Chapter 9 



Uptake by Fresh-ivater Organisms 



91 



physiological processes of fresh-water organ- 

 isms. Coffin, et al. (1949) and other workers 

 have shown that a large fraction of the P^- 

 which was added to fresh-water lakes under 

 natural conditions was quickly fixed in the bot- 

 tom sediments where it was essentially unavaila- 

 ble to the organisms. Thus it is apparent that 

 elements which are introduced into an environ- 

 ment as insoluble or tightly fixed compounds, 

 or become parts of such compounds shortly 

 after their introduction, may be of little or no 

 use to the organisms even though the particu- 

 lar element involved normally enters into their 

 metabolic processes. 



Another factor in the concentration of radio- 

 materials by fresh-water organisms about which 

 there is only limited information available is 

 the effect of the presence of one chemical on 

 the uptake of another. For example, it was 



Methods of accumulation of radiomaterials by 

 organ is 7ns 



Radiomaterials may become associated with 

 fresh-water organisms in one of three ways: 

 (1) through adsorption to surface areas, (2) 

 through absorption from the surrounding me- 

 dium, or (3) through ingestion as food. The 

 first of these methods is primarily a physical 

 process whereas the last two are largely bio- 

 logical in nature and make up an integral part 

 of the physiological processes necessary for the 

 metabolism of the population. 



In some instances, especially in those organ- 

 isms which have a large surface-to-volume ra- 

 tio, adsorption to surfaces is very important. For 

 example, Foster and Davis (1955), working 

 with organisms from the Columbia River, 

 showed that the amounts of radioactivity in 



TABLE 3 Absorption of Various Elements from Solution By Fresh-water Fish 



Element Organism 



Strontium Goldfish 



Barium-Lanthanum Goldfish 



Sodium Goldfish 



Calcium Guppy 



Probable 



concentration 



factor 



150 



150 



30 



1000 



Investigator 

 Prosser, et al., 1945 

 Prosser, et al., 1945 

 Prosser, et al., 1945 

 Estimated from Rosenthal, 1956 



shown by Prosser and co-workers (1945) that 

 the amount of calcium present in the water af- 

 fected the amount of strontium taken up by 

 goldfish; as the amount of calcium was in- 

 creased, the uptake of strontium decreased. 



The amount of a radionuclide taken up by an 

 aquatic organism is dependent not only upon 

 the concentration of the nuclide in the water 

 (microcuries per milliliter) but also upon its 

 specific activity.^ As the specific activity is de- 

 creased by increasing the concentration of "car- 

 rier" over a certain range, the stable form of the 

 element becomes more readily available to satisfy 

 the requirements of the organism, and the 

 amount of radioisotope taken up by the organ- 

 ism will generally decrease. Such isotopic dilu- 

 tion has a non-linear relationship, however, and 

 may be ineffective in instances where low con- 

 centrations occur (Whittaker, 1953; Kornberg, 

 1956). 



1 Specific activity as used here refers to the ratio be- 

 tween the amount of radioisotope present and the 

 total amount of all other isotopes, both radioactive 

 and stable, of that same element. 



sponges and diatoms remained comparatively 

 high at a season when the amounts of radio- 

 activity in other organisms were quite low. 



All of the nutrient materials, and thus the 

 biologically important radioisotopes, that are 

 metabolized by plants are absorbed directly from 

 the environment (Rediske, Cline, and Selders, 

 1955). Direct absorption of a few radionu- 

 clides by fresh-water organisms has been ob- 

 served under laboratory conditions. Gross es- 

 timates of concentration factors which appear 

 to have occurred in these studies are listed in 

 Table 3. For the most part, these are short- 

 term tests in which the particular test organism 

 was immersed in the radioactive solution. En- 

 tirely different values would result if the organ- 

 ism had also acquired the isotope through the 

 food web. 



The principal mode of accumulation of ra- 

 diomaterials by fishes is through ingestion. Ol- 

 son (1952) found that young trout which had 

 been immersed in dilute effluent from the Han- 

 ford reactors failed to concentrate radiophos- 

 phorous, whereas similar fish, which were fed 



