Elucidation of actual process of radiocesium ageing in soil by isotope ratio analysis

2021 Fiscal Year Final Research Report

• Project/Area Number: 18K18211
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 64010:Environmental load and risk assessment-related
• Research Institution: National Agriculture and Food Research Organization
• Principal Investigator: Wakabayashi Shokichi 国立研究開発法人農業・食品産業技術総合研究機構, 東北農業研究センター, 主任研究員 (80707654)
• Project Period (FY): 2018-04-01 – 2022-03-31
• Keywords: 農地土壌 / 放射性セシウム / エイジング / 同位体比 / 交換性画分

Outline of Final Research Achievements

Radioactive cesium (137Cs) deposited in soil becomes fixed to the interlayer of micaceous minerals over time and becomes less leachable. This phenomenon is called as the "ageing" of soil 137Cs. This study investigated the process of the ageing after the accident at the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant using a new analytical index (137Cs/133Cs ratio in exchangeable fraction). Analyzing the dynamics of the index in many farmlands, the progression rate of long-term ageing (the decline rate of 137Cs/133Cs ratio in exchangeable fraction) was evaluated as 0.04 /y on average and 0.07 /y at the maximum. Additionally, some analytical results indicated that there were differences in the ageing progress between upland fields and paddy fields, and that soil potassium fertility affected the behavior of 137Cs.

Free Research Field

土壌学

Academic Significance and Societal Importance of the Research Achievements

土壌中における放射性セシウムのエイジングは、農作物の汚染リスクが時間経過とともにどの程度低減するかを見積もる上で重要である。本研究で評価したエイジングの進行速度に、土壌中の放射性セシウム濃度の減少速度（放射性壊変や土壌からの溶脱による）を評価し加算することで、農作物の汚染リスク（ある条件下で栽培された農作物の放射性セシウム濃度）の経年変化を見積もることができる。農作物の放射性セシウム濃度が基準値を超過することを中長期にわたり防ぐ上で、汚染リスクが過去に比べてどの程度低下したかを見積もることは、今後の対策や調査の必要性・規模について議論するための判断材料となる。