82 



Atomic Radiation and Oceanography and Fisheries 



it is evident that at low concentrations all the 

 zinc was removed after about four days. The 

 lowest concentration used was still ten times 

 higher than the average zinc concentration of 

 sea water. 



The rate of uptake of zinc"^ by Nitzschia 

 cells is shown in Figure 2. At the normal con- 



FiGURE 2. Uptake of Zinc^^ by Nitzschia Cells 

 from Culture Medium Containing 10 Micrograms of 

 Zinc/Liter. 



centration of zinc in sea water, a dividing cul- 

 ture of Nitzschia depleted the zinc'^'' in a closed 

 system in less than one day. Apparently phyto- 

 plankton cells concentrate zinc relative to sea 

 water and any radioactive zinc present in the 

 water will be quickly taken up in large amounts. 

 The radioisotopes so far discussed are very 

 likely always ionic in sea water. Ruthenium 

 solution, however, forms colloids and particles 

 when put into sea water. Ruthenium^o*^ ob- 

 tained as an acid solution from Oak Ridge was 

 added to a sea water culture of Nitzschia cells. 

 Figure 3 shows that the cells continued to take 

 up the ruthenium for the 12 days of the experi- 

 ment. Tlie amount of ruthenium per cell de- 

 creased, however, since the cells of the culture 

 were dividing continually. One may conclude 

 from this experiment, that since the ruthenium 

 concentration in sea water is low, dividing 

 planktonic algae would take up large amounts 

 of any radioactive ruthenium present. 



Second trophic level 



The work reported in this section was also 

 done at the R.L.F.W.S. Larvae of the brine 

 shrimp Artemia were put into filtered sea water 

 containing radiostrontium and the daughter 



Figure 3. Uptake of Ru^*^ by Nitzschia Cultures 

 in the Light. 



yttrium^". These larvae rapidly took up the 

 SR*^-Sr^°Y^° and reached an apparent steady- 

 state in a few hours. After exposure of the or- 

 ganisms to the isotopes for one day, it was 

 found that the amount of radioactivity /g of 

 Artemia was only 70 per cent of that of an 

 equal weight of the sea water. A count of the 

 samples 30 days after their preparation indi- 

 cated that a considerable amount of Y°^ was 

 taken up. Other crustaceans used were the 

 shrimp Penaeus setiferus and the edible blue 

 crab Callinectes sapidtis. The molluscan shell- 

 fish studied included oysters (Crassostrea vir- 

 ginica), clams (Venus mercenaria), and scal- 

 lops (Pecten irradians) . 



All of these organisms accumulated stron- 

 tium rapidly from sea water. The internal dis- 

 tribution of strontium in oysters is shown in 

 Table 3. This table indicates that the bulk of 

 the radioactivity accumulates in the shell. When 



TABLE 3 Distribution of Radioactivity in 



Oysters Following Exposure to Sea 



Water Containing Sr-' 



Per cent Per cent Per cent 



of total of total of soft 



Tissues weight activity tissues 



Mantle 2.5 4.1 25.0 



Gills 1.7 3.1 17.5 



Adductor 



muscle 1.9 2.4 19-2 



Other 3.8 5.1 38.3 



Total soft 



tissues 9.9 14.7 — 



Shell 90.1 85.3 — 



Per cent 

 of 



activity 

 of soft 

 tissues 



27.7 



21.2 



16.2 

 34.9 



