In additLon to biological controls, the medium was checked sorption on 

 the flask walls and MF filters. Ten ml aliquots of cell-free medium containing 

 the various concentrations of radioisotopes were filtered through Millipore 

 filter pads. Each filter was washed with ten milliliters of distilled water 

 before drying. All dried filter pads were counted with a thin mica window 

 Geiger-Mueller tube using either an Atomic or Berkley Scaler. 



Because of the great differences in decay rates and beta energies between 

 Sr90 and Y90 it was possible to determine the differences in selectivity by 

 the cells. Counts were made on each filter disc with an without an aluminum 

 absorber. An aluminum absorber of222.7 milligrams per square centimeter was 

 used. It was determined that all the counts from Sr wer absorbed while 32.9% 

 of the Y was counted. Periodic counts were made on the filters with the final 

 count on the 35th day after filtration. After 35 days the Y which had been 

 retained by cells had decayed to less than 1/ 1000th and the Sr retained had 

 again reached secular equilibrium. 



Before proceeding with the uptake study using the radioisotope Cs-137, 

 a preliminary investigation was made of the retention of this Isotope on 

 Millipore filter discs. Since differences in counts on Millipore filter discs 

 has been noted in the Sr-Y study, the investigation was to determine whether 

 these differences In counts were due to differences In retention of the cells 

 or the ions. To determine whether or not there was any differences in cell 

 retention by the filter discs, multiple aliquots of two unlalgal cultures G. 

 s imp lex and D. tert iolecta were filtered onto Millipore filter discs. The 

 chlorophyll a was extracted and was used as an index of Phytoplankton retention, 

 The coefficient of variation for G. simplex was 8.6 and for D. tertiolecta 

 was 11.8. From this It was concluded that the differences noted were not 

 from phytoplankton retention but from the variation in amounts of radioisotope 



-6- 



