Behavior of radiocesium derived from irrigation water in paddy fields and its effects on radioactivity in rice

2021 Fiscal Year Final Research Report

• Project/Area Number: 19H03072
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 41030:Rural environmental engineering and planning-related
• Research Institution: Niigata University
• Principal Investigator: HARADA NAOKI 新潟大学, 自然科学系, 教授 (50452066)
• Co-Investigator(Kenkyū-buntansha): 吉川 夏樹 新潟大学, 自然科学系, 教授 (90447615) ; 鈴木 一輝 新潟大学, 研究推進機構, 助教 (40801775) ; 宮津 進 新潟大学, 自然科学系, 助教 (30757844)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 放射性セシウム / イネ / 水田 / 灌漑水 / 水口 / 懸濁態画分 / 溶存態画分

Outline of Final Research Achievements

The purpose of this study was to elucidate the mechanisms by which the inflow of irrigation water containing low concentrations of radiocesium (rCs) increases rCs concentration in rice plants near the water inlet. 137Cs in irrigation water was monitored in an agricultural channel in Hamadori district, Fukushima, and the stock of 137Cs in the water vegetation was estimated. The tracer experiment confirmed that dissolved 137Cs migrates from the base of rice plants to the paddy. 137Cs in the irrigation water-derived sediments added to the soil surface was shown to be absorbed by rice plants. A model rice field filled with non-contaminated soil installed in Namie Town showed the two-dimension deposition of 137Cs in irrigation water onto the soil surface. It was concluded that dissolved 137Cs bottomed up rice 137Cs concentration, while suspended 137Cs was transferred to rice plants after deposition on the soil surface near the water inlet, further increasing the rice 137Cs concentration.

Free Research Field

土壌学

Academic Significance and Societal Importance of the Research Achievements

本研究では，放射性セシウム(rCs)を低濃度に含む灌漑水の流入が有意に水口のイネのrCs濃度を高める原因の解明のため，現地調査と模型水田実験およびポット実験等に取り組んだ。その結果，灌漑水中に含まれる溶存態rCsは水口イネのrCs濃度のボトムアップ的な増加に寄与し，さらに懸濁態137Csが水口近傍の土壌表面に沈着後，イネに移行してそのrCs濃度をさらに上昇させることが示された。本研究により，灌漑水に含まれるrCsの水田内での詳細な動態とイネへ移行してそのrCs濃度の上昇に至るメカニズムが初めて明らかとなった。