nuclear-news

The News That Matters about the Nuclear Industry Fukushima Chernobyl Mayak Three Mile Island Atomic Testing Radiation Isotope

104th protest in front of TEPCO’s head office, “Net for the Realization of No Exposure to Radiation” issued a full-length letter of offer summarizing the actual damage caused by exposure to radiation.

August 1, 2022
Children suffering from radiation exposure: “Acknowledge the relationship between the nuclear accident and childhood thyroid cancer
The Network for the Realization of No Exposure to Radiation Takae Miyaguchi

The Fukushima nuclear power plant accident spread enormous amounts of radiation.
 After the accident, many people gathered in front of the TEPCO headquarters in protest. 14 years ago, a joint protest began on the first Wednesday night of every month, and this May marked the 104th such event.
 About 100 people gather each time. Before the protest, drums are beaten and a microphone relay is used to protest and make a request to TEPCO. Each time, we hand the TEPCO a written request, and if there is any doubt about the response, we submit it again.
 This is the first time that the “Network for the Realization of Exposure Free Japan,” which I am involved with, has submitted a written request to the TEPCO. The content of the letter is a reflection of the situation and thoughts I have been experiencing through my support for the “Children’s Lawsuit for Exposure to Radiation” and other activities.
The following is a summary of the letter.
 Eleven years have passed since the accident at TEPCO’s Fukushima nuclear power plant, but the declaration of a nuclear emergency remains in effect. At the Fukushima nuclear power plant, exposure work with no foreseeable future and convergence work continue amidst the remaining debris with high concentrations of radioactive materials that are inaccessible to humans. Radioactive materials have been released into the air and are flying into the Tokyo metropolitan area on the wind. The Fukushima nuclear accident has not ended.
 TEPCO understands the despair, grief, and anger of the victims of the nuclear accident, and in an effort to hold TEPCO accountable, victims have filed lawsuits against TEPCO in various regions, and the courts have confirmed TEPCO’s responsibility for the nuclear accident, but the amount of compensation awarded by the courts to each person is shockingly small compared to the extent of the damage.
 What the victims truly desire is the return of their hometowns as they were before the nuclear accident, where people made their living, families lived, children cheered, and people laughed, and where life was normal, rooted in the local climate, and connected to history! This is what we have been trying to achieve for the past 11 years.
 Eleven years later, the evacuation designation has been lifted except for some areas that are difficult to return to.
The policy of forcing people to return to their hometowns because their annual exposure level is below 20 mSv, 20 times the allowable annual exposure level of 1 mSv for the public, is unacceptable. We denounce the depth of TEPCO’s crimes of spreading massive amounts of radioactive materials, polluting the mountains, rivers, and land of Fukushima, destroying our hometowns, and depriving people of their livelihoods.

In the face of radiation taboos and discrimination
Young People Who Courageously Stood Up Against Radiation Taboo and Discrimination

He continued.
 In January of this year, six young people who had developed childhood thyroid cancer rose to their feet. Three or four years later, many of them were found to have pediatric thyroid cancer in a Fukushima health survey, and all of them underwent surgery.
 Thyroid cancer is a slow-growing cancer, and the prognosis for surgery is good, according to the committee’s experts. However, some of the plaintiffs had recurrence after surgery, reoperation, RAI isotope treatment, and some were found to have distant metastasis in the lungs.
 Their health did not recover even after the surgery, they dropped out of college, resigned from the company where they worked, were not hired when they were told they had cancer, etc. They have thought about, worried about, and suffered from the despair of having the door closed to them at the starting line of their lives, anxiety about the recurrence of cancer in the future, treatment costs, work, and whether or not they will be able to make a living independently.
 Why is it that nearly 30 out of 380,000 children in Fukushima have developed thyroid cancer, compared to only one or two out of a million children in Japan? Why have nearly 300 cases been reported among 380,000 children in Fukushima? The Prefectural Health Study Review Committee acknowledges the high incidence of childhood thyroid cancer, but denies any causal relationship with the nuclear accident, saying that it is overdiagnosis.
 Last July, the Hiroshima A-bomb “black rain” victims’ lawsuit recognized that internal exposure is not a matter of quantity, but that if even a small amount of radiation enters the body’s tissues and is deposited, it damages cells and causes cancer. In the case of the Chernobyl nuclear power plant accident, a causal relationship between childhood thyroid cancer and the nuclear power plant accident was recognized. The plaintiffs want to clarify why they developed pediatric thyroid cancer.
 The relationship between childhood thyroid cancer and the nuclear power plant accident” is a taboo subject, and the plaintiffs have been hiding their illness for a long time for fear of being discriminated against, but they want to make their illness public and have the court find a “causal relationship between childhood thyroid cancer and exposure to radiation. They have stood up courageously to make TEPCO pay compensation for their illness. We demand the following
TEPCO must admit that it is the perpetrator of the Fukushima nuclear power plant accident and the spreading of radioactive materials.
Please admit the causal relationship between radioactive iodine released from the Fukushima nuclear power plant and childhood thyroid cancer as soon as possible.
Please take responsibility for the future of these six young people.
We ask that you take responsibility for the future of these six young people.
 The fight to leave a world without radiation exposure to children continues.
https://note.com/jinminshinbun/n/n137ff335aaa0?fbclid=IwAR2FJl-KiOLqm4GjfTdOT6uBxZ_xlAzh7BOiwkkUyeOXHsyAUXBc88jeFck

August 4, 2022 Posted by | Fuk 2022 | , , , | Leave a comment

Indonesia lifts restrictions on post-Fukushima food imports at Japan summit

TOKYO, July 27 (Xinhua) — Japanese Prime Minister Fumio Kishida and visiting Indonesian President Joko Widodo held talks in Tokyo on Wednesday ahead of this year’s Group of 20 major economies’ summit in Bali in November which Widodo will host.

Following a summit meeting between the leaders, Kishida told a joint press conference that Indonesia has lifted all restrictions on imports of Japanese food products that were imposed in the wake of the Fukushima nuclear crisis in 2011.

Kishida said he was thankful for the move and that the lifting of import restrictions on food products from seven previously affected prefectures here would “encourages people in the disaster-hit areas.”

Widodo, for his part, said he asked Japan to ease or scrap tariffs it imposes on Indonesian tuna, pineapples and bananas.

He also passed on his condolences over the fatal shooting of former Prime Minister Shinzo Abe, who was gunned down during a stump speech earlier this month.

Widodo will conclude his visit to Japan with a meeting with Emperor Naruhito later in the day and will then depart for South Korea, government officials here said.

http://www.china.org.cn/world/Off_the_Wire/2022-07/27/content_78344112.htm

July 31, 2022 Posted by | Fuk 2022 | , , | Leave a comment

Persistent impact of Fukushima decontamination on soil erosion and suspended sediment.

Published: 14 July 2022

Abstract

In Fukushima, government-led decontamination reduced radiation risk and recovered 137Cs-contaminated soil, yet its long-term downstream impacts remain unclear. Here we provide the comprehensive decontamination impact assessment from 2013 to 2018 using governmental decontamination data, high-resolution satellite images and concurrent river monitoring results. We find that regional erosion potential intensified during decontamination (2013–2016) but decreased in the subsequent revegetation stage. Compared with 2013, suspended sediment at the 1-year-flood discharge increased by 237.1% in 2016. A mixing model suggests that the gradually increasing sediment from decontaminated regions caused a rapid particulate 137Cs decline, whereas no significant changes in downstream discharge-normalized 137Cs flux were observed after decontamination. Our findings demonstrate that upstream decontamination caused persistently excessive suspended sediment loads downstream, though with reduced 137Cs concentration, and that rapid vegetation recovery can shorten the duration of such unsustainable impacts. Future upstream remediation should thus consider pre-assessing local natural restoration and preparing appropriate revegetation measures in remediated regions for downstream sustainability.

Main

Radioactive material leakage from nuclear industry activities or nuclear accidents poses a major threat to the environment and the economy1,2. Historically, widespread radioactive contamination has been observed several times, such as the Kyshtym accident (Soviet Union) in the 1940s–50s3, Windscale accident (England) in 1957 (ref. 4) and Chernobyl accident (Soviet Union) in 1986 (ref. 5). Long-term radiation exposure and radiophobia have increased the health risk and psychological pressure on the people of these regions, resulting in the abandonment of large areas rich in environmental resources and consequently in constrained sustainable human development6,7. As a key means for recovering contaminated regions, mechanical decontamination has been implemented in many legacy sites, including Hanford (United States)8 and Chernobyl9. However, almost all attention has been directed to understanding in situ decontamination effects10,11 and atmospheric particle resuspension issues12 and little is known about if these perturbations would have secondary environmental impacts on their downstream catchments for the long-term.

On 11 March 2011, the most recent large-scale nuclear accident happened at the Fukushima Daiichi Nuclear Power Plant (FDNPP), Japan13. Over 2.7 PBq of fallout 137Cs (half-life T1/2 = 30.1 yr) from the FDNPP was deposited in the terrestrial environment, causing long-term radioactive contamination on large-scale neighbouring catchments13,14. To recover contaminated soil and decrease the exposure dose in Fukushima, the Japanese government evacuated the residents in 2011 and large-scale decontamination was implemented in contaminated villages15,16 in 2012. Within a few years, dramatic land-cover changes occurred in the agricultural regions where 5 cm of the surface soil and vegetation were removed and replaced with uncontaminated soil (Fig. 1), with the subsequent natural restoration promoting revegetation in these decontaminated regions11,13,16.

The effectiveness of such intensive decontamination at reducing radiation exposure in situ is apparent, with air dose rates decreasing by 20–70% after decontamination13. However, as 137Cs can firmly bind to clay minerals, it is transported along with suspended sediments (particulate 137Cs) in the river system to the Pacific Ocean17,18. Comprehensively assessing the impacts of land-use changes in decontaminated regions on the downstream ecosystem is also necessary from the perspective of environmental sustainability. Moreover, recent studies have shown notable differences in the reduction in the particulate 137Cs concentration over time across 30 rivers in Fukushima19,20, further underscoring the need to study land-use impacts on downstream particulate 137Cs discharge into the ocean.

In addition to contaminant migration, land-use changes induced by strong perturbations (for example, decontamination) also alter land–ocean sediment transfer patterns21,22, which in turn affect elemental cycles23, biodiversity24 and global climate25. Systematically assessing the perturbations’ impacts on downstream river suspended sediments (SS) has thus become a joint goal of many related disciplines and a key part of developing science-based catchment management strategies26,27,28,29. However, owing to the limited availability of reliable and concurrent river monitoring data, how downstream river SS variations and land-use changes are linked remains unclear21.

With approximately 11.9% of the watershed area subjected to government-led decontamination between 2013 and early 2017, the Niida River Basin in Fukushima (Fig. 2a)11,30 provides an excellent opportunity to examine the long-term impact on the dynamics of SS and particulate 137Cs in river systems. Previous short-term river studies19,20,31,32,33,34 have suggested an increased river SS load and decreased particulate 137Cs concentrations during decontamination. Several studies that analysed geochemical fingerprints in deposited sediments have implied a significant contribution of sediment sources from the decontaminated regions to the river35,36,37. Yet, given that threats to sustainable catchment management from anthropogenic perturbations are often long-term28,29, more comprehensive and reliable data on quantified land cover and continuous river records are required to explore the effect of decontamination on river SS and particulate 137Cs discharge.

Here we provide a comprehensive assessment of the impacts of land-use changes in decontaminated regions on river SS and particulate 137Cs dynamics, as well as the downstream discharge. We mapped the evolution of decontaminated region boundaries using governmental decontamination documents (Fig. 2b), photographed the land cover in the decontaminated regions using drones and quantified the land-use changes using the normalized difference vegetation index (NDVI) at 10 m spatial resolution. Meanwhile, we conducted a long-term field investigation (Methods and Supplementary Table 1) spanning the decontamination (2013–2016) and natural restoration (2017–2018) stages to continuously record the fluctuations in water discharge and turbidity (10 min temporal resolution) and particulate 137Cs concentrations, both upstream and downstream. Combining the above quantitative data, we systematically reveal that long-term land-use changes in upstream decontaminated regions greatly affect sediment and 137Cs discharge from downstream river systems into the Pacific Ocean.

Land-cover changes in decontaminated regions

Regional decontamination was accomplished in March 2017, spanning over 22.9% and 11.9% of the upstream (Notegami) and downstream (Haramachi) watershed areas, respectively (Fig. 2c). In 2014, agricultural land (18.02 km2) was one of the major land uses in the regions where decontamination was ordered, with a significant increase of over 720% compared with that in 2012. Conversely, the changes in the ordered grassland (1.93 km2) were minimal, with an approximately 26% increase between 2012 and 2014. Given that overall land-cover changes were more pronounced in agricultural lands than in grasslands or residential lands, large-scale agricultural land decontamination may severely alter landscape erodibility and consequently the sediment supply. Moreover, the proximity of the decontaminated agricultural land to rivers increases sediment transport from terrestrial environments.

Drone photographs (Fig. 3a and Supplementary Fig. 1) showed significant land-cover changes in the upstream decontaminated regions. For instance, the agricultural land at the Hiso site (D3, Fig. 3a) was almost bare in August 2016 when the decontamination was completed. However, natural restoration caused the recovery of vegetation during the post-decontamination stage (August 2018). Considering the decontamination sequence and seasonal dependence of the plant growth cycle38, drastic spatiotemporal land-cover changes in the decontamination regions are conceivable.

To quantitatively estimate and compare land-cover changes in the decontaminated regions, we generated NDVI maps in these regions based on the available satellite images from Sentinel 2 and the Moderate Resolution Imaging Spectroradiometer (MODIS) between 2011 and 2018. The comparison between realistic scenarios and Sentinel 2-based NDVI maps (spatial resolution: 10 m) from drone observation sites (Fig. 3a and Supplementary Fig. 1) confirmed the feasibility of NDVI images in distinguishing bare land and agricultural land with vegetation cover. To improve the temporal–spatial resolution of the NDVI dataset, we used the enhanced spatial and temporal adaptive reflectance fusion model (ESTARFM)39 to fuse Sentinel 2 and MODIS maps. Subsequently, we used interpolation to link these newly generated NDVI data (spatial resolution: 10 m) and plotted daily NDVI variations for all decontaminated regions between 2011 and 2018 (Fig. 3b).

In the daily NDVI variation curve, the peak NDVI during 2013–2014 was similar to the pre-decontamination stage (2012) but decreased by approximately 10% in 2016. After decontamination, the peak value presented an increasing trend under the influence of vegetation recovery. However, as the government lifted the evacuation zone after 2017 and allowed the residents to return, vegetation was again removed from some areas planned for agricultural activities in 2018 (Supplementary Fig. 1b). Further analyses of the NDVI variations in the decontaminated regions scheduled in 2012 (Fig. 3c), 2013 (Fig. 3d) and 2014 (Fig. 3e) showed that the NDVI peaks were decreased by approximately 12%, 11% and 15%, respectively, within 2–3 years after decontamination was ordered, thereby providing unambiguous evidence for decreasing vegetation land cover caused by decontamination.

We converted all NDVI maps derived from ESTARFM-images to C × P (cover management and support practice factors, respectively) maps using empirical models40,41. We then estimated erosion potential (that is, K × LS × C × P in the revised Universal Soil Loss Equation (RUSLE); Methods) maps using the LS (slope length and slope steepness factors, respectively) map (Supplementary Fig. 2) and K (soil erodibility) factor in the decontaminated regions. We found that the slopes of decontaminated regions were generally similar for each decontamination-ordered year (Supplementary Fig. 2), suggesting that the erosion potential was consistent with the NDVI in the decontaminated regions. Therefore, we also estimated the daily variation curve of the erosion potential using the mean CP, LS and K factors in the decontaminated regions.

Here we show the ESTARFM-based NDVI (Fig. 3f) and erosion potential (Fig. 3g) during the summer season for each year (specific periods in Supplementary Table 2). NDVI showed a decreasing trend from 2013 to 2016, while the erosion potential peaked in 2016, representing approximately 98% and 52% increases over the pre-decontamination (2011) and natural restoration (2018) stages, respectively. Combining the corresponding NDVI (Supplementary Fig. 3) and erosion potential maps (Supplementary Fig. 4), significant changes in the spatial differences between the land cover and erosion potential during decontamination were also observed.

Response of river SS to land-cover changes

The downstream river SS load (L; Fig. 4a) exhibited a strong correlation with water discharge (Q) during the monitoring periods (Supplementary Fig. 5 and Supplementary Table 3). Under the range of water discharges from 0.1 to 100 m3 s−1, river SS carrying capacity exhibited a considerable increase from 2013 to 2016 and a slight decrease after decontamination (2017 to 2018). Contrastingly, the range of water discharges was relatively narrow upstream, and a steady decrease in SS loads has been observed since 2015. Although the above result suggests an increase in SS supply during the decontamination stage, the high SS carrying capacity in 2015 is not consistent with the actual decontamination progress. Since decontaminated regions tend to be bare land, sediment loads are prone to increasing during rainstorms due to soil erosion. Governmental decontamination plans showed that over 50% of agricultural land decontamination was planned to be implemented in 2016, implying that the erosion potential of the decontaminated regions should have been higher in 2016, rather than in 2015.

The variations in downstream river SS loads over the 6 years (Supplementary Table 4) exhibited a similar trend to peak river SS load in 2015 (126.7 ± 0.3 Gg yr−1). This was an approximately 1,776%, 140% and 215% increase relative to that of 2013, 2016 and 2018, respectively. The historical rainfall records (Fig. 4b) show that the rainfall in September 2015 (551 mm) was more than two-fold greater than that during the same period in 2016 (274 mm), implying that the SS peak may be related to strong runoff. Here we estimate the SS loads at 1-year-flood discharge (Q = 95 m3 s−1) using established LQ curves, which allow for the comparison of dynamic variations in SS loads under the same flood conditions. In Fig. 4b, a significant increasing trend during the decontamination period is shown, with a 237.1% increase in 2016 compared with 2013. After decontamination, the SS loads drastically decreased by approximately 41% from 2016 to 2017, implying changes in sediment yield and transfer patterns due to natural restoration. These results reveal that river SS loads responded closely to land-cover changes during the study period.

To better explore the response of river SS load to land-cover changes, we extracted river monitoring data during each rainfall event and quantitatively linked the river SS to the corresponding soil loss from the decontaminated regions. We found that SS loads during rainstorms were highly correlated with water discharges in both upstream and downstream areas (Supplementary Fig. 6). Comparing similar rainfall events, significantly greater SS concentrations are observed in 2015–2016 than in other years (Supplementary Figs. 7 and 8). Considering that the land-cover changes induced by decontamination were more pronounced in the summer season, the regression was performed for SS loads between May and October and soil loss during the corresponding period. A more significant correlation was observed (Fig. 4c) between estimated soil loss by RUSLE and SS load upstream (R2 = 0.55, P < 0.01, N = 34) than downstream (R2 = 0.27, P < 0.01, N = 52). Eliminating the effect of rainfall and normalizing by discharge (Fig. 4d) results in a more evident relationship between the erosion potential and SS loads downstream (R2 = 0.35, P < 0.01, N = 52). Overall, these results demonstrate the connection between river SS dynamics and land-cover changes in the decontaminated regions. The short distance between the upstream catchment and decontaminated regions makes soil erosion a critical driver for upstream river SS transport, whereas the downstream river is dependent on long-distance SS transport, making water discharge an important driver for the downstream catchment.

Long-term impact on river SS and 137Cs discharge

From August 2014 to March 2017, the particulate 137Cs concentration in Haramachi exhibited a steep decrease, contrasting remarkably with the limited 137Cs variation observed in the early decontamination stages (January 2013 to August 2014; Fig. 5a). The effective half-life of the particulate 137Cs (eliminated by the natural attenuation factor) during this decontamination period (1.87 yr) was considerably faster than that of physical decay of 137Cs (30.1 yr), the early decontamination period (16.9 yr) and the surrounding contaminated catchments (mean of 4.92 yr)20. Such a sharp decrease in the 137Cs concentration was also observed at the other three monitoring sites (Supplementary Fig. 9a). Because the 137Cs concentration in decontaminated soil was considerably lower than that in the contaminated soil37,42, these results suggest the contribution of sediment from decontaminated regions to the river system. Moreover, strong negative correlations were observed between measured 137Cs levels and decontamination progress at all monitoring sites (Fig. 5b and Supplementary Fig. 9b), which further supports our interpretation. The observed 137Cs concentration increased by approximately 150% in 2018 compared with that at the end of 2016, which may be caused by the weakened sediment supply from decontaminated regions owing to natural restoration and resulting in a relatively increased contribution of sediments from contaminated forest regions13.

Given that the variation in 137Cs concentrations reflects a change in sediment source, the deviations between the measured 137Cs and the natural decrease in 137Cs derived from surrounding contaminated catchments provide a way to quantitatively estimate the contribution of sediment from decontaminated regions (Fig. 5c). In the early decontamination period, our results showed slight variations in the 137Cs concentration (Fig. 5a), which could be attributed to the contribution of sediment from upstream regions with different degrees of contamination. During the main decontamination period, the erosion potential in the summer of 2015 was approximately 22% higher than that in 2014 and the heavy rainfall caused the largest flooding event during the study period (26-year flood). This may result in the sediment from decontaminated regions not being the dominant source for downstream. In 2016, decontamination caused an increase by approximately 59% in the erosion potential compared with 2013, with the contribution percentage steadily increasing over this period to a maximum of 75.7% ± 3.2% (value ± 95% uncertainty). After decontamination, the decreased contribution of sediment from decontaminated regions and the increased 137Cs concentrations can both be attributed to the reduction of soil loss from upstream due to natural restoration.

The 137Cs discharge from contaminated catchments around the Fukushima region into the Pacific Ocean is another ecological issue of global concern. Our data show that the export flux of particulate 137Cs from the downstream of the Niida river (that is, Haramachi) peaked in 2015 (1.24 TBq yr−1, equalling 0.65% 137Cs loss), which is an approximately 667%, 233% and 429% increase relative to that in 2013, 2016 and 2018, respectively (Fig. 5d). Although such 137Cs loss is negligible compared with the terrestrial inventory, it is approximately 105 times greater than that in the pre-Fukushima stage43,44. Accordingly, the dynamic variations in 137Cs discharge from terrestrial environments into the Pacific Ocean, and its drivers, require more attention in the future.

Here we used SS loads at one-year-flood discharge to normalize the 137Cs flux and found its peak occurred in 2015 (Fig. 5e). Additionally, the reduction of the normalized 137Cs flux from 2013 to 2016 (~32%) was similar to natural attenuation in the non-contaminated catchment (~34%) over same period, which may be due to the increased SS load during decontamination offsetting the role of declining 137Cs concentrations in reducing 137Cs emission. During the subsequent natural restoration period, the rapid NDVI increase (Fig. 3f) suggested vegetation recovery in decontaminated regions and a decrease in regional erosion potential (Fig. 3g). This resulted in an approximately 24% decrease in sediment yield from the catchment and an approximately 31% decrease in the contribution of sediment from decontaminated regions (Fig. 5c) from 2016 to 2018. Due to the mutual balance of these effects, there were no significant changes in normalized particulate 137Cs flux in 2018 compared with 2016.

Discussion

Our work highlights the great potential of interdisciplinary analyses for understanding river SS variation and quantifying the contribution of sediment from specific regions. Fukushima decontamination practices, like a controllable validation experiment, justified the reliability of using long-term 137Cs monitoring data for tracing sediment source dynamics due to specific perturbation. Combining the long-term dataset of 137Cs (or other fallout radionuclides) in SS with remote sensing images would provide additional evidence to determine if the changes in the downstream SS transport pattern are linked to the upstream perturbation.

With these interdisciplinary analyses, we systematically reveal how changes in land use in the decontaminated regions significantly influences downstream river SS and 137Cs discharge into the ocean. Indeed, the secondary environmental impacts of surface remediation are being increasingly considered in the broader field concerning remediation of regions contaminated with hazardous materials (for example, heavy metals and organic contaminants)45. The concept of environmental sustainability-centred green remediation has also been brought up in many scenarios46,47. The Fukushima decontamination practice provides evidence showing that mechanical remediation can cause persistently excessive SS load downstream, though it also reduced river 137Cs concentrations. Since persistently excessive turbidity in rivers affects not only surrounding residents’ water use but also trophic level structure in aquatic environments48, the unsustainable downstream impacts caused by upstream decontamination should be highly regarded. The vegetation recovery after land development is highly dependent on local conditions49, and the soil used for decontamination and local high rainfall amount in Fukushima promoted rapid vegetation recovery11,13, which shortened the duration of such unsustainable impacts. Therefore, future upstream contaminated lands that await mechanical remediation need to consider the pre-assessment of local natural restoration conditions or the preparation of appropriate revegetation measures in the catchments’ regulatory frameworks, which would minimize the impact of long-term decontamination on downstream sustainability.

Methods

Study region

The Niida River Basin (265 km2) is located about 40 km northwest of the damaged FDNPP. The topography of its upstream is almost mountainous and its soil types are mainly cambisols and andosols, while fluvisols are the dominant soil type in the downstream plain50. The monitoring data from the Japan Meteorological Agency show that the average rainfall in the Niida River Basin is greater than 1,300 mm, with more than 75% of the rainfall occurring between May and October. According to the third airborne monitoring survey by the Japanese government, the 137Cs inventory in the Niida River Basin was over 700 kBq m−2 (ref. 14). Because of particularly high contamination in its upstream watershed (over 1,000 kBq m−2)51, the government-led decontamination was implemented in the upstream basin from 2013 to 2016 (~1% of the area was extended to March 2017).

Land-cover observation

We constructed the vector decontamination maps based on the paper maps from the Ministry of the Environment, Japan. The boundaries of the decontaminated regions with different land-use types were first outlined by creating polygons using Google Earth. Subsequently, the projections of these polygons were imported to ArcMap v.10.3 to quantitatively evaluate their area.

During the decontamination (2016) and post-decontamination stages (2018), drone photography was utilized (Fig. 2a, triangle) to compare land-cover changes. A commercially available drone (Phantom 4, DJI product) was employed at 100 m above the ground in Matsuzuka (D1; 37.689° N, 140.720° E), Iitoi (D2; 37.663° N, 140.723° E) and Hiso (D3; 37.613° N, 140.711° E) to take photographs.

Quantification of land-cover changes in decontaminated regions

We calculated NDVI within the boundary of the decontaminated regions to quantify the land-cover changes. Through the spectral reflectance dataset in the red (R, nm) and near-infrared (NIR, nm) regions, the NDVI was calculated as52:

NDVI=NIR−RNIR+R.

(1)

The available satellite images from 2011 to 2018 from Sentinel 2 were downloaded from the United States Geological Survey53, while the concurrent MODIS images were derived from the National Aeronautics and Space Administration’s Reverb54. The wavelength bands and spatiotemporal resolutions of the satellite images used here are summarized in Supplementary Tables 5 and 6.

To confirm the reliability of the newly generated NDVI variation curve, NDVIs for the same date as the Sentinel 2 images were estimated using the interpolation and compared with the Sentinel 2-based NDVI. The linear regression analysis showed that the fitting R2 was 0.99 (N = 16, P < 0.01). We also calculated the NDVI in the decontaminated region based on available satellite images of Landsat 5/7/8 (ref. 53) and established a daily NDVI variation curve. The linear regression analysis also showed a high R2 between two daily NDVI curves (R2 = 0.97, N = 2868, P < 0.01). Therefore, these NDVIs calculated by different satellite images confirmed the reliability of the NDVI variation curve based on ESTARFM.

Estimation of erosion potential in decontaminated regions

To link the land-cover changes in decontaminated regions with the soil erosion dynamics, we defined an erosion potential (K × LS × C × P) based on the RUSLE.

The soil loss (A, t ha−1 yr−1) of a specific region can be estimated as55:

A=R×K×LS×C×P,

(2)

where R is the precipitation erosivity factor (MJ mm ha−1 h−1 yr−1), K represents the soil erodibility factor (t h MJ−1 mm−1), L and S are slope length factor (dimensionless) and slope steepness factor (dimensionless), respectively, and C and P are the cover management factor (dimensionless) and support practice factor (dimensionless), respectively. Because these parameters are often set as fixed values, it is difficult to assess the soil loss dynamics during anthropogenic disturbances. To address this problem, we used daily NDVI data to estimate C × P and then considered these dynamic factors in RUSLE.

Wakiyama et al.40 reported a correlation between vegetation cover in Fukushima and the sediment discharges from the standard USLE plot (that is, soil loss, A) that have been normalized by R, K, S and L factors40,56. Therefore, this empirical equation reflects the quantitative relationship between vegetation fractions (VF) and C × P.

To quantify daily C × P changes in decontaminated regions, we first converted the interpolated daily NDVI into the VF by a semi-empirical equation41:

VF=1−(NDVI−NDVI∞NDVIs−NDVI∞)0.6175,

(3)

where NDVIs and NDVI represent the NDVI value for land cover corresponding to no plants and 100% green vegetation cover, respectively. Since these values mainly depend on plant species and soil types, we followed previous methods applied to agricultural land and set NDVIs and NDVI as 0.05 and 0.88, respectively41.

Subsequently, the C × P was estimated by the empirical equation derived from uncultivated farmlands and grasslands (R2 = 0.47, N = 145)40:

C×P=0.083×e−5.666×VF.

(4)

Since the soil type used for decontamination is generally the same, the K factor was set as a constant (0.039; ref. 40). For the LS factor, we downloaded a digital elevation model from the Geospatial Information Authority of Japan (spatial resolution: 10 m) to build an LS map using55:

LS=[QM22.13]y×(0.065+0.045×Sg+0.0065×S2g),

(5)

where Qa is the flow accumulation grid, Sg represents the grid slope as a percentage, M is the grid size and y is a parameter depended on slope steepness. We here used the y values recommended by a published study, ref. 55.

The calculated LS-factor map (Supplementary Fig. 2) showed a relatively consistent LS distribution in space. Based on the ESTARFM-generated satellite images, we compared C×P and erosion potential (K × LS × C × P) and found a significant correlation (R2 = 0.99, P < 0.01, N = 174). Since these results suggest that LS factors in decontaminated regions have a negligible effect on the erosion potential, the mean LS factor and interpolated NDVI based on the daily variation curve (Fig. 3b) were used to estimate the daily erosion potential.

Monitoring of river discharge and turbidity

The water-level gauges (in situ Rugged TROLL100 Data Logger) and a turbidimeter (ANALITE turbidity NEP9530, McVan Instruments) were installed in each monitoring site to continuously recording the water level and turbidity with a temporal resolution of 10 min. As ocean tides may influence the accuracy of water-level monitoring, the Sakekawa site (M4 in Fig. 2) was excluded from the river monitoring programme.

The recorded water level (H, m) was converted to the water discharge (Q, m3 h−1) based on the annual HQ curves for each monitoring site. These curves were calibrated using a synchronous monitoring dataset of 10-min-resolution water level and discharge provided by the Fukushima prefecture’s official monitoring network57. Because of occasional damage to the water-level gauge at the Haramachi site, the available monitoring data with a temporal resolution of 10 min recorded by the Fukushima prefecture’s official monitoring network57 were used to fill the gaps. The percentages of filling data from official monitoring network were all less than 34% except for 2015 (56.6%). Although similar situations occurred in Notegami, we were unable to fill in gaps with other data due to the lack of a concurrent monitoring network.

The hourly SS concentration (Css, g m−3) at each monitoring site was calculated from the measured turbidity (T, mV) using a calibrated curve20. As the turbidimeter was susceptible to the moss and debris flowing in the river, the dataset was verified with an automated check by HEC-DSSVue (The U.S. Army Corps of Engineers’ Hydrologic Engineering Center Data Storage System) before transforming the data.

The SS load was estimated as the product of the corresponding datasets of discharge and SS concentration, after which we can obtain the annual SS load (L, ton yr−1) by taking the sum:

L=∑(Q×Css).

(6)

We estimated values for gaps including missing and abnormal data through a linear model established by 10-min-resolution monitoring data at the same site. The reliability of the gap-filling strategies used in this study has been documented by Taniguchi et al.19,20 These procedures vastly enhance the possibility of reconstructing the complete dataset. In this study, only the error in converting from water discharge to SS load was considered in the uncertainty assessment, and all estimates were within 0.5% (95% confidential interval) in this case. To reduce the uncertainty of LQ fitting, the 10-min monitoring dataset (discharge and SS load) was transformed to a 1-hour dataset.

Considering the river SS is often transported by discharge, we used downstream LQ curves to estimate river SS loads at 1-year-flood discharge (Q = 95 m3 s−1), which eliminates the influence caused by different annual water discharges. The 1-year-flood discharge was calculated from the daily maximum discharge data from 1 January 2013 to 30 September 2020 at the Haramachi site.

To compare river SS dynamics during rainfall events, we here defined a rainfall event as the increase in water discharge exceeding 1.4 and 1.6 times the baseflow before precipitation for the upstream and downstream catchments, respectively. As a result, a total of 64 and 72 rainfall events from the Notegami and Haramachi sites were identified.

To study the dynamic relationship between soil loss from decontaminated regions and river SS load, we estimated eroded soil amount during each rainstorm using RUSLE. Specifically, the NDVI during a specific rainfall was determined by interpolation. Subsequently, the corresponding C × P can be estimated using equations (3) and (4). With the mean values of the K and LS factors, the erosion potential can then be calculated. Finally, precipitation erosivity factor (Supplementary Table 7) for each rainfall event can be calculated as58:

R=1nj=1nk=1mj(EI30)k,

(7)

where n is the number of years used, mj is the number of precipitation events in each given year j and E and I30 represent each event’s kinetic energy (MJ) and maximum 30 min precipitation intensity (mm h−1), respectively, for each event k. The event’s erosivity, EI30, can be calculated as58:

EI30=(∑r=10ervr)I30,

(8)

where er denotes the unit rainfall energy (MJ ha−1 mm−1) and vr provides the rainfall volume during a set period (r) (mm). For this calculation, the criterion for the identification of a precipitation event is consistent with previous work, that is, the cumulative rainfall of an event is greater than 12.7 mm (ref. 58). If another rainfall event occurs within 6 h of the end of a rainfall event, they are counted as one event. Therefore, the unit rainfall energy (er) can be derived for each time interval based on rainfall intensity (ir, mm h−1)58:

er=0.29[1−0.72e(−0.05×ir)].

(9)

The calculation’s required parameters were derived from the historical precipitation record from the Japan Meteorological Agency59. For the Notegami catchment, the precipitation monitoring data were derived from Iitate. For the Haramachi catchment, the precipitation was obtained from three adjacent monitoring sites (that is, Haramachi, Iitate and Tsushima) with the specific weights of 0.143, 0.545 and 0.312, respectively. These weights were determined by the Voronoi diagram method in a Geographic Information System60.

River monitoring of particulate 137Cs

At each monitoring site, the suspended sediment sampler proposed by Phillips et al.61 was installed at 20–30 cm above the riverbed for the time‐integrated sampling of river suspended sediment. The reliability of this sampler has been widely proven in past studies19,20. After sampling, the trapped turbid water and SS samples were transferred into a clean polyethylene container and stored until laboratory analysis.

The SS samples were separated from the collected water mixture via natural precipitation and physical filtration, dried at 105 °C for 24 h and subsequently packed into a plastic container. The activities of 137Cs in the SS samples (C, Bq kg−1) were determined via the measurement system, which consists of a high-purity germanium γ-ray spectrometer (GCW2022S, Canberra−Eurisys, Meriden) coupled to an amplifier (PSC822, Canberra, Meriden) and multichannel analyser (DSA1000, Canberra, Meriden). The measurement system was calibrated with the standard soil sample from the International Atomic Energy Agency. Under the 662 keV energy channel, each measurement batch would take approximately 1–24 h to make the analytical precision of the measurements within 10% (95% confidential interval). All measured 137Cs concentrations were decay-corrected to their sampling date. Moreover, the results obtained in this study were also normalized by their initial average 137Cs inventory in the catchment (D, Bq m−2) to eliminate the effect caused by spatial differences.

As 137Cs concentration in the sediment sample depends on particle size19,20, we conducted a particle size correction for all measured data in Takase, Ukedo and Haramachi to eliminate this effect. The particle size distributions for dried SS samples were analysed using the laser diffraction particle size analyser (SALD-3100, Shimadzu Co., Ltd.). With the parameterized particle size distributions, the particle size correction coefficient (Pc) can be calculated by19:

Pc=(SsSr)v,

(10)

where Sr and Ss represent the reference and collected samples’ specific surface areas (m2 g−1). The exponent coefficient, v, is a fitting parameter associated with chemical and mineral compositions. In this study, the same parameters measured in the Abukuma River, the major river in the Fukushima area, were applied for Sr (0.202 m2 g−1) and v (0.65). The specific surface area for collected SS samples was estimated by the following equation under a spherical approximation20:

Ss=∑(6×ρ−1×d−1i×p−1i),

(11)

where ρ is the particle density and di and pi denote the ratio and diameter of the particle size fraction for particle i. Therefore, the 137Cs concentration corrected for particle size can be obtained by dividing the measured 137Cs concentration by Pc.

Considering that the decrease in particulate 137Cs concentration in a catchment was also affected by natural attenuation, there is a need to eliminate this effect from the declining trend of our observed 137Cs dataset to highlight the impacts of decontamination. The Ukedo and Takase are rivers surrounding the Niida River with similar contaminated situations. Our long-term 137Cs monitoring data from downstream of these two catchments showed that their 137Cs decline trends were relatively steady. Although there is a dam reservoir upstream of Ukedo, the 137Cs concentration observed both upstream and downstream showed a similar declining trend62. Therefore, the above evidence suggests that natural attenuation was the dominant factor controlling the 137Cs decrease in these two rivers. Here we assumed that the natural attenuation trend of 137Cs in the surrounding catchments (Ukedo and Takase) with little effect by decontamination was similar to that of the Haramachi catchment. Thus, we fitted their time change curves of 137Cs concentration (normalized by average 137Cs inventory of the corresponding catchment) using an exponential model. We then estimated the 137Cs concentration at the same sampling time as Haramachi in the two catchments by using the fitting models. Finally, we calculated the mean value of the two datasets and recalculated the effective half-life (Teff = ln(2)/λ; λ is the fitting exponential term) of the natural attenuation by the exponential model.

The 137Cs flux (LCs, Bq) for each monitoring site was estimated by the product of the SS flux and the 137Cs concentration in the suspended sediment sample. We then took the sum over that year:

LCs=∑(Q×Css×C).

(12)

According to the law of error propagation, we considered the error from SS load and 137Cs measurement in the combined uncertainty assessment for 137Cs fluxes and found their values are all within 1.1% (95% confidential interval).

Using 137Cs as a tracer in estimating SS source contribution

Although 137Cs has been widely used in tracing sediment source, the spatial variability of the 137Cs deposition inventory in the Fukushima catchment hinders the estimation of the source contribution from a specific region. However, for the decontaminated catchments, as the 137Cs concentration in decontaminated soil was much lower than that in contaminated regions (for example, forested regions and the riverbank)11,13,63, the fluctuations in the particulate 137Cs concentration can help to identify the sediment from the decontamination regions. Specifically, we assumed that the particulate 137Cs concentrations in surrounding contaminated watersheds (that is, having similar land-use composition) follow a similar decline trend driven by natural reasons, while the decontamination-induced land-cover changes cause other sediment sources to mix with the original river SS and thus result in a deviation in observed 137Cs concentrations from this natural trend. Therefore, the relative contribution (RC) of the specific sediment source can be expressed as:

RC=(Cm−Cn)(Cs−Cn),

(13)

where the Cm is the measured 137Cs concentration and Cs and Cn represent the 137Cs concentration in a specific sediment source and the naturally varied 137Cs concentration at the same time as the measured 137Cs. For data comparability, all 137Cs concentrations presented here were corrected by their particle size and 137Cs inventory. We also excluded the samples with collection weights below 0.5 g from the calculations due to their high uncertainty in Pc measurement.

In this study, the specific sediment source is the decontaminated soil in the Niida River Basin where the 137Cs concentration was approximately 53.99 ± 40.90 Bq kg−1 (refs. 37,42; mean ± standard deviation, N = 8). The natural decline of the 137Cs concentration (that is, λ) was established using temporal variation in 137Cs data originating from the Ukedo and Takase rivers, which were scarcely influenced by decontamination. The first measured 137Cs data in Haramachi were set as the starting point of its natural decline curve. The total uncertainty for the contribution percentage of SS from the decontaminated regions was calculated by the propagation of error from each part with the uncertainties originating from the measured 137Cs concentration, 137Cs concentration in a specific source and the natural 137Cs concentration. For the uncertainty in the 137Cs concentration in decontaminated soil (Cs), we set the standard deviation as its error source, while the natural 137Cs concentrations were calculated by the propagation of the 95% confidential interval of the fitting curves.

Reporting summary

Further information on research design is available in the Nature Research Reporting Summary linked to this article.

Data availability

Ordered decontamination process data are available from http://josen.env.go.jp/plaza/info/weekly/weekly_190607.html. Particulate 137Cs monitoring data in Haramachi, Takase and Ukedo during 2012–2017 are available from: https://doi.org/10.34355/Fukushima.Pref.CEC.00014, https://doi.org/10.34355/CRiED.U.Tsukuba.00020 and https://doi.org/10.34355/Fukushima.Pref.CEC.00021. The rest of data presented in this study are available from the corresponding author upon request.

References

  1. Anspaugh, L. R., Catlin, R. J. & Goldman, M. The global impact of the Chernobyl reactor accident. Science 242, 1513–1519 (1988).CAS  Article  Google Scholar 
  2. Ten Hoeve, J. E. & Jacobson, M. Z. Worldwide health effects of the Fukushima Daiichi nuclear accident. Energy Environ. Sci. 5, 8743–8757 (2012).Article  CAS  Google Scholar 
  3. Shagina, N. B. et al. Reconstruction of the contamination of the Techa River in 1949–1951 as a result of releases from the “MAYAK” Production Association. Radiat. Environ. Biophys. 51, 349–366 (2012).CAS  Article  Google Scholar 
  4. Jones, S. Windscale and Kyshtym: a double anniversary. J. Environ. Radioact. 99, 1–6 (2008).CAS  Article  Google Scholar 
  5. Beresford, N. A. et al. Thirty years after the Chernobyl accident: what lessons have we learnt? J. Environ. Radioact. 157, 77–89 (2016).CAS  Article  Google Scholar 
  6. Steinhauser, G., Brandl, A. & Johnson, T. E. Comparison of the Chernobyl and Fukushima nuclear accidents: a review of the environmental impacts. Sci. Total Environ. 470–471, 800–817 (2014).Article  CAS  Google Scholar 
  7. Fesenko, S. V. et al. An extended critical review of twenty years of countermeasures used in agriculture after the Chernobyl accident. Sci. Total Environ. 383, 1–24 (2007).CAS  Article  Google Scholar 
  8. Poston, T. M., Peterson, R. E. & Cooper, A. T. Past radioactive particle contamination in the Columbia River at the Hanford site, USA. J. Radiol. Prot. 27, A45 (2007).CAS  Article  Google Scholar 
  9. Voitsekhovitch, O., Nasvit, O., Los’y, I. & Berkovsky, V. Present thoughts on the aquatic countermeasures applied to regions of the Dnieper River catchment contaminated by the 1986 Chernobyl accident. Stud. Environ. Sci. 68, 75–85 (1997).Article  Google Scholar 
  10. Ramzaev, V., Barkovsky, A., Mishine, A., Andersson, K. G. & Well-being, H. Decontamination tests in the recreational areas affected by the Chernobyl accident: efficiency of decontamination and long-term stability of the effects. J. Soc. Remediat. Radioact. Contam. Environ. 1, 93–107 (2013). Google Scholar 
  11. Evrard, O., Patrick Laceby, J. & Nakao, A. Effectiveness of landscape decontamination following the Fukushima nuclear accident: a review. Soil 5, 333–350 (2019).CAS  Article  Google Scholar 
  12. Kinase, T. et al. The seasonal variations of atmospheric 134,137Cs activity and possible host particles for their resuspension in the contaminated areas of Tsushima and Yamakiya, Fukushima, Japan. Prog. Earth Planet. Sci. 5, 12 (2018).
  13. Onda, Y. et al. Radionuclides from the Fukushima Daiichi Nuclear Power Plant in terrestrial systems. Nat. Rev. Earth Environ. 1, 644–660 (2020).CAS  Article  Google Scholar 
  14. Kato, H., Onda, Y., Gao, X., Sanada, Y. & Saito, K. Reconstruction of a Fukushima accident-derived radiocesium fallout map for environmental transfer studies. J. Environ. Radioact. 210, 105996 (2019).CAS  Article  Google Scholar 
  15. Remediation of Contaminated Areas in the Aftermath of the Accident at the Fukushima Daiichi Nuclear Power Station. Overview, Analysis and Lessons Learned. Part 1. A Report on the “Decontamination Pilot Project” (Japan Atomic Energy Agency, 2015); https://jopss.jaea.go.jp/pdfdata/JAEA-Review-2014-051.pdf
  16. Decontamination Guidelines 2nd edn (Ministry of the Environment, 2013); http://josen.env.go.jp/en/%0Aframework/pdf/decontamination_guidelines_2nd.pdf
  17. Iwagami, S. et al. Temporal changes in dissolved 137Cs concentrations in groundwater and stream water in Fukushima after the Fukushima Dai-ichi Nuclear Power Plant accident. J. Environ. Radioact. 166, 458–465 (2017).CAS  Article  Google Scholar 
  18. Aoyama, M., Tsumune, D., Inomata, Y. & Tateda, Y. Mass balance and latest fluxes of radiocesium derived from the Fukushima accident in the western North Pacific Ocean and coastal regions of Japan. J. Environ. Radioact. 217, 106206 (2020).CAS  Article  Google Scholar 
  19. Taniguchi, K. et al. Transport and redistribution of radiocesium in Fukushima fallout through rivers. Environ. Sci. Technol. 53, 12339–12347 (2019).CAS  Article  Google Scholar 
  20. Taniguchi, K. et al. Dataset on the 6-year radiocesium transport in rivers near Fukushima Daiichi Nuclear Power Plant. Sci. Data 7, 433 (2020).
  21. Walling, D. E. Human impact on land–ocean sediment transfer by the world’s rivers. Geomorphology 79, 192–216 (2006).Article  Google Scholar 
  22. Borrelli, P. et al. An assessment of the global impact of 21st century land use change on soil erosion. Nat. Commun. 8, 2013 (2017).
  23. Piao, S. et al. Changes in climate and land use have a larger direct impact than rising CO2 on global river runoff trends. Proc. Natl Acad. Sci. USA 104, 15242–15247 (2007).CAS  Article  Google Scholar 
  24. Jung, M., Rowhani, P. & Scharlemann, J. P. W. Impacts of past abrupt land change on local biodiversity globally. Nat. Commun. 10, 5474 (2019).
  25. Borrelli, P. et al. Land use and climate change impacts on global soil erosion by water (2015–2070). Proc. Natl Acad. Sci. USA 117, 21994–22001 (2020).CAS  Article  Google Scholar 
  26. Overeem, I. et al. Substantial export of suspended sediment to the global oceans from glacial erosion in Greenland. Nat. Geosci. 10, 859–863 (2017).CAS  Article  Google Scholar 
  27. Giam, X., Olden, J. D. & Simberloff, D. Impact of coal mining on stream biodiversity in the US and its regulatory implications. Nat. Sustain. 1, 176–183 (2018).Article  Google Scholar 
  28. Hackney, C. R. et al. River bank instability from unsustainable sand mining in the lower Mekong River. Nat. Sustain. 3, 217–225 (2020).Article  Google Scholar 
  29. Wang, S. et al. Reduced sediment transport in the Yellow River due to anthropogenic changes. Nat. Geosci. 9, 38–41 (2016).CAS  Article  Google Scholar 
  30. Environmental Remediation (Ministry of the Environment, Government of Japan, 2021); http://josen.env.go.jp/en/decontamination/
  31. Niizato, T. & Watanabe, T. 137Cs outflow from forest floor adjacent to a residential area: comparison of decontaminated and non-decontaminated forest floor. Glob. Environ. Res. 24, 129–136 (2021); http://www.airies.or.jp/ebook/Global_Environmental_Research_Vol.24No.2.pdf Google Scholar 
  32. Sakuma, K. et al. Evaluation of sediment and 137Cs redistribution in the Oginosawa River catchment near the Fukushima Dai-ichi Nuclear Power Plant using integrated watershed modeling. J. Environ. Radioact. 182, 44–51 (2018).CAS  Article  Google Scholar 
  33. Iwagami, S. et al. Six-year monitoring study of 137Cs discharge from headwater catchments after the Fukushima Dai-ichi Nuclear Power Plant accident. J. Environ. Radioact. 210, 106001 (2019).CAS  Article  Google Scholar 
  34. Ochiai, S. et al. Effects of radiocesium inventory on 137Cs concentrations in river waters of Fukushima, Japan, under base-flow conditions. J. Environ. Radioact. 144, 86–95 (2015).CAS  Article  Google Scholar 
  35. Evrard, O. et al. Impact of the 2019 typhoons on sediment source contributions and radiocesium concentrations in rivers draining the Fukushima radioactive plume, Japan. Collect. C. R. Geosci. 352, 199–211 (2020). Google Scholar 
  36. Evrard, O. et al. Quantifying the dilution of the radiocesium contamination in Fukushima coastal river sediment (2011–2015). Sci. Rep. 6, 34828 (2016).
  37. Evrard, O. et al. Radionuclide contamination in flood sediment deposits in the coastal rivers draining the main radioactive pollution plume of Fukushima Prefecture, Japan (2011–2020). Earth Syst. Sci. Data 13, 2555–2560 (2021).Article  Google Scholar 
  38. Chu, H., Venevsky, S., Wu, C. & Wang, M. NDVI-based vegetation dynamics and its response to climate changes at Amur-Heilongjiang River Basin from 1982 to 2015. Sci. Total Environ. 650, 2051–2062 (2019).CAS  Article  Google Scholar 
  39. Zhu, X., Chen, J., Gao, F., Chen, X. & Masek, J. G. An enhanced spatial and temporal adaptive reflectance fusion model for complex heterogeneous regions. Remote Sens. Environ. 114, 2610–2623 (2010).Article  Google Scholar 
  40. Wakiyama, Y., Onda, Y., Yoshimura, K., Igarashi, Y. & Kato, H. Land use types control solid wash-off rate and entrainment coefficient of Fukushima-derived 137Cs, and their time dependence. J. Environ. Radioact. 210, 105990 (2019).CAS  Article  Google Scholar 
  41. Gao, L. et al. Remote sensing algorithms for estimation of fractional vegetation cover using pure vegetation index values: a review. ISPRS J. Photogramm. Remote Sens. 159, 364–377 (2020).Article  Google Scholar 
  42. Nemoto, T. & Matsuki, N. Soil Stratification Survey on Farmland Soil after Decontamination in Iitate Village (in Japanese) (Fukushima Agricultural Technology Centre, 2015).
  43. Wakiyama, Y., Onda, Y., Mizugaki, S., Asai, H. & Hiramatsu, S. Soil erosion rates on forested mountain hillslopes estimated using 137Cs and 210Pbex. Geoderma 159, 39–52 (2010).Article  Google Scholar 
  44. Fukuyama, T., Takenaka, C. & Onda, Y. 137Cs loss via soil erosion from a mountainous headwater catchment in central Japan. Sci. Total Environ. 350, 238–247 (2005).CAS  Article  Google Scholar 
  45. Hou, D., Gu, Q., Ma, F. & O’Connell, S. Life cycle assessment comparison of thermal desorption and stabilization/solidification of mercury contaminated soil on agricultural land. J. Clean. Prod. 139, 949–956 (2016).CAS  Article  Google Scholar 
  46. Ding, D., Song, X., Wei, C. & LaChance, J. A review on the sustainability of thermal treatment for contaminated soils. Environ. Pollut. 253, 449–463 (2019).CAS  Article  Google Scholar 
  47. Hou, D. & Al-Tabbaa, A. Sustainability: a new imperative in contaminated land remediation. Environ. Sci. Policy 39, 25–34 (2014).Article  Google Scholar 
  48. Kemp, P., Sear, D., Collins, A., Naden, P. & Jones, I. The impacts of fine sediment on riverine fish. Hydrol. Process. 25, 1800–1821 (2011).Article  Google Scholar 
  49. Copeland, S. M., Munson, S. M., Bradford, J. B. & Butterfield, B. J. Influence of climate, post-treatment weather extremes, and soil factors on vegetation recovery after restoration treatments in the southwestern US. Appl. Veg. Sci. 22, 85–95 (2019).Article  Google Scholar 
  50. Lepage, H. et al. Investigating the source of radiocesium contaminated sediment in two Fukushima coastal catchments with sediment tracing techniques. Anthropocene 13, 57–68 (2016).Article  Google Scholar 
  51. Delmas, M., Garcia-Sanchez, L., Nicoulaud-Gouin, V. & Onda, Y. Improving transfer functions to describe radiocesium wash-off fluxes for the Niida River by a Bayesian approach. J. Environ. Radioact. 167, 100–109 (2017).CAS  Article  Google Scholar 
  52. E. I. Jazouli, A. et al. Soil erosion modeled with USLE, GIS, and remote sensing: a case study of Ikkour watershed in Middle Atlas (Morocco). Geosci. Lett. 4, 25 (2017).
  53. EarthExplorer (USGS, accessed November 2021); https://earthexplorer.usgs.gov/
  54. EARTHDATA SEARCH (NASA, accessed November 2021); https://search.earthdata.nasa.gov/search?lat=-0.0703125
  55. Ganasri, B. P. & Ramesh, H. Assessment of soil erosion by RUSLE model using remote sensing and GIS—a case study of Nethravathi Basin. Geosci. Front. 7, 953–961 (2016).Article  Google Scholar 
  56. Yoshimura, K., Onda, Y. & Kato, H. Evaluation of radiocaesium wash-off by soil erosion from various land uses using USLE plots. J. Environ. Radioact. 139, 362–369 (2015).CAS  Article  Google Scholar 
  57. River Monitoring Network in Fukushima Prefecture (Fukushima Prefecture, accessed November 2021); http://kaseninf.pref.fukushima.jp/gis/
  58. Panagos, P. et al. Rainfall erosivity in Europe. Sci. Total Environ. 511, 801–814 (2015).CAS  Article  Google Scholar 
  59. Historical Meteorological Record (Japan Meteorological Agency, accessed November 2021); https://www.jma.go.jp/jma/indexe.html
  60. Di, Z. W. et al. Centroidal Voronoi tessellation based methods for optimal rain gauge location prediction. J. Hydrol. 584, 124651 (2020).Article  Google Scholar 
  61. Phillips, J. M., Russell, M. A. & Walling, D. E. Time-integrated sampling of fluvial suspended sediment: a simple methodology for small catchments. Hydrol. Process. 14, 2589–2602 (2000).Article  Google Scholar 
  62. Funaki, H., Sakuma, K., Nakanishi, T., Yoshimura, K. & Katengeza, E. W. Reservoir sediments as a long-term source of dissolved radiocaesium in water system; a mass balance case study of an artificial reservoir in Fukushima, Japan. Sci. Total Environ. 743, 140668 (2020).CAS  Article  Google Scholar 
  63. Laceby, J. P., Huon, S., Onda, Y., Vaury, V. & Evrard, O. Do forests represent a long-term source of contaminated particulate matter in the Fukushima Prefecture? J. Environ. Manage. 183, 742–753 (2016).

Acknowledgements

We appreciate B. Matsushita for his valuable suggestions on satellite image processing and NDVI calculation, J. Chen for sharing the code for ESTARFM, J. Takahashi for sharing 137Cs in decontaminated soil data, H. Kato for his suggestions on presenting the results, S. Fujiwara for his assistance on calculating the precipitation erosivity factor, Y. Yamanaka and T. Kubo for their work on decontamination map development, field investigation and preliminary data analysis and Y. He and F. Yoshimura for their constructive suggestions on improving figure quality. We also acknowledge funding support from the commissioned study from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) FY2011–2012, Nuclear Regulation Authority FY2013–2014, Japan Atomic Energy Agency-funded FY2015–2021, Grant-in-Aid for Scientific Research on Innovative Areas grant number 24110005, Grant-in-Aid for Scientific Research (A) 22H00556, Agence Nationale de la Recherche ANR-11-RSNR-0002 and the Japan Science and Technology Agency as part of the Belmont Forum.

Author information

Authors and Affiliations

  1. Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, Japan Bin Feng, Yuichi Onda, Asahi Hashimoto & Yupan Zhang
  2. Institute of Environmental Radioactivity, Fukushima University, Fukushima, JapanYoshifumi Wakiyama
  3. National Institute of Technology, Tsuyama College, Tsuyama, JapanKeisuke Taniguchi

Contributions

B.F. and Y.O. conceived the study; B.F. performed the data evaluation and all analyses, interpreted the data, wrote the manuscript and prepared all figures and tables in close discussion with Y.O.; Y.O. provided funding support for the field monitoring and all needed resources; K.T. and Y.Z outlined the boundary of the decontamination regions and implemented the drone observations of the sites; and Y.W. and K.T. performed the field river monitoring and determined the particulate 137Cs concentration. B.F., A.H. and Y.Z. prepared all satellite images, ran the NDVI calculation and processed ESTARFM. All listed authors contributed to the editing of the manuscript and approved the final version.

Source: https://www.nature.com/articles/s41893-022-00924-6

July 16, 2022 Posted by | Fuk 2022 | , , , | Leave a comment

Decadal trends in 137Cs concentrations in the bark and wood of trees contaminated by the Fukushima nuclear accident.

Published: 04 July 2022

Abstract

Understanding the actual situation of radiocesium (137Cs) contamination of trees caused by the Fukushima nuclear accident is essential for predicting the future contamination of wood. Particularly important is determining whether the 137Cs dynamics within forests and trees have reached apparent steady state. We conducted a monitoring survey of four major tree species (Japanese cedar, Japanese cypress, konara oak, and Japanese red pine) at multiple sites. Using a dynamic linear model, we analyzed the temporal trends in 137Cs activity concentrations in the bark (whole), outer bark, inner bark, wood (whole), sapwood, and heartwood during the 2011–2020 period. The activity concentrations were decay-corrected to September 1, 2020, to exclude the decrease due to the radioactive decay. The 137Cs concentrations in the whole and outer bark samples showed an exponential decrease in most plots but a flat trend in one plot, where 137Cs root uptake is considered to be high. The 137Cs concentration ratio (CR) of inner bark/sapwood showed a flat trend but the CR of heartwood/sapwood increased in many plots, indicating that the 137Cs dynamics reached apparent steady state within one year in the biologically active parts (inner bark and sapwood) and after several to more than 10 years in the inactive part (heartwood). The 137Cs concentration in the whole wood showed an increasing trend in six plots. In four of these plots, the increasing trend shifted to a flat or decreasing trend. Overall, the results show that the 137Cs dynamics within forests and trees have reached apparent steady state in many plots, although the amount of 137Cs root uptake in some plots is possibly still increasing 10 years after the accident. Clarifying the mechanisms and key factors determining the amount of 137Cs root uptake will be crucial for predicting wood contamination.

Introduction

After the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March of 2011, a wide area of forests in eastern Japan was contaminated with radionuclides. In particular, radiocesium (137Cs) has the potential to threaten the forestry and wood production in the contaminated area for many decades because it was released in large amounts (10 PBq)1 and has a relatively long half-life (30 years). Radiocesium levels for some wood uses are strictly regulated in Japan (e.g., 40 Bq kg−1 for firewood2 and 50 Bq kg−1 for mushroom bed logs3), meaning that multipurpose uses of wood from even moderately contaminated areas are restricted. Although a guidance level of radiocesium in construction wood has not been declared in Japan, the permissible levels in some European countries (370–740 Bq kg−1)4,5,6 suggest that logging should be precautionary within several tens of kilometers from the FDNPP, where the 137Cs activity concentration in wood potentially exceeds 1,000 Bq kg−1 [refs. 7,8]. To determine whether logging should proceed, the long-term variation in wood 137Cs concentration must be predicted as accurately as possible. Many simulation models successfully reproduce the temporal variations in the early phase after the FDNPP accident, but produce large uncertainties in long-term predictions9. To understand the 137Cs dynamics in forests and trees and hence refine the prediction models, it is essential to provide and analyze the observational data of 137Cs activity concentrations in tree stem parts.

Accident-derived 137Cs causes two types of tree contamination: direct contamination by 137Cs fallout shortly after the accident, and indirect contamination caused by surface uptake from directly contaminated foliage/bark10,11 and root uptake from contaminated soil12. The 137Cs concentration in bark that pre-exists the accident was affected by both 137Cs drop/wash off from bark surfaces and 137Cs uptake because the bark consists of a directly contaminated outer bark (rhytidome) and an indirectly contaminated inner bark (phloem). Given that the 137Cs content was 10 times higher in the outer bark than in the inner bark in 201213 and the 137Cs concentration in the whole bark decreased during the 2011–2016 period at many study sites8, the temporal variation in the whole bark 137Cs concentration during the early post-accident phase must be mainly contributed by drop/wash off of 137Cs on the outer bark surface.

In contrast, stem wood (xylem) covered by bark was contaminated only indirectly. Although 137Cs distribution in sapwood (outer part of stem wood; containing living cells) and heartwood (inner part of stem wood; containing no living cells) is non-uniform and species-specific8,13,14,15, the 137Cs concentration in whole wood depends on the amount of 137Cs uptake. Because the dissolvable 137Cs on the foliar/bark surface decreased significantly within 201116, the main route of 137Cs uptake since 2012 is likely root uptake rather than surface uptake. A monitoring survey during 2011–2016 showed that the temporal trend in the whole wood 137Cs concentration can be increasing, decreasing, or flat8, suggesting that 137Cs root uptake widely differs among sites and species.

Meanwhile, many simulation models have predicted an initial increase in the whole wood 137Cs concentration after the accident, followed by a gradual decline9. The initial increase is attributable to the increase in soil 137Cs inventory, and the following decline is mainly attributed to radioactive decay, dilution by wood biomass increment, and immobilization in the soil. Therefore, the trend shift from increasing to decreasing is a good indicator that shows the 137Cs dynamics within the forest have reached apparent steady state, which is characterized by slower changes in 137Cs concentration, bioavailability, and partitioning in the forest12,17,18. However, the timing of the trend shift predicted by the models have large uncertainty, varying from several years to a few decades from the accident9. Moreover, the trend shift has not been confirmed by observational data after the FDNPP accident. Although our monitoring survey cannot easily identify the key driving factors of the temporal trends, it can directly discern the trend shift from increasing to decreasing, and the timeframe of the increasing trend. The confirmation of the trend shift will accelerate the understanding of key factors of 137Cs root uptake, because important parameters such as transfer factor and CR are originally defined for a steady state condition18.

The present study aims to clarify the temporal trends of 137Cs concentrations in bark and wood of four major tree species (Japanese cedar, Japanese cypress, konara oak, and Japanese red pine) at multiple sites during the 10 years following the FDNPP accident. Detecting a trend shift from increasing to decreasing in the wood 137Cs concentration was especially important to infer whether the 137Cs dynamics within the forest have reached apparent steady state. We update Ohashi et al.8, who analyzed the monotonous increasing or decreasing trends during 2011–2016, with observational data of 2017–2020 and a more flexible time-series analysis using a dynamic linear model (DLM). The DLM is suitable for analyzing data including observational errors and autocorrelation, and has the advantage of being applicable to time-series data with missing years. For a more detailed understanding of bark contamination and the 137Cs dynamics in tree stems, we also newly provide data on the 137Cs concentrations in the outer and inner barks. The temporal trends in the 137Cs CRs of outer bark/inner bark, heartwood/sapwood, and inner bark/sapwood were analyzed to confirm whether the 137Cs dynamics within the trees have reached apparent steady state.

Materials and methods

Monitoring sites and species

The monitoring survey was conducted at five sites in Fukushima Prefecture (sites 1–4 and A1) and at one site in Ibaraki Prefecture (site 5), Japan (Fig. 1). Sites 1, 2, and A1 are located in Kawauchi Village, site 3 in Otama Village, site 4 in Tadami Town, and site 5 in Ishioka City. Monitoring at sites 1–5 was started in 2011 or 2012, and site A1 was additionally monitored since 2017. The tree species, age, mean diameter at breast height, initial deposition density of 137Cs, and sampling year of each sample at each site are listed in Table 1. The dominant tree species in the contaminated area, namely, Japanese cedar (Cryptomeria japonica [L.f.] D.Don), Japanese cypress (Chamaecyparis obtusa [Siebold et Zucc.] Endl.), konara oak (Quercus serrata Murray), and Japanese red pine (Pinus densiflora Siebold et Zucc.) were selected for monitoring. Japanese chestnut (Castanea crenata Siebold et Zucc.) was supplementally added in 2017. The cedar, cypress, and pine are evergreen coniferous species, and the oak and chestnut are deciduous broad-leaved species. Sites 1 and 3 each have three plots, and each plot contains a different monitoring species. Site A1 has one plot containing two different monitoring species, and the remaining sites each have one plot with one monitoring species, giving ten plots in total.

Locations of the monitoring sites and initial deposition densities of 137Cs (decay-corrected to July 2, 2011) following the Fukushima nuclear accident in Fukushima and Ibaraki Prefectures. Open circles indicate the monitoring sites and the cross mark indicates the Fukushima Dai-ichi Nuclear Power Plant. Data on the deposition density were provided by MEXT19,20 and refined by Kato et al.21. The map was created using R (version 4.1.0)22 with ggplot2 (version 3.3.5)23 and sf (version 1.0–0)24 packages.

Sample collection and preparation

Bulk sampling of bark and wood disks was conducted by felling three trees per year at all sites during 2011–20168,25 and at sites 3–5 and A1 during 2017–2020. Partial sampling from six trees per year was conducted at sites 1 and 2 during 2017–2020 (from seven trees at site 2 in 2017) to sustain the monitoring trees. All the samples were obtained from the stems around breast height. During the partial sampling, bark pieces sized approximately 3 cm × 3 cm (axial length × tangential length) were collected from four directions of the tree stem using a chisel, and 12-mm-diameter wood cores were collected from two directions of the tree stem using an automatic increment borer (Smartborer, Seiwa Works, Tsukuba, Japan) equipped with a borer bit (10–101-1046, Haglöf Sweden, Långsele, Sweden). Such partial sampling increases the observational errors in the bark and wood 137Cs concentrations in individual trees26. To mitigate this error and maintain an accurate mean value of the 137Cs concentration, we increased the number of sampled trees from three to six. The sampling was conducted mainly in July–September of each year; the exceptions were site-5 samples in 2011 and 2012, which were collected irregularly during January–February of the following year. The collected bark pieces were separated into outer and inner barks, and the wood disks and cores were split into sapwood and heartwood. The outer and inner bark samples during 2012–2016 were obtained by partial sampling of barks sized approximately 10 cm × 10 cm from 2–3 directions on 2–3 trees per year.

The bulk samples of bark, sapwood, and heartwood were air-dried and then chipped into flakes using a cutting mill with a 6-mm mesh sieve (UPC-140, HORAI, Higashiosaka, Japan). The pieces of the outer and inner bark were chipped into approximately 5 mm × 5 mm pieces using pruning shears, and the cores of the sapwood and heartwood were chipped into semicircles of thickness 1–2 mm. Each sample was packed into a container for radioactivity measurements and its mass was measured after oven-drying at 75 °C for at least 48 h. Multiplying this mass by the conversion factor (0.98 for bark and 0.99 for wood)8 yielded the dry mass at 105 °C.

Radioactivity measurements

The radioactivity of 137Cs in the samples was determined by γ-ray spectrometry with a high-purity Ge semiconductor detector (GEM20, GEM40, or GWL-120, ORTEC, Oak Ridge, TN). For measurements, the bulk and partial samples were placed into Marinelli containers (2.0 L or 0.7 L) and cylindrical containers (100 mL or 5 mL), respectively. The peak efficiencies of the Marinelli containers, the 100-mL container, and the 5-mL container were calibrated using standard sources of MX033MR, MX033U8PP (Japan Radioisotope Association, Tokyo, Japan), and EG-ML (Eckert & Ziegler Isotope Products, Valencia, CA), respectively. For the measurement of the 5-mL container, a well-type Ge detector (GWL-120) was used under the empirical assumption that the difference in γ-ray self-absorption between the standard source and the samples is negligible27. The measurement was continued until the counting error became less than 5% (higher counting errors were allowed for small or weakly radioactive samples). The activity concentration of 137Cs in the bark (whole) collected by partial sampling was calculated as the mass-weighted mean of the concentrations in the outer and inner barks; meanwhile, the concentration in the wood (whole) was calculated as the cross-sectional-area-weighted mean of sapwood and heartwood concentrations. The activity concentrations were decay-corrected to September 1, 2020, to exclude the decrease due to the radioactive decay.

Discussion

Causes of temporal trends in bark 137Cs concentration

The 137Cs concentration in the whole bark decreased in many plots, clearly because the outer bark 137Cs concentration decreased. However, the whole bark 137Cs concentration showed a relatively small decrease or even a flat trend in some plots (site-2 cedar and site-1 cypress and oak). In the site-1 cypress plot, where the whole bark 137Cs concentration decreased relatively slowly, the inner bark 137Cs concentration notably increased. Similarly, although we lack early phase monitoring data in the site-2 cedar and site-1 oak plots, the inner bark 137Cs concentration in both plots is considered to have increased prior to monitoring because the sapwood 137Cs concentration increased in both plots and the CR of inner bark/sapwood was constant in all other plots. Therefore, the low-rate decrease or flat trend in the whole bark 137Cs concentration in some plots was probably caused by an increase in the inner bark 137Cs concentration, itself likely caused by high 137Cs root uptake (as discussed later).

The 137Cs concentration in the outer bark decreased in all four plots monitored since 2012 (site-1 and site-3 cedar, site-1 cypress, and site-3 pine), confirming the 137Cs drop/wash off from the bark surface. The constant (exponential) decrease in three of these plots indicates that the 137Cs drop/wash off was still continuing in 2020 but with smaller effect on the outer bark 137Cs concentration. In contrast, the decrease in the site-1 cypress plot seemed to slow down since around 2017. Furthermore, Kato et al.32 reported no decrease in 137Cs concentration in the outer bark of Japanese cedar during the 2012–2016 period. Such cases cannot be fitted by a simple decrease of the outer bark 137Cs concentration. As a longer-term perspective, in the outer bark of Norway spruces (Picea abies) affected by the Chernobyl nuclear accident, the biological half-life of 137Cs concentration was extended in areas with higher precipitation, suggesting that high root uptake of 137Cs hinders the decreasing trend33. The present study showed that 70–80% or more of the 137Cs deposited on the bark surface (outer bark) was removed by drop/wash off after 10 years from the accident and that the 137Cs CR of outer bark/inner bark became constant in some plots. These facts suggest that the longer-term variations in outer bark 137Cs concentration will be more influenced by 137Cs root uptake, although it is uncertain whether root uptake caused the slowing down of the decrease rate seen in the site-1 cypress plot. Further studies are needed to understand the 137Cs concentration in newly formed outer bark and to determine the 137Cs CR of outer bark/inner bark at steady state.

Causes of temporal trends in wood 137Cs concentration

The temporal trends of the 137Cs concentration in the whole wood basically corresponded to those in the sapwood. The exceptions were the site-3 and site-4 cedar plots, where the sapwood 137Cs concentration did not increase but the whole wood 137Cs concentration was raised by the notable increase in the heartwood 137Cs concentration. This behavior can be attributed to a species-specific characteristic of Japanese cedar, which facilitates Cs transfer from sapwood to heartwood8,15,34. The present study newly found that the increase in the 137Cs CR of heartwood/sapwood in the cedar plots became smaller or shifted to a flat trend around 2015–2016, indicating that 137Cs transfer between the sapwood and heartwood has reached apparent steady state at many sites 10 years after the accident. Therefore, after 2020, the whole wood 137Cs concentration in cedar is unlikely to increase without a concomitant increase in the sapwood 137Cs concentration.

The increasing trends in the 137Cs concentrations in whole wood and sapwood (site-2 cedar, site-1 cypress, and site-1 and site-3 oak plots) are seemingly caused by the yearly increase in 137Cs root uptake; however, the wood 137Cs concentration can also increase when the 137Cs root uptake is constant or even slightly decreases each year. This behavior can be shown in a simple simulation of the temporal variation in the wood 137Cs content (the amount of 137Cs in stem wood of a tree). If the 137Cs dynamics within a tree have reached steady state and the proportion of 137Cs allocated to stem wood become apparently constant, the wood 137Cs content in a given year can be considered to be determined by the amount of 137Cs root uptake and the amount of 137Cs emission via litterfall. The flat 137Cs CR trend of inner bark/sapwood during 2012–2020 (see Fig. 5) indicates that the 137Cs dynamics, at least those between the inner bark and sapwood, reached apparent steady state within 2011. Here we assume that (1) the annual amount of 137Cs root uptake is constant, (2) the proportion of 137Cs allocated to stem wood is apparently constant, and as assumed in many forest Cs dynamics models17,35,36,37, (3) a certain proportion of 137Cs in the stem wood is lost via litterfall each year. Under these conditions, the simulated amount of 137Cs emission balanced the amount of 137Cs root uptake after sufficient time, and the wood 137Cs content approached an asymptotic value calculated as [root uptake amount × allocation proportion × (1/emission proportion − 1)]. Note that the asymptotic value increases with increasing root uptake amount and decreasing emission proportion and does not depend on the amount of 137Cs foliar/bark surface uptake in the early post-accident phase. Nevertheless, the amount of 137Cs surface uptake in the early phase critically determines the trend of the wood 137Cs content. More specifically, the trend in the early phase will be increasing (decreasing) if the surface uptake is smaller (larger) than the asymptotic value. Finally, the temporal variation of the 137Cs concentration in wood is thought to be the sum of the dilution effect of the increasing wood biomass and the above-simulated variation in the wood 137Cs content. Therefore, in the early post-accident phase, the wood 137Cs concentration will increase when the wood 137Cs content increases at a higher rate than the wood biomass. As the wood 137Cs content approaches its asymptotic value (i.e., steady state), its increase rate slows and the dilution effect proportionally increases. Then, the wood 137Cs concentration shifts from an increasing trend to a decreasing trend. The trends of the 137Cs concentrations in whole wood and sapwood in the site-3 oak plot follow this basic temporal trend, which is similarly predicted by many simulation models9.

In other plots with the increasing trend (site-2 cedar and site-1 cypress and oak), the increase in the 137Cs concentrations in whole wood and sapwood became smaller or shifted to a flat trend around six years after the accident; however, it did not shift to a decreasing trend. This lack of any clear shift to a decreasing trend, which was similarly seen at sites with hydromorphic soils after the Chernobyl nuclear accident38,39, cannot be well explained by the above simulation. A core assumption of the simulation that the yearly amount of 137Cs root uptake is constant is probably violated in these plots, leading to underestimations of the root uptake amount. Although the inventory of exchangeable 137Cs in the organic soil layer has decreased yearly since the accident, that in the mineral soil layer at 0–5 cm depth has remained constant40. In addition, the downward migration of 137Cs has increased the 137Cs inventory in the mineral soil layer below 5-cm depth41,42. If the steady state 137Cs inventory of the root uptake source can be regarded as sufficient for trees, any increase in the 137Cs root uptake is likely explained by expansion of the root distribution and the increase in transpiration (water uptake) with tree growth. When the wood 137Cs content increases at a similar rate to the wood biomass, the increasing trend will not obviously shift to a decreasing trend. Therefore, assuming the 137Cs allocation and emission proportions in the mature trees do not change considerably with time, the amount of 137Cs root uptake is considered to be increasing yearly in these four plots.

In the remaining plots with the decreasing or flat trend (site-1 cedar, site-4 cedar without outliers, site-5 cypress, and site-3 pine), according to the above simulation, the amount of initial 137Cs surface uptake was larger than or similar to the asymptotic value, i.e. the amount of 137Cs root uptake is relatively small and/or the proportion of 137Cs emission via litterfall is relatively high. However, the amount of 137Cs root uptake in the plots with the flat trend is possibly increasing because the flat trend has not shifted to a decreasing trend. In these plots, although it is difficult to confirm apparent steady state of the soil–tree 137Cs cycling because of the lack of an initial increasing trend, the recent flat trends in the 137Cs CRs of heartwood/sapwood and inner bark/sapwood indicate that the 137Cs dynamics, at least within the trees, have reached apparent steady state.

Various factors were found to increase the 137Cs root uptake after the Chernobyl nuclear accident; for example, high soil water content, high soil organic and low clay content (i.e., low radiocesium interception potential [RIP]), low soil exchangeable K concentration, and high soil exchangeable NH4 concentration12,43. After the FDNPP accident, the 137Cs transfer from soil to Japanese cypress and konara oak was found to be negatively correlated with the soil exchangeable K concentration44,45 and the 137Cs mobility is reportedly high in soils with low RIP46. However, neither the soil exchangeable K and Cs concentrations nor the RIP have explained the different 137Cs aggregated transfer factors (defined as [137Cs activity concentration in a specified component/137Cs activity inventory in the soil]) of Japanese cedars at sites 1–446,47. Because the 137Cs dynamics within the forest and trees in many plots reached apparent steady state at 10 years after the FDNPP accident, the 137Cs aggregated transfer factor is now considered to be an informative indicator of the 137Cs root uptake. Therefore, a comprehensive analysis of the 137Cs aggregated transfer factor and the soil properties at more sites than in the present study will be important to understand key factors determining the amount of 137Cs root uptake by each tree species at each site.

Validity and limitation of the trend analyses

Although the application of the smooth local linear trend model failed in plots monitored for less than five years, it was deemed suitable for analyzing the decadal trend because it removes annual noises, which are probably caused by relatively large observational errors (including individual variability)26. Moreover, the algorithm that determines the trend and its shift between 2 and 4 delimiting years was apparently reasonable, because the detected trends well matched our intuition. However, when judging a trend, the algorithm simply assesses whether the true state values significantly differ between the delimiting years. Therefore, it cannot detect changes in the increase/decrease rate (i.e., whether an increasing/decreasing trend is approaching a flat trend). For example, the whole bark 137Cs concentration in the site-1 cypress plot was determined to decrease throughout the monitoring period. In fact, the decrease rate slowed around 2014 and the decreases were slight between 2014 and 2020 (see Fig. 2). Similarly, the sapwood 137Cs concentration in the site-1 cypress and oak plots was determined to increase throughout the monitoring period, but the increase rate has clearly slowed since around 2017. To more sensitively detect the shift from an increasing/decreasing trend to a flat trend, other algorithms are required. Nevertheless, this algorithm is acceptable for the chief aim of the present study; that is, to detect a trend shift from increasing to decreasing.

Conclusions

In many plots monitored at Fukushima and Ibaraki Prefectures, the 137Cs concentrations in the whole and outer bark decreased at almost the same yearly rate for 10 years after the FDNPP accident, indicating that the direct contamination of the outer bark was mostly but not completely removed during this period. Moreover, the 137Cs concentration in the whole bark decreased at relatively low rates or was stable in plots where the 137Cs root uptake was considered to be high. This fact suggests that indirect contamination through continuous root uptake can reach the same magnitude as direct contamination by the accident.

In all of our analyzed plots, the 137Cs CR of inner bark/sapwood has not changed since 2012, indicating that 137Cs transfer among the biologically active parts of the tree stem had already reached apparent steady state in 2011. In contrast, the 137Cs CR of heartwood/sapwood in six out of nine plots increased after the accident. In four of these plots, the 137Cs CR of heartwood/sapwood plateaued after 3–6 years; in the other two plots, the plateau was not reached even after 10 years. Therefore, saturation of 137Cs in heartwood (an inactive part of the tree stem) requires several years to more than one decade.

The 137Cs concentration in the whole wood showed an increasing trend in six out of nine plots. In four of these plots, the increasing trend shifted to a flat or decreasing trend, indicating that the 137Cs dynamics in many forests reached apparent steady state at 10 years after the accident. However, the lack of the clear shift to a decreasing trend indicates that the 137Cs root uptake is probably still increasing in some plots. Continuous monitoring surveys and further studies clarifying the complex mechanisms of 137Cs root uptake in forests are needed in order to refine the simulation models and improve their prediction accuracy.

https://www.nature.com/articles/s41598-022-14576-1

July 10, 2022 Posted by | Fuk 2022, Fukushima continuing, Reference | , , , | Leave a comment

Radioactivity in fish and shellfish samples from the west coast of Canada after Fukushima (2011-18)

June 13, 2022

The purpose of this post is to bring the public up to date on monitoring efforts of a research program into the impact of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on environmental and public health here in North America. This post is part of an ongoing series summarizing work carried out by the Integrated Fukushima Ocean Radionuclide Monitoring (InFORM) project which I led from 2014-2022. Radioactive contamination of the Pacific Ocean following the FDNPP accident raised public concern about seafood safety, particularly in coastal Indigenous communities in British Columbia where I live. To address this, InFORM along with Health Canada,  Department of Fisheries and Oceans Canada and First Nations partners have collected and analyzed a total of 621 samples of commonly consumed salmon, ground fish, and shellfish from the Canadian west coast from 2011 to 2018. We examined the activities of cesium radioisotopes (134Cs half-life ~2 years and 137Cs half-life ~30 years) that were released in relatively large quantities from the Fukushima Dai-ichi Nuclear Power Plant (FDNNP) disaster in 2011 and would be most likely to pose radiological health concerns for human consumers of marine animals. Through careful analysis to determine the amount of radioactive isotopes in the seafood we have been able to carry out a health impact assessment. I wish to thank the following First Nations from British Columbia, Canada, for their generous donation of fish: Tr’ondëk Hwëch’in, Selkirk, Champagne and Aishihik, Taku River Tlingit, Tahltan, Nisga’a, Wet’suwet’en, Wuikinuxv, ‘Namgis, Hupacasath, Syilix, and Vuntut Gwich’in. I also thank Kayla Mohns and Brenna Collicutt of the Hakai Institute for assistance with the collection of shellfish samples. These results have recently been published in the peer-reviewed scientific literature in the Journal of Environmental Radioactivity and can be accessed here

Highlights of the paper and key findings:

  • the vast majority of fish and shellfish did not have detectable levels of 137Cs or 134Cs where the minimum detectable level was 0.7 — 1.0 Bq kg-1 fresh weight for 6 hours of analysis by counting with a sensitive gamma emission spectrometer
  • 19 fish that had detectable levels of 137Cs were freeze dried and recounted for 336 hours and found to have an average 137Cs content of 0.29±0.02 Bq kg-1 fw
  • 2 of these 19 fish had detectable levels of 134Cs, the short-lived isotope, which showed clearly that fallout from the FDNPP was present in these particular fish. Given that the ratio of 137Cs:134Cs in the releases from the FDNPP was 1:1 we determined that the contribution of contamination in these fish from the nuclear accident was 49% and 24% respectively with the majority of caesium contamination coming from other sources like nuclear weapons testing and the Chernobyl disaster in the 20th century
  • 38 shellfish showed no contamination from FDNPP in either their shells or meat
  • 8 years of measurements showed that radioactivity in fish was dominated by naturally occurring radioisotopes and that levels of human-made radioisotopes remained small in the Pacific off North American following the FDNPP disaster
  • upper bounds for ingested doses of ionizing radiation from 137Cs was determined to be ~0.26 micro-Sieverts per year and far below the annual effective dose of 2400 micro-Sieverts from exposure to other sources of radiation
  • we conclude that fish and shellfish from the Canadian west coast are not a radiological health concern despite the FDNPP accident of 2011

What we did

Samples were collected with the help of 13 First Nations, the Department of Fisheries and Oceans and the Hakai Institute in coastal waters and rivers of western Canada at sites indicated on the map below.

Figure 1 (a) Map of fish samples collected from 2014 to 2018 through the InFORM project. (b) Map of shellfish (bivalves) collected in 2016 and 2017.

For fish we removed the skin and bone to measure fillets which are typically consumed. Whole-body tissues of mussels, oysters, and clams were processed as they are generally eaten whole, but for scallops only the muscle itself was processed. In addition, we crushed up the shells of the individual shellfish to determine if radiocesium had accumulated in the shell as they are sometimes used to fertilize garden beds or adjust the hardness of rainwater used for home gardens.  We measured the radiocesium and naturally occurring radioisotopes in the samples using gamma spectrometry which you can learn about here. All samples were analyzed for 6 hours to screen samples for the presence of 137Cs and a subset of 19 were counted for a further 336 hours to determine if any 134Cs was present. This represents 10110 hours (more than 421 days) of counting time.

What we found

Results of the 6 hour counts and the extended counting samples can be found in here and here respectively. Given the extremely low levels of 137Cs present in the fish tissue (almost always below our minimum detectable concentration for individual fish) we averaged the gamma emission spectra of all fish collected in each year to determine the average 137Cs content. 137Cs content of all fish samples in each year fell between 0.18 and 0.25 Bq kg-1 fresh weight with the highest average concentration in 2017 and the lowest 2015. Data are here. The challenge of measuring and quantifying the amount of 137Cs can be understood by looking at the gamma emission spectrum and the averages for each year between 2014 and 2018 in the following figure.

Figure 2 Spectral summation of fish samples from 2014 to 2018, normalized to sample number. (a) Overlay, 150–2000 keV (b) Overlay with focus on the principal emission line for 137Cs at 661.7 keV.

What the figure shows is that even after averaging the results for every fish collected in each year it was difficult for our team to detect human-made caesium isotopes. There was also no clear trend in time with 137Cs neither increasing nor decreasing with time in Pacific fish. In fact, the level of 137Cs found in the Pacific salmon was similar to levels found in Atlantic salmon (Table 4, 0.20 Bq kg-1) we collected in 2017 and analyzed from the Miramichi River on Canada’s east coast in New Brunswick. Careful analysis of 19 fish with longer counting times led us to be able to detect 2 fish with measurable levels of 134Cs which was an unmistakable sign of contamination from the FDNPP. However, given our understanding of the releases of 137Cs and 134Cs from the FDNPP following the disaster, most of the 137Cs present in the fish reflected contamination in the Pacific from nuclear weapons testing and the Chernobyl disaster rather than events following the 2011 meltdowns at FDNPP. For shellfish harvested from Canada’s west coast in 2016 and 2017, spectral summation of fresh weight samples (tissue and shell, respectively) yielded no detectable radiocesium or any other anthropogenic isotopes.

What it means

From 2011 to 2018, radioactivity measurements were made by the Fukushima InFORM project of 621 fish and shellfish samples harvested from Canada’s west coast. To investigate the impact of the oceanic contamination plume of Fukushima radioactivity to coastal waters, we used highly sensitive analyses and data reduction techniques to show that the concentration of 137Cs in the tissue of marine fish has not changed (0.18–0.25 Bq·kg−1 fw) from 2014 to 2018 while that of shellfish was undetectable. Relative to the abundance of naturally occurring isotopes like 210-Polonium in the same fish samples or to the annual dose exposure due to naturally occurring background radiation, it is abundantly clear that, by any metric, the radiocesium content of fish and shellfish from Canada’s west coast does not constitute a health risk, despite the FDNPP accident of 2011. The ecosystem and public health on the west coast of North America was never under threat from the FDNPP accident.

https://m.dailykos.com/stories/2022/6/13/2100768/-Radioactivity-in-fish-and-shellfish-samples-from-the-west-coast-of-Canada-after-Fukushima-2011-18

June 18, 2022 Posted by | Fuk 2022 | , , | Leave a comment

Radiation still hitting flora, fauna in forests in Fukushima

Radiation levels in mountain forests in Fukushima Prefecture remain relatively high compared with residential areas that have undergone decontamination work. The photo was taken in Namie in the prefecture in December. (Keitaro Fukuchi)

March 11, 2022

SENDAI—On a chilly night in early February, Masatoshi Suzuki hauled a black plastic bag containing four macaque carcasses into his lab at Tohoku University.

The monkeys were killed as agricultural pests, but for researchers like Suzuki, the animals are invaluable specimens to determine the effects of radiation from the Fukushima nuclear disaster.

Nearly 11 years after the triple meltdown at the Fukushima No. 1 nuclear plant, questions remain over the extent of damage to animals and plants caused by the radioactive substances released in the accident.

Suzuki, who specializes in radiobiology, hopes his studies will provide clues on the possible impact of the radiation on humans.

He and his colleagues have studied 709 macaques in Fukushima Prefecture since 2012. Of all the wild species available for study in the contaminated areas, macaques are most similar to humans.

Masatoshi Suzuki, a researcher of radiobiology, at his lab at Tohoku University in Sendai on Feb. 8 (Keitaro Fukuchi)

The four dead macaques were given to Suzuki by farmers who destroyed the animals several hours earlier in Namie, a town that lies about 4 kilometers from the crippled nuclear plant. Parts of Namie are still off-limit due to high radiation levels.

Other primates used in the studies have come from off-limit areas in Minami-Soma, a city north of the nuclear plant, and elsewhere in the prefecture.

The researchers dissect the carcasses to determine if the livers, lungs, thyroid glands and muscle tissues were affected by radiation from the nuclear accident.

Deformations in plant lice and fir trees have been reported since the nuclear disaster started.

But Suzuki said he has seen no credible reports of such physical abnormalities in wild animals, including macaques, as well as domestic livestock.

However, damage might be occurring at the cellular level in the animals.

Background radiation levels in most of the mountain forests in Fukushima and neighboring prefectures are higher than those in residential areas, which have undergone decontamination procedures.

In the nature-filled areas that have not been decontaminated, macaques continue to be exposed to radioactive materials while feeding on polluted fruits and other food sources.

According to Suzuki’s studies, the muscles showed the highest concentration of radioactive cesium among all of the macaques’ organs.

The average radioactivity level in the thigh muscles was about 40,000 becquerels per macaque captured in Namie in fiscal 2013.

In fiscal 2018, the figure was down to about 20,000 becquerels per macaque.

The researchers found that macaques exposed to higher radiation doses had slightly fewer blood-producing cells in bone marrow compared with the animals with lower exposure readings. The nuclear accident may have compromised some macaques’ ability to make blood.

The researchers used the density of radioactive cesium in the macaques’ muscles and in soil at areas where they were captured to calculate the level of radiation doses the animals were exposed to both internally and externally.

Suzuki also said they detected chromosomal abnormalities resulting from radiation damage to genes.

He said radiation exposure can increase the stress level in one organ, but the same dose could have the opposite effect in a different organ. One possible reason for this is that the animal’s defense system was galvanized to curb stress levels following exposure.

Suzuki emphasized the need to continue monitoring macaques and other animals to determine the impact from prolonged radiation exposure.

“So far, we have discovered no significant health hazards in the individual macaques studied,” he said. “But they continue to display changes in their cells and organs, albeit minor ones. We do not know what these changes will translate into in the long run.”

CESIUM PASSED THROUGH FOOD CHAIN

A study by other scientists showed that radioactive cesium from the nuclear accident could be traveling through food chains in the environment.

“If we can track down the movement of radioactive cesium in the food chain, the findings would show us its cycling mechanism in the ecosystem,” said Sota Tanaka, a researcher of radioecology at Akita Prefectural University.

He believes that studying the cycling mechanism of cesium will help to predict its long-term movement and lead to improved use of resources in mountain forests and the rebuilding of agriculture in contaminated areas.

Joint research by Tanaka and Taro Adachi, professor of applied entomology at the Tokyo University of Agriculture, found that radioactivity levels have decreased year after year in rice-field grasshoppers in Iitate, a village west of the stricken nuclear plant that still has some off-limit areas.

In 2016, all of the grasshoppers monitored had radioactivity readings below 100 becquerels per kilogram.

But garden web spiders in Iitate showed a wide range of readings from one year to the next. Their radioactivity levels were actually higher in 2015 than in 2014.

In 2016, one spider had a reading of more than 300 becquerels per kilogram.

Radioactive cesium remains on the ground even after rainfalls.

Plants rarely absorb cesium through their roots, but can become contaminated by falling cesium particles. And the researchers believe the cesium levels in grasshoppers have dropped steadily because they feed on the leaves of living plants.

As for the spiders, they are eating bugs that have high cesium levels because they feed on contaminated dead leaves mixed with contaminated soil, according to Tanaka.

That may be why the eight-legged predators are showing higher radioactivity readings than the grasshoppers, he said.

Their study also found that earthworms had radioactivity levels higher than those for the grasshoppers and spiders, likely because they are eating contaminated soil and withered leaves.

https://www.asahi.com/ajw/articles/14567194?fbclid=IwAR0sgko2lq2dlSUS-Qtzo3-7-hv1JvrLScAZ1TUEAofs5gKPvkQZOX53E4Q

March 14, 2022 Posted by | Fuk 2022 | , , | Leave a comment

(11 Years after the Great East Japan Earthquake) Forest untouched by decontamination, creatures exposed to radiation continue to be affected at the cellular level

Tohoku University lecturer Masatoshi Suzuki arranges samples of Japanese macaques in Sendai City on February 8.

March 8, 2022
 Eleven years have passed since the accident at TEPCO’s Fukushima Daiichi Nuclear Power Plant.

While decontamination has progressed mainly in residential areas and other areas where people live, vast areas of forests remain largely untouched.

A wild Japanese monkey in a mountain forest in Fukushima Prefecture, Iitate Village, Fukushima Prefecture, in December 2021.

What effect do radioactive materials remaining in the forests have on living creatures and how do they move through the food chain? Researchers are continuing their investigations. (Keitaro Fukuchi)

Image of radioactive cesium transfer through the food chain

https://www.asahi.com/articles/DA3S15226522.html?iref=pc_photo_gallery_bottom

March 11, 2022 Posted by | Fuk 2022 | , , | Leave a comment

River fishing limits remain 11 years after nuclear disaster

Researchers catch fish in the Otagawa river in Minami-Soma, Fukushima Prefecture, on Dec. 14, 2021, to survey the concentration of radioactive materials. (Keitaro Fukuchi)

March 7, 2022

FUKUSHIMA–A sign along the Manogawa river that runs through Minami-Soma, Fukushima Prefecture, is faded, but the message is clear–and perhaps unnecessary.

“Regulations have yet to be lifted,” it says. “Please do not conduct fishing activities.”

The sign is located on a riverbank about 30 kilometers north of the stricken Fukushima No. 1 nuclear power plant run by Tokyo Electric Power Co.

The area used to be crowded with people trying to catch “ayu” (sweetfish). But anglers from near and far stopped visiting the area long ago, and now, hardly anyone is around to see the sign.

After the 2011 nuclear disaster, a local association of fisheries cooperative set up the “no fishing” signs at about 50 locations along the river.

Calls to suspend shipments of river fish and to refrain from fishing have continued since the nuclear disaster started 11 years ago, even for rivers outside the Tohoku region.

In the Manogawa river, ayu, “ugui” (Japanese dace) and “yamame” (masu trout) were found with concentrations of radioactive substances that exceeded the national safety standard.

“There are people who say, ‘I don’t think I can go fishing again in my lifetime,” said Yukiharu Mori, 60, who owns a fishing goods store in Minami-Soma.

His shop’s sales have plummeted, and many other fishing goods shops in the city’s area have gone out of business, he said.

RESTRICTIONS LIFTED FOR SEAFOOD

The nuclear disaster led to restrictions on shipments of seafood products in five prefectures, stretching from Aomori to Ibaraki.

These restrictions have been lifted in stages because radioactive substances more easily diffuse in the sea, and fish species have been confirmed safe to eat.

Currently, the shipment restrictions apply only to “kurosoi” (black rockfish) caught off Fukushima Prefecture.

But all restrictions remain for catches from 25 rivers and lakes in five prefectures–Fukushima, Miyagi, Ibaraki, Gunma and Chiba.

In some areas along the Agatsumagawa river in western Gunma Prefecture, shipments of “iwana” (char) and yamame are still restricted.

According to Gunma prefectural officials, radiation doses were relatively high in certain areas around the Agatsumagawa river immediately after the nuclear disaster due to the wind direction and geographical features. That has led in part to the prolonged restrictions.

In a 2020 prefectural survey, the radioactivity concentration level in iwana was 140 becquerels per kilogram. In a 2019 survey, the level for yamame was 120 becquerels per kilogram.

The national standard for both fish is 100 becquerels per kilogram.

“Even when the figure goes down and we think it is safe, we find fish with high figures every few years,” a Gunma prefectural official said. “That makes it difficult for us to take a step toward lifting the restrictions.”

Toshihiro Wada, an associate professor of fish biology at Fukushima University, said river fish “have continued to consume radioactive materials from food” provided through forests that have yet to be decontaminated.

The central government has conducted decontamination work mainly in residential areas of Fukushima Prefecture and surrounding prefectures.

But such work has not been done in most parts of large forested areas. Insects and other critters ingest still-contaminated tree leaves or algae at river bottoms. The river fish then consume the creatures, which has kept radioactive concentrations high in the fish.

A team of researchers from Fukushima University, the Fukushima prefectural government and the National Institute for Environmental Studies has surveyed areas along the Otagawa river that stretches from Namie to Minami-Soma in Fukushima Prefecture since 2018.

The study includes checking radioactivity levels in the river fish and insects.

The upper part of the Otagawa river is located in a “difficult-to-return” zone because of still-high radiation levels.

In an on-site survey in December, the researchers found the radiation dose rate in the air of an upstream forested area within the difficult-to-return zone was 2 to 3 microsieverts per hour. That level was 20 to 30 times higher than the dose rate in the city of Fukushima.

The researchers also found up to 9,000 becquerels of radioactive materials per kilogram in yamame caught in the upper portion of the river in 2018, and up to 12,000 becquerels per kilogram in iwana.

The radioactivity concentrations in tree leaves and river algae were several thousand to tens of thousands of becquerels. Crickets, bees and other land and aquatic creatures found in the yamame’s stomachs are believed to have eaten the contaminated leaves and algae.

Insects in the area contained radioactivity levels of several hundred to several thousand becquerels, the researchers said.

Yumiko Ishii, a team member and a chief researcher at the NIES, said that larger yamame had radioactivity concentration levels that were higher than those in the food that the fish ate.

“Unless you do something about the radioactive materials in forests, the radioactivity concentration levels in fish will not go down,” she said. “But decontaminating forests is not realistic, either.”

(This article was written by Keitaro Fukuchi and Nobuyuki Takiguchi.)

https://www.asahi.com/ajw/articles/14566055

March 11, 2022 Posted by | Fuk 2022 | , , | Leave a comment

The Fukushima taboo

“Coming out” on thyroid cancer from Fukushima is an act of bravery in today’s Japan

By Linda Pentz Gunter

In the midst of the arcane fight over whether to include nuclear power in the European Union’s green “Taxonomy”, five former prime ministers of Japan made an unprecedented statement. They roundly condemned any inclusion of nuclear power as a green or sustainable energy, even as a so-called bridging fuel.

The current Japanese government glossed over the climate arguments in the former prime ministers’ argument, quickly seizing upon one tiny phrase concerning conditions in Japan post-Fukushima that read: “many children are suffering from thyroid cancer”.

The ruling Liberal Democratic Party even went so far as to approve a resolution condemning the five former prime ministers, one of whom, Junichiro Koizumi, is from that party. The resolution alleges that their statement was not “scientific” and that they were reigniting prejudice and encouraging people to view people from Fukushima as pariahs. 

The party’s Policy Research Board said it would submit its resolution to current prime minister, Fumio Kishida.

On the same day — January 27, 2022 — as the former prime minister’s letter was submitted to the EU, six young people who were children at time of the March 2011 Fukushima Daiichi nuclear disaster, filed a lawsuit in the Tokyo District Court against TEPCO, the owner and operator of the nuclear plant. 

The six, ages 17 to 27, hold the company responsible for the thyroid cancers each of them developed after being exposed to the radiation released by the nuclear disaster.

In filing suit and thus making the issue public, the six were immediately on the receiving end of an unprecedented level of abuse for speaking out. In this video of their testimony, they were obliged to keep their physical appearances concealed for fear of further reprisals.

Voice of 6 plaintiffs who “spent 10 years without telling anyone” – Childhood thyroid cancer patients file lawsuit against TEPCO.

“Coming out” on thyroid cancer — or indeed about any negative health impacts resulting from the Fukushima nuclear disaster — remains largely taboo in Japan.  Studies that conclude the medical impacts are significant or even substantial, are met with equal hostility, stoniness or just plain silence.

When epidemiologist, Toshihide Tsuda and colleagues, published a paper in 2016 — Thyroid Cancer Detection by Ultrasound Among Residents Ages 18 Years and Younger in Fukushima, Japan: 2011 to 2014 — it was reportedly largely ignored rather than challenged.

The study concluded: “An excess of thyroid cancer has been detected by ultrasound among children and adolescents in Fukushima Prefecture within 4 years of the release, and is unlikely to be explained by a screening surge.”

This contradicted the prevailing and enduring view among the establishment that there are now more thyroid cancers found among children after Fukushima simply because there is more testing. 

The “more testing” myth served as a convenient pretext to reduce testing for thyroid cancers in schools — on the basis such testing would upset children too much, hardly “scientific”.

The very public lawsuit may transform all this, as the testimonies leave an indelible picture of the toll taken on children and families by the Fukushima nuclear disaster.  

In a two-part series, investigative journalist, Natsuko Katayama, reported on the case for the Tokyo Shimbun on January 19 and January 27 this year.

She wrote that among the plaintiffs, “Two of them had a lobe of the thyroid removed, and the other four had to have the whole thyroid removed because of recurrence (in the case of one of them, metastasis had spread to the lungs). All of them had to stop their studies or their professional activity in order to undergo these surgical procedures and medical treatments. They live in fear and anxiety of a recurrence, and their daily lives have been curtailed due to fatigue and weakness caused by the disease.”

One of the plaintiffs said they had all kept silent about their thyroid cancers for 10 years, not daring to go public because of the inevitable backlash of discrimination. 

Toshihide Tsuda: “Pediatric Thyroid Cancer after the Fukushima Accident”

Many of those suffering illnesses related to the Fukushima nuclear disaster find themselves the new “Hibakusha”, the name originally given to those ostracized and rejected by Japanese society because of their exposure to radiation from the Hiroshima and Nagasaki atomic bombings.

Choking with emotion, one of the plaintiffs described in the press conference how she and the others had to give up their work and educational hopes and dreams due to the constrictions of illness and the necessary treatments. “Four of the six plaintiffs have had a recurrence or mestatasis of their disease,” she said. 

Thyroid cancers among those exposed to Fukushima radiation as children have increased 20 times the expected rate, with about 80% metastasizing, meaning surgery was medically indicated and screening necessary.

“I am very worried about the future and cannot think about marriage or other plans,” said one of the young women, also a plaintiff in the trial, whose voice could be heard at the press conference, and whose cancer had returned and spread. All of them have faced considerable financial hardships due to the expense of their treatment and the loss of work.

The plaintiffs expressed the hope that the trial would help other children suffering from thyroid cancer, believed to number at least 300. But, with the suppression of testing and reporting, and the taboo surrounding any admission of thyroid cancer, the numbers could well be a lot higher.

The plaintiffs’ lawyers argue that Tepco will need to prove that there is no causal relationship between their clients’ thyroid cancer and the Fukushima Daiichi nuclear disaster. It seeks compensation for the victims.

“I try to believe that all will be well,” said one of the plaintiffs, a 26-year old woman who was 17 at the time her thyroid cancer was diagnosed, “even as I ask myself, ‘why me’?”

The 3.11 Children’s Thyroid Cancer Network was launched to support this lawsuit.

Headline image shows 2013 IAEA team member overseeing TEPCO moving nuclear fuel assemblies from Reactor Unit 4 to the Common Spent Fuel Pool. (Photo: IAEA)

March 7, 2022 Posted by | Fuk 2022 | , | Leave a comment

Fukushima Thyroid-Cancer Victims Take TEPCO to Court

March 2, 2022

PRESS CONFERENCE: Fukushima Thyroid-Cancer Victims Take TEPCO to Court

Kenichi Ido, Attorney, Lead Counsel for the 3.11 Children’s Thyroid Cancer Lawsuit

Hiroyuki Kawai, Attorney, Co-counsel for the 3.11 Children’s Thyroid Cancer Lawsuit

March 3, 2022 Posted by | Fuk 2022 | , , | Leave a comment

DPP uses Taiwan people’s health as bargaining chip

Taiwan’s Fukushima food ban lifting viewed from mainland China

Photo taken on July 21, 2019 from Xiangshan Mountain shows the Taipei 101 skyscraper in Taipei, China’s Taiwan.

February 25, 2022

The Taiwan authorities formally lifted the ban on food imports from Japan’s Fukushima and four other prefectures on Monday. The ban was imposed after the Fukushima nuclear disaster in 2011.

The island authorities’ move is similar to the ruling Democratic Progressive Party’s decision in 2021 to lift the restrictions on the import of pork with ractopamine, a feed additive harmful to human health, from the United States. In fact, it is also to please the US that the DPP is opening up the island’s market to food products from Fukushima ignoring the high risk of nuclear contamination.

By ignoring the health concerns about the food products from Fukushima, the DPP is putting Taiwan residents’ health and lives in danger.

After a devastating earthquake-triggered tsunami caused a meltdown of three of the Fukushima Daiichi nuclear power plant’s six nuclear reactors on March 11, 2011, governments around the world imposed restrictions on food imports from five Japanese prefectures-Fukushima, Ibaraki, Tochigi, Gunma and Chiba. The Taiwan authorities imposed the ban in late March that year.

Yet since taking power in 2016, the DPP has been trying to lift the ban in exchange for Japan’s support for its “Taiwan independence” agenda. In fact, the DPP has lifted the ban despite a 2018 referendum in which people voted overwhelmingly to continue the ban.

Ironically, the DPP won many Taiwan residents’ support because of its anti-nuclear stance. “Use love to generate electricity” was a slogan the DPP used at the time to lure people to its side. But since coming to power six years ago, the DPP in its bid to split the island from the motherland has reneged on its anti-nuclear promise.

The lifting of the ban on Fukushima food products in a desperate attempt to boost ties with Japan to counter the Chinese mainland is an apt example of the DPP’s subterfuge.

For the same reason, the DPP accepted US conditions and resumed the import of US pork, ignoring the health hazards it poses to Taiwan residents.

The DPP believes compromising food safety to get security guarantee from the US and Japan is very cost-effective. That’s why it used every possible trick to brainwash Taiwan residents and convince them that food products from those five Japanese prefectures are not “food with radioactivity” but “food with blessing”.

Also, the DPP has been claiming that the lifting of the ban will boost Taiwan’s chances of joining the Comprehensive and Progressive Agreement for Trans-Pacific Partnership. In fact, Chen Chi-chung, the official in charge of the island’s agriculture, said that with the withdrawal of the ban, the island’s imports from Japan will increase by a maximum of $70 million a year while Japan’s import of Taiwan’s pineapples-18,000 tons last year and 30,000 tons this year-alone will exceed that amount.

It seems the DPP considers eating nuclear-contaminated food in exchange for exporting pineapples a good deal. The DPP’s arbitrary and anti-people decision is the result of its obscurantist and narrow policies.

Many Taiwan residents still believe in the DPP’s propaganda to the extent of blindly following its diktats even though those diktats are against their well-being and interests. Those people who voted the DPP to power for the second time only to end up eating pork with ractopamine from the US and radiation-exposed food from Fukushima are swallowing their own bitter fruits.

The DPP’s rule is nothing but a reign of terror. A party which uses the health and lives of the people as a bargaining chip in exchange for the support of anti-China forces will become more brazen in its quest to fulfill its narrow benefits. So Taiwan residents who voted for the DPP have to suffer the consequences of their choice.

The author is deputy director of the Institute of Taiwan Studies, Beijing Union University.

https://global.chinadaily.com.cn/a/202202/25/WS6218136da310cdd39bc88c70.html

February 28, 2022 Posted by | Fuk 2022 | , , , | Leave a comment

Taiwan partially lifts import bans on Japanese foods

Political expediancy, lies and cover up, propaganda!

Feb. 21, 2022

Taiwan says it has partially lifted import bans on Japanese foods on Monday that have been in force since the 2011 Fukushima nuclear power plant accident.

Taiwan had stopped importing all food items from Fukushima and the nearby prefectures of Ibaraki, Tochigi, Gunma and Chiba. The ban excluded alcoholic drinks.

Officials announced earlier this month that they would lift the ban, except for wild bird and animal meat as well as mushrooms from those prefectures.

They said the move was based on global standards and ‘scientific proof’and noted that most countries have eased restrictions.

Taiwanese authorities say they sought feedback from the public about the decision and ‘received only a few objections’.

Food from the five prefectures must still be accompanied by test results for radioactive materials, and all items will be subject to inspections in Taiwan.

All prefectures must also still provide proof of origin.

Officials in Japan say the safety of the food has been scientifically proven and they will continue asking Taiwan to lift all the regulations.

February 23, 2022 Posted by | Fuk 2022 | , , , , | 1 Comment

Taiwan officially scraps ban on food from 5 Japanese prefectures

Political expediancy sacrificing people’s health…

Decision to lift ban announced earlier this month as government eyes CPTPP entry

People shop for Japanese seafood in Taiwan

2022/02/21

TAIPEI (Taiwan News) — The ban on food from parts of Japan affected by the 2011 Fukushima nuclear disaster was formally lifted on Monday (Feb. 21).

The Taiwan Food and Drug Administration promulgated the removal of the ban on Feb. 21 after reviewing public feedback. Three dozen comments were submitted, including 17 in favor of ending the ban and four against, as well as 15 inquiries and suggestions.

The goods in question are from five Japanese prefectures: Fukushima, Gunma, Chiba, Ibaraki, and Tochigi. With the scrapping of the ban, which has been in place for a decade, goods from these areas will be subject to risk controls when imported.

Food products that are prohibited from circulating within Japan, such as wildlife meat and mushrooms from those five prefectures, will not be allowed to enter Taiwan. Radiation safety and product origin certificates are required for items deemed to be high-risk, such as tea and aquatic products.

Despite the government’s pledge to implement rigorous border inspections, some believe more needs to be done to ensure food safety. Earlier this month, the New Power Party aired concern about possible traces of strontium-90 in the Japanese imports, as the isotope is not on the radiation watch list, and exposure to it may increase the risk of bone cancer.

https://www.taiwannews.com.tw/en/news/4450300

February 23, 2022 Posted by | Fuk 2022 | , , , | Leave a comment

I just wanted to live a normal life – Akiko Morimatsu

February 15, 2022

It will soon be 11 years since the accident at TEPCO’s Fukushima Daiichi Nuclear Power Plant.
It is estimated that 27,000 people have evacuated from Fukushima Prefecture and 39,000 people have evacuated to 915 cities, towns, and villages in 47 prefectures across Japan (all figures as of January 12, 2022, compiled by the Reconstruction Agency). (As of January 12, 2022, according to the Reconstruction Agency.) However, the exact number of evacuees is still unknown due to discrepancies between the totals of Fukushima Prefecture and those of municipalities, as well as cases where the government has mistakenly deleted evacuee registrations.

The accident is still ongoing.
We would like to share with you some of the stories we have heard from the evacuees.
This time, we would like to introduce Ms. Akiko Morimatsu, who gave a speech with Greenpeace at the UN Human Rights Council on the current situation of the victims.
(All information in this article is current as of 2018)

Akiko Morimatsu’s eldest daughter, who was a newborn infant at the time of the accident at TEPCO’s Fukushima Daiichi Nuclear Power Plant, is now in elementary school. In the seven years since she left Fukushima Prefecture, she has never lived with her father.
Her eldest son, who was three years old, is a father’s child. Whenever his father came to see his evacuated family once a month, he would return to Fukushima Prefecture, and I could not tell you how many times I wet my pillow with tears of loneliness and sadness.

In March of this year, Ms. Morimatsu made up her mind to stand on the stage of the United Nations Human Rights Council in Geneva, Switzerland.

Ms. Morimatsu is a so-called “voluntary evacuee. Housing support, which was the only support for “voluntary evacuees” from outside the evacuation zone, has been cut off, and now there are even eviction lawsuits against “voluntary evacuees” who cannot pay their rent.

In the fall of 2017, Greenpeace, together with the victims of the nuclear accident, appealed to the member countries of the United Nations Human Rights Council about these human rights violations that the victims continue to suffer. Many people who supported us with signatures and donations supported this project.

Subsequently, recommendations for correction were issued by Germany, Austria, Portugal, and Mexico. Greenpeace is calling on the Japanese government to accept these recommendations.
We hope that as many people as possible will know why Mr. Morimatsu decided to speak directly with Greenpeace about the current situation in front of the representatives of each country at the time when the decision to accept the recommendations will be announced.

A nursery school in Fukushima Prefecture in 2011

In the midst of impatience, anxiety, and unpredictable fear

It was during the Golden Week holidays, two months after the disaster, that Ms. Morimatsu decided to evacuate.
Until then, she had been trying to rebuild her life in Fukushima Prefecture.

However, even though no evacuation order had been issued for the area called Nakadori, where he was living at the time, the kindergarten distributed disposable masks to all the children and instructed them to wear long sleeves and long pants. Elementary and junior high school students in the neighborhood drive their own cars to school, even if it is within walking distance. They are not allowed to go outside without permission, and of course they are not allowed to play outside either at the kindergarten or around their homes.

On weekends, the whole family travels to Yamagata and Niigata prefectures on the highway to take the children out to play. Radioactive materials have been detected in tap water and fresh food. We could not hang our laundry or futons outdoors.

No matter what we did, we had to first think about the possible effects of radiation on our children and pay close attention to everything.

No one can tell us what is the right thing to do.

I don’t even know if I should continue to live here. I feel impatient, anxious, and unpredictable.

One by one, families in the neighborhood and kindergartens were leaving Fukushima Prefecture, and it was the fathers of the children who first suggested to Ms. Morimatsu that she take the children to the Kansai region, where she had spent her school days, as they were planning to use the holidays to reorganize their living environment.

What she saw there was a media report about the danger of radioactive contamination, which had not been reported at all in Fukushima Prefecture.

What can we do to protect the future of children who are highly sensitive to radiation?

Only I, as a parent, could protect them.

It was time to make a decision.

Greenpeace radiation survey at a kindergarten in Fukushima Prefecture, 2011.

I separated the children from their father.

With the encouragement of relatives and friends in the Kansai region, and with the agreement of her husband, who continues to work in Fukushima Prefecture, Morimatsu decided to evacuate with her children.

No evacuation order was issued for the area where the Morimatsu family was living. They had to pay separate rents and utility bills for the rental house they rented to replace their house that was damaged in the earthquake, and for the house they rented to house their mother and child in Osaka (*Housing support for voluntary evacuees ended in March 2017. Because Ms. Morimatsu had left public housing early, which had a short move-in period, she was not provided with housing after that and is not counted in the number of evacuees, forcing her to continue living as an evacuee completely on her own).

Even for fathers to come to see their young children, the high cost of transportation is prohibitive.

What kind of impact will not being able to see their fathers most of the time have on the children’s mental development?

How do fathers feel when they can’t watch their adorable children grow up?

Was the evacuation really the right thing to do, forcing families to live apart?

Mr. Morimatsu was in agony, but he decided to find a job in the evacuation area so that he could see his father and children as often as possible.

However, there was no way to take care of her oldest daughter, who was only one year old at the time, at the evacuation site.

Because of the risk of not receiving information from the local government regarding public support and health surveys for children, victims who are voluntarily evacuating cannot inadvertently report their departure. As a result, they were not able to receive services such as day-care centers smoothly in their evacuation areas.
As a result, although she was able to be placed on a waiting list for childcare, her childcare fees were also determined based on her household income, so her own income, which she had begun to work to supplement her double life, was added to her household income, which was quite high. Since she is not a widow, she is not eligible to receive subsidies for single-mother households.

Empty playground of local day nursing school called “Soramame” in Fukushima city. Before Nuclear crisis, this school was taking care of 24 kids. However, since most of them have evacuated to other places with their families, now only 7 kids left. A director of the school, Sadako Monma 48 says “After March 11th, kids are not playing on the playground and instead they are playing inside the school all the time due to nuclear issues”. Since many kids left the school, Monma is thinking about closing the school which has been running for the past 15 years due to financial situation. Fukushima prefecture.

The Best Choice in the Worst Situation

The number of people like Ms. Morimatsu who evacuated from areas where evacuation orders were not issued is a small minority compared to the total number of victims of the nuclear accident. She said that she felt guilty and conflicted about evacuating from a place where even temporary housing could be built for victims from areas where evacuation orders had been issued.

But no one would willingly abandon their current life to evacuate.

Ms. Morimatsu’s husband chose to continue working in Fukushima Prefecture even if it meant leaving his family.

Whether to evacuate or not, each victim’s decision should be respected as the best choice under the worst circumstances.

Voicing one’s anxiety or pointing out what one feels is wrong should not be denied.

But we are practically forced to close our eyes, keep our mouths shut, and pretend to forget about it.

The biggest victims are “children”.

Seven years have passed since the accident, and yet the “right to health” of children, who are the most vulnerable to radiation exposure, has not been given equally to everyone’s children?

I just want to live a normal life together with my child.

I want my children to live a long and healthy life, even if it’s just for a minute or a second.

It is a natural wish for parents to long for this.

The current situation is such that even this desire is being ignored.

Akiko Morimatsu (photo taken in 2021) ©️ Greenpeace / Kosuke Okahara

Protecting the Human Rights of Victims of the Nuclear Accident

The right to avoid radiation exposure and protect one’s health continues to be violated regardless of whether one evacuates or not.

Is the right to avoid radiation exposure, in other words, the right to evacuate, equally recognized for those who want to evacuate?

The policy of not recognizing the right to evacuate, discontinuing the provision of housing without medical support or information, and effectively forcing victims to return home through economic pressure is a violation of human rights for the Morimatsu family and other victims of the nuclear accident.

If the same thing happened to you, what would you protect?

What would you value the most?

The right to life and health is a fundamental human right given to every individual, from the newborn baby to the elderly person whose life will end tomorrow.

Mr. Morimatsu is still evacuating with his children.

Greenpeace’s activities are based on scientific evidence derived from the results of radiation surveys conducted in the area immediately after the accident.
We will continue our research activities and human rights protection activities for the people affected by the accident.

February 21, 2022 Posted by | Fuk 2022 | , , , | Leave a comment

Fukushima Disaster’s Impact on Health Will Be Challenged in Court 

By Thisanka Siripala

February 17, 2022

A link between radiation from the Fukushima nuclear disaster and cancer will be the focal point of the civil court case against operator TEPCO.

Almost 11 years have passed since the Fukushima Daiichi nuclear power plant catastrophe. But even as Fukushima prefecture gets ready to launch a new revitalization slogan – “Making Fukushima’s reconstruction a reality one step at a time” – it is still struggling to overcome the lingering aftereffects of the accident. Earlier this month, a group of six men and women diagnosed with thyroid cancer as children filed a class action case against Tokyo Electric Power Company (TEPCO), seeking $5.4 million in compensation.

Eastern Japan was hit by a massive magnitude 9.1 earthquake and 15-meter tsunami on March 11, 2011. The disaster shut off power and cooling to three reactors at the Fukushima Daiichi nuclear power plant, triggering the release of radiation for up to six days.

The plaintiffs, who are aged between 17 and 27, are seeking to hold TEPCO responsible for the thyroid cancer they developed. Two have had one side of their thyroid removed and four others have had a complete thyroidectomy and are planning or undergoing radiation therapy. The treatment has forced them to drop out of school or college and give up on their dreams. The plaintiffs argue that their thyroid cancer has created barriers to their education and employment as well as marriage and starting a family.

The Fukushima Daiichi meltdown was the worst nuclear accident since Chernobyl in 1986, which was followed by a spike in cancer cases in the region. In Japan a health survey conducted by the Fukushima prefecture found 266 cases of cancer among the 380,000 people aged under 18 at the time of the accident. The lawyers representing the plaintiffs argue that pediatric thyroid cancer is extremely rare, with an annual incident rate of two cases in one million people.

The plaintiffs added that in the past decade they have been forced to stay silent due to social pressure and the risk of public outrage over speaking out about the connection between the Fukushima nuclear accident and their thyroid cancer.

The Federation of Promotion of Zero-Nuclear Power and Renewable Energy, a civic group that includes five former Japanese prime ministers, sent a letter to the EU urging the elimination of nuclear power. In the letter, they stated that many children are suffering from thyroid cancer as a result of the Fukushima nuclear power plant accident.

However, the Japanese government believes there is no causal link between exposure to radiation from the accident and the children developing thyroid cancer. Prime Minister Kishida Fumio said at a House of Representatives Budget Committee meeting that “it is not appropriate to spread false information that children from Fukushima are suffering from health problems.”

At a press conference Takaichi Sanae, chairperson of the ruling LDP’s Policy Research Council refuted the letter sent by the federation. She stressed the government’s position that the cases of childhood thyroid cancer have been assessed by experts who have determined the accident is unlikely to have caused cancer.

Fukushima prefecture’s expert panel say there could be the possibility of “over-diagnosis” due to increased vigilance after the disaster, suggesting that some patients diagnosed with cancer did not need treatment. They say they are continuing to investigate the nature of each diagnosis. The Ministry of Environment also said they will continue to disseminate knowledge based on scientific findings to dispel rumors about the health effects of radiation.

Last week, the Fukushima reconstruction and revitalization council met to discuss the “diverse needs of the prefecture” and a long term response to support evacuees. Governor of Fukushima Uchibori Masao acknowledged that the prefecture is “facing many difficulties including the reconstruction and rehabilitation of evacuated areas and rebuilding the lives of evacuees and victims of the disaster.” There are also plans to establish a new national research and education organization in Fukushima that will devise measures to prevent and dispel rumors fueling discrimination toward evacuees and Fukushima food.

Taiwan recently lifted its blanket food import ban on Fukushima produce introduced in the wake of the disaster but there are 14 countries and regions that still maintain import restrictions. Additionally, Japan’s decision to discharge more than one million tonnes of low-level radioactive water from the crippled Fukushima nuclear power plant into the sea is another issue attracting negative publicity abroad.

https://thediplomat.com/2022/02/fukushima-disasters-impact-on-health-will-be-challenged-in-court/

February 20, 2022 Posted by | Fuk 2022 | , , | Leave a comment