RADIO-ACTIVE FISSION-PRODUCTS IN THE HUMAN FOOD CHAIN 



into the analysis of tlic various ilt ins ol llu' liunian fcKxl chain for ^"Sr. 

 Reports have been issued jieriodically by Bryant, Chamberlain and their 

 colleagues. This eflort in what might be called 'l)iological monitoring' has 

 had as a by-product a better understanding of certain aspects of plant and 

 animal jihysiology. In 1957, because of the increasing importance of this 

 work and because of the physiological implications, there was a redistribution 

 of effort. By agreement between the Atomic Energy Authority, the Agri- 

 cultural Research Council and the Medical Research Council, the Atomic 

 Energy Research Establishment will continue to be responsible for the 

 monitoring of the atmosphere, of rainfall and water supplies and for the 

 assay of human bones. The Agricultural Research Council is taking over 

 the responsibility for the monitoring of materials in the food chain and for 

 interpretation of the data within their sphere. The Medical Research Council 

 is responsible for the interpretation of the results as they affect the human 

 population. 



To retrace the past, Bryant and his colleagues found in 1956^ that the 

 accumulated deposition of ^"Sr in soil varied from about 2000 to 10,000 

 (X[ji.C/m-. The variation is of course due to the variation of rainfall. As 

 useful information in plant and animal physiology had been obtained from 

 comparison of strontium to calcium ratios in tissues with that in precursors 

 {e.g., bone to diet or plant to nutrient), it was perhaps natural for Bryant et al. 

 to express their results in a similar fashion in strontium-units ([jL[j.C ^^Sr/g 

 calcium). This gave figures of • 15 to 800 S.U. — a range of about 5000 — for 

 the different soils. However, it is extremely doubtful if these figures have 

 any meaning, since in many soils the calcium is largely unavailable to the 

 plant. The grass from the same sites in terms of [X[xC'jm'^ was some hundred 

 times less radio-active than soil and was in the range of 15 to 150 for the 

 accumulated growth. It is acceptable to express the radio-activity of grass 

 in terms of strontium-units w^hen it is being considered as diet for animals 

 and the observed variation is 25 to 2000 S.U. The higher figures of stron- 

 tium-units were found in hill pasture, on acid soils with lime deficiency. It 

 is notable of course that such soils are not only deficient in calcium but other 

 nutrients as well and the total growth under these conditions is poor. Never- 

 theless, sheep are put out to graze on these natural highland pastures and 

 consequently ingest a relatively high concentration of ^^Sr/kg of diet. This 

 is reflected in the bones of these sheep which were some twenty times as 

 radio-active in terms of ^''Sr/g Ca as sheep from lowland pasture. The 

 figures for sheep bone of 150 S.U. and thereabouts have led to expressions 

 of anxiety in the press and Parliament. However, there is no reason to 

 suppose that such levels or even levels many times greater will be deleterious 

 to the sheep with their relatively short economic life. The generally accepted 

 permissible levels for man in radiological occupations is equivalent to 1000 

 S.U. and it has been suggested that for domestic animals \vith their much 

 shorter expectation of life the permissible dose might be some ten times 

 greater. What is important about these levels of 100 and more strontium- 

 units is to predict what will be the future state of affairs. 



In summary — do the present levels reflect the accumulated deposit of 

 the last few years or the annual rate of deposit? If the value in sheep bone 

 is a function of the accumulated deposit, since there is much ^"Sr in the 



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