Chapter 7 



Ecology of Uptake by Aquatic Organisms 



77 



elide was phosphorus 32, which has a physical 

 half -life of about 14 days. It is apparent that 

 when following the steady-state transport of 

 radiomaterials through the ecosystem the follow- 

 ing parameters must be considered: (1) the 

 physical half-life of the radionuclide, (2) the 

 distance of the organism from the source of 

 radioactive contamination, and (3) the dilution 

 of the radiomaterials between the point of in- 

 troduction and the area in which the organism 

 lives. 



The results from acute exposure cannot be as 

 definitely approximated as for chronic exposure. 

 In such instances, the time element is very im- 

 portant, and the following must be known: (1) 

 the rate of dilution of the radioactive water 

 mass with non-radioactive water; (2) the rate 

 of transfer of radiomaterials from one trophic 

 level to another with the concurrent dilutions 

 and losses or gains in concentration by the or- 

 ganisms; and (3) the life span of the organ- 

 isms involved. 



In general, the radiomaterials taken up by 

 organisms of the first trophic level will be pri- 

 marily in the ionized state although a certain 

 amount of particulate radiomaterials will be ad- 

 sorbed to the body surfaces. When uptake oc- 

 curs, the rate of uptake will probably be more 

 rapid than the rate of uptake in the other 

 trophic levels. 



Particulate radiomaterials tend to be concen- 

 trated in the second trophic level. Findings 

 from the Wigwam and Castle tests (Goldberg, 

 unpublished data) showed that the principal or- 

 ganisms which concentrated particulate radio- 

 materials were the mucous, ciliary, and pseudo- 

 podial feeders among the zooplankters. These 

 organisms contained much more radioactivity 

 per unit weight than either the algae or the setal 

 or rapacious feeders. 



In addition to the differences in concentration 

 of radiomaterials from one trophic level to an- 

 other, there are marked differences among spe- 

 cies in the same level. For instance, it has been 

 shown by Chipman, et al. (1953), that some 

 phytoplankters will concentrate radiostrontium 

 by a factor of about 20 times whereas others 

 will concentrate the radioelement by factors as 

 much as 1500 times. Comparable data have been 

 recorded by Krumholz (1954) for the accumu- 

 lation of radiophosphorus by the phytoplankters 

 of White Oak Lake. 



Differences also exist between individuals of 



the same species. Very large differences in the 

 amounts of radiomaterials accumulated by indi- 

 vidual fishes in White Oak Lake were described 

 by Krumholz (1956) . For instance, he reported 

 that the amounts of radiostrontium in the bones 

 of three bluegills {Lepomis macrochirus') dif- 

 fered by more than five-fold. These three fish 

 were taken from the same place in the lake on 

 the same day, August 27, 1952. Comparable 

 differences were found in the amounts of ac- 

 cumulated radiomaterials in most other tissues. 



The transfer of radiomaterials from one 

 trophic level to another is not only dependent 

 upon the concentration of the radiomaterial in 

 the organism but also is governed by the rate 

 of growth of the organism and the rate of in- 

 crease in the size of the population. These fac- 

 tors of transfer are of particular importance in 

 the event of an acute exposure because the dilu- 

 tion brought about through cell division and 

 growth may well minimize any radiation effect. 

 In any event, there is always a loss in the total 

 amount of radiomaterials in the transfer from 

 one trophic level to another (though not nec- 

 essarily a decrease in the concentration in indi- 

 vidual organisms). Such a loss may be rela- 

 tively small or it may be very great depending 

 upon the organism and the particular food web 

 involved. 



Not all radiomaterials that enter the first 

 trophic level are passed on to higher levels. At 

 each trophic level there are certain species that, 

 for one reason or another, are not widely used 

 as food by the organisms of higher levels. Also, 

 some of the plants of the first trophic level may 

 die before they are eaten and thus will be re- 

 turned to the environment as organic matter. 

 In this case the primary producers may be of 

 little or no importance as a source of radioma- 

 terials to the organisms of the second and third 

 trophic levels. 



If relatively large quantities of radiomaterials 

 are accumulated in certain hard parts of an or- 

 ganism, such as the shell of an oyster or the 

 bones of a fish, they will, in all probability, re- 

 main in those parts during the greater part of 

 the life of the animal concerned, and will not 

 be available to other animals in the biosphere 

 until the animal dies. 



Chipman and co-workers (1953) showed 

 that oysters fed on Cblorella assimilated only 

 very little of the radiophosphorus from these 



