Soil to rice transfer factors of plutonium: a field study in Japan

Plutonium has been introduced into the environment by nuclear activities. Due to its long half-life and high chemical toxicity, it is important to study the soil to rice 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-rice transfer factor (TF) data of Pu has been ever reported. In this study rice samples and their corresponding soil samples were collected from 5 prefectures in Japan to obtain TF of Pu. After sampling, 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 using an Apex-Q sample introduction system. The results showed that the 240Pu/239Pu atom ratios of studied soil samples ranged from 0.160-0.182, indicating that global fallout is the main Pu source; thus Pu has been contacted with soil for about 50 yr. TFs of Pu were further calculated based on the 239Pu concentrations in rice and soil. The obtained TFs (in a dry weight basis) were in a range of 2.0 × 10-5 to 8.2 × 10-5. TF for rice reported in this study improved the present Pu TF database by supplementing 5 new data; however, more data should be obtained in further studies concerning the necessity of improving the representativeness of the existed data