Uptake of Radioactivity by Aquatic Plants and Location in the Cells I. THE EFFECT OF pH ON THE STRONTIUM-90 AND YTTRIUM-90 UPTAKE BY THE GREEN ALGAULVA LACTUCAAND THE EFFECT OF STABLE YTTRIUM ON YTTRIUM-90 UPTAKE

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Abstract
The uptake of strontium-90 and yttrium-90 by Ulva lactuca from sea water was measured over a period of 179 days. In sea water at normal pH (8.0) and without added carrier Ulva reached a strontium-90 equilibrium at 0.32 times the concentration in the water within 3 hrs, but rapidly depleted the water of yttrium-90. Addition of 0.15 ppm of non-radioactive (stable) yttrium led to the establishment of an yttrium-90 equilibrium within 3 hrs, with the Ulva having a concentration factor of 550. It was found that without added carrier the yttrium-90 remained on the outer surface of the plants, but when carrier was added the yttrium-90 taken up mainly entered the cells and was laid down in the protoplasmic inclusions. The strontium-90 was located only in the protoplasmic inclusion. Uptake was investigated in a pH range 5.1 to 8.0. Progressive reductions of pH from 8.0 to 6.5 led to a small increase in the amount of strontium-90 uptake but to large increase in the yttrium-90 uptake. However, in the pH range 5.8 to 5.1 the yttrium-90 uptake was greatly reduced. External pH below 6.0 caused death of the alga within 5 days. The effect of pH on strontium uptake is thought to be due to changes in equilibrium in the carbonate-bicarbonate system. The effects of pH and stable yttrium concentration on yttrium-90 uptake are discussed in terms of changes in the state of yttrium in the sea water, resulting in increased availability to the plant, and of changes in the nature of the plant surface resulting from its physiological response to lowered pH.

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