Presentation Soil to crop transfer factor of plutonium: a field study in Japan

王, 鍾堂  ,  鄭, 建  ,  曹, 立国  ,  田上, 恵子  ,  内田, 滋夫

Plutonium was introduced into the environment by human nuclear activities. Due to its long half-life and high chemical toxicity, it is important to study the soil to crop transfer of Pu for the purpose of radiological assessment because ingestion is one of the most important pathways to transfer Pu into the human body. However, very limited soil-to-crop transfer factor (TF) data of Pu has been ever reported. In this study, for the first time, crop samples (vegetable, fruit and rice) and their corresponding soil samples were collected from 6 prefectures in Japan to obtain TF of Pu.In the experiment, Pu was separated and purified from the samples by a two-stage anion chromatographic method. Finally, Pu isotopes were analyzed by a sector field inductively coupled plasma mass spectrometry (SF-ICP-MS, Thermo Fisher Scientific, Element XR) using an Apex-Q sample introduction system.The results of SF-ICP-MS measurement showed that the 240Pu/239Pu atom ratios of studied soil samples ranged from 0.160-0.197, indicating that global fallout is the main Pu source; thus Pu has been contacted with soil for about 50y. Soil to crop transfer factors of Pu were further calculated based on the 239Pu concentrations in crop and soil. The obtained soil to rice grain TFs (in a dry weight basis) in the present study, which are in a range of 2.0E-5 to 8.2E-5, were the first data-set on soil to rice of Pu ever reported for Japanese soil. For vegetable and fruit, the determined TF of Pu was an order of magnitude higher than TF of rice, in the range from 1.1E-4 to 7.5E-4.In general, the obtained soil to rice TFs of Pu in this study ranged from 2.0E-5 to 8.2E-5, which were an order of magnitude higher than those for vegetable and fruit: 1.1E-4 to 7.5E-4. In general, the soil to crop TF data of Pu reported in this study improved the present Pu TF database to some extent. However, more data should be obtained in further studies concerning the status of the absence of TF data for some species and the necessity of improving the representativeness of the existed data.

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