70 



Atomic Radiation and Oceanography and Fisheries 



processes; in some instances assimilation may 

 take place following the engulfment of living 

 or inert particulate matter. A radionuclide may 

 also be incorporated into an organism by simple 

 exchange of the radioactive isotope for the sta- 

 ble isotope of the same species. It is therefore 

 important to know the physical and chemical 

 state necessary for metabolism, the mode of 

 entry, and the ability of all organisms at each 

 of the different trophic levels to concentrate the 

 various radionuclides. 



Physical and Chemical Factors Concerned with 

 the Uptake of Radionuclides by Living 

 Organisms 



a. Acute versus chronic exposure 



Chronic exposure of an aquatic organism, 

 even to low concentrations of radiomaterials, 

 usually has a markedly different effect on the 

 organism than an acute exposure; the principal 

 difference lies in the amount of radiomaterial 

 accumulated in the tissues. Because many 

 aquatic organisms have the ability to concentrate 

 radiomaterials from their environments by fac- 

 tors up to several hundred thousand, much ra- 

 diomaterial may be accumulated during a 

 chronic exposure for a relatively long period of 

 time. A state of equilibrium is ultimately 

 reached at which there is a constant uptake and 

 a constant loss with a resultant constant maxi- 

 mum level of accumulation. Conversely, in an 

 acute exposure, such as a single feeding or a 

 single injection of radiomaterials, only a certain 

 relatively small fraction of the radiomaterial is 

 accumulated in the body and the remainder is 

 lost. In such an instance, the maximum level to 

 which an organism is capable of accumulating 

 the radiomaterial in question is seldom reached 

 and certainly not maintained. 



Krumholz and Rust (1954) reported an ac- 

 cumulation of one microcurie of strontium 90 

 per gram of bone in the entire skeleton of a 

 muskrat {Ondatra zibethica) which had been 

 utilizing foods of its own choice in the area 

 contiguous to the Oak Ridge National Labora- 

 tory. Certainly this instance can be presumed to 

 represent a chronic exposure inasmuch as the 

 animal was at least two years old and had 

 probably lived in the area during her entire life- 

 time. Aquatic organisms in the Columbia River 

 below the Hanford Works and those in White 

 Oak Creek, Tennessee, below the Oak Ridge 



National Laboratory, have all suffered chronic 

 exposures to radiomaterials and have accumu- 

 lated considerable amounts of those materials 

 in their tissues. Hiatt, Boroughs, Townsley, and 

 Kau (1955) found that the daily feeding of 

 strontium 89 to the fish Tilapia for short pe- 

 riods of time (four days) did not increase the 

 level of strontium retention after an apparent 

 steady-state condition had been reached. How- 

 ever, there are no published reports of the re- 

 sults of long-term, controlled experiments of 

 chronic exposures of aquatic organisms to radio- 

 materials. 



The literature contains many reports con- 

 cerned with acute exposures of aquatic organ- 

 isms to radiomaterials. Martin and Goldberg 

 (unpublished data), who gave single feedings 

 of strontium 90 to Pacific mackerel (Pneumato- 

 phorus japonic us die go), found that less than 

 five per cent of the amount fed was retained in 

 the body after 48 hours. Much of the five per 

 cent that was incorporated in the skeleton re- 

 mained there for the duration of the experiment 

 (235 days). Boroughs et al. (1956) reported 

 that between only one and two per cent of the 

 strontium 89 fed to ten yellowfin tuna {Neo- 

 thunnus macropterus) remained in the body 

 after 24 hours. The small amount retained in 

 the body was largely incorporated into the skele- 

 tal structures. However, other fish {Tilapia) 

 which had been fed similarly prepared stron- 

 tium 89 capsules retained about 20 per cent of 

 the ingested material after 24 hours. After four 

 days, the amount retained finally levelled off at 

 values that ranged from 1.5 to 19.5 per cent of 

 the amount ingested; the average amount re- 

 tained was about 7.5 per cent. Here, again, the 

 retained materials were incorporated mainly in 

 the skeletal structures and integument. 



b. Chemical and physical states of the ele- 

 ments in the environment. 



The chemical composition of the marine en- 

 vironment cannot be rigorously defined. The 

 concentrations of elements depend upon the 

 type and location of the water mass. Although 

 more than 90 per cent of marine waters occur 

 at depths greater than 1000 meters, the majority 

 of chemical analyses have been made for shal- 

 lower waters. Because of the biological ac- 

 tivity of the oceans and the movements and 

 origins of water masses, the abundance of cer- 

 tain elements appears to vary by factors greater 

 than two orders of magnitude. However, as a 



