OCEANOGRAPHY AND FISHERIES 81 



■'fera4(-l) 



Ire=I 



Irf is the amount of the radioisotope per unit volume of seafood, and hence is comparable 

 to the (MPC)w values for the gastro-intestinal tract given in Handbook 69. In this publica- 

 tion, it is assumed that a human being drinks 15 liters of water per week. This is about 10 

 times the amount of seafood eaten, even for those human beings who obtain all their protein 

 from seafood. Hence the radioactivity per unit volume in the intestinal tract can be diluted by 

 a factor of 10. We conclude that 



For isotopes in which the radioactive half-life is much longer than the biological half-life 

 in marine organisms, eq. (6) reduces to 



Ire^lO p (6a) 



In two previous reports of this Committee (2, 3), eq. (6a) was used in all cases to com- 

 pute Ire, the permissible concentration of radioactive isotopes in sea water. Following the 

 recommendations of the National Committee on Radiation Protection and Measurements, 

 one-tenth of the MPC values in drinking water given in Table 1 of Handbook 69 for the 

 critical body organ were employed in the calculations. These are the recommended values 

 for the general public outside of areas of occupational exposure. As has been stated above, 

 this procedure is clearly applicable for long-lived elements in which the gastro-intestinal tract 

 is the critical organ. It errs on the side of safety for short-lived elements in which the gastro- 

 intestinal tract is critical, and may give either too large or too small values when accumula- 

 tion of radioisotopes in other organs is critical. 



A more correct procedure in all cases is to compute Ire from both eq. (6a) and (5b), 

 introducing in (6a) one-tenth of the MPC values for the gastro-intestinal tract given in Hand- 

 book 69 and in (5b) one-tenth of the specific activity permissible for the critical body organ. 

 (This is equal to the permissible total body burden for the critical organ given in Handbook 

 69 divided by the total amount of the non-radioactive isotope in the body. Most values for 

 the latter are given in Handbook 52). The permissible concentration in sea water is then the 

 smaller of these two values. Table 1 illustrates the computations. The tentatively accepted 

 values are underlined. At least for adults, these are undoubtedly quite conservative for ele- 

 ments with relatively long effective biological half-lives in the marine food chain (see pages 

 79, 80). 



Comparisons of the permissible sea water concentrations calculated by the above method 

 with those previously published by this Committee, and with the maximum permissible con- 

 centrations in drinking water, are given in Table 2. Our previously published values have 

 been corrected for the changes made by Handbook 69 for the maximum permissible concen- 

 trations in drinking water. It will be noted that the permissible sea water concentrations for 

 S"', Ca^\ and Sr"" are larger by factors of 15 to 30 than the maximum permissible concentra- 

 tions for drinking water. The stable isotopes of these elements are present in relatively large 

 amounts in the oceans, and they are not greatly concentrated by marine organisms. On the 

 other hand, such substances as P^-, Fe'", Co"", Zn"\ and Ce"' have permissible sea water con- 

 centrations 1/1,000 to 1/10,000 of the maximum permissible concentrations for drinking 

 water. Here, the quantities of the stable isotopes in sea water are quite small, and these ele- 

 ments are heavily concentrated by marine organisms. 



