Temporal changes in the radiocesium distribution in forests over the five years after the Fukushima Daiichi Nuclear Power Plant accident

Self Cite

Most of the area contaminated by the Fukushima Daiichi Nuclear Power Plant accident is covered by forest. In this paper, we updated model predictions of temporal changes in the 137Cs dynamics using the latest observation data and newly provided maps of the predicted 137Cs activity concentration for wood, which is the most commercially important part of the tree body. Overall, the previous prediction and latest observation data were in very good agreement. However, further validation revealed that the migration from the soil surface organic layer to the mineral soil was overestimated for evergreen needleleaf forests. The new prediction of the 137Cs inventory showed that although the 137Cs distribution within forests differed among forest types in the first 5 years, the difference diminished in the later phase. Besides, the prediction of the wood 137Cs activity concentrations reproduced the different trends of the 137Cs activity concentrations for cedar, oak, and pine trees. Our simulation suggests that the changes of the wood 137Cs activity concentration over time will slow down after 5–10 years. Although the model uncertainty should be considered and monitoring and model updating must continue, the study provides helpful information on the 137Cs dynamics within forest ecosystems and the changes in wood contamination.

mentioning

confidence: 99%

“…At the time of the fallout, needles/leaves, branches, and stems trapped 137 Cs, and a part of the fallout was deposited directly on the soil surface 2,3 . However, these distributions drastically change with time, particularly within a couple of years 3 . During that early phase, the major migration flux is from the tree to the soil surface.…”

mentioning

confidence: 99%

New predictions of 137Cs dynamics in forests after the Fukushima nuclear accident

Hirano

Imamura

Kaneko

et al. 2020

Self Cite

“…After the FDNPP accident, serious radionuclide fallout occurred over extensive areas of north-eastern Japan. As most of this region is covered by forests (approximately 70%), the long-term 137 Cs contamination of forestry ecosystems has been a concern 12 . Due to its long-term retention (ca.…”

mentioning

confidence: 99%

Relationship between radiocaesium in muscle and physicochemical fractions of radiocaesium in the stomach of wild boar

Saito

Nemoto

Tsukada

2020

After the accident at the TEPCO Fukushima Daiichi Nuclear Power Plant in 2011, it became important to study radiation dynamics, assess internal radiation exposure and specify factors affecting radionuclide variation in wildlife. Therefore, it is necessary to investigate which physicochemical fractions of radiocaesium ( 137 Cs) are absorbed from ingested material in species with high activity concentrations of 137 Cs, such as wild boar. This study analysed the physicochemical fractions of 137 cs in the stomach contents of wild boar to evaluate the transfer from ingested food to muscle. The 137 cs activity concentration in muscle showed a significantly positive relationship with the 137 cs activity concentration in the exchangeable fraction, and the sum of the 137 cs activity concentrations in the exchangeable and bound to organic matter fractions. Seasonal variations were also found in the 137 cs activity concentration in the exchangeable fraction, and the sum of the 137 cs activity concentrations in the exchangeable and bound to organic matter fractions. These findings suggest that the proportions of the physicochemical fractions of 137 Cs in the exchangeable and bound to organic matter fractions in the stomach contents are important factors affecting the increases and seasonal dynamics of the activity concentrations of 137 cs in wild boar muscle. Scientific RepoRtS |(2020) 10:6796 | https://doi.

“…The transfer of 137 Cs from soil to tree can be influenced by many factors, such as the initial contamination process, the season, the tree's physiology and age, and the 137 Cs distribution and availability in the soil 15,20,[50][51][52] . Therefore, T ag values change over time as a result of changes in such factors, and normally decrease until 137 Cs cycling within a forest ecosystem reaches a quasi-steady state 29,30 .…”

Section: Discussionmentioning

confidence: 99%

“…Deciduous broadleaved forests (49.1% of the forested area) and evergreen coniferous forests (47.7%) were the dominant forest types in the area heavily contaminated with 137 Cs from the Fukushima NPP accident 6 . These forests greatly differ in their tree phenology and the initial contamination process (e.g., initial interception of 137 Cs by the tree canopy and subsequent input to the forest floor via litterfall and throughfall 55 ); it is therefore likely that the behavior of 137 Cs in forest ecosystems after atmospheric fallout differs depending on the forest type 25,36,52 . An investigation conducted in an evergreen coniferous forest affected by the Fukushima NPP accident showed a slower migration of 137 Cs from the litter layer to the mineral soil compared with deciduous broadleaved forest 25 .…”

Section: Discussionmentioning

confidence: 99%

Effectiveness of decontamination by litter removal in Japanese forest ecosystems affected by the Fukushima nuclear accident

Koarashi

Atarashi-Andoh

Nishimura

et al. 2020

The Fukushima Daiichi nuclear power plant accident caused serious radiocesium ( 137 Cs) contamination of forest ecosystems over a wide area. The removal of the forest floor litter layer has been considered a potential method for forest decontamination; however, its effectiveness remains largely unknown. We conducted a pilot-scale decontamination study in a deciduous broadleaved forest in Fukushima. The entire forest was decontaminated by removing the litter layer in July 2014, approximately 3.3 years after the accident, with the exception of two untreated plots. For three years after decontamination, we quantified 137 Cs contamination levels in the litter and topsoil layers and in the tree leaves, in the untreated and decontaminated areas. The decreased inventories of litter materials and the litter-associated 137 Cs in the decontaminated areas were observed only in the first year after decontamination. Generally, no decontamination effects were observed on the 137 Cs transfer in tree leaves. The primary reason for this was the rapid shift in the main reservoir of 137 Cs from litter layers to the underlying mineral soil, which differs from the observations in post-Chernobyl studies of European forest ecosystems. The results suggest that litter-removal decontamination can only be successful if it is implemented more quickly (within 1-2 years after the accident) for Japanese forest ecosystems.The accident at the Fukushima Daiichi nuclear power plant (NPP) in March 2011 released large quantities of radionuclides into the atmosphere 1 and consequently caused serious radioactive contamination of terrestrial ecosystems over a wide area of eastern Japan 2 . Among the radionuclides deposited onto the terrestrial ecosystems, radiocesium ( 137 Cs), with a physical half-life of 30.1 years, is the primary cause for concern because 137 Cs-contaminated ecosystems can increase the radiation exposure to the local population for many years, via both an elevated ambient dose rate in the air (external exposure) and the consumption of contaminated food products (internal exposure) 3 .Decontamination is an important post-accident countermeasure to reduce the radiological impact of a nuclear accident on humans and ecosystems 3,4 . Although since the Fukushima NPP accident, decontamination efforts have been progressing in residential and agricultural areas, forested areas have received a low priority in the decontamination decision-making process, as in the case of the Chernobyl NPP accident 3 , and has not been carried out on a large scale 5 , even though forests provide a wide range of social, cultural, and economic values. This is because the forested areas are vast, occupying approximately 70% of the land in the heavily contaminated area 6 , but are generally not where people live permanently or regularly spend much time. Another reason may be that the forested areas in Japan are concentrated in mountainous and hilly regions with steep terrain, which makes them very sensitive areas to soil erosion. Technical, radiological, and econ...