| Popis: |
Summary Milk has received attention as a source of strontium-90 (Sr-90), since it is the major source 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 atomic 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 various 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 conclusions 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. |
