Effectiveness of non-exchangeable potassium quantified by mild tetraphenyl‑boron extraction in estimating radiocesium transfer to soybean in Fukushima

• Published in: The Science of the total environment 2022-05, Vol.820, p.153119, Article 153119
• Main Authors: Wakabayashi, Shokichi, Eguchi, Tetsuya, Nakao, Atsushi, Azuma, Kazuki, Fujimura, Shigeto, Kubo, Katashi, Saito, Masaaki, Matsunami, Hisaya, Yanai, Junta
• Format: Article
• Language: English
• Subjects: Boron - analysis; Cesium Radioisotopes - analysis; Fixation; Fukushima; Fukushima Nuclear Accident; Glycine max; Japan; Non-exchangeable potassium; Potassium - analysis; Radiation Monitoring; Radiocesium; Soil Pollutants, Radioactive - analysis; Soybean; Tetraphenyl‑boron
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.153119

Non-exchangeable K released from soil minerals can reduce radiocesium transfer to plants, as well as exchangeable K. We investigated the effect of non-exchangeable K on radiocesium transfer to soybean, and the non-exchangeable K extraction method most suitable for estimating the transfer risk. In Fukushima Prefecture, Japan, 106 soils were collected from 89 soybean fields during 2014–2018 to analyze non-exchangeable K contents using three methods: boiling nitric acid extraction, tetraphenyl‑boron extraction, and mild tetraphenyl‑boron extraction. The non-exchangeable K contents quantified by the former two methods were dependent on the amount of micas, which are K-bearing minerals. The non-exchangeable K content by mild tetraphenyl‑boron extraction depended on the amount of K fertilizer application and K-fixing minerals but not on micas, indicating that it reflects fertilizer K fixed by the minerals. The soil-to-plant transfer factor of radiocesium was most correlated with the non-exchangeable K content by the mild extraction (rs = −0.67). This correlation was also stronger than that between exchangeable K and the transfer factor (rs = −0.40). As non-exchangeable K content increased, the exchangeable radiocesium fraction decreased, indicating that radiocesium was fixed together with K. Additionally, multiple regression analysis indicated that non-exchangeable K by the mild extraction significantly decreased the transfer factor even if the exchangeable radiocesium fraction was kept constant. Thus, the fixed K was considered to repress radiocesium transfer to soybean through both radiocesium fixation and K supply. With the criterion of total extracted K, the sum of exchangeable and non-exchangeable K, as 65 mg K2O 100 g−1 by the mild extraction, fields with high and low transfer factors were able to be differentiated more effectively than with a current criterion of exchangeable K as 50 mg K2O 100 g−1. The results revealed that mild tetraphenyl‑boron extraction is effective for estimating radiocesium transfer to soybean. [Display omitted] •Ne-K content analysis by 3 methods showed varied patterns in Fukushima soils.•Ne-K by TPBM method was the most correlated with radiocesium transfer to soybean.•TPBM-Ne-K content increased, reflecting K fixation, causing radiocesium fixation.•Fixed K repressed radiocesium transfer to soybean through fixation and K supply.•TPBM extraction method effectively estimated radiocesium transfer risk to soybean.