subsequent use of these latter values in the determination of the saie 

 rate of discharge of nuclides into the various marine environments, the 

 following considerations must be taken into account. The ultimate 

 major source of dilution water for the most restrictive environment 

 (harbors, estuaries, and inshore waters) is the next most restrictive 

 environment, the waters of the continental shelf. Likewise, the ability 

 of the waters of the continental shelf to receive wastes depends, in part, 

 upon the rate of exchange of these waters with the waters of the open 

 sea. These dilution waters must have, in each case, significantly lower 

 average concentrations than the ppc values of the neighboring more in- 

 shore environment. The environmental ppc values computed below thus 

 cannot be considered to represent the average permissible concentration 

 throughout the entire volume of each of the subject marine environments. 

 While these ppc values may apply to substantial areas of each environ- 

 ment in an absolute sense, such areas must be only a relatively small 

 fraction of the entire area of the respective marine subdivision. The 

 manner in which this condition is satisfied is presented in a later sec- 

 tion of this report entitled "Basis for Evaluating Safe Discharge Rates". 



PARTIAL PERMISSIBLE CONCENTRATIONS IN THE ENVIRONMENT 



Having estimated ppc's in marine food organisms, we can esti- 

 mate ppc's in the environment if we know the factor by which the food 

 organisms concentrate the isotope in question in their bodies from their 

 environment. Concentration factors from seawater to the edible parts 

 of marine invertebrates and marine fishes have been estimated by the 

 authors noted in the footnotes to Table 2. Values are tabulated here 

 for soft (edible) parts of marine invertebrates and for the soft parts 

 cuid the bones of fish. The latter have been included because some fish 

 (especially canned fish, such as salmon, mackerel, and sardines) are 

 often eaten bones and all. Where the fish bones are eaten, it seems ap- 

 propriate to use l/lO of the concentration factor for fish bone (since 

 that is roughly the ratio of bone to whole fish) in obtaining a weighted 

 average concentration factor to use in further computations. 



Based on whichever of the concentration factors (that for inver- 

 tebrates or that for fish) is the higher for each isotope, we have calcu- 

 lated and tabulated the ppc in the environment according to the relation 



/ • 4.\ ppc (food) 



ppc (environment) = ^^ — ^. 7 — r • 



^^ ^ concentration factor 



The resulting ppc's in the various subdivisions of the marine environ- 

 ment are tabulated in the last five columns of Table 2. 



Some investigators have questioned this method of computing 

 ppc values for the marine environment since certain pertinent features 

 of human body chemistry are not evidently included. For the case of 

 strontium 90, an alternate method of computation is based on the so- 

 called "sunshine unit". This computation does not explicitly include the 

 concept of "concentration factors" used in the above evaluation. 



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