Cesium-137 contamination of oak (Quercus petrae Liebl.) from sub-mediterranean zone in South Bulgaria |
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Authors: | Miglena Zhiyanski Maria Sokolovska Alexandros Clouvas Viktor Badulin |
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Institution: | a Forest Ecology Department, Forest Research Institute, BAS, 132 Kliment Ohridski Blvd., 1756 Sofia, Bulgaria b Faculty of Biology, University of Barcelona, 645 Diagonal Blvd., Barcelona, Spain c Nuclear Technology Laboratory, Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, GR 54124 Thessaloniki, Greece d Institute for Nuclear Research and Nuclear Energy, 72 Tzarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria e National Centre of Radiobiology and Radiation Protection, Ministry of Health, 132 Kliment Ohridski Blvd., 1756 Sofia, Bulgaria |
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Abstract: | This study focuses on the cesium-137 (137Cs) contamination in grass and in different compartments of oak trees growing in ecosystems, located in the zone with sub-mediterranean climate in South Bulgaria, characterized with high summer temperatures, low precipitation and often periods of drought. In 2008, three experimental sites - PP1, PP2, PP3 - were sampled in oak ecosystems from Maleshevska Mountain at 900 m above sea level. Samples from grass species and oak tree leaves, branches with different diameter, wood disks and bark were analyzed for 137Cs activity with γ-spectrometry. The soil-to-plant transfer factor (TF) values for 137Cs were estimated differentiating different tree compartments. Our findings showed relatively high activity concentrations of 137Cs in oak trees even 22 years after the Chernobyl accident. The grass under oak was less contaminated compared with the oak trees. The different organs of oak trees could be distinguished according to the 137Cs contamination as follows: bark > branches (d < 1 cm) > leaves > branches (d > 3 cm) > wood. The relatively higher contamination of bark compared with the new-formed biomass suggested that a significant part of 137Cs was accumulated as a result of direct adsorption at the time of the main contamination event. The TF values obtained and the presence of 137Cs in the branches, leaves and in the wood formed after 1986 confirmed that 22 years after the contamination, the main mechanism of 137Cs entrance in tree biomass was the root uptake. |
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Keywords: | Caesium-137 Transfer factor Oak tree compartments Grass vegetation South Bulgaria |
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