Chapter 7 



ECOLOGICAL FACTORS INVOLVED IN THE UPTAKE, ACCUMULATION, 

 AND LOSS OF RADIONUCLIDES BY AQUATIC ORGANISMS ' 



Louis A. Krumholz, Department of Biology, University of Louisville, Louisville, Kentucky 



Edward D. Goldberg, Scripps Institution of Oceanography, University of California, 



La Jolla, California 



Howard Boroughs, Hawaii Marine Laboratory, University of Hawaii, Honolulu, T. H. 



Introduction 



This paper is concerned with the uptake, ac- 

 cumulation, and loss by living organisms, of 

 radioactive materials that may be added to or 

 induced in an aquatic environment. These 

 aquatic organisms may live in either fresh, salt, 

 or brackish water and include vascular plants, 

 algae, protozoans, plankton, all the other in- 

 vertebrate forms such as aquatic insects, bottom- 

 living crustaceans and molluscs, and representa- 

 tives of each of the five classes of vertebrate 

 animals. 



The accumulation and loss of any radioiso- 

 tope will depend not only upon its own physical 

 half-life but also upon the biological factors 

 that contribute to its incorporation in, reten- 

 tion by, and disappearance from the organism 

 involved. In general, all isotopes of any one 

 chemical element are similar in chemical behav- 

 ior, and thus it can be assumed, when tracing 

 the paths of most chemical elements through 

 biological systems, that a radioactive atom will 

 behave in the same way as a non-radioactive 

 atom of the same species. However, relatively 

 little is known about the actual mechanisms of 

 uptake, accumulation, and loss by marine and 

 fresh-water organisms of the elements whose 

 isotopes constitute fission products and other 

 radiomaterials. 



For the purposes of this discussion, the fol- 

 lowing terms will be defined: 



Uptake is the amount of material that enters the 

 organism in question and the speed at which the 

 material enters is the rate of uptake. 



1 Contribution No. 9 (New Series) from the De- 

 partment of Biology, University of Louisville. Con- 

 tribution from the Scripps Institution of Oceanography, 

 New Series, No. 901a. Contribution from the Hawaii 

 Marine Laboratory, No. 94. 



Loss is the amount of material that leaves the 

 organism, and the speed at which it leaves is 

 the rate of loss. 



Accumulation is the amount of material that is 

 present in the organism at a given time, and the 

 rate of accumulation is the amount accumulated 

 per unit time. In practice, the accumulation is 

 the difference between the uptake and the loss. 



Metabolic processes include all the chemical 

 changes concerned in the building up and de- 

 struction of living protoplasm. During these 

 changes, energy is provided for the vital proc- 

 esses and for the assimilation of new materials. 



Specific activity is the ratio between the amount 

 of radioactive isotope present and the total 

 amount of all other isotopes of that same ele- 

 ment, both radioactive and stable. Most com- 

 monly, it is given as the microcuries of radio- 

 isotope per gram of total element. 



Although the higher animal forms are de- 

 pendent upon the primary concentrators, the 

 plants, for their source of energy, these animals 

 may or may not be dependent upon the lower 

 forms for many elements. Some elements may 

 enter the bodies of the higher forms directly 

 from the water, while others must be supplied 

 from the lower trophic levels through the food 

 web. These food webs are not the same for all 

 organisms and may even be different for the 

 same organism at various seasons of the year. 

 In some instances certain elements, although 

 present in the environment, are not in the 

 proper physical and/or chemical state to be util- 

 ized by the organisms and thus are not available 

 for metabolism. 



Radionuclides may become associated with an 

 organism either through adsorption to surface 

 areas, through engulfment, or through metabolic 



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