Chapter 8 



Laboratory Experi7?7ents on Uptake 



83 



the radioactive shellfish were returned to a nor- 

 mal sea water environment, the radioactivity 

 present in the soft tissues declined within one 

 day to 10 per cent or less of the maximum con- 

 centration. This residual amount was held by 

 the tissues for several days. 



The uptake of radiostrontium by oysters from 

 food was studied by growing Carteria cells in 

 sea water to which Sr®^ was added. Oysters in 

 Sr^^ sea water served as the controls ; the treated 

 oysters were kept in Sr*^ sea water to which the 

 labelled Carteria cells were added. Fresh sea 

 water and plankton suspensions were prepared 

 each day. The curves in Figure 4 show that an 



Figure 4. The Increased Accumulation of Sr^^ by 

 Oysters Feeding on Sr''®-Fed Algae. 



apparent steady-state is reached in eight days. 

 In the unfed oysters the concentration of Sr^^ 

 in the soft parts is approximately the same as 

 the concentration in the sea water. The oysters 

 which fed on the radioactive algae, however, 

 concentrated the Sr^^ by a factor slightly greater 

 than two, based on the radioactivity of the sus- 

 pension per unit of weight. These filter-feeding 

 organisms removed the algal cells from many 

 volumes of water. 



The uptake of cesium^^" by clams, Venus 

 mercenaria L., is shown in Figure 5. At the 

 end of 20 days the soft parts of clams had con- 

 centrated the cesium by a factor of six over the 

 cesium concentration of sea water. Obviously a 

 steady state had not occurred, so that it is not 

 possible to say what the final concentration fac- 

 tor of clams might be for cesium in solution. 

 Similar experiments using the bay scallop. Pec- 

 ten irradians L., show that the concentration 

 factor of cesium is greater than eight, since the 

 uptake was still increasing at the end of 10 

 days. 



Figure 5. The Accumulation of Cesium^^^ by Clams 

 as a Function of Time. 



Bay scallops immersed for two hours in sea 

 water containing Zn^^ very rapidly accumulated 

 this isotope. Table 4 lists the internal distribu- 

 tion of zinc*'^ in the various tissues. The con- 

 centration factor for each organ is readily cal- 

 culated since the activity of the sea water was 

 10 m/iC/g. This means that the figures given in 

 the second column divided by 10 equal the con- 

 centration factors. The over-all concentration 

 factor of the soft tissues of the bay scallop was 

 20 for this short interval. Other observations 

 showed that these scallops contained close to 

 35,000y of zinc per gram (wet weight) and 

 thus had a concentration factor for this element 

 of about 3500. 



Oysters that were kept in sea water with 

 added Zn^^ also quickly accumulated the iso- 

 tope to very high levels. The zinc content of 

 fresh oyster tissue measured almost 170,000y 

 per gram. This represents a concentration fac- 

 tor of 17,000, since the zinc concentration of 

 the sea water in which the oysters lived was 

 about 10 mcgm/1. 



Ruthenium^''^ was one of the separated fis- 

 sion products used to study the uptake of par- 

 ticulate radioisotopes by organisms in the sec- 

 ond trophic level. Ruthenium was co-precipi- 

 tated with calcium carbonate, dried, and ground 



TABLE 4 Distribution of Zn*^ in the Organs of 

 The Bay Scallop After a Two Hour Immersion 



Tissue miic Zn®^/g. Total m/tc 



Kidney 1384 824 



Liver 243 507 



Gills 218 857 



Testes and ovaries 138 193 



Foot 131 25 



Rectum 120 8 



Heart 105 13 



Adductor muscle 100 375 



Mantle 92 321 



