Phytoavailability of 137Cs and stable Cs in soils from different parent materials in Fukushima, Japan

Publication date: March 2019

Source: Journal of Environmental Radioactivity, Volume 198

Author(s): Sho Ogasawara, Tetsuya Eguchi, Atsushi Nakao, Shigeto Fujimura, Yoshihiko Takahashi, Hisaya Matsunami, Hirofumi Tsukada, Junta Yanai, Takuro Shinano

Abstract

Weathered micaceous minerals (micas) are able to release potassium ion (K⁺) and fix caesium-137 (¹³⁷Cs), both of which reduce soil-to-plant transfer of ¹³⁷Cs. Among micas, trioctahedral micas such as biotite is expected to have a stronger ability to supply nonexchangeable K⁺ and a higher amount of Cs fixation sites than dioctahedral micas such as illite. Although biotite is predominant in granitic soils (G soils), illite is mainly dominant in sedimentary rock soils (S soils). Therefore, we hypothesized that G soils have a lower ¹³⁷Cs transfer risk than S soils because of this difference in mineralogy. The objective of the present study was to determine the transfer factor (TF) of ¹³⁷Cs and stable Cs (SCs) and to elucidate the determinant factors of TFs for G and S soils in Fukushima, Japan. Pot experiments were carried out with rice (Oryza sativa L. cv. Hokuriku 193) in G and S soils to determine the TF of ¹³⁷Cs (TF-¹³⁷Cs) and stable Cs (TF-SCs) under K-deficient conditions. TF-¹³⁷Cs and TF-SCs were highly correlated, and both were significantly lower for G soils than for S soils. Higher TF values were shown for soils with lower amounts of exchangeable and nonexchangeable K or with higher percentages of exchangeable ¹³⁷Cs (ex¹³⁷Cs). The percentage of ex¹³⁷Cs was negatively correlated with the amount of Cs fixation sites, represented by the radiocaesium interception potential. Thus, we concluded that smaller TF values for G soils were caused by a stronger ability to supply nonexchangeable K⁺ and a higher amount of Cs fixation sites. These findings will contribute to the establishment of soil screening techniques based on ¹³⁷Cs transfer risk in Fukushima prefecture.

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