~ 23 The effect of locality is more important, ..owever,
particularly in the effect of caicium deficiency in “he
soils. Careful consideration of this question indic ses
that there will be very few individuals who show a s rontium=
90 content which is strictly inversely proportional 29 the
available calcium concentration of the soil in their region.
This is due to the fact that food distribution syste.is
automatically average over a wide area and people assimilate
their calcium slowly.
Most people drink milk and eat cheese
and other calcium-bearing foods from a rather wide area, and
this effect reduces by an estimated factor of ten the potential effect of calcium deficiency in the local soils.
On the basis of laboratory experiments the human
body concentration of strontium-90 at equilibrium will be
between 13 and 30 times less than that in the top soil.
The present data indicate that the higher figure is closer
to the truth, and so we will be conservative in taking the
figure of 20 for this ratio.
Therefore, the present burden
of 50 Sunshine Units in the top soil of the United States
may eventually lead to as much as 2.5 Sunshine Units in the
human bones, but more likely will lead to about 1.7.
Of course, as testing continues and more fallout
occurs, the levels will rise. The strontium-90 that still
resides in the stratosphere at the present will fall out
according to our expectations at a rate which just about
compensates for the decay of the material already descosited,
so that no great additionai increase from this source is to
be expected from weapons fired in the past.
If the testing
should continue at about the same rate as it has averaged
over the last five years, then we should at equilibriw 5
after an infinite time, approach a level of 8 times the
present rate, since the average life of strontium-90 is 40°
years. This assumes that the future testing will be conducted so as to give in each future five-year period the
same as the last five have.
And so we would expect in the
United States at that time an average human strontiun-90
concentration of 20 Sunshine Units with the conservative
factor of 2C between the top soil concentration and the
concentration in human bone, or 5 Sunshine Units if the
factor of 80 is used.
In other words, in the United States
something between 5 and 20 Sunshine Units would be the
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