RADIATION STANDARDS, INCLUDING FALLOUT
89
Supplementation of human diets is not recommended. Thisis primarily because widespread excessive calcium intakes could lead to
health problems; in addition, the effectiveness of such procedures and
the proper balance of supplemental mineral intakes are not known.
It is especially important that individuals do not take medically
unsupervised action. When calcium supplementation is required for
medical or nutritional purposes, thought should be given to the fact
that calcium supplements derived from animal bone contain Sr®.
Experience has shownthat there is no advantagein the use of stable
strontium to reduce Sr® deposition in the body or secretion into milk.
This is because the Sr® behavior is governed by thetotal level of both
alkaline earths (calcium and strontium) and the amounts of strontium
required to increase this total level appreciably are sufficient to produce
side effects.
For purposes of prediction of future levels of Sr® it is necessary
to consider the two major pathways in the food chain. These are indicated in chart 8. The pathways are (1) surface contamination of
plants which are then consumed by man or grazing animals (the
dietary contamination produced by this pathwayis entirely dependent
upon the rate of fallout) and (2) the accumulation of Sr®in the soil
with subsequent uptake through the plant roots (contamination produced by this pathway is dependent upon the cumulative total in the
soil).
Whenthe fallout rate is high compared to the cumulativetotal, the
first or rate-dependent pathway predominates as indicated in the
chart.
For example, in 1957, when the milk contained about seven picocuries per gram of calcium,itis calculated that about four picocuries
came from the rate dependent path and three from the cumulative dependent path. In 1961, however, one can see that the pathway from
the cumulative total began to redominate when there was 9.5 picocuries
per gram of calcium, 8 came from the cumulative pathway and 1.5
from the rate dependent pathway.
Because the plant foods that maneats are usually washed or skinned,
the expected tenfold difference in the Sr°°/Ca ratio between milk
and plant foods is decreased. As indicated, the cumulative-dependent
pathway becomes dominant with time after the cessation of testing
or even with a constantrate of testing.
Underthese conditions, as implied in chart 9, plant foods are contaminated throughoutand surface cleansing would not greatly reduce
their Sr/Ca ratio.
Mathematical relationships have been derived from measurements
of fallout rate, cumulative totals and levels in milk. The presently
accepted factors are indicated in chart 10.
The picocuries of strontium 90 per gram of calcium in the milk
equals a rate component plus a cumulative component. The rate component. can be expressed as some factor, a factor that we now use as
0.3 times the millicuries per square mile per year, plus the cumulative
component, the factor 0.12 times the total deposition which is milli-
curies per square mile.
This formula allows calculation for the future levels. It should
be pointed out that these factors are quite variable, especially if converted to use with total diets, and should be applied only to large areas.
Another matter that needs to be taken into account is that Sr® in
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