Long-term study on the transfer of 137Cs and 90Sr from Chernobyl-contaminated soils to grain crops

The level of 137Cs and 90Sr transfer to four grain crops and the change in transfer with time have been studied on two soils contaminated with fragments of nuclear fuel released during the Chernobyl accident. Field experiments were carried out in 1987–1994 inside the heavily contaminated zone around Chernobyl Nuclear Power Plant. Shortly after the deposition, the rate of 90Sr accumulation by crops was comparable with, or even slower, than that of 137Cs, which is in disagreement with the usual findings. In the following years, 137Cs uptake by plants was reduced by a factor in excess of than 50, whereas the soil-to-plant concentration ratio of 90Sr increased within one order of magnitude, and has remained on approximately the same level since 1991. Changes of the 90Sr and 137Cs concentration ratios for grain crops with time have been used to evaluate the rate of radionuclide leaching from fuel particles and the ageing processes.