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Reprinted from JOURNAL or Damy Sctencr, December, 1958, Vol. 41, No. 12, pages 1647-1662
SIGNIFICANCE OF STRONTIUM-90 IN MILK. A REVIEW
B. L. LARSON anp K. BE. EBNER
Laboratory of Biochemistry, Department of Dairy Science,
University of Iilinois, Urbana
SUMMARY
Milk has received attention as a source of strontium-90 (Sr-90), since it is the
major souree of calcium and, hence, Sr-90, in the diet of most Western countries.
Although several biologically active radioactive isotopes are produced in a uranium-235
atomie bomb explosion, Sr-90 is the major problem when considering long-term fallout,
because of its slow fallout from the atmosphere, its long half-life of 28 yr., and its
biological similarity to calcium. There are several discrimination steps against Sr-90
in its route to the bones of man after its deposition in soil from the atmosphere.
These include the plant, the gut, the kidneys, the placenta, and the mammary gland.
Compared to bone radiation received from other natural sources, the radiation from
Sr-90 present in bone constitutes a small proportion, both now and if nuclear tests
continue at the same rate. Milk contains much less Sr-90 per unit of calcium than do
vegetables and cereals because of several discrimination factors in its formation, including the mammary gland. A comparison of diets consumed by vartous countries
‘of the world indicates that those countries consuming a higher percentage of milk have
lower relative Sr-90 intakes in their diets. Reliable data from which to draw sound
conelusions are crucially lacking in many areas of the long-term fallout problem. The
present knowledge strongly suggests that the current and projected levels of Sr-90
in milk should not cause us concern when compared to radiation received from natural
sources; but further studies are necessary to be certain if this is true.
Although man has been concerned with the damagingeffects of radiation for
the past 30 yr., the threat of nuclear warfare and the current controversy over
the testing of atomic devices have brought the problem to the immediate focus
of public attention. The public has been made aware of the aceumulation of
radioactive materials from nuclear debris in its environment and of the possible
damaging effects of this increase in radiation. In particular, the passage of strontium-90 (Sr-90) from the atmosphere into food and its accumulation in bone have
been publicized.
It is recognized that milk is the principal source of calcium (and, hence,
Sr-90) in the diet of most Western countries, including the United States.
Various opinions on the significance of this fact have been advanced. One investigator (3) has proposed that all the calcium (and Sr-90)} present in milk
should be removed and replaced with calcium from uncontaminated ‘‘ancient
sources’’; conversely, it has been concluded that the levels of Sr-90 in milk are
so low that we need not be concerned (24).
The recognition of how much Sr-90 is present in milk and an interpretation
and comparisonof this level with that present in other food products, is of practieal importance to the dairy industry. It is the opinion of the authors that there
has been too much willingness on the part of the dairy industry to allow others
not concerned with the industry to collect and to interpret the basic information
relative to milk. Accusing fingers have been pointed at milk without proper
Received for publication August 13, 1958.
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