Radiocesium Concentrations Research Articles

Temporal Analysis of Radiocesium Concentration in Sewage Sludge after Fukushima Daichi Nuclear Power Plant Accident

Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in April 2011 had released radioactive substances to the environment. Radiocesium transported from the urban area to the sewerage system by transfer wash-off mechanism. Eventually, radiocesium accumulated in the sludge produced by the wastewater treatment plant. This study was aimed to evaluate the possibility of using the time-series of Radiocesium concentrations in sewage sludge to quantify the wash off rate of the radionuclide on the surface of an urban area. This study used monitoring data from four WWTPs in Fukushima Prefecture and daily concentrations of Radiocesium in their sewer sludge over 8 years were collected. The results show time-dependent of Radiocesium concentration in sludge fitted with double exponential regression which means there are two rates: rapid rate (22 – 36 months) and slow rate (123 – 213 months). Values of the model parameters based on temporal analysis of radiocesium concentrations in sewage sludge are consistent with radiocesium wash off after the Chernobyl accident indicating that the decreasing rate of radiocesium concentrations in sewage sludge reflect the wash off rates on the surface of the corresponding urban area.

Retrospective and current state of forest territories of the border areas of the Bryansk region exposed to radioactive contamination

The aim of the study is to analyze the accumulated data on the study of forest territories of the border regions of the Bryansk region that have been exposed to radioactive contamination for their involvement in economic activity, as well as the possible transfer of radioactive materials in forest fires. The area of recorded and unaccounted forests was estimated according to the “Forest Plan of the Bryansk Region for the period 2019-2028” and the results of the analysis of remote sensing data of the earth, the assessment of radiation pollution – according to the radiation surveys of the forest fund and radioecological monitoring of forests, assessment of cesium-137 content – according to radiation monitoring. In the course of the work, the dynamics of the transition of forests from the range of a high level of radioactive contamination to lower ones from 1991 to 2018 slightly changes the total area of contaminated forests by regions was revealed. Top-level values of cesium-137 content in the main types of forest combustible materials, which a dangerous factor is contributing to a significant increase in the content of radiocesium in atmospheric air and the transfer of radionuclides beyond the limits of radioactive contamination zones in a forest fire. The most radiation-hazardous is the forest litter, which contains more than 70% of the total cesium-137 reserve in forest combustible materials, the values of which reach values of 224 kBq / kg in the Krasnogorsk district of the Bryansk region. The obtained forecast of cesium-137 content in the forest litter by the zones of radioactive contamination of forests in the most polluted areas of the Bryansk region for the period up to 2046 indicates the preservation of a high degree of radioactive contamination of forests in the Krasnogorsk and Novozybkovsky districts after more than 60 years after the Chernobyl accident power plants. Due to the high class of natural fire hazard of forests in the south-west of the Bryansk region and the high risk of fires in contaminated areas, it is necessary to assess the degree of danger in the prevention and suppression of radioactive forest fires, especially criterion of the absorbed dose for workers in order to avoid the deterministic effect.

Advanced approach for screening soil with a low radiocesium transfer to brown rice in Fukushima based on exchangeable and nonexchangeable potassium

Phytoavailable K in soil is a key to control the transfer factor of radiocesium from soil to brown rice. The transfer factors were determined for paddy fields cultivated in 2017 and 2018 under different K fertilization regimes in Fukushima Prefecture, Japan. Two phytoavailable forms of K, the exchangeable and nonexchangeable K contents were investigated for the surface soil sampled after the transplanting and fertilization as well as after harvest of rice in the same paddy fields. The exchangeable K content largely decreased from after transplanting and fertilization to after harvest, and the exchangeable K of the soil after harvest was negatively correlated with the transfer factor (rs = −0.70, p < .001). Most soil samples after harvest showed that the transfer factors exponentially increased as the exchangeable K decreased; however, some of the samples indicated considerably low transfer factors (<0.005) despite being exchangeable K deficient, i.e., exchangeable K < 25 mg K2O 100 g−1. Even though this value before usual fertilization has been effectively used as a threshold to determine whether supplemental K fertilization is required to reduce the radiocesium content in brown rice, additional screening was needed to estimate this radiocesium transfer more precisely. Thus, we found that not only the exchangeable K but also nonexchangeable K contents had a negative correlation with the transfer factor (rs = −0.60, p < .001) of the soil samples after harvest but were not correlated with each other (rp = −0.10). Furthermore, the results revealed that soil with nonexchangeable K > 50 mg K2O 100 g−1 indicated a considerably low transfer factor, even if exchangeable K deficient. Thus, via our field-scale experiments, we concluded that the criterion nonexchangeable K > 50 mg K2O 100 g−1 can be used as another threshold for use along with that of exchangeable K to differentiate soil with a low radiocesium transfer rate from exchangeable K deficient soil.

Distributions of radiocesium and radium isotopes in the western Bering Sea in 2018

We examined the spatial variations in radiocesium (134Cs and 137Cs) and radium (226Ra and 228Ra) concentrations (activities) in and around the western Bering Sea in August 2018. 134Cs concentrations in the surface seawater samples were 1.1–2.0 mBq/L, decay-corrected to the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident date. The northward slope current-dominated water of the Bering Sea exhibited higher 134Cs concentrations (345 Bq/m2 of the column inventory at a site near the slope), along with higher 228Ra concentrations and lower salinities relative to the Aleutian Basin area in the western Bering Sea. The observed features were considered to be a consequence of the arrival of FDNPP-derived radiocesium-rich and lower salinity Alaskan Stream water from the Pacific Ocean side, and subsequent mixing of the 228Ra-rich shelf water in the eastern slope area of the Bering Sea.

Radiocesium concentrations in wild boars captured within 20\u2009km of the Fukushima Daiichi Nuclear Power Plant

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011 released large amounts of artificial radioactive substances into the environment. In this study, we measured the concentration of radiocesium (134Cs + 137Cs) in 213 muscle samples from wild boars (Sus scrofa) captured in Tomioka town, which is located within 20 km of the FDNPP. The results showed that 210 (98.6%) muscle samples still exceeded the regulatory radiocesium limit (100 Bq/kg) for general foods. Radiocesium (134Cs + 137Cs) levels ranged from 87.1–8,120 Bq/kg fresh mass (FM), with a median concentration of 450 Bq/kg FM. The median committed effective dose was estimated to be 0.070–0.26 μSv/day for females and 0.062–0.30 μSv/day for males. The committed effective dose for one-time ingestion of wild boar meat could be considered extremely low for residents in Tomioka. The relatively high levels of radioactivity found in this study suggest that the high variability of food sources may have led to the large accumulation of radioactive substances. These results suggest that comprehensive long-term monitoring is needed to identify risk factors affecting recovery from a nuclear disaster.

Control of radiocesium recontamination by plant removal along a decontaminated riverside in Fukushima, Japan

The accident at the Fukushima Dai-ichi Nuclear Power Plant in March 2011 resulted in the widespread deposition of radiocesium in and around Fukushima prefecture. Riversides have an additional contamination risk through deposition of material containing radiocesium transported from upstream. In our previous research (Nishikiori and Suzuki, 2017) we developed a decontamination method in a river bank in 2014; however, the decontaminated site had a recontamination risk. In this study, we evaluated the effectiveness of plant removal as a countermeasure against recontamination because plants favor the deposition of highly-contaminated fine particles. Although suspended solids with high radiocesium concentrations were transported, under plant-removal conditions (2015–2016), sediment deposited in the flood channel was sandy with low radiocesium concentrations. In 2017, one year after the plant recovery, somewhat muddy sediment with high radiocesium concentrations was deposited during medium rainfall events; the plant biomass would explain the amount of fine sediment that was deposited. Additionally, large typhoons introduced sandy sediment even on the densely vegetated flood channel. Thereby, the air dose rates did not increase during the observation period. Plant removal may control the deposition of highly contaminated sediments and be an effective countermeasure for recontamination in the flood channel.

Comparative Estimation of the Plutonium (238Pu, 239+240Pu) and Radiocesium (137Cs) Content in Bottom Sediments and Hydrobionts of the Yenisei River

The contents of isotopes of plutonium (238Pu and 239, 240Pu) and 137Cs in samples of bottom sediments and hydrobionts (water moss, amphipods, and caddisfly larvae with casings) taken in the Yenisei River in the vicinity of the radioactive discharge from the Mining and Chemical Combine in 2012 and 2018 were comparatively estimated. It is shown that the content and ratios between the specific activities of plutonium isotopes (238/239 and 240) in samples of BSs and hydrobionts increased after the recommencing of plutonium discharges into the Yenisei due to the beginning of MOX fuel production. The background content and the ratio between plutonium isotopes in BSs of the Yenisei were estimated for the first time. Hydrobionts and BSs were ranged differently according to the content of plutonium and 137Cs: we recorded the highest content of 137Cs in BSs and that of plutonium in water moss. The plutonium content in hydrobionts of the Yenisei River varies considerably, which permits specification of representatives of biota (water moss and caddisfly larvae with casings) that, along with BSs, can be used as effective indicators of ecosystem pollution with plutonium.

Activity concentration of Fukushima-derived radiocesium in the western subarctic area of the North Pacific Ocean in summer 2017

Vertical profiles of radiocesium (134Cs and 137Cs) were measured in the western subarctic area of the North Pacific in 2017. The highest concentration of 134Cs, which was derived from the accident of the Fukushima Dai-ichi Nuclear Power Plant in 2011, was 0.14 Bq m−3 (or 1.19 Bq m−3 after the decay correction to the accident date). Although the vertical inventory of 134Cs decreased between 2014 and 2017, the inventory in 2017 was larger than that expected. That was probably arose from the return of some portion of the high-concentration water mass along with the anticlockwise subarctic gyre current.

Radiocesium transfer from Andosols to brown rice in the northern and northwest areas of Tochigi Prefecture, in the first 3 years following the 2011 Fukushima Daiichi nuclear power plant accident

ABSTRACT Following the Fukushima Daiichi Nuclear Power Plant accident of 2011, the potential for radiocesium transfer from contaminated soils, such as Andosols, to agricultural crops became a significant concern. Andosols account for up to 70％ of paddy soils in the northern and northwest areas of Tochigi Prefecture, where the radiocesium concentration is 1000 Bq kg−1 or greater in the soil of some fields. The present study was carried out in order to determine the phytoavailability of radiocesium in Andosols by comparing it with that of gray lowland soils in the first 3 years following the accident. The transfer factor (TF) tended to be higher in Andosols than in gray lowland soils, leading to higher radiocesium concentrations in brown rice grown in Andosols. The exchangeable potassium (Ex-K2O) in Andosols was highly and negatively correlated with TF, followed by clay. The Ex-K2O value was positively correlated with the clay/total carbon (T-C) value, suggesting that a high T–C ratio could weaken K2O adsorption on clay mineral sites; hence, the low clay/T-C values can partially explain the relatively large TF values of Andosols. Samples with Ex-K2O contents less than 200 mg kg−1 and with low clay/T-C values showed striking decreases in TF values from 2011 to 2012. However, the decrease from 2012 to 2013 was quite small; radiocesium in these samples was potentially available for rice uptake for a long time, likely due to the reversible adsorption and fixation characteristics of allophane. Most gray lowland soil samples showed very low TF values over the 3 years of the study, except for those with TF values greater than 0.1 due to low Ex-K2O and clay contents; the geometric mean (GM) value of TF was below 0.01 in 2012. The extraction of exchangeable radiocesium (Ex-Cs) with a 1 mol L−1 ammonium acetate solution may not be an appropriate method for explaining the variability in radiocesium TF in Andosols. This is because the Ex-Cs value was significantly correlated with Ex-K2O in Andosols, but not in gray lowland soils, indicating that Ex-K2O explained this variability in relation to Ex-Cs.

Reduction in the Radiocesium in Meats of the Sika Deer and Wild Boar by Cooking

The behavior of radiocesium in wild animal meats upon cooking was investigated. The ratio of the concentration change (processing factor, Pf), remaining ratio (food processing retention factor, Fr), and removal ratio of radiocesium in the meats by grilling, boiling, and steaming were determined. Differences in cooking methods, rather than differences in meat parts or animal species, clearly influenced the Pf, Fr, and removal ratios. The mean Fr values were 0.9 (range, 0.7 to 1.0) for grilling, 0.6 (range, 0.4 to 0.7) for boiling, and 0.5 (range, 0.4 to 0.7) for steaming. The removal effect of grilling (11%) was lower than that of boiling (41%) or steaming (47%). The mean value of Pf was 1.2 (range, 1.1 to 1.6) for grilling, 0.8 (range, 0.6 to 0.9) for boiling, and 0.8 (range, 0.7 to 1.0) for steaming. The radiocesium concentration in the meats increased only upon grilling, but not by boiling or steaming. This difference is due to the lower removal effect of grilling than that of boiling and steaming. Therefore, boiling and steaming were more effective than grilling for removing radiocesium and reducing its concentration in wild animal meats. Furthermore, the ratio of water content fluctuations due to boiling was negatively correlated with Pf and Fr. It was evident that greater reductions in water content resulted in lower concentrations and improved radiocesium removal in the meats. These results suggest that some of the radiocesium naturally present in the meats is soluble in water and that the radiocesium dissolved in water can be removed from the meat with the release of water from the tissue.

Effect of metal ions in groundwater to radiocesium sorption into bentonite mineral from Tasikmalaya

Karawang and Sumedang areas were two of the preferred sites for radioactive waste disposal facilities in the future, and the effect of coexistence ions in their groundwater to radiocesium sorption in bentonite sample has been studied. Bentonite material is placed in the surrounding of disposal facility and usually is used as an engineered barrier to prevent the migration of radiocesium from the facility to the environment by sorption mechanism. The concentration of cation in groundwater such as K+, Na+, Ca2+ and Mg2+ have been obtained from the field work and could many folds higher when compared with the assumed radiocesium concentration releases to the environment. The existed cations in groundwater were predicted to be able affected to the radiocesium sorption into the bentonite sample. Coefficient of distribution (Kd) was used as the indicator of radiocesium sorption into bentonite sample. The result showed that increased in cation concentration in groundwater reduced the Kd value of radiocesium into bentonite samples up to 21 % compared with no cation exists condition in groundwater.

Fogwater deposition of radiocesium in the forested mountains of East Japan during the Fukushima Daiichi Nuclear Power Plant accident: A key process in regional radioactive contamination

Because of limited environmental monitoring data, the regional-scale impact of the deposition of fogwater radiologically contaminated by the Fukushima Daiichi Nuclear Power Plant (F1NPP) accident remains unclear. To redress this situation, we present an observational report of the radiocesium concentration in fogwater and its deposition in a Japanese forest during the early stages of the F1NPP accident (March 2011). The data were acquired by using a passive collector to capture fogwater above the forest canopy on a monthly basis. In addition, the radiocesium concentrations in monthly throughfall and stemflow were measured under the canopies of four tree species. The 137Cs activity concentration in fogwater during the observational period was 45.8 Bq L−1, which was twice as high as that present in bulk precipitation. The ratio of 137Cs in throughfall to that in bulk precipitation (TF/BP ratio) ranged from 1.0 to 2.5. The high TF/BP ratios may have been caused by the high radiocesium concentration in fogwater deposition. Based on this assumption, we assessed the TF/BP ratio according to the 137Cs activity concentrations of throughfall and bulk precipitation measured in various mountainous regions in East Japan. Our results reveal that the TF/BP ratio is high at some sites and that it increases with elevation. Sites with a high TF/BP ratio were almost entirely situated in areas of fogwater deposition, as predicted by an atmospheric dispersion model. In addition, sites with a high TF/BP ratio were above the cloud base at the time when plumes with high atmospheric 137Cs activity concentrations passed through the areas. Thus, these measurements of radiocesium in fogwater during the early stages of the F1NPP accident provide evidence that fogwater with high radioactive contamination was deposited in the forested mountain areas of East Japan. Given the major impact of fogwater deposition of radiocesium, its role should be considered carefully to better understand radiocesium cycling in forest ecosystems.

Установление опорного значения удельной активности цезия-137 на распахиваемых склонах в перигляциальной области бассейна Верхней Оки: применение спутниковых снимков, ГИС и агрохимических показателей почвы

The paper deals with the issues of determining the reference value of specific activity of cesium-137 of Chernobyl origin when applying the radiocesium method to assess the loss of gray forest soil in the areas of spread of the microrelief of paleocryogenic origin in the periglacial region of the upper Oka basin. Paleocryogenic microrelief is recognized in spring satellite imagery available on Google EarthTM. The necessity of choosing a reference plot for a specific field that differs in microrelief, exposure, and the nature of soil cultivation is substantiated. The authors analyze the data, which they obtained during the field research in 2016-2019, on three agricultural fields located on the arable slopes of the northern and southern exposure in the upper Oka basin within the Orel district of the Orel Region. Three experimental plots, selected in close proximity to one another, differed both in exposure and in the content of humus, labile phosphorus and radiocaesium in the arable layer. Layer-by-layer soil sampling at block elevations within the reference plots located on watershed surfaces, gamma-spectrometric and agrochemical analyzes of soil samples allowed us to draw a number of systematically important conclusions. The first is that the reference value of radiocaesium in the arable layer should be determined within block elevations on the watershed surface of the slope or on inter-valley micro-water divisions on the water-divide surface (if it is not possible to select a reference plot on the watershed surface). The second is that the dimensions of the reference plots are determined by the size of the block elevations (the sizes of blocks in the area under study are 10-20 m). The third is that the reference value of radiocaesium should be determined individually for each field that differs in exposure and in the nature of the soil treatment. In the experimental plot, the reference value of the specific activity of cesium-137 increases in the following order: a field located on the water-divide surface of the northern exposure slope, with a grain rotation, with regular fertilizing (130.5 Bq/kg) — a field located on the watershed surface of the eroded slope southern exposure (174.7 Bq/kg) — a field located on the water-divide surface of a less fertilized and less eroded slope of the northern exposure (180 Bq/kg). The results of the study show that the use of the radiocaesium method in periglacial areas requires testing a fundamentally new approach to its implementation: at the stage of determining the reference value of radiocaesium, it is necessary to take into account the polygonal-block structure of the watershed surfaces.

Risk assessment for radiocesium concentration in brown rice cultivated in paddy field

Risk assessment for radiocesium concentration in brown rice cultivated in paddy field

Radiocesium (137Cs) concentrations in the two-toed amphiuma (Amphiuma means) and the lesser siren (Siren intermedia)

This study sought to determine radiocesium (137Cs) concentrations in two species of aquatic salamanders – the two-toed amphiuma (Amphiuma means) and the lesser siren (Siren intermedia) on the Savannah River Site. Concentrations (137Cs Bq/g, dry wt) of the two species were similar at both 137Cs-contaminated (A. means = 0.733 ± 0.242, n = 5; S. intermedia = 0.839 ± 0.722, n = 5) and reference sites (A. means = 0.028 ± 0.020, n = 5; S. intermedia = 0.042 ± 0.027, n = 11). Salamanders captured in areas impacted by 137Cs contamination exhibited significantly higher 137Cs concentrations than individuals captured at reference sites (U = 146, p < 0.001). Salamander size (snout-vent length) was not correlated with whole-body 137Cs. An analysis of our data using the ERICA tool suggests that negative impacts due to 137Cs exposure are unlikely in these species. Overall, these data indicate that A. means and S. intermedia inhabiting contaminated sites bioaccumulate but do not biomagnify 137Cs.

Снижение перехода 137Cs в молоко коров при использовании модифицированных кормовых добавок с ферроцином

The problem of livestock production that meets sanitary standards in radioactively contaminated territories remains relevant and is of great practical and scientific interest. The use of sorbents from the class of ferrocyanides promotes the production of livestock products (milk) that comply with accepted hygienic standards. The studies were conducted to evaluate the effectiveness of new formulations of feed additives based on potassium–iron (III) hexacyanoferrate (II) (azure iron milori) compared with 137Cs Bifezh sorbent to reduce the content of radiocaesium, on the productivity of dairy cows and qualitative milk indicators. The tests were carried out under production conditions on the basis of the SEC “Rabochii” of the Gordeevsky district of the Bryansk region. The farm was exposed to radioactive contamination as a result of the Chernobyl accident. Agricultural land of the farm is characterized by relatively high pollution densities at 137Сs and high variability. The use of ferrocine-containing preparations as part of new formulations of modified feed additives made it possible to reduce the concentration of 137Cs in cow’s milk by 2–4 times on day 15 and by 4–5 times on day 30 as compared to the control and did not affect the qualitative indicators of cow’s milk, except for a significant increase fat content of milk in all groups of animals by the end of the experiment.

On the challenges of dating alluvial sediments with radiocesium: a caveat from the Wurm River, Central Europe

The activity of radiocesium in alluvial sediment is a widely used proxy for sediment age determination for the period after its first occurrence in the environment in 1952. In a continuous and undisturbed sediment archive, the results of this method are reliable as shown by various studies. However, depending on the specific characteristics of an archive provided by alluvial sediment, the results might be unreliable or biased. This article describes the challenges and ambiguous results obtained by the measurement of radiocesium in a soil profile that provides a time marker with a concrete structure of known age. The applicability of radiocesium for the study area was successfully tested on a floodplain profile. The results showed radiocesium peaks up to 22.5 Bq/kg that correspond to the years 1963 and 1986. As a result of different hydromorphological conditions and sedimentation rates at the sampling locations, the peaks occurred in different depths. In the floodplain, the 137Cs-peaks are significantly more distinguished than in the profile at the concrete structure. There, the radiocesium content is scattered, which queries the function of the structure as a chronological marker. The scattering might be caused by various syn-sedimentary and post-sedimentary processes and factors, such as scouring and redeposition of contaminated sediment, topsoil recycling by vegetation uptake and dieback, or input of eroded sediments from the hinterland forest soils. Thus, the concrete structure creates and at the same time destroys the possibility of using it as a chronological marker.

Spatial variability of vertical profiles of radiocesium in a paddy field measured by conventional core sampling

ABSTRACT Our analyses revealed the spatial variability of the vertical distribution of fallout radiocesium measured in small cylindrical soil cores taken in a non-disturbed paddy field contaminated by the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in 2011. The field is in Iitate Village 40km northwest of FDNPP and had been designated as an off-limit area. In December 2012, soil samples were taken along a longitudinal and transverse line in the field at intervals of 1 or 2 m. In May 2013, 36 additional soil samples were taken from a 1m2 plot at 20cm intervals, where the ground undulated considerably. The core samples were carefully cut into slices, dried, and subjected to measurement of the radiocesium concentration. The coefficient of variation in the total radiocesium inventory (i.e. the radioactivity of total radiocesium in the unit area of the soil profile) and the averaged radiocesium concentration at 0～10 cm were 47.8 % and 53.5 %, respectively, demonstrating that the mean of a few representative points in a paddy lot provides huge uncertainty. Our analysis of semivariograms for the mean radiocesium concentration revealed no spatial correlation even between the shortest lag distance (2 m). It should thus be noted that the mean concentration determined from a small core sample cannot represent the tendency around the sampled point. However, the result of the 20 cm2 grid samplings suggested that undulations on a 10-cm scale can cause radiocesium to migrate to a concave spot. Among the 82 sampling points, 50 % of the vertical profiles of the radiocesium concentration had a concentration peak at the ground surface, but the other points had an s-shape or bell shape, suggesting variation in the water flow regime among the sampled profiles. The apparent convective velocity of the radiocesium ranged widely from 0.00 to 3.38 cmy-1 with a mean of 0.75 cm y-1.

Siltation and radiocesium pollution of small lakes in different catchment types far from the Fukushima Daiichi nuclear power plant accident site

The Fukushima Daiichi nuclear power plant accident caused radioactive pollution in northeastern Honshu Island, Japan. This study examined the influence of snowmelt and rainfall on soil erosion processes and siltation of small lakes in Miyagi Prefecture (150 km northwest of the power plant). Two sets of slopes and lakes, respectively in pasture and forest catchments, were examined. Snowpack thickness, soil infiltration, surface runoff volume, soil and sediment physicochemical properties, Cs concentration of precipitation, meltwater, and rainwater, and lake siltation rates were determined. The total radioactive Cs content in precipitation was 0.7–7.4 BqˑL−1 and was below the Japanese standard (10 BqˑL−1). Total radioactive Cs was at the allowable level in water flowing down the pasture catchment slope (0.1–9.2 BqˑL−1) during snowmelt and rainfall, as well as in pasture (0.9–8.8 BqˑL−1) and forest (0.7–5.2 BqˑL−1) catchment lake water. There was no soil erosion (surface runoff) in the forest catchment. Soil losses in the pasture catchment were 23 due to rainfall and 9 kg ha−1 yr−1 following spring snowmelt. After snowmelt, a 0.5 and 0.2 mm thick layer of silt was deposited in pasture and forest catchment lakes, respectively, and 1.4 and 0.6 mm were deposited during the rainfall period. Average siltation rates were 1.9 and 0.8 mmˑyr−1 for pasture and forest catchment lakes, respectively. The upper layer of lake bottom sediments is represented mainly by silt fractions (2–50 μm), with high organic matter (4.0–5.7%) and radiocesium (1100–1600 kgˑha−1) contents.

Extensive analysis of radiocesium concentrations in wild mushrooms in eastern Japan affected by the Fukushima nuclear accident: Use of open accessible monitoring data

After the Fukushima Daiichi Nuclear Power Plant accident, there has been an increasing concern regarding the contamination of wild mushrooms with radiocesium (134Cs and 137Cs) in eastern Japan. In this study, we analyzed the radioactivity monitoring data of 3189 wild edible mushrooms of 107 species collected by the 265 local municipalities in eastern Japan to investigate the radiocesium levels in wild mushrooms. Results of the analysis showed that radiocesium concentrations in mushrooms were normalized with radioactivity deposition data from aircraft monitoring, and then we evaluated the effects of species, sampled location, sampling year and regional deviation between 134Cs and 137Cs activity of specimens using a hierarchical Bayesian approach considering spatial autocorrelation (an intrinsic CAR model). Normalized activity concentration by species ranged from 1.1×10−4 to 2.3×10−2 (m2 kg−1, fresh weight). As reported in previous studies, the mycorrhizal species tended to have higher radiocesium concentrations. Some saprophytic species (e.g. Pholiota lubrica) also had high concentrations. For the mushroom species that were also evaluated in the post-Chernobyl studies, we found that the same species had similar trends of absorption capacities. Our results indicate the extensive analysis of public monitoring data is helpful to understand the situation of mushroom contamination and evaluate the internal dose by ingestion of wild mushrooms according to species and areas.