Horemans Nele, Nauts Robin, Vives I Batlle Jordi, Van Hees May, Jacobs Griet, Voorspoels Stefan, Gaschak Sergey, Nanba Kenji, Saenen Eline
Belgian Nuclear Research Centre (SCK•CEN), Biosphere Impact Studies, Boeretang 200, B-2400, Mol, Belgium; Centre for Environmental Research, University of Hasselt, Universiteitslaan 1, 3590, Diepenbeek, Belgium.
Belgian Nuclear Research Centre (SCK•CEN), Biosphere Impact Studies, Boeretang 200, B-2400, Mol, Belgium.
J Environ Radioact. 2018 Dec;192:405-416. doi: 10.1016/j.jenvrad.2018.07.012. Epub 2018 Jul 25.
The long-term radiological impact to the environment of the nuclear accidents in Chernobyl and Fukushima is still under discussion. In the course of spring of 2016 we sampled two Brassicacea plants, Arabidopsis thaliana and Capsella bursa-pastoris native to Ukraine and Japan, respectively, alongside a gradient of radiation within the exclusion and difficult to return zones of Chernobyl (CEZ) and Fukushima (FEZ). Ambient dose rates were similar for both sampling gradients ranging from 0.5 to 80 μGy/h at plant height. The hypothesis was tested whether a history of several generations of plants growing in enhanced radiation exposure conditions would have led to changes in genome-wide DNA methylation. However, no differences were found in the global percentage of 5-methylated cytosines in Capsella bursa pastoris plants sampled in FEZ. On the other hand a significant decrease in whole genome methylation percentage in Arabidopsis thaliana plants was found in CEZ mainly governed by the highest exposed plants. These data support a link between exposure to changed environmental conditions and changes genome methylation. In addition to methylation the activity concentration of different radionuclides, Cs, Sr, Am and Pu-238,239,240 for CEZ and Cs for FEZ, was analysed in both soil and plant samples. The ratio of 5.6 between Cs compared to Cs was as expected five years after the FEZ accident. For CEZ Cs is the most abundant polluting radionuclide in soil followed by Sr. Whereas Am and Pu-isotopes are only marginally present. In the plant tissue, however, higher levels of Sr than Cs were retrieved due to a high uptake of Sr in the plants. The Sr transfer factors ranged in CEZ from 5 to 20 (kg/kg) depending on the locality. Based on the activity concentrations of the different radionuclides the ERICA tool was used to estimate the total dose rates to the plants. It was found that for FEZ the doses was mainly contributable to the external Cs-isotopes and as such estimated total dose rates (0.13-38 μGy/h) were in the same range as the ambient measured dose rates. In strong contrast this was not true for CEZ where the total dose rate was mainly due to high uptake of the Sr leading to dose rates ranging from 1 to 370 μGy/h. Hence our data clearly indicate that not taking into account the internal contamination in CEZ will lead to considerable underestimation of the doses to the plants. Additionally they show that it is hard to compare the two nuclear accidental sites and one of the main reasons is the difference in contamination profile.
切尔诺贝利和福岛核事故对环境的长期放射性影响仍在讨论之中。2016年春季，我们分别在切尔诺贝利（CEZ）和福岛（FEZ）的禁区及难以返回区域内，沿着辐射梯度对两种十字花科植物进行了采样，这两种植物分别是原产于乌克兰的拟南芥和原产于日本的荠菜。两个采样梯度的环境剂量率相似，在植物高度处范围为0.5至80μGy/h。我们检验了一个假设，即几代植物在增强辐射暴露条件下生长的历史是否会导致全基因组DNA甲基化发生变化。然而，在FEZ采样的荠菜植物中，5 - 甲基化胞嘧啶的总体百分比未发现差异。另一方面，在CEZ中，主要是受最高暴露水平影响的拟南芥植物全基因组甲基化百分比显著下降。这些数据支持了暴露于变化的环境条件与基因组甲基化变化之间的联系。除了甲基化，还对CEZ的土壤和植物样本中不同放射性核素（铯、锶、镅和钚 - 238、239、240）以及FEZ的铯的活度浓度进行了分析。FEZ事故五年后，铯与铯的比值为5.6，符合预期。对于CEZ，土壤中污染最严重的放射性核素是铯，其次是锶。而镅和钚同位素仅微量存在。然而，在植物组织中，由于植物对锶的高吸收，回收的锶含量高于铯。在CEZ，锶的转移因子根据地点不同在5至20（kg/kg）之间。基于不同放射性核素的活度浓度，使用ERICA工具来估计植物的总剂量率。结果发现，对于FEZ，剂量主要归因于外部铯同位素，因此估计的总剂量率（0.13 - 38μGy/h）与测量的环境剂量率在同一范围内。与之形成强烈对比的是，CEZ并非如此，其总剂量率主要是由于对锶的高吸收导致剂量率范围为1至370μGy/h。因此，我们的数据清楚地表明，在CEZ中不考虑内部污染将导致对植物剂量的严重低估。此外，数据还表明，很难比较这两个核事故地点，主要原因之一是污染特征的差异。
