-21eliminated altogether.
In contracts, the Sr-90 of the soil
constitutes a relatively long lived reservoir for future uptake.
Diminution will result only from redioactive decay or if the
Sr-90 is leached beyond the root zone.
At the present time, it is not known to what extent the
Sr-90 which occurs in milk may be due to direct deposition on
leaves.
This fraction presumably diminishes with time as the
accumulation in soil increase and the rate of fallout remains
approximately constant.
For our purposes it will be assumed
that all of the Sr-90 in milk is metabolized by way of the roots.
This is a conservative assumption which tends to exaggerate the
forecast of future levels.
The milk in a large metropolitan area for which data ere
available since early 1954, averaged 5 ppic/g Ca in October 1956
when the soils were sampled.
If ve neglect the effect of fresh
fallout, and further essime that the Sr-90 in milk is proportional
to the amount in soil, the future level may be estimated as
5.0 x 1.8 = 9 ppc Sr-90/g Ca.
This prediction is in good
agreement of 8.3 pne/g Ca which was similerly estimated by the
data available in the summer of 1955.
In a previous publication it was assumed thatapplying a
factor of 3 to these particular milk values would be emple
to define the upper limit of hazard elsewhere in the United States.
This factor of 3 continues to appear reasonable.
On this basis
~ the meximum foreseeable concentration in milk would approximate
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