Effect of humic acid on the bioavailability of radionuclides to rice plants

We investigated the effect of humic acid and solution pH on the uptake of the radionuclides, 83 Rb, 137 Cs, 54 Mn, 65 Zn, 88 Y, 102 Rh, and 75 Se in rice plants by the multitracer technique. The addition of humic acid to a culture medium containing SiO 2 increased the uptake of Mn and Zn at pH 4.3, whereas their uptake was decreased at pH 5.3. Humic acid depressed the uptake of Y at both pHs. The uptake of Se, which does not interact with humic acid, was not affected by its presence. These results suggest that uptake of the radionuclides by the rice plant is regulated by the affinity of radioactive nuclides for humic acid, as well as by the soil solution's pH.