Equilibrium of radiocesium with stable cesium within the biological cycle of contaminated forest ecosystems

Concentrations of 137Cs and stable Cs were determined in plant, mushroom, lichen and soil samples collected at two forest sites with different contamination levels in Belarus in 1998. The concentration of 137Cs in soil was the highest in near-surface organic layers (Of and Oh horizons) and decreased with depth in the mineral layers, whereas the concentrations of stable Cs were almost constant in the soil profile. The levels of 137Cs and stable Cs in biological samples varied depending both on the species and the plant part sampled. Even though different species and parts of the same species were included, the concentration ratios of 137Cs to stable Cs were fairly constant for samples collected at the same forest site, and were in the same order of magnitude as the 137Cs to stable Cs ratios for the organic soil layers. This finding suggests that 137Cs, mainly deposited on the forest ecosystems from the Chernobyl accident in 1986, was well mixed with stable Cs within the biological cycle in the forest ecosystems by 1998. The transfer factor for each biological sample of 137Cs was almost the same as that of stable Cs, if they were calculated based on the concentrations in the Of+Oh layer. This suggests that the stable-Cs-based transfer factor could be used as equilibrium transfer factor of 137Cs for different types of biological samples in the forest