76 BIOLOGICAL EFFECTS OF ATOMIC RADIATION 



concentrations originating from nuclear-powered ships may be ten times those for drinking 

 water. 



5. The open sea, considered to comprise those ocean areas more than 12 miles from 

 shore having depths greater than 200 fathoms: permissible seafood concentrations from 

 nuclear-powered ships may be five times those for drinking water for known fishing areas, and 

 twenty-five times outside of fishing areas. 



Based on these maximum permissible concentrations in seafood, specific and detailed 

 recommendations were made concerning the types and amounts of waste that can safely be 

 introduced into the various types of marine environments. 



3. Suggested Methods of Calculation of the Permissible Concentrations of Radioactive Iso- 

 topes in Sea Water. 



The fate of radioactive materials introduced into the marine environment depends on five 

 things: the physical and chemical form of the material; initial mechanical dilution in the 

 receiving waters; advection and turbulent diffusion; uptake by suspended silt and bottom 

 sediments; and concentration by organisms. Evaluation of the quantity of radioactive mate- 

 rials that can be introduced into any particular marine locality involves a step-by-step con- 

 sideration of all these factors, especially as they affect the possible return of the radioactive 

 material to man. Figure 1, taken from NAS-NRC Publication 658(3), presents in schematic 

 form such a step-by-step procedure. The solid arrows between blocks in the diagram indicate 

 the route taken by the radioactive material in returning to man, while the dashed arrows in- 

 dicate the reverse course taken in the evaluation. The evaluation depends on the maximum 

 permissible rate of exposure of different body organs to radiation. These permissible rates of 

 exposure are published and revised from time to time by the national and international com- 

 mittees on radiation protection. 



Radioactive isotopes in the sea may affect man principally through his use of marine 

 plants and animals as food. Consequently, the quantities of radioactive materials that can 

 safely be introduced into the marine environment can be most directly controlled from the 

 results of monitoring the radioactivity in edible marine organisms. (It is also necessary to 

 consider the rate at which human beings consume marine foods and the fraction of the total 

 radiation exposure that can safely be assigned to marine sources.) Adequate monitoring is 

 costly and difficult, however, and must of necessity lag behind the first stages of the disposal 

 program. In planning for marine disposal and in choosing between different disposal sites and 

 methods, it is thus essential to be able to make as realistic estimates as possible of the maxi- 

 mum permissible concentrations of various radioactive isotopes in sea water. It should be 

 emphasized that this is only one step in the solution of the problem and the calculated per- 

 missible concentrations in sea water are not to be regarded in the same way as the published 

 permissible concentrations in drinking water. In the present state of knowledge, the permis- 

 sible concentrations in sea water can be regarded only as interim values; moreover, they 

 should be thought of as average values for the relatively large volumes of water from which 

 edible marine animals and plants extract their body materials. 



In making estimates of permissible concentrations in sea water, account must be taken of 

 the fact that sea water is a solution of almost all the elements; that the concentrations of many 

 elements are known and are constant within more or less well-defined limits; and that marine 

 plants and animals concentrate, often by very large factors, both radioactive and non-radio- 

 active isotopes. 



