Changes In 137Cs Concentrations Research Articles

Applicability of reconstruction of temporal changes in 137Cs concentrations in pond water based on the vertical distribution of bottom sediments: a case in three ponds in the Fukushima evacuation zone.

Long-term changes in particulate and dissolved 137Cs concentrations in rivers and dam reservoirs have been reconstructed using 137Cs depth distributions in bottom sediments near Chornobyl and Fukushima. However, few studies have applied this method to pond water. This study tested the applicability of this reconstruction method in ponds within the Fukushima evacuation zone. Bottom sediments in ponds were collected in November 2019. Our reconstruction of a shallow closed pond disagreed with our observations. Even in ponds where the reconstruction agreed well with observations, underestimations may have occurred because the time constant for the decrease in 137Cs concentration was lower than those previously reported. We conclude that the present reconstruction method may be applied to deeper Fukushima ponds with inflow and outflow, but underestimations of initial 137Cs concentrations in water may lead to uncertainties. For realistic reconstruction, attention should be paid to pond characteristics, catchment conditions, and sediment core selection.

Impact of Bottom-Sediment Removal on 137Cs Contamination in an Urban Pond

Many irrigation ponds in Fukushima Prefecture were decontaminated due to the contamination of radiocesium released from Fukushima Daiichi Nuclear Power Plant. To evaluate the impact of decontamination on 137Cs dynamics in an urban pond in Koriyama City, Fukushima Prefecture, Japan, temporal changes in 137Cs concentrations in bottom sediments and pond water were investigated before and after bottom-sediment removal. Post-decontamination, 137Cs inventories in bottom sediments decreased by 46–89%. 137Cs inventories in bottom sediments were relatively high in fine sediments before decontamination, and were also high at points near the water inlet after decontamination. Following decontamination, the mean 137Cs concentration in suspended solids (SS) and the mean dissolved 137Cs concentration in pond water decreased by 52% and 5%, respectively. Even after decontamination, the normalized 137Cs concentrations in SS and in water, which were calculated by dividing the 137Cs concentrations by the mean 137Cs inventories in each area, were higher than those in rivers, dam reservoirs, and ponds elsewhere in Fukushima. The positive correlations between δ15N values, an indicator of the source contribution to bottom sediments, and 137Cs concentrations in the upper 5 cm of bottom sediments after decontamination implied that SS from urban areas gradually increased the 137Cs inventories in the pond. The results underline the importance of secondary inputs of 137Cs from highly urbanized catchments.

Modeling the Dynamic Behavior of Radiocesium in Grazing Reindeer.

Radiocesium contamination in Norwegian reindeer and the factors influencing contamination levels have been studied for more than 50 years, providing significant amounts of data. Monitoring contamination in reindeer is of utmost importance for reindeer husbandry and herders in Norway and will need to be studied for many years because of the persistent contamination levels due to the 1986 Chernobyl fallout. This paper presents a novel dynamic model that takes advantage of the large data sets that have been collected for reindeer monitoring to estimate 137Cs in reindeer meat at any given time. The model has been validated using detailed 137Cs data from one of the herds most affected by the fallout. The model basis includes detailed 137Cs soil data from aerial surveys, GPS-based knowledge of reindeer migration, and local soil-to-vegetation 137Cs transfer information. The validation exercise shows that the model satisfactorily predicts both short- and long-term changes in 137Cs concentrations in reindeer meat and suggests that the model will be a useful tool in estimating seasonal changes and evaluating possible remedial actions in case of a future fallout event.

Impacts of freeze-thaw processes and subsequent runoff on 137Cs washoff from bare land in Fukushima

The deposited 137Cs is one of the long-lived radionuclides, that was released following the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, has been hydrologically transported as particulates in the terrestrial environment of the Fukushima region. The impact of freeze-thaw processes and subsequent runoff affecting the 137Cs flux and concentration in sediment discharge were revealed in bare land erosion plot following the FDNPP accident by detailed monitoring and laser scanner measurement on the soil surface. We found that surface topographic changes due to the frost-heaving during the winter-spring period, and rill formation during the summer. We also found the evident seasonal changes in 137Cs concentration; high during the early spring and gradually decreased thereafter, then surface runoff from the plot frequently occurred during spring and autumn when rainfall was high and reached a maximum in summer. From these results, the higher 137Cs concentration in spring was caused by a mixture of unstable surface sediment following freeze-thaw processes and then transported in the early spring, but erosion amount is not significant because of the less rainfall event. The sediment with a lower 137Cs concentration, which was supplied from the rill erosion and its expansion, was wash-offed during the summer, contributing most of the flux from erosion in bare land in Fukushima region. In case, heavy rainfall occurs in the early spring, caution is required because high concentrations of cesium may flow down into the river.

Temporal Changes in 137Cs Concentrations in Fish, Sediments, And Seawater off Fukushima Japan.

We analyzed publicly available data of Fukushima 137Cs concentrations in coastal fish, in surface and bottom waters, and in surface marine sediments and found that within the first year of the accident pelagic fish lost 137Cs at much faster rates (mean of ∼1.3% d-1) than benthic fish (mean of ∼0.1% d-1), with benthopelagic fish having intermediate loss rates (mean of ∼0.2% d-1). The loss rates of 137Cs in benthic fish in the first year were more comparable to the decline of 137Cs concentrations in sediments (0.03% d-1), and the declines in pelagic fish were more comparable to the declines in seawater. Retention patterns of 137Cs in pelagic fish were comparable to that in laboratory studies of fish in which there were no sustained 137Cs sources, whereas the benthopelagic and benthic fish species retained 137Cs to a greater extent, consistent with the idea that there is a sustained additional 137Cs source for these fish. These field data, based on 13 511 data points in which 137Cs was above the detection limit, are consistent with conclusions from laboratory experiments that demonstrate that benthic fish can acquire 137Cs from sediments, primarily through benthic invertebrates that contribute to the diet of these fish.

Processes affecting long-term changes in 137Cs concentration in surface sediments off Fukushima

Temporal changes in cesium-137 (137Cs) concentrations in the surface (0–10 cm) layer of seabed sediment were quantified from continuous observation data at 71 stations within a 150-km radius of the Fukushima Daiichi Nuclear Power Plant, and the primary processes affecting temporal changes were identified. From March 2011 to the end of 2015, about 80% of the initially deposited 137Cs in the surface sediment in the coastal region (bottom depth ≤100 m) region has dissipated (radioactive decay is not included). Such a remarkable change in the 137Cs concentration was not observed in the offshore (>100 m) region. This paper focuses on the following three processes that affected the decrease in the 137Cs concentrations, and assesses their relative importance; (1) resuspension and transport of 137Cs-bound sediment, (2) desorption of 137Cs from the sediment, and (3) dilution of 137Cs by vertical mixing of sediment. Consequently, it was estimated that the first two processes together have potentially contributed to reduce the 137Cs inventory in the top 10 cm of the coastal region by at most 35%. Furthermore, by applying a pulse input sediment mixing model to the observed vertical distribution of sedimentary 137Cs, it was also estimated that more than 43% of the 137Cs in the surface sediment was transported to deeper sediment layers by vertical mixing of the sediment. This indicates that the decrease of 137Cs concentrations in coastal sediments was mainly affected by mixing of 137Cs-bound surface sediment with less contaminated sediment in the deeper layers.

Impacts of the Fukushima nuclear accident on fish and fishing grounds

1 Introduction: Overview of Our Research on Impacts of the Fukushima Dai-ichi Nuclear Power Plant Accident on Fish and Fishing Grounds.- Part I Seawater and Plankton.- 2 134Cs and 137Cs in the Seawater Around Japan and in the North Pacific.- 3 Temporal Changes in 137Cs Concentration in Zooplankton and Seawater off the Joban-Sanriku Coast, and in Sendai Bay, After the Fukushima Dai-ichi Nuclear Accident.- Part II Sediments and Benthos.- 4 Three-Dimensional Distribution of Radiocesium in Sea Sediment Derived from the Fukushima Dai-ichi Nuclear Power Plant.- 5 Radiocesium Concentrations in the Organic Fraction of Sea Sediments.- 6 Bottom Turbidity, Boundary Layer Dynamics, and Associated Transport of Suspended Particulate Materials off the Fukushima Coast.- 7 Investigation of Radiocesium Translation from Contaminated Sediment to Benthic Organisms.- Part III Marine Fish.- 8 Detection of 131I, 134Cs, and 137Cs Released into the Atmosphere from FNPP in Small Epipelagic Fishes, Japanese Sardine and Japanese Anchovy, off the Kanto Area, Japan.- 9 Radiocesium Concentration of Small Epipelagic Fishes (Sardine and Japanese Anchovy) off the Kashima-Boso Area.- 10 Why Do the Radionuclide Concentrations of Pacific Cod Depend on the Body Size?.- 11 Radiocesium Contamination Histories of Japanese Flounder (Paralichthys olivaceus) After the 2011 Fukushima Nuclear Power Plant Accident.- Part IV Mechanisms of Severe Contamination in Fish.- 12 Evaluating the Probability of Catching Fat Greenlings (Hexagrammos otakii) Highly Contaminated with Radiocesium off the Coast of Fukushima.- 13 Analysis of the Contamination Process of the Extremely Contaminated Fat Greenling by Fukushima-Derived Radioactive Material.- 14 Contamination Levels of Radioactive Cesium in Fat Greenling Caught at the Main Port of the Fukushima Dai-ichi Nuclear Power Plant.- Part V Freshwater Systems.- 15 Comparison of Radioactive Cesium Contamination of Lake Water, Bottom Sediment, Plankton, and Freshwater Fish Among Lakes of Fukushima Prefecture, Japan, After the Fukushima Fallout.- 16 Radiocesium Concentrations and Body Size of Freshwater Fish in Lake Hayama 1 Year After the Fukushima Dai-Ichi Nuclear Power Plant Accident.- 17 Spatiotemporal Monitoring of 134Cs and 137Cs in Ayu, Plecoglossus altivelis, a Microalgae-Grazing Fish, and in Their Freshwater Habitats in Fukushima.- 18 Radiocesium Concentrations in the Muscle and Eggs of Salmonids from Lake Chuzenji, Japan, After the Fukushima Fallout.- 19 Assessment of Radiocesium Accumulation by Hatchery-Reared Salmonids After the Fukushima Nuclear Accident

Changes in radiocesium concentrations in epigeic earthworms in relation to the organic layer 2.5 years after the 2011 Fukushima Dai-ichi Nuclear Power Plant accident

We reported previously that radiocesium (137Cs) concentrations in earthworms increased with those in litter and/or soil in Fukushima Prefecture forests 0.5 y after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. This study provides further results for 1.5 and 2.5 y after the accident and discusses temporal changes in 137Cs concentrations and transfer factors (TF) from litter to earthworms to better understand the mechanisms by which 137Cs enters soil food webs. The concentration of 137Cs in accumulated litter on the forest floor rapidly decreased, and the concentration in soil (0–5-cm depth) increased over time from 0.5 to 1.5 y, but changed only moderately from 1.5 to 2.5 y. The concentration of 137Cs in earthworms consistently decreased during the study period; values 2.5 y after the accident were 18.8–68.5% of those 0.5 y after the accident. The TFs from accumulated litter to earthworms decreased over time: 0.24 ± 0.08 (mean ± SD) at 0.5 y and 0.16 ± 0.04 at 2.5 y. This decrease may be a result of decreases in the bioavailability of 137Cs in litter and the surface soil layer. Changes in 137Cs bioavailability should be continuously tracked to determine any changes in the relationship between radiocesium concentrations in earthworms and that in accumulated litter or soil.

Cesium-137 discharge into the freshwater fishery ground of grazing fish, ayu Plecoglossus altivelis after the March 2011 Fukushima nuclear accident

The Fukushima nuclear accident led to deposition of radionuclides into the freshwater fishery ground of ayu Plecoglossus altivelis. For the purpose of more comprehensive understanding of the radioactive contamination, cesium-137 (137Cs) was analyzed in running water, muddy sediment, attached algae, and ayu using samples from three river systems with different levels of contamination within Fukushima Prefecture in summer and autumn 2011. The amount of 137Cs contained in water as well as in sediment declined over an interval of two months, although the concentration in sediment samples was up to 10,000-fold higher than that in water samples. The changes in 137Cs concentration of algae showed different courses among the three river systems, the concentration being greater in autumn in the river systems with high and moderate radioactive contamination. 137Cs detected within a single stock of ayu appeared to be excreted rather rapidly with a calculated half-life of approximately 39 days, while the concentration ratio ranged from 103 to 104 l/kg, attaining higher levels than previously reported. These findings indicate that the most important pathway of 137Cs into ayu is via intake of algae as food but that the retention time of 137Cs inside ayu is relatively short.

Changes in 137Cs concentrations in soil and vegetation on the floodplain of the Savannah River over a 30 year period

137Cs released during 1954–1974 from nuclear production reactors on the Savannah River Site, a US Department of Energy nuclear materials production site in South Carolina, contaminated a portion of the Savannah River floodplain known as Creek Plantation. 137Cs activity concentrations have been measured in Creek Plantation since 1974 making it possible to calculate effective half-lives for 137Cs in soil and vegetation and assess the spatial distribution of contaminants on the floodplain. Activity concentrations in soil and vegetation were higher near the center of the floodplain than near the edges as a result of frequent inundation coupled with the presence of low areas that trapped contaminated sediments. 137Cs activity was highest near the soil surface, but depth related differences diminished with time as a likely result of downward diffusion or leaching. Activity concentrations in vegetation were significantly related to concentrations in soil. The plant to soil concentration ratio (dry weight) averaged 0.49 and exhibited a slight but significant tendency to decrease with time. The effective half-lives for 137Cs in shallow (0–7.6 cm) soil and in vegetation were 14.9 (95% CI = 12.5–17.3) years and 11.6 (95% CI = 9.1–14.1) years, respectively, and rates of 137Cs removal from shallow soil and vegetation did not differ significantly among sampling locations. Potential health risks on the Creek Plantation floodplain have declined more rapidly than expected on the basis of radioactive decay alone because of the relatively short effective half-life of 137Cs.