Transfer of ¹³⁷Cs into Maize (Zea mays L.) at Different Growth Stages in the Area Contaminated by the Chernobyl Fallout

Accumulation of radionuclides in crop products can pose public health risks. Parameters of ¹³⁷Cs root uptake by maize were investigated at four growth stages, from leaf development to ripening (June-September), in the post-Chernobyl area of the Plavsk radioactive hotspot (the Tula region of Russia). It was established that the chernozem of the agrosystem still contains about 180 kBq ¹³⁷Cs m^-2. Seasonal trends of ¹³⁷Cs activity concentrations in above- and belowground parts of maize differ appreciably. In aerial parts, the ¹³⁷Cs accumulation rate increases as vegetative organs develop from June to July, then drops when generative organs appear in August. In the belowground biomass, the ¹³⁷Cs content increases with the growth of fine roots, which serve as relative concentrators of the radionuclide. However, at all stages of growth, radionuclide transfer to maize occurs with low intensity. It does not directly depend on changes in biomass, dry matter content, or ⁴⁰K content, and only slightly relates to the ash content. The transfer factor is estimated to be 6.2 × 10^-3 for cob kernels (grain) and 3.8 × 10^-2 for stems and leaves, which corresponds to the IAEA-recommended values and ensures acceptable levels of ¹³⁷Cs accumulation in crop products produced in the territory.