PERMISSIBLE CONCENTRATIONS OF RADIOISOTOPES IN SEA WATER 
AND UPTAKE BY MARINE ORGANISMS 
We have noted previously that we consider the return of radio- 
active wastes to man in the form of contaminated marine food products 
to be the most serious potential hazard that might be created by the use 
of near-shore areas as disposal sites. 
The ability of aquatic organisms to concentrate certain substances 
within themselves at higher levels than exists in their environment is 
well known, From earlier studies involving the concentration of the 
major nutrients, carbon, nitrogen, and phosphorus by phytoplankton and the 
aquatic plants, and the passage of these materials from plants to animals 
through successive prey - predator steps, we have a generalized picture 
of the nutrient cycles in which many kinds of aquatic organisms are in- 
volved. Following these early studies with the major nutrients, several 
of the trace metals that appear as minor but essential nutrients were 
studied, and recently the behavior of radioisotopes of several biologi- 
cally important elements has become known, This information was 
discussed in detail in NAS-NRC publication 551, chapters 7, 8, and 9 
(5). Using this information, plus the results of studies completed since 
1957, we can estimate the quantities of many radionuclides that will be 
contained within a variety of aquatic organisms when their environment 
contains stated concentration of the same nuclides. 
We have combined this information regarding the probable quan- 
tities of radionuclides in commercially landed fish with figures for max- 
imum permissible concentrations in drinking water, to obtain the quan- 
tity of radionuclides that will be returned to man in marine food pro- 
ducts, as follows: 
1. The MPC values (3) are based upon acquiring a permissible 
body burden of a given radionuclide, below which no observable biolog- 
ical damage will occur, by drinking approximately 15,000 milliliters 
(15 liters) of water per week, at MPC levels, for 30 years. Thus, the 
MPC values permit the calculation of a permissible weekly intake for 
each of the nuclides listed. For example, the MPC value for Sr is 
8x 10°? uc/ml. We calculate the permissible weekly intake of Sr90 to 
be Vi2-x 10-2 jc, 
2. Using the permissible weekly intake as calculated above and 
figures for the quantity of fish eaten per person per week, it should be 
possible to compute the maximum permissible concentration of any 
nuclide in fish. 
In contrast to the drinking of water, man's seafood eating habits 
are extremely variable. According to Taylor (13) the average U.S. con- 
sumption of seafood is approximately 10 pounds per year. Comparable 
figures for other countries are France, 20; Great Britain, 48; Japan, 
111 pounds per year. The average consumption of seafood, however, 
has little significance since large proportions of the population live far 
from the sea coast and eat little or no fish or other marine products. 
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