra226 and Ra228 is due mostly to foods.
In special localities it is
known that intaké of potable water can increase the contributions of
these radium isotopes by a factor of 10.
In attempting to evaluate the bearing of the report on the contribution.
of short-lived isotopes and "hot spots" resulting from fallout to the
estimation of induced genetic effects, the following comments may be made:
If the total 39-year gamma exposure of the United States population from
past testing is 9 million man rads, and the dose to the population around