Characterizing vertical migration of Cs in organic layer and mineral soil in Japanese forests; Four-year observation and model analysis

Muto, Kotomi; Atarashi-Andoh, Mariko; Matsunaga, Takeshi*; Koarashi, Jun

Journal of Environmental Radioactivity, 208-209, p.106040_1 - 106040_10, 2019/11

https://doi.org/10.1016/j.jenvrad.2019.106040

Vertical distributions of Cs in the soil profile were observed at five forest sites with different vegetation types for 4.4 years after the Fukushima Dai-ichi Nuclear Power Plant accident, and Cs migration in the organic layer and mineral soil was analyzed based on a comparison of models and observations. Cesium-137 migration from the organic layer was faster than that observed in European forests, suggesting that the mobility and bioavailability of Cs could be suppressed rapidly in Japanese forests. The diffusion coefficients of Cs in the mineral soil were estimated to be 0.042-0.55 cmy, which were roughly comparable with those of European forest soils affected by the Chernobyl Nuclear Power Plant accident. Model predictions indicated Cs mainly distributed in the surface mineral soil at 10 years after the accident. It suggest that the Cs deposited onto Japanese forest ecosystems will be retained in the surface layers of mineral soil for a long time.

Radiocesium distribution in aggregate-size fractions of cropland and forest soils affected by the Fukushima nuclear accident

Koarashi, Jun; Nishimura, Shusaku; Atarashi-Andoh, Mariko; Matsunaga, Takeshi*; Sato, Tsutomu*; Nagao, Seiya*

Chemosphere, 205, p.147 - 155, 2018/08

https://doi.org/10.1016/j.chemosphere.2018.04.092

There is little understanding of how soil aggregation can affect the mobility and bioavailability of Cs in soils. To explore this, soil samples were collected at seven sites under different land-use conditions in Fukushima and were separated into four aggregate-size fractions. The fractions were then analyzed for Cs content and extractability and mineral composition. In forest soils, aggregate formation was significant, and Cs was largely associated with large-sized aggregates. In contrast, there was less aggregation in agricultural field soils, and most of Cs was in the clay- and silt-sized fractions. Across all sites, the Cs extractability was higher in the large-sized aggregate fractions than in the clay-sized fractions. The results demonstrate that large-sized aggregates are a significant reservoir of potentially mobile and bioavailable Cs in organic-rich (forest and orchard) soils.

Vertical distributions of global fallout Cs and C in a Japanese forest soil profile and their implications for the fate and migration processes of Fukushima-derived Cs

Koarashi, Jun; Atarashi-Andoh, Mariko; Amano, Hikaru*; Matsunaga, Takeshi

Journal of Radioanalytical and Nuclear Chemistry, 311(1), p.473 - 481, 2017/01

https://doi.org/10.1007/s10967-016-4938-7

Vertical distributions of global fallout Cs and C were investigated in a Japanese forest soil in 2001. Even 38 years after the fallout, Cs was still observed mostly in the uppermost 5 cm. A preferential accumulation of Cs was found in a 1-cm-thick transition layer between organic-rich A and underlying B horizons. This unique observation indicated that Cs migrated through the A horizon at a rate of 0.20% y and the transition layer acted as a barrier for Cs migration to deeper layers. The vertical distributions of Cs and C were significantly correlated, suggesting a coupled downward migration of Cs and organic matter on a time scale of decades, along the same physical pathways.

Year-round variations in the fluvial transport load of particulate Cs in a forested catchment affected by the Fukushima Daiichi Nuclear Power Plant accident

Matsunaga, Takeshi; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Muto, Kotomi; Tsuzuki, Katsunori; Nishimura, Shusaku; Koarashi, Jun; Otosaka, Shigeyoshi; Sato, Tsutomu*; et al.

Journal of Radioanalytical and Nuclear Chemistry, 310(2), p.679 - 693, 2016/11

AA2015-0821.pdf:3.78MB

https://doi.org/10.1007/s10967-016-4840-3

Particulate Cs in stream water was collected continuously for two years in order to assess the long-term trend of the Cs discharge from the forest environment. Sampling was conducted from December 2011 to December 2013 in a mountainous stream, which received the Cs from the Fukushima Daiichi Nuclear Power Plant accident. A seasonal increase in fluvial transport load of particulate Cs associated with suspended solids (SS) was observed in August and September when rainfall was abundant. The particulate Cs concentration decreased at a faster rate than the rate due to radioactive decay. This decrease might be resulted from redistribution of the easily eroded and polluted soil surface due to heavy rain events such as typhoons. These findings indicate that the particulate Cs load was subject to the inter-annual variations in rainfalls, and decreased gradually over a long period of time due to a decrease in Cs concentration in SS.

Catchment-scale distribution of radiocesium air dose rate in a mountainous deciduous forest and its relation to topography

Atarashi-Andoh, Mariko; Koarashi, Jun; Takeuchi, Erina; Tsuzuki, Katsunori; Nishimura, Shusaku; Matsunaga, Takeshi

Journal of Environmental Radioactivity, 147, p.1 - 7, 2015/09

AA2014-0585.pdf:2.18MB

https://doi.org/10.1016/j.jenvrad.2015.05.004

We collected a large amount of radiocesium air dose rate data by mountain-walking with a small -ray survey system, KURAMA-II, to create an air dose rate map of a mountainous deciduous forest that received radiocesium from the Fukushima Dai-ichi Nuclear Power Plant accident. Measurements were conducted in a small stream catchment 0.6 km in size in August and September 2013, and the relationship between air dose rates and the mountainous topography was examined. Air dose rates increased with elevation, suggesting that more radiocesium was deposited on ridges, and that it had remained there for 2.5 years with no significant migration due to soil erosion or water drainage. Slope aspect also strongly affected air dose rates. By the continuous measurement using KURAMA-II, we describe the variation in air dose rates in a mountainous area and suggest that it is important to consider topography when selecting sampling points to estimating dose rates or contaminant deposition.

A Passive collection system for whole size fractions in river suspended solids

Matsunaga, Takeshi; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Tsuzuki, Katsunori; Nishimura, Shusaku; Koarashi, Jun; Otosaka, Shigeyoshi; Sato, Tsutomu*; Nagao, Seiya*

Journal of Radioanalytical and Nuclear Chemistry, 303(2), p.1291 - 1295, 2015/02

https://doi.org/10.1007/s10967-014-3491-5

An innovative, yet simple method for the passive collection of radioactive materials in river water has been developed and validated. The method employes large filter vessels, containing multiple cartridge filters. River water is led to the system naturally using a drop of the riverbed by hose from upstream. This method makes long-term, unmanned monitoring possible. In addition to regular radioactivity analyses, this method provides an opportunity for the characterization of suspended materials based on its ample collection quantities (more than several tens of grams). This method may also be applicable to sediment-bound chemicals.

Temporal variations in metal enrichment in suspended particulate matter during rainfall events in a rural stream

Matsunaga, Takeshi; Tsuzuki, Katsunori; Yanase, Nobuyuki; Kritsananuwat, R.*; Ueno, Takashi; Hanzawa, Yukiko; Naganawa, Hirochika

Limnology, 15(1), p.13 - 25, 2014/01

https://doi.org/10.1007/s10201-013-0409-9

We studied a discharge of heavy metals/metalloids in rainfall events to a rural stream in Kuji River basin of central Japan. In terms of elemental enrichment with respect to the crustal composition, we found similarity between atmospheric deposits and suspended particulate matter (SPM) at a rural stream. Both exhibited distinctive enrichment in several metals (Ni, Cu, Pb, Sb, and Cd). Elemental analysis of SPM in the stream in rainfall events at short intervals revealed that the metal enrichment factors in SPM were progressively decreased with an increase of flow rate. Judging from features of SPM, this phenomenon was probably caused by alternative change of SPM matrices from upper soil constituents to more lithologic material with increasing stream flow rate. In quantification of respective contributions of metals of different origins to fluvial discharge, change of SPM matrices during a rainfall event and involvement of dissolved fraction need to be taken into consideration.

Retention of potentially mobile radiocesium in forest surface soils affected by the Fukushima nuclear accident

Koarashi, Jun; Moriya, Koichi*; Atarashi-Andoh, Mariko; Matsunaga, Takeshi; Fujita, Hiroki; Nagaoka, Mika

Scientific Reports (Internet), 2, p.1005_1 - 1005_5, 2012/12

https://doi.org/10.1038/srep01005

The fate of Cs derived from the Fukushima nuclear accident fallout and associated radiological hazards are largely dependent on its mobility in the surface soils of forest ecosystems. Thus, we quantified microbial and adsorptive retentions of Cs in forest surface (0-3 cm) soils. The KSO extraction process liberated 2.1%-12.8% of the total Cs from the soils. Two soils with a higher content of clay- and silt-sized particles, organic carbon content, and cation exchange capacity showed higher Cs extractability. Microbial biomass was observed in all of the soils. However, the Cs extractability did not increase after destruction of the microbial biomass by chloroform fumigation, providing no evidence for microbial retention of the Fukushima-fallout Cs. The results indicate that uptake of Cs by soil microorganisms is less important for retention of potentially mobile Cs in the forest surface soils compared to ion-exchange adsorption on non-specific sites provided by abiotic components.

Migration of atmospherically derived radionuclides in river systems; Findings from researches related to the Chernobyl accidents and nuclear weapon tests

Matsunaga, Takeshi; Tkachenko, Y.*

Nihon Genshiryoku Gakkai-Shi ATOMO, 53(10), p.684 - 688, 2011/10

https://doi.org/10.3327/jaesjb.53.10_684

Features of radionuclides migration behavior in river systems have been summarized. Referred researches are those related to the global fallout due to weapon tests and the fallout due the Chernobyl accident. This summary aims to serve to provide basic findings on an occasion of the Fukushima nuclear accident. Migration of radionuclides in river systems is a persistent process including various time scale events. Differences by radionuclides appear clearly in their input fractions from the ground, and also in their long-range transport. For river systems' contamination, it is considered that countermeasures at stages of water treatment and aquatic food intake. Several decision support systems, which compare effectiveness and adverse effects of various countermeasures, must be very useful to examine that applicability comprehensively.

Environmental behavior of plutonium isotopes studied in the area affected by the Chernobyl accident

Matsunaga, Takeshi; Nagao, Seiya*

Humic Substances Research, 5/6(1), p.19 - 33, 2009/00

The environmental behavior of Chernobyl-derived plutonium has been reviewed in the soil and the aquatic environment in Ukrainian affected areas. Dissolution of released fuel particles was an initiation for migration in the environment for the Chernobyl-derived plutonium. Once dissolved, the plutonium distributed persistently over surface soil layer with a limited infiltration ability. This relative immobility of plutonium in the soil environment can be attributed to its affinity for soil organics, based on chemical partitioning investigations. The relative immobility of plutonium was also seen in its fluvial transport along the Dnieper River. Dissolved organic matter, most probably humic substances, helped stabilize dissolved plutonium in the lake waters.