Adsorption of radionuclides on silica and their uptake by rice plants from silica-multitracer solutions: the effects of pH.

We investigated the effect of solution pH on the adsorption on silica of a mixture radionuclides 83Rb, 85Sr, 54Mn, 65Zn, 88Y, and 75Se generated from irradiation of Ag in a 135-MeV/nucleon 12C beam accelerated by the RIKEN Ring Cyclotron and 137Cs obtained commercially. Then, we related these findings to their uptake by a rice plant (Oryza sativa L. cv. Koshihikari) from a silica-multitracer solution at pH 4.3 +/- 0.2 and at 5.3 +/- 0.2. To evaluate both adsorption and uptake, precisely we used a multitracer technique that simultaneously tracked the movements of all of the radionuclides. There was an increase in the uptake of Rb, Cs, Sr, Mn, and Zn by the rice plants with the increase in pH from 4.3 to 5.3. By contrast, the uptake of Y and Se was less at the higher pH. Our findings suggest that the uptake of these elements is governed by their transport systems on the plasma membrane and by their affinity to silica, both of which are regulated by H+ concentration.