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Factors controlling the abilities of Allophanic Andosols (representative of Japanese volcanic ash soils) to retain radiocesium (RCs) were assessed. The hypothesis was that retention is largely controlled by traces of micaceous minerals deposited as components of aeolian dust. The radiocesium interception potentials (RIPs), mica K contents were determined in the 2- to 20- and <2.0-μm particle fractions of 23 soil samples from agricultural fields in areas representative of Japanese Allophanic Andosols. Quartz contents were determined in the 2- to 20-mm particle fractions of the same soil samples. The oxygen isotope ratio (δ18O) in the quartz isolated from each 2- to 20-mm particle fraction was determined to identify the origin of the quartz in each soil sample. The mean RIP for the 2- to 20- and <2-mm particles was 1.7 ± 0.8 and 2.6 ± 1.3 mol kg-1, respectively, and the mica K contents were 3.2 ± 1.3 and 3.4 ± 1.7 g kg-1, respectively, corresponding to micaceous mineral contents of <5% by mass in each size fraction. In spite of their rather low values, the RIPs and mica K contents in each fraction positively correlated (p < 0.01), indicating that the abilities of the soils to retain RCs were mainly controlled by the micaceous mineral contents. The mica K content was proportional to the quartz content in the <20-mm particles, and the mean δ18O in the quartz was +14.8‰, similar to those in fine quartz in Chinese loess. These results strongly indicate that the abilities of Allophanic Andosols to retain RCs are largely controlled by micaceous minerals probably originating in aeolian dust. [ABSTRACT FROM AUTHOR]

Sediment that has deposited after the flood generated by the 2019 typhoon (referred to as Flood Sediment, FS) was collected along two rivers in eastern Fukushima Prefecture, Japan to determine the total and exchangeable radiocesium (137Cs), and acid-extractable potassium (K) contents. Then, these FS parameters were compared with those of decontaminated soils (DS) in nearby agricultural fields to discuss the potential transfer risk of 137Cs from rivers to nearby remediated soils. While FS had about four times higher total 137Cs content, it showed a three-times lower exchangeable 137Cs content than DS. Furthermore, acid-extractable K referred to as non-exchangeable K (Nex-K) content was high enough to restrict 137Cs transfer from soil to crops for both FS and DS. From these comparisons, we concluded that deposition of FS onto DS may not increase the transfer of 137Cs from soil to crops. [ABSTRACT FROM AUTHOR]

The Fukushima nuclear accident inMarch 2011 generated a 3000 km² plume of soils heavily contaminated with 137Cs. Decontamination was completed early in 2019. Typhoon Hagibis was the first extreme event that occurred in the region after decontamination. Its impact on sediment sources and sediment 137Cs contamination was investigated through the application of a sediment fingerprinting procedure using spectrocolorimetry and geochemical properties. Sediment deposits (n = 24) were collected in the Mano and Niida River catchments after the 2019 typhoons, and their signature was compared to that of potential sources (e.g., cropland, forests, and subsurface; n = 57). Results demonstrate the dominance of cropland as the main source of sediment (mean: 54%) followed by forests (41%) with much lower contributions of subsurface material (5%). Overall, 137Cs concentrations in sedimentwere on average 84%--93%lower than the levels recorded after the accident in 2011, which demonstrates the effectiveness of cropland decontamination. [ABSTRACT FROM AUTHOR]