remains unaccounted for were to settle out slowly from the upper atmosphere over a period of many years and be subjected to this four-fold
increase, then consideration must be given to this in future hazard
calculations.
This analysis is an oversimplification, since no account
is taken of the decrease in world-wide distribution due to local fallout, the relative efficiency of the fall-out collecting system and the
possible increase, with time, in the number of Sunshine Units in bone
due to the strontium-90 already fallen out.
The Lamont Laboratory aatat3/ suggest that the younger age
groups in the more recent samples have a quantity of strontium-90 lodged
in bone approximating 1.0 Sunshine Unit.
body calcium comes from dairy products.
In the United States 85% of
If the young age group in an
area of high dairy product intake is considered as the critical segment
of the population for risk assessment, it would appear then that dairy
products should be correlated with bone deposition.
If the current
data can be assumed to be a reflection of a maintained or increasing
rate of uptake, then the bone of newborns should approach the strontium90/calcium ratio present in milk products.
Due to the lower saturation
of the mother cow, there is a lowering of the potential ratio of
strontium/calcium in the milk and calf.
The same mechanism applies in
the transport of strontium and calcium from cow's milk through the
human mother to the fetus.
Thus the current strontium-90 values in
bone and milk products are lower than would be expected for the current
fall-out, if the mother cow and the human mother had both grow up in
this same contaminated environment.
Since the hazard calculation seeks to find the most sensitive
population at risk we cannot accurately project current data to a situation of a long-term, maintained contaminated environment.
The data
can be extrapolated, to some extent, if allowance is made for the fact
that eventually all parts of the chain transporting strontium-90 to
43/
Kupl, J.L., Project SUNSHINE Annual Progress Report, March, 1955.
114