Deposition density of 134Cs and 137Cs and particle size distribution of soil and sediment profile in Hibara Lake area, Fukushima: an investigation of 134Cs and 137Cs indirect deposition into lake from surrounding area

Radioactivity of anthropogenic and natural radionuclides in marine sediments of the Chaun Bay, East Siberian Sea

Natural radioactive isotopes serve as a useful proxy of geological and geochemical processes in marine environment, while radiocesium serves as an indicator of man-made contamination. Monitoring of natural and anthropogenic radioactivity under conditions of the climate changes in the Arctic region is of high importance in investigations of this natural system. For the first time, we report the data on spatial distribution of natural (232Th, 226Ra, 40K) and anthropogenic (137Cs) radionuclide activities in the marine sediments from Chaun Bay (East Siberian Sea). The measured activity concentrations varied in the range 23.7-77.9 (mean 39.2) Bq kg-1 for 232Th, 16.5-39.3 (mean 26.6) Bq kg-1 for 226Ra, 535-991 (mean 726) Bq kg-1 for 40K, and 0.5-4.7 (mean 2.0) Bq kg-1 for 137Cs. The radiocesium level in the sediments showed no local sources of anthropogenic pollution in the Chaun Bay, while the average activity concentration of 40K was 1.8 times higher than worldwide.

Spatial and vertical distribution of 137Cs activity concentrations in lake sediments of Turawa Lake (Poland)

The main objective of this research was to study the spatial and vertical distribution of 137Cs activity concentrations in the bottom sediments of Turawa Lake 32 years after the Chernobyl fallout to investigate possible factors responsible for the post-fallout migration and accumulation of 137Cs in the selected reservoir. The results demonstrated a strong relationship between the increasing 137Cs and 40K activity concentrations and the decreasing grain size of sediments. Significant amounts of 137Cs were detected in the bottom sediments deposited in the deeper parts of the reservoir (especially near the dam). Therefore, this research showed that Turawa Lake can be an important trap for sediments polluted with 137Cs. Moreover, disturbed vertical distribution of 137Cs activity concentrations in the sediment columns collected from the littoral zone of this lake was observed, which is probably related to the bottom erosion intensified by wind-wave action, bioturbations, and water-level fluctuations. In the profundal zone, the vertical distribution of 137Cs activity concentrations was undisturbed, which indicates stable sedimentation conditions in this part of Turawa Lake.

Ten years of investigations of Fukushima radionuclides in the environment: A review on process studies in environmental compartments

In March 2011, severe nuclear accident happened at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) after the gigantic earthquake and following huge tsunami wave. A lot of investigations to assess environmental and radiological impacts of released radionuclides have been conducted by domestic and international organizations. Environmental radioactivity research related to the FDNPP accident has spread widely over different scientific fields due to specific features of the accident, and specifically its impact on the marine environment. The present paper summarizes major lessons learned from the environmental investigations of the FDNPP accident. Environmental radioactivity studies have typical interdisciplinary character; especially physics and chemistry are fundamental as a base of process studies in the environment. In this sight, we review chemical aspects regarding FDNPP-derived radiocesium transfer within and between compartments (atmosphere, ocean and land). We also discuss future trends in investigations of behavior of anthropogenic radionuclides in the environment, important not only for a better understanding of impacts of the FDNPP accident on the environment, but also for improving our general knowledge of the total environment in the Anthropocene era and its protection for the future.

Improvement of Cs detection performance and formation of CsCl and Cs nanoparticles by tuning graphene oxide quantum dot-based nanocomposite

A new nanocomposite was developed using functionalized graphene oxide quantum dots (GOQDs) with cesium green molecules for the first time. Although the cesium green molecule works effectively only in the solid-state, without water, and in basic conditions, the functionalized GOQDs with cesium green made the nanocomposite work well as a cesium (Cs) detector in mixed solution (distilled water/THF). The nanocomposite can be employed as a Cs detector in both acidic and basic conditions. The present study revealed that the nanocomposite of GOQDs with cesium green showed an enhanced photoluminescence in basic conditions, while the intensity of the photoluminescence in acidic conditions is the superposition of the photoluminescence of the corresponding components. The photoluminescence of the nanocomposite was quenched (turned OFF) after Cs treatment in basic conditions. On the other hand, in the acidic conditions it was found that the photoluminescence intensity of this nanocomposite was enhanced (turned ON) by the Cs addition in two different Cs concentrations, 0.06 mmol L^-1 and 0.12 mmol L^-1. In addition, the movement of the nanocomposite (after Cs addition) under the electron beams through TEM measurement was observed. The formation of CsCl and Cs nanoparticles was identified. Specifically, the Cs cluster occurrence is discussed by taking into account the mobility effect of the adatoms on the composite layer under electron beam irradiation.

Long-term prediction of [Formula: see text]Cs in Lake Onuma on Mt. Akagi after the Fukushima accident using fractional diffusion model

The Fukushima Daiichi Nuclear Power Plant accident also contaminates lakes in Japan. Especially in closed lakes, there is a problem of prolonged low-level [Formula: see text]Cs contamination because the activity concentration of [Formula: see text]Cs declines sharply immediately after the accident, but then begins to decrease slowly. In this paper, we derived a long-term prediction formula based on the fractional diffusion model (FDM) for the temporal variation in [Formula: see text]Cs activity concentrations of the water in Lake Onuma on Mt. Akagi, one of the closed lakes, and of pond smelt (Hypomesus nipponensis), a typical fish species inhabiting in the lake. The formula reproduced well the measured [Formula: see text]Cs activity concentration of the lake water and pond smelt for 5.4 years after the accident. Next, we performed long-term prediction for 10,000 days using this formula and compared it with the prediction results of the two-component decay function model (TDM), which is the most common model. The results suggest that the FDM prediction will lead to a longer period of contamination with low-level [Formula: see text]Cs than the TDM prediction.

Cs Adsorption and CsCl Particle Formation Facilitated by Amino Talc-like Clay in Aqueous Solutions at Room Temperature

Amino talc-like clay with an increased number of active sites and dispersion in a colloidal system has been synthesized and used for contaminant adsorption and support for nanoparticle formation. Amino talc-like clays having different number of layers and aminoalkyl ligands were synthesized and their Cs uptake behavior was examined. Cs uptake through Cs adsorption and CsCl particle formation facilitated by amino talc-like clay in a colloidal aqueous solution at room temperature are reported. The amino talc-like clay demonstrated better Cs uptake with a high initial Cs concentration than talc and montmorillonite. This might have been caused by a high concentration of trapped Cs and Cl ions in exfoliated amino clay, which eventually became CsCl particles. The formation of the CsCl particles in the amino clay depended on the clay concentration and ethanol treatment. The exfoliation of the basal sheets of the amino clay as a result of a high salt concentration and the protonation of amine induced by ethanol treatment was shown to be a precondition for CsCl particle formation. These results could promote amino talc-like clay for high-concentration Cs uptake and the green synthesis of Cs-halide particles in an aqueous solution.

Radiocesium and 40K distribution of river sediments and floodplain deposits in the Fukushima exclusion zone

In this study, radiocesium and ⁴⁰K analysis were accomplished for samples of riverbed sediments and floodplain deposits collected from five rivers in the vicinity (<20 km) of the damaged Fukushima Daiichi Nuclear Power Plant after seven years of the accident. Sediment particle size distribution and major oxide content were determined also for six selected samples to understand the retention and migration process of radiocesium in river environments. The radiocesium activity concentration varied from 103 ± 6 Bq·kg^-1 to 22,000 ± 500 Bq·kg^-1 in riverbed sediments and from 92 ± 5 Bq·kg^-1 to 117,000 ± 2000 Bq·kg^-1 in floodplain deposits. The ¹³⁴Cs/¹³⁷Cs ratio (decay corrected to 15 March 2011) was 1.02 in the both samples. Compared to monitoring results in 2011, it was proved that the radiocesium distribution pattern had been changed remarkably during seven years. The radiocesium was primarily attached to fine clay particles but its sorption on sand and coarse sand particles was also considerable. The sorption process of radiocesium was not affected by the presence of water and moreover, after seven years of the Fukushima accident, a significant radiocesium migration cannot be expected without particle migration. Consequently, radiocesium will remain for a long time in the river environments and its redistribution is mainly affected by the erosion process of the sediments. The average ⁴⁰K activity concentration of riverbed sediment and floodplain deposit samples was 640 ± 152 Bq·kg^-1 changing from 319 ± 18 Bq·kg^-1 to 916 ± 41 Bq·kg^-1. In the river estuary zones, significant activity concentration decrements were observed for both radionuclides. This suggests that seawater intrusion has a decreasing effect on both natural and artificial radionuclides via wash-out of particulate radiocesium and ⁴⁰K, and desorption of these radionuclides, but to reveal the detail of this process further investigations are required. The analysis of ⁴⁰K can help in a simple and easy way to reveal the mineral composition differences of sediment samples.