On the basis of the allowable body burden in man of strontium 90 

 and of the total amount of body calcium, it has been shown that, for the 

 population as a whole, the ratio of strontium 90 to total body calcium 

 must not exceed 0.1 txc per kg, i. e. 



Sr 90 / Ca < 0.1 p-c Sr 90 / kg body Ca. 



Man apparently discriminates against strontium in the uptake of calcium 

 and strontium by a factor of 8:1. Therefore, if man receives his total 

 protein requirements from fish, and the fish contain strontium 90, we 

 must have in the fish: 



Sr 90 / Ca < 0.8 ^c Sr 90 / kg Ca. 



Assuming that fish do not discriminate against strontium in the up- 

 take of calcium and strontiunn (probably a conservative assumption), 

 the above limiting relation must also hold for the ratio of strontium 90 

 to calcium in sea water. The calcium concentration in sea water of 

 34^00 salinity is approximately 400 ppm, or 0.40 g of calcium per kg of 

 sea water. Therefore, there must be less than 0.8 lic of strontium 90 

 per 2,500 kg of sea water. Hence the maximum permissible value for 

 strontium 90 in the marine environment, assuming that man receives 

 all his protein requirement from fish harvested from that environment, 

 and assunaing that this is man's only source of ingestion of radioactive 

 materials, would be 3.2 x 10"^ M,c/ml. Since for the coastal environment 

 we have assigned only one-tenth the maximum permissible dose to the 

 effects of wastes from nuclear-powered ships, the ppc value for coastal 

 water would be 3.2 x 10"^ |ic/ml. 



It is seen that this value differs from the corresponding value 

 given in Table 2 by a factor of only about 6.5. The two methods of com- 

 putation would agree if a concentration factor of about 3, rather than 20, 

 had been used in obtaining the ppc value for the marine environment, 

 for strontium 90, given in Table 2. Thus there is some evidence that 

 slightly conservative values of the concentration factors were employed 

 in computation of the ppc values for the marine environment given in 

 the Table. 



It is not readily seen how the concept of the "sunshine unit" can 

 be applied to all the radioisotopes with which we are concerned. Also, 

 in view of the many uncertainties involved, conservative estimates 

 must be made at this time. Hence, for our further computations, the 

 approach used to obtain Table 2 is employed in this report. 



The values thus calculated for ppc's in the environment are prob- 

 ably fairly reliable guides where the "environment" is the water and 

 the food organisms are obtaining their nutrients from the water. This 

 will apply where there is no uptake by organisms of isotopes from 

 bottom sedinnents. 



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