Root intake of 137Cs in pasture grasses

The accumulation of ¹³⁷Cs in plants can carry risks to animal and human health due to its entry into the body through the food chain. The purpose of the study was to estimate the transition coefficients 137Cs in pasture mixed grasses from the dominant soil types of Ukraine and their dynamics during the growing season. The experiment was conducted on three types of soils, namely: sod-podzolic loam, podzolic chernozem, and typical chernozem. Soils for the experiment were selected in the Kyiv and Zhytomyr oblasts. The density of artificial surface contamination of all soils was the same and amounted to 336 kBq m-2. Radionuclide was applied to the soil surface in a water-soluble form. The plants were grown in a greenhouse in pots with regular watering without fertilisation. The results obtained showed that bioavailability of 137Cs is determined by soil conditions and significantly decreases in the series: sod-podzolic soil > podzolic chernozem > typical chernozem. The obtained average values of the radionuclide transition coefficients to grass for the first mowing ranged from 50 to 4 (Bq·kg-1) /(kBq·m-2) and were maximal for sod-podzolic soil. At the end of the growing season, bioavailability of 137Cs significantly decreased by half for sod-podzolic soil and typical chernozem. No significant changes in the bioavailability of radionuclide were observed on podzolic chernozem. The accumulation coefficients of the stable isotope of caesium (133Cs) are estimated. Compared to the radioactive isotope, stable caesium is characterised by significantly lower bioavailability for plants, but the nature of its dependence on soil conditions is identical to that of 137Cs. Since stable caesium is in the soil in a state of equilibrium, the coefficients of its accumulation by the mixture of grasses did not change during the growing season. The obtained transition parameters, in accordance with soil conditions, can be used in radiological models for conservative estimation of radiation doses of radiation exposure to the population in the first year after radionuclide entry into the environment