Chapter 7 



Ecology of Uptake by Aquatic Organisms 



73 



In different organisms, ionized or particulate 

 fission-product wastes and other radiomaterials 

 may be either adsorbed, engulfed, or accumu- 

 lated by metabolic processes. For example, 

 Rothstein and his associates (1951) demon- 

 strated that uranium as the uranyl ion was ad- 

 sorbed by yeast cells. Hamilton and co-workers 

 (see Hevesy, G., 1948, p. 441) showed that 

 particulate radiomaterials such as various un- 

 complexed rare earths at physiological pH's 

 were adsorbed by the gut lining of rats. In 

 these experiments practically no accumulation of 

 these particular radiomaterials by the animal 

 was observed. On the other hand, Goldberg 

 (1952) demonstrated with radioactive iron that 

 a marine diatom assimilated particles of hy- 

 drated iron oxide, but that these organisms were 

 unable to take up ionic iron in a complexed 

 form. 



The first biological experiments in which ra- 

 dioactive atoms were used were performed by 

 Hevesy in 1923. In those classical experiments 

 it was demonstrated that plants could take up 

 lead from solution and translocate it throughout 

 the vascular system. 



The accumulation of radioelements is also de- 

 pendent upon many chemical characteristics of 

 the water in question. Among the parameters 

 affecting accumulation are the salinity, percent- 

 age composition of the dissolved solids, pH, the 

 oxygen-carbon dioxide ratio, and the presence 

 of complexing agents. 



a. Chemical composition of marine organisms 



A modern systematic study of the inorganic 

 constituents of marine organisms is yet to be 

 made. The best summary of existing knowledge 

 may be found in Vinogradov (1953). 



However, certain generalizations can be 

 drawn from the recent literature on the concen- 

 tration of metals by marine organisms. Gold- 

 berg (in Treatise of Marine Ecology, volume II, 

 edited by J. Hedgpeth, in press) has pointed 

 out that the marine biosphere tends to concen- 

 trate such heavy metals as copper, nickel, zinc, 

 etc., over the marine hydrosphere by factors of 

 100 to 100,000 on a weight-f or- weight basis 

 (Table 4) . These metals are strongly bound in 

 the organisms and cannot be easily removed by 

 elution. Further, the elements most strongly 

 concentrated in the biosphere are those that 

 form the most stable complexes with organic 

 chelating agents. As an example, copper is con- 

 centrated over sea water in the soft parts of 



most marine organisms by factors of 10^ to 10* 

 whereas calcium shows concentration factors of 

 less than 1 to 50. Copper forms very strong 

 complexes with many organic compounds 

 whereas calcium does not. Although the exact 

 role of most metals in the physiology of organ- 

 isms is not known, nevertheless, one might a 

 priori expect that some heavy metals introduced 

 into the ocean from nuclear reactions would 

 concentrate in the biosphere. 



b. Concentration in the etivironment 



The concentration of a given radiomaterial 

 by an organism is sometimes proportional to 

 the concentration of that material in the en- 

 vironment. This generalization applies both to 

 aquatic and to terrestrial organisms. The uptake 

 of cesium 137 by the oyster (Crassostrea vir- 

 ginica) has been shown to be dependent upon 

 the external concentration of cesium in the sea 

 water (Chipman, et al., 1954). Prosser, et al. 

 (1945), noted that with the addition of stron- 

 tium to the environment there was an increase 

 in the uptake of that element by goldfish {Car as • 

 sitis auratus). Also, it has been demonstrated 

 that as the carrier concentration in the nutrient 

 environment is increased, the concentration fac- 

 tor for a particular fission product in terrestrial 

 plants tends to increase (Rediske, et al., 1955). 



c. Effect of the presence of one element on 

 the uptake of another element 



The uptake of one radioelement by an organ- 

 ism may be altered by the relative abundance 

 of another element in the environment. In 

 instances in which more than one element is 

 involved, one of three phenomena may be 

 observed : 



First, elements of similar chemical properties 

 may substitute for one another. For example, 

 it has been shown by Prosser, et al. (1945), 

 that when the amount of calcium in the water 

 was low, there was an increase in the uptake of 

 strontium 89 by goldfish. Conversely, as the 

 amount of calcium was increased, the uptake of 

 strontium decreased. Rice (1956) observed that 

 cells of Carteria grown in artificial sea water 

 took up strontium in proportion to the stron- 

 tium/calcium ratio in the medium. Bevelander 

 and Benzer (1948) have shown that a modifica- 

 tion of the constituents of sea water resulted 

 in a change in the constituents of the shells de- 

 posited by mollusks. 



Second, some elements may have an inhibi- 

 tory effect on others. A classical example of this 



