RADIATION STANDARDS, INCLUDING FALLOUT
97
ucts is reduced without compensating addition of minerals, the body has to use
plant sources of calcium for building and replacement of bone. In effect, this
means that the reduction of the intake of dairy products will raise the Sr*®/Ca
intake and therefore the body burden of Sr®. At present and foreseeable levels
of Sr” it appears best to follow accepted nutritional! practiée.
The question is often raised as to the advisability of supplementation of diets
with stable calcium or stable strontium, for purposes of reducing the body burden
of Sr”. This matter is now considered, leaving aside the question as to whether
reduction of present and foreseeable body levels of Sr” would in fact improve
ealth.
The Sr”/Ca ratio of the diet can be decreased by supplementation with uncontaminated stable calcium and this in principle should decrease the Sr™ levels
produced in the body or milk. Although such reductions have been demonstrated
in experiments with laboratory and domestic animals, there are many considerations and unknownvariables that restrict practical application.
Experiments with dairy cows have shown that long-term supplementation of
rations with stable calcium can reduce the Sr” levels in milk, but probably not
greater than a factor of four even under the best conditions, because of abnormality of diets. There are uncertainties in regard to the effects of animal nutrition and health from high calcium intakes over long periods of time, and in
regard to the length of time it requires for calcium supplementation to become
effective.
Supplementation of human diets is not recommended.
This is primarily be
cause 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 shown that there is no advantage in 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 the total level of both alkaline earths (calcium and
strontium) and the amounts of strontium required to increase this total level appreciably are sufficient to produceside 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). When
the fallout rate is high compared to the cumulative total, the first or ratedependent pathway predominates as indicated in the chart.
Because the plant foods that man eats 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 constant rate of testing.
Under these conditions, as implied in chart 9, plant foods are contaminated
throughout and 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. It should be pointed out that these factors are qvrite
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 soil may
become less available to plants by a few percent per year because of runoff,
redistribution by wind, removal in crops, and possibly fixation in the soil.
CESIUM
137
Cesium 13y, much like Sr, can enter plants both from surface contamination,
a rate-dependent process, and from the soil, a cumulative-dependent process.
Absorption of cesium 137 fromsoil, however, is inefficient, it being estimated that
soil absorption of Cs“ ig only one-tenth to one-twenty-fifth that of Sr.
This
SOREsAestateapesataagg aban eS pcaneshschad CagRenee ReaNTN
Sree
Ne