Migration Of 137Cs Research Articles

A novel method to infer historical DDT use on Cape Cod, Massachusetts (USA), based on ΣDDT degradation and 210Pb dating in lake sediment cores

Dichlorodiphenyltrichloroethane was used on Cape Cod, Massachusetts (USA), for mosquito and gypsy moth mitigation, from 1948 until the insecticide was banned in the 1970s. There are historical accounts of major spray events, and DDT was expected to have remained immobile in the organic-rich sediments of local ponds. We investigated the potential for sediment cores from lakes on Cape Cod to reveal the depositional history of DDT. This compound and its metabolites dichlorodiphenyldichloroethane and dichlorodiphenyldichloroethylene (ΣDDT) were examined in sediment cores from four kettle lakes on Cape Cod that lie between the towns of Brewster and Harwich, where there is a detailed history of aerial spraying. Sediment cores were dated via 210Pb and analyzed for water content, total carbon, total organic carbon, and organochlorine pesticide concentrations. Use of fallout 137Cs to confirm 210Pb dates was unsuccessful, probably because of post-depositional migration of 137Cs. ΣDDT inventories in each lake were determined to be ~ 10 ng cm−2, which represents about 0.1% on an aerial basis of the quantity known to have been sprayed. Compared to the recorded spraying history, the concentration-depth maxima appear decades later than expected. The overall low quantity and unexpected temporal distribution of pesticide residues are probably explained by natural degradation of DDT in the sediment. A novel mathematical correction to DDT concentrations was applied and yielded adjusted inventories close to expected values, and moved the pesticide concentration maxima to the 1950s and 1960s, when they were expected to have occurred.

РАДІОАКТИВНЕ ЗАБРУДНЕННЯ 137СS МОХОВО-ЛИШАЙНИКОВОГО ПОКРИВУ В УМОВАХ СВІЖОГО СУБОРУ

Досліджено сучасне радіоактивне забруднення мохово-лишайникового покриву в умовах свіжого субору в лісах Українського Полісся. Щільність радіоактивного забруднення ґрунту в межах пробної площі варіювала у широких діапазонах – від 315 до 708 кБк/м2. Виявлено значні коливання величин питомої активності та показників інтенсивності надходження 137Cs для всіх досліджуваних видів зелених (брієвих) мохів та епігейних лишайників. Так, на пробній площі для дикрану багатоніжкового середній вміст 137Сs становив 11538±1022 Бк/кг; для плевроцію Шребера – 9312±679 Бк/кг. З'ясовано, що радіоактивне забруднення дикрану багатоніжкового істотно вище, ніж у плевроцію Шребера (в 1,2 раза). Концентрація 137Cs у лишайниках загалом змінювалась в широкому діапазоні – від 3975 до 9182 Бк/кг. Найменші значення вмісту 137Cs встановлено у кладонії м'якої, а найбільші – у кладонії дюймової. Коефіцієнт накопичення 137Cs для лишайників був у діапазоні від 3,2 до 6,5, а для зелених (брієвих) мохів – від 3,8 до 7,7. Коефіцієнт переходу 137Cs у лишайниках родини Кладонієвих змінювався від 11,8 до 24,4 м2·кг-1·10-3. За інтенсивністю накопичення 137Cs епігейні лишайники можна розмістити таким чином: кладонія дюймова > кладонія струнка > кладонія оленяча > кладонія м'яка. Щодо зелених мохів, то для дикрану багатоніжкового середній показник коефіцієнта переходу становив 29,2±0,9 м2·кг-1·10-3, майже в 2 рази більше, ніж для плевроцію Шребера – 16,3±0,06 м2·кг-1·10-3. Значення концентрації 137Сs у мохово-лишайниковому покриві має тісний лінійний зв'язок з величиною щільності радіоактивного забруднення ґрунту.

Отмирание воздушно-водных растений как фактор миграции 137Cs в водоемах

Отмирание воздушно-водных растений как фактор миграции 137Cs в водоемах

Parameters Affecting 137Cs Migration within Soil Profile

SEVERAL studies have been carried out on the adsorption, distribution and migration of 137Cs within soil profile in the vicinity of the Nuclear Research Center, Atomic Energy Authority, Egypt, in addition to Ismailia Canal areas. The soil physicochemical and mineralogical characteristics were carried out and indicated that the soil samples consist mainly of sand (quartz) and silt fractions. The kinetics of caesium adsorption and its related adsorption isotherms for the tested soils were also studied. The sorption of 137Cs by soil minerals markedly affects its migration rate. The natural background of both locations under study indicated that the 137Cs concentration in the reactor site were found to be 30.82 Bq/kg while that at the canal site was found to be 0.87 Bq/kg. 137Cs in the reactor site may be originated from the fallout and from the external contamination which affected the background level. The vertical distribution and the migration rate of 137Cs have been studied for the soil profiles in both locations. These rates were found to be 0.056 and 0.031 cm/year for the reactor and canal site respectively.

Vertical distribution of 137Cs in grassland soils disturbed by moles (Talpa europaea L.)

Activity of biota is one of the factors influencing vertical migration of radionuclides deposited from the atmosphere onto the ground surface. The goal of this work was to study the vertical distribution of 137Cs in grassland soils disturbed by moles (Talpa europaea L.) in comparison with undisturbed grassland soils. Field observations and soil sampling were carried out in the areas of eight settlements in the Klintsovskiy, Krasnogorskiy and Novozybkovskiy districts of the Bryansk region, Russia in six years during the period 1999–2016. The study sites had been heavily contaminated by Chernobyl fallout in 1986. Activity of 137Cs in soil samples was determined by γ-ray spectrometry. 137Cs surface ground contamination levels at the studied plots (n = 17) ranged from 327 kBq m−2 to 2360 kBq m−2 with a mean of 1000 kBq m−2 and a median of 700 kBq m−2. The position of the 137Cs migration centre in the soil in 2010–2016 was significantly (the Mann-Whitney U test, P < .01) deeper at mole-disturbed plots (median = 5.99 cm or 6.64 g cm−2, n = 6) compared to the undisturbed ones (median = 2.48 cm or 2.35 g cm−2, n = 6). The 137Cs migration rate at mole-disturbed plots (median = 0.26 g cm−2 y−1, mean = 0.31 g cm−2 y−1) was significantly higher (by a factor of 3) than at undisturbed plots (median = 0.08 g cm−2 y−1, mean = 0.10 g cm−2 y−1). The difference in the migration rates between the mole-disturbed and undisturbed plots (median = 0.18 g cm−2 y−1, mean = 0.21 g cm−2 y−1) reasonably corresponded to the mass of soil that might be ejected by moles per unit area per year. The results of this study indicate that the burrowing activity of moles has increased vertical migration of Chernobyl-derived radiocaesium in the grassland soils.

Radiocesium migration in the litter layer of different forest types in Fukushima, Japan

Cesium-137 (137Cs) migration in the litter layer consists of various processes, such as input via throughfall, output via litter decomposition, and input from deeper layers via soil organism activity. We conducted litter bag experiments over 2 years (December 2014–November 2016) to quantify the inputs and outputs of 137Cs in the litter layer in a Japanese cedar plantation (Cryptomeria japonica) and a mixed broadleaf forest dominated by Quercus serrata located 40 km northwest of the Fukushima Dai-ichi Nuclear Power Plant. The experiments included four conditions, combining contaminated and non-contaminated litter and deeper layer material, and the inputs and outputs were estimated from the combination of 137Cs increases and decreases in the litter layer under each condition. The 137Cs dynamics differed between the two forests. In the C. japonica forest, some 137Cs input via throughfall remained in the litter layer, and downward 137Cs flux passed through the litter layer was 0.42 (/year).Upward flux of 137Cs from the deeper layer was very restricted, < 0.017 (/year). In the broadleaf forest, migration of 137Cs in throughfall into deeper layers was restricted, downward 137Cs flux was less than 0.003 (/year).Upward input of 137Cs from the deeper layer was prominent, 0.037 (/year). 137Cs output via litter decomposition was observed in both forests. The flux in the C. japonica forest was slower than that in the broadleaf forest, 0.12 and 0.15 (/year), respectively.

Adaptive Capability of the VERT_MIG Algorithm to Simulate Vertical Migration of Radionuclides in Soils

The possibility of using the VERT_MIG algorithm in simulation models of the vertical migration of radionuclides in soil is discussed. The algorithm was successfully used to develop models of 137Cs and 90Sr migration for radioactive contamination of different soils as a result of the accidents at the Chernobyl and Fukushima-1 nuclear power plants. The modeling results are given. Prospects for further use of this algorithm and some aspects of using imitation modeling in this area are discussed.

Agricultural aspects of radiocontamination induced by the Fukushima nuclear accident - A survey of studies by the Univ. of Tokyo Agricultural Dept. (2011-2016).

Immediately after the Fukushima nuclear power plant accident, a team of 40–50 researchers at the Graduate School of Agricultural and Life Sciences at the University of Tokyo began to analyze the behavior of radioactive materials in the fallout regions. The fallout has remained in situ and become strongly adsorbed within the soil over time. 137Cs was found to bind strongly to the fine clay, weathered biotite, and organic matter in the soil; therefore, it has not mobilized from mountainous regions, even after heavy rainfall. In farmland, the quantity of 137Cs in the soil absorbed by crop plants was small. The downward migration of 137Cs in soil is now estimated at 1–2 mm/year. The intake of 137Cs by trees occurred through the bark and not from the roots. This report summarizes the findings of research across a wide variety of agricultural specialties.

Effect of mass of organic layers on variation in 137Cs distribution in soil in different forest types after the Fukushima nuclear accident

ABSTRACT Forests over a wide area were contaminated with radiocesium following the Fukushima nuclear accident in March 2011. Most radiocesium in the forests migrated into the soil a year after the accident and it is therefore necessary to clarify the distribution pattern of radiocesium in soil to evaluate the actual state and possible future changes of the radiocesium cycle in forest ecosystems. We investigated the stock and vertical distribution patterns of 137Cs in soil under evergreen and deciduous tree species from 2012 to 2014 in a mountainous area in Fukushima Prefecture. The 137Cs stock in soil was higher in evergreen forests than in deciduous forests. This was likely caused by the difference in tree leaf biomass at the time of the initial deposition, when deciduous trees were defoliated. The organic layer (particularly the humified layer) retained 137Cs in high concentration and stock, indicating limited migration of 137Cs into the mineral layer during the study period. This may reflect the incorporation of 137Cs into organic matter and the retention of fungi in the organic layer. Analyses of these data and those from other studies conducted in regions contaminated by the accident showed that the ratio of radiocesium stock in the organic layer to the total amount in soil was positively correlated with the mass of the organic layer (organic layers with a mass of >2.0 kg/m2 retained more than 50% of total radiocesium). Thus, the status of the organic layer is an important factor regulating the downward migration of radiocesium.

In-column immobilization of Cs-saturated crystalline silicotitanates using phenolic resins.

The in situ immobilization of granulated Cs-saturated crystalline silicotitanates (Cs-CST) in fixed-bed columns has been investigated using commercially available phenol formaldehyde (PF) resin as a binding agent. Two types of PF resin were investigated as part of this study both being prepared from resol polymer having a formaldehyde:phenol ratio of 3:1. However, one of the resol polymers had water as the primary solvent and the other ethanol. Both resol polymers were observed to completely infiltrate the space between the Cs-CST beads and also the pores within the beads themselves. PF resin monoliths prepared after curing the water-based resol at 180°C were considerably less porous than the ethanol-based counterparts cured under the same conditions. The enhanced macroporosity of the resin prepared from the ethanol-based resol was presumably the result from enhanced gas bubble generation. Little or no micro- or mesoporosity was measured using nitrogen porosimetry. For both resins cured at 180°C, intimate contacts with the Cs-CST beads were observed that were not modified even after complete immersion in water over long time frames. Little or no migration of Cs from Cs-CST to the resin binder was observed. The compressive strength of the Cs-CST-PF resin monoliths was measured and benchmarked against cement monoliths and was found to be two to three times higher than cement in the case of the water-based resin. Leaching of the monoliths was conducted in demineralized water at 90°C. Normalized Cs mass losses of the order of 1.0g/m2 were measured after 30days for the ethanol-based resin monoliths. For the less porous water-based monoliths, the normalized mass loss was one order of magnitude lower. The leaching of monoliths irradiated with a 2-MGy dose of γ radiation showed no difference in Cs mass loss suggesting that the ability to retain Cs of either the CST or PF resin was not affected. PF resins are capable of acting as a mechanically robust, radiation-resistant, and impermeable active secondary barrier reducing the likelihood of Cs entry into the biosphere.

Downward migration of radiocesium in an abandoned paddy soil after the Fukushima Dai-ichi Nuclear Power Plant accident

After the Fukushima Dai-ichi Nuclear Power Plant accident on March 2011, continuous monitoring of the detailed vertical distribution of radiocesium in soil is required to evaluate the fate of radiocesium and establish strategies for remediation and management of the contaminated land. It is especially important to investigate paddy soil because little knowledge has been accumulated for paddy soil and wetland rice is a major staple in Japan. Therefore, we monitored the vertical distribution of 137Cs in abandoned paddy soil in a planned evacuation zone from June 2011 to March 2016. The decontamination works (i.e., 5 cm of surface soil removal and re-covering with uncontaminated soil) were conducted by the government in 2015. As a result of monitoring, the 137Cs gradually migrated downward with time and the 137Cs concentration in the 0–10 cm soil was almost homogenous in October 2014, although it was non-cultivated. The liner relationship was obtained between the median depth, which is the thickness of a soil layer containing half of the total 137Cs inventory, and the time after the accident, indicating the migration rate was constant (1.3 cm y−1) before the decontamination works. After the decontamination works, the 137Cs concentration in the uppermost surface layer was reduced by 90%, however the total 137Cs inventory was reduced by only 50–70%. It was shown that the efficiency of 137Cs removal by the decontamination works decrease linearly over time in fields like the studied paddy, in which the homogenization of 137Cs concentration occurred. Conversely, the downward migration of 137Cs to subsurface layers deeper than 10 cm (i.e., plowpan layer) with low permeability rarely occurred. It is expected that these unique trends in distribution and migration of 137Cs would be found in abandoned paddy soils with properties similar to the studied soil, sandy loam but poorly drained because of the low permeable plowpan layer, although further validation is necessary.

Radioactive Contamination of Alluvial Soils in the Taiga Landscapes of Yakutia with 137Cs, 226Ra, and 238U

The concentrations and distribution of 137Cs in alluvial soils (Fluvisols) of the upper and middle reaches of the Markha River in the northwest of Yakutia and 226Ra and 238U in alluvial soils within the El’kon uranium ore deposit in the south of Yakutia have been studied. It is shown that the migration of radiocesium in the permafrost-affected soils of Yakutia owing to alluviation processes extends to more than 600 km from the source of the radioactive contamination. The migration of 137Cs with water flows is accompanied by its deposition in the buried horizons of alluvial soils during extremely high floods caused by ice jams. In the technogenic landscapes of southern Yakutia, active water migration of 238U and 226Ra from radioactive dump rocks. The leaching of 238U with surface waters from the rocks is more intense than the leaching of 226Ra. The vertical distribution patterns of 238U and 226Ra in the profiles of alluvial soils are complex. Uranium tends to accumulate in the surface humus horizon and in the buried soil horizons, whereas radium does not display any definite regularities of its distribution in the soil profiles. At present, the migration of 238U and 226Ra with river water and their accumulation in the alluvial soils extend to about 30 km from the source.

Effects of NH4+, K+, Mg2+, and Ca2+ on the Cesium Adsorption/Desorption in Binding Sites of Vermiculitized Biotite.

The reversibility of cesium adsorption in contaminated soil is largely dependent on its interaction with micaceous minerals, which may be greatly influenced by various cations. Herein, we systematically investigated the effects of NH4+, K+, Mg2+, and Ca2+ on the adsorption/desorption of Cs+ into different binding sites of vermiculitized biotite (VB). Original VB was initially saturated by NH4+, K+, or Mg2+; we then evaluated the adsorption of Cs+ on three treated VBs, and the desorption by extraction with NH4+, K+, Mg2+, or Ca2+ was further evaluated. Our structural analysis and Cs+ extractability determinations showed that NH4+ and K+ both collapsed the interlayers of VB, resulting in the dominant adsorption of Cs+ to external surface sites on which Cs+ was readily extracted by NH4+, K+, Mg2+, or Ca2+ irrespective of their species, whereas Mg2+ maintained the VB with expanded interlayers, leading to the overwhelming adsorption of Cs+ in collapsed interlayer sites on which the Cs+ desorption was difficult and varied significantly by the cations used in extraction. The order of Cs+ extraction ability from the collapsed interlayers was K+ ≫ Mg2+ ≈ Ca2+ ≫ NH4+. These results could provide important insights into Cs migration in soil and its decontamination for soil remediation.

Relationship between 137Cs concentration and potassium content in stem wood of Japanese cedar (Cryptomeria japonica)

To utilize forest resources in areas affected by fallout from the Fukushima Daiichi Nuclear Power Plant accident, it is important to understand the mechanisms of 137Cs movement through the stem wood of contaminated trees. Understanding the mechanism of absorption and migration of 137Cs to stem wood is necessary for clues to the future prediction of the transition of 137Cs to xylem. In the present study, radial variations in 137Cs concentration were investigated in Japanese cedar (Cryptomeria japonica D. Don) trees collected 1 year and 10 months after the accident. Additionally, the relationship between 137Cs concentration and potassium (K) content was established. Trees with a higher moisture content and lower lightness value in heartwood tended to have a higher 137Cs concentration in the heartwood. In these trees, 137Cs concentration peaked at the heartwood–sapwood boundary and gradually decreased toward the pith. By contrast, K content within the heartwood remained nearly constant along the radial direction. The heartwood-to-sapwood ratio of 137Cs concentration was significantly positively correlated with that of K content. Based on these results, we suggest that 137Cs movement from sapwood to heartwood might be related to the K content ratio of heartwood and sapwood.

Reprint of “Vertical migration of radio-caesium derived from the Fukushima Dai-ichi Nuclear Power Plant accident in undisturbed soils of grassland and forest”

The vertical distribution of radio-caesium (137Cs and 134Cs) in undisturbed soil profiles of grassland and forest soils, derived from the Fukushima-Daiichi Nuclear Power Plant (FDNPP) accident that occurred on 11 March 2011, was studied. Surface soil and depth profile soil samples were collected from six locations within the 20km zone of FDNPP, during November 2012 and June 2013. The activity ratio for 137Cs and 134Cs was found to be almost constant about 1 within the soil profiles as well as in the surface soil, indicative of FDNPP accident origin. From soil depth profile distribution of Cs activity, it is observed that Cs is strongly bound to soil materials, which slows Cs migration. >90% of the activity was found to be retained within the upper 5cm layer. Retardation of Cs movement has been quantified by measuring sorption of Cs in soil in terms of distribution coefficient (Kd) using the laboratory batch method. Faster migration has been observed in case of forest land soil compared to grassland soil. The empirical migration velocity of Cs radio isotope was estimated from the depth profile Cs concentration and found to vary from 1.1 to 1.7 and 0.85 to 3.5cmy−1 in grassland and forest soil, respectively. The residential half life for Cs isotopes was found to be 1.03–7.75y and 1.18–4.67y for grassland and forest land respectively using a compartmental model. In addition to the empirical analysis of the profiles, analytical models were fitted to the data which may help elucidate the physical nature of the transport of trace elements.

Landscape–biogeochemical factors of transformation of the Cs-137 contamination field in the Bryansk region

Data are presented on the distribution of Chernobyl-derived 137Cs in different landscapes of the Bryansk region. The role of different landscape-biogeochemical factors in the transformation of the 137Cs contamination field is examined. The distribution of 137Cs in the typical soil catenary junction of predpolessie, predopolje, and opolje landscapes is analyzed. The role of biogeochemical barriers in the 137Cs accumulation is considered. It is revealed that the slope exposure affects the intensity of geochemical migration. In particular, the intensity of lateral migration of 137Cs on the slopes of the southern and southwestern exposure is much higher than that on the slopes of the northern and northeastern exposure. The different types of geochemical lateral structure of landscape are analyzed on the basis of the catenary 137Cs distribution.

Quantitative analysis of radiocesium retention onto birnessite and todorokite

Although the Cs adsorption onto soil minerals has been widely studied, the structural factor of Mn oxides affecting the adsorption behavior of trace amounts of Cs is unclear. In order to elucidate the adsorption mechanisms of radioactive Cs at trace levels and the role of Mn oxides on Cs migration in the terrestrial environment, the Cs adsorption onto birnessite and todorokite was investigated for a wide range of concentrations (1×10−10mol/L to 0.1mol/L) and an ion-exchange model was used to interpret the adsorption data. Although birnessite showed a higher Cs adsorption capacity than todorokite, most of the Cs adsorbed onto birnessite was desorbed by ion exchange. Two types of adsorption sites were observed for todorokite. Despite low density, the selectivity coefficient was much higher for the T1 site (LogNaCsKsel = 4.2) than for the T2 site (LogNaCsKsel=−0.6). Sequential extraction was carried out at Cs concentrations of 1×10−9mol/L and 1×10−3mol/L. At lower concentrations, approximately 34% of the adsorbed Cs was residual in the todorokite after the sequential extraction; this value was much higher than the results for the Cs-adsorbed birnessite as well as the Cs-adsorbed todorokite at higher concentrations. The present results indicate that the structural factors of Mn oxides significantly affect the retention capacity of radioactive Cs. Aside from phyllosilicate minerals, todorokite also contributes to the fixation of radioactive Cs in soils.

Decline in radiocesium in seafloor sediments off Fukushima and nearby prefectures

Radioactivity has been monitored in seafloor sediments off Fukushima and nearby prefectures regularly. During the initial monitoring period (May–September 2011), 137Cs concentrations in the surface sediments (0–3 cm) generally increased to 8–580 Bq/kg. Subsequently, concentrations decreased at variable rates. In the latest data, from February 2016, concentrations were still higher at 0.8–141 Bq/kg than the pre-accident level. The geometric mean concentration declined steadily from 47 Bq/kg in September 2011 to 13 Bq/kg in February 2016. The 137Cs abundance (Bq/m2) in the surface sediment at each station decreased similarly. The rate of decrease of surface abundance varied spatially by almost one order of magnitude, ranging from 1.1 × 10−4 to 1.7 × 10−3/day, equivalent to halving times of 16–1.1 years, respectively. The rate of decrease was related to the median sediment grain size at each station. In addition, bottom-water dynamics, through the redistribution of bottom sediments, may have caused spatial variability in the rate of decrease, whereas vertical profiles of 137Cs concentrations in the sediment suggest that vertical migration of 137Cs was not a major mechanism reducing the surface 137Cs concentration. From September 2011 to February 2016, the overall halving time of 137Cs in the surface sediment in the monitoring area, excluding the area inside a 30-km radius from the Fukushima Dai-ichi Nuclear Power Plant, was 2.3 years. Thus, 76% of the originally deposited 137Cs (46 × 1012 Bq) in the surface sediment was transported out of the area during that period.

Downward migration of 137Cs within the humus layer under temperate coniferous stands in the Czech Republic

This study examined the current distribution and downward migration of 137Cs in the humus horizon under temperate coniferous stands in the Czech Republic. Depth distribution profiles of lithogenic alkali metals (K, Rb, and Cs) were also traced to find any indication regarding the 137Cs dynamics within the humus horizon. Soil (bulk soil) samples were collected manually from the uppermost down to a depth of 20 cm at three points situated 10–20 m apart in three locations diversely affected by the Chernobyl accident in 1986. Humus samples (about 6 cm in thickness) were separately collected at three points adjacent to the bulk soil sampling. The humus samples were divided into three fractions (upper, middle, and lower) denoted to Hu, Hm, and Hl, respectively, depending on their depths. Activity concentration of 137Cs and the amount of alkali metals (K, Rb, and Cs) in each humus fraction were determined with gamma spectrometry and ICP spectrometry, respectively. Some properties (pH, density, SOM, and identification of clay minerals), of both bulk soils and humus horizons were also investigated. The highest activity concentration of 137Cs (Bq kg−1) appeared in the upper portion of the soil (mainly humus horizon) under three coniferous stands about 30 years after the Chernobyl accident. Increasing activity of 137Cs (Bq) was found in the lower humus fraction (Hl, 4~6-cm depth range) with no appreciable amounts of clay minerals like illite and smectite in the investigated sites. The findings suggest that the fallout 137Cs moves downward at a speed of 0.13~0.19 cm year−1 with degrading organic matter within the humus horizon. Possible association of 137Cs with alkali metals (K, Rb, and Cs) was suggested by depth distribution profiles of lithogenic alkali metals (K, Rb, and Cs) in humus. The humus horizon under temperate coniferous stands plays an important role in retaining fallout 137Cs for a long time. Comparing the depth distributions of the fallout radionuclide 137Cs with the depth distributions of lithogenic alkali metals (K, Rb, and Cs) gives valuable information for clarifying mechanism of 137Cs movement in humus. Further investigation is needed to elucidate mechanism of 137Cs migration within humus horizon by tracing 137Cs speciation and decomposing soil organic matter simultaneously.

Vertical distribution and temporal dynamics of dissolved 137Cs concentrations in soil water after the Fukushima Dai-ichi Nuclear Power Plant accident

Radiocesium (137Cs) migration from headwater forested areas to downstream rivers has been investigated in many studies since the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, which was triggered by a catastrophic earthquake and tsunami on 11 March 2011. The accident resulted in the release of a huge amount of radioactivity and its subsequent deposition in the environment. A large part of the radiocesium released has been shown to remain in the forest. The dissolved 137Cs concentration and its temporal dynamics in river water, stream water, and groundwater have been reported, but reports of dissolved 137Cs concentration in soil water remain sparse.In this study, soil water was sampled, and the dissolved 137Cs concentrations were measured at five locations with different land-use types (mature/young cedar forest, broadleaf forest, meadow land, and pasture land) in Yamakiya District, located 35 km northwest of FDNPP from July 2011 to October 2012. Soil water samples were collected by suction lysimeters installed at three different depths at each site. Dissolved 137Cs concentrations were analyzed using a germanium gamma ray detector. The dissolved 137Cs concentrations in soil water were high, with a maximum value of 2.5 Bq/L in July 2011, and declined to less than 0.32 Bq/L by 2012. The declining trend of dissolved 137Cs concentrations in soil water was fitted to a two-component exponential model. The rate of decline in dissolved 137Cs concentrations in soil water (k1) showed a good correlation with the radiocesium interception potential (RIP) of topsoil (0–5 cm) at the same site. Accounting for the difference of 137Cs deposition density, we found that normalized dissolved 137Cs concentrations of soil water in forest (mature/young cedar forest and broadleaf forest) were higher than those in grassland (meadow land and pasture land).