137Cs, 239,240Pu and 241Am in boreal forest soil and their transfer into wild mushrooms and berries

Distributions of fallout 137Cs, 239+240Pu and 241Am in a soil core from South Central China

The source and vertical distribution of ¹³⁷Cs,^239+240Pu and ²⁴¹Am activity concentrations in a soil core from Hunan Province, China were investigated. The maximum ¹³⁷Cs and ^239+240Pu activity concentrations were 15.45 ± 0.76 mBq/g and 0.819 ± 0.066 mBq/g, respectively. While the maximum ²⁴¹Am activity concentration in samples obtained from the core was 0.341 ± 0.019 mBq/g. The ²⁴⁰Pu/²³⁹Pu atom ratio and the ¹³⁷Cs/^239+240Pu activity ratio were 0.183 ± 0.011 and 19.5 ± 1.8, respectively, and both were consistent with the characteristic value of global fallout. The integrated ²⁴¹Am/^239+240Pu activity ratio for global fallout was also re-estimated. The measured ²⁴¹Am/^239+240Pu activity ratio (average 0.43 ± 0.07) in the samples was very close to the estimated value (0.45), which suggested their ²⁴¹Am also came from the global fallout. Regarding the vertical distribution of ¹³⁷Cs, ^239+240Pu and ²⁴¹Am in these red soil samples, all these radionuclides had higher concentrations in upper layers of several centimeters of soil while they had slightly lower concentrations in lower soil layers down to 30 cm. Vertical distributions of ¹³⁷Cs/^239+240Pu and ²⁴¹Am/^239+240Pu activity ratios indicated the migration velocity was Am ≈ Pu > Cs. The intrinsic chemical properties of the radionuclides as well as soil type and properties (acidic, nutrient-deficient and low in organic matter and cation exchange capacity) might be reasons for the differences in their migration behaviors.

Determination of 241Am in Environmental Samples: A Review

The determination of ²⁴¹Am in the environment is of importance in monitoring its release and assessing its environmental impact and radiological risk. This paper aims to give an overview about the recent developments and the state-of-art analytical methods for ²⁴¹Am determination in environmental samples. Thorough discussions are given in this paper covering a wide range of aspects, including sample pre-treatment and pre-concentration methods, chemical separation techniques, source preparation, radiometric and mass spectrometric measurement techniques, speciation analyses, and tracer applications. The paper focuses on some hyphenated separation methods based on different chromatographic resins, which have been developed to achieve high analytical efficiency and sample throughput for the determination of ²⁴¹Am. The performances of different radiometric and mass spectrometric measurement techniques for ²⁴¹Am are evaluated and compared. Tracer applications of ²⁴¹Am in the environment, including speciation analyses of ²⁴¹Am, and applications in nuclear forensics are also discussed.

Estimation of radionuclides global fallout levels in the soils of CIS and eastern Europe territory

This study is devoted to the estimation of radionuclides global fallout levels in the soils of Commonwealth of Independent States (CIS) and Eastern Europe territory as a result of nuclear explosions. 58 standard soil samples were used, which were selected in different soil and climatic areas of the territory of CIS and Eastern Europe in 1978-2018. All samples were measured by gamma spectrometry. Determination of plutonium isotopes and strontium was performed according to the method of the joint determination of these radionuclides from one sample. IN the samples considered in this work, the content of ⁶⁰Co, ¹⁵⁴Eu, ¹⁵⁵Eu was below the detection limits, which were 0.4; 1.0 and 1.0, respectively. Natural radionuclides analysis results indicated that the obtained samples are typical soil samples without its abnormal contents. The content of ¹³⁷Cs, ⁹⁰Sr, ^239+240Pu in a 20 cm soil layer due to global fallout is (3.9 ± 1.7), (2.2 ± 0.8), (0.18 ± 0.08) Bq/kg respectively, which considering the distribution of these radionuclides by depth and average soil density is (1.2 ± 0.5) kBq/m² for ¹³⁷Cs, (0.42 ± 0.15) kBq/m²- ⁹⁰Sr and (55.0 ± 24.0) Bq/m²- ^239+240Pu. The isotopic ratios¹³⁷Cs/⁹⁰Sr and ¹³⁷Cs/^239+240Pu for the territory of CIS and Eastern Europe are at the level (2.0 ± 0.71) and (25 ± 15), respectively.

137Cs and 40K activity concentrations in edible wild mushrooms from China regions during the 2014–2016 period

Introduction. Contamination by radiocaesium of edible wild mushrooms after major nuclear accidents is a long-lasting process in some regions of the world. Following greater awareness of radioactive pollution in Asia, particularly after the Fukushima accident, this study investigated the radioactivity of 137Cs and 40K contamination in edible wild mushrooms in China. Study objects and methods. The objects of the research were edible wild mushrooms collected during 2014 to 2016, from the Inner Mongolian and Yunnan regions of China. To obtain an insight into any environmental impacts to distant regions of mainland Asia, the mushrooms were analyzed for 137Cs activity. In parallel, the natural activity of 40K was also determined and used to estimate the content of total K. The topsoil underneath the mushrooms was also investigated from a few sites in Bayanhushu in Inner Mongolia in 2015. Results and discussion. The results showed that in 4 to 6 mushrooming seasons after the accident, mushrooms from both regions were only slightly contaminated with 137Cs, which implied negligible consequences. The activity concentrations of 137Cs in dried caps and whole mushrooms in 63 of 70 lots from 26 locations were well below 20 Bq kg–1 dry weight. Two species (Lactarius hygrophoroides L. and Lactarius volemus L.), from Jiulongchi in Yuxi prefecture showed higher 137Cs activities, from 130 ± 5 to 210 ± 13 Bq kg–1 dw in the caps. 40K activities of mushrooms were around two- to three-fold higher. A composite sample of topsoil (0–10 cm layer) from the Bayanhushu site (altitude 920 m a.s.l.) in Inner Mongolia showed 137Cs activity concentration at a low level of 6.8 ± 0.7 Bq kg–1 dw, but it was relatively rich in potassium (40K of 595 ± 41 Bq kg–1 and total K of 17000 ± 1000 mg kg–1 dw). Conclusion. Wild mushrooms from the Yunnan and Inner Mongolia lands only slightly affected with radioactivity from artificial 137Cs. Lack of 134Cs showed negligible impact from Fukushima fallout. Ionizing radiation dose from 137Cs in potential meals was a fraction of 40K radioactivity. The associated dietary exposure to ionizing irradiation from 137Cs and 40K contained in mushrooms from the regions studied was considered negligible and low, respectively. Mushroom species examined in this study are a potentially good source of dietary potassium.

Europe-Wide Atmospheric Radionuclide Dispersion by Unprecedented Wildfires in the Chernobyl Exclusion Zone, April 2020

From early April 2020, wildfires raged in the highly contaminated areas around the Chernobyl nuclear power plant (CNPP), Ukraine. For about 4 weeks, the fires spread around and into the Chernobyl exclusion zone (CEZ) and came within a few kilometers of both the CNPP and radioactive waste storage facilities. Wildfires occurred on several occasions throughout the month of April. They were extinguished, but weather conditions and the spread of fires by airborne embers and smoldering fires led to new fires starting at different locations of the CEZ. The forest fires were only completely under control at the beginning of May, thanks to the tireless and incessant work of the firefighters and a period of sustained precipitation. In total, 0.7-1.2 TBq ¹³⁷Cs were released into the atmosphere. Smoke plumes partly spread south and west and contributed to the detection of airborne ¹³⁷Cs over the Ukrainian territory and as far away as Western Europe. The increase in airborne ¹³⁷Cs ranged from several hundred μBq·m^-3 in northern Ukraine to trace levels of a few μBq·m^-3 or even within the usual background level in other European countries. Dispersion modeling determined the plume arrival time and was helpful in the assessment of the possible increase in airborne ¹³⁷Cs concentrations in Europe. Detections of airborne ⁹⁰Sr (emission estimate 345-612 GBq) and Pu (up to 75 GBq, mostly ²⁴¹Pu) were reported from the CEZ. Americium-241 represented only 1.4% of the total source term corresponding to the studied anthropogenic radionuclides but would have contributed up to 80% of the inhalation dose.

Analyzing alpha emitting isotopes of Pu, Am and Cm from NPP water samples: an intercomparison of Nordic radiochemical laboratories

Radioanalytical methods for the determination of isotopes of Pu, Am and Cm in water samples from nuclear power plants were compared and further developed in a Nordic project (Optimethod) through two intercomparison exercises among Nordic laboratories. With this intercomparison, the analytical performance of some laboratories was improved by modification of the analytical method and adopting new techniques. The obtained results from the two intercomparisons for alpha emitting transuranium isotopes are presented, and the lessons learnt from these intercomparison exercises are discussed.

Sediment profile dating and reconstructing nuclear events from annually laminated lake sediments in northern Finland

The sediments deposited in Lake Kevojärvi (69°45N, 27°00'E) in northernmost Finland were investigated for radioactivity. Freeze cores recovered from the 35-m deep basin has preserved a distinct succession of annual laminations deposited between 1909 and 2015. The basic varve structure is composed of a detrital snowmelt layer and an organic-rich post-snowmelt layer lying on top of the snowmelt layer. The past nuclear events have been preserved in the lake sediment. In order to study these, sediment freeze with annual sediment laminations were recovered from the lake bottom and measured for gamma emitting radionuclides. A total of 53 sediment subsamples, each incorporating sediment from one to two varves i.e. sediment deposited during one to two years, were taken for gamma spectroscopy measurements using low-background HPGe detector system. The measurements showed large variations in ¹³⁷Cs and ²⁴¹Am concentrations between different laminae marking different nuclear events in history. This highly resolved profile revealed a detailed record of anthropogenic radioactive fallout from atmospheric nuclear weapons testing during 1950s and 1960s and the Chernobyl accident in 1986. The measured ¹³⁷Cs concentrations varied between 0.6 and 229 Bq/kg dry weight (dw) while the measured ²⁴¹Am concentrations varied between 0.6 and 6.4 Bq/kg dw. The ¹³⁷Cs showed downward migration in the sediment column since ¹³⁷Cs was also found in varves dating before 1945. The first clear increase in ¹³⁷Cs concentration was observed in 1956 varve and the ¹³⁷Cs concentrations were found to peak in the 1964, 1970 and 1986 varves. The ²⁴¹Am was first observed in 1957 varve and the concentrations peaked in 1960-1962, 1964 and 1970 varves. This demonstrated that ²⁴¹Am can be a complementary chronostratigraphic marker to ¹³⁷Cs in sediment. A time delay of one to two years was observed between the years of intensive atmospheric nuclear weapons testing and the increased ¹³⁷Cs and ²⁴¹Am concentrations in the sediment varves. In the ²¹⁰Pb concentrations long-time periods of low (~1930-1950 and ~1990-2000) and high concentrations (~1950-1980) were observed. The reason for large variation was the amount of sediment input. The Constant rate of supply (CRS) model results showed good agreement with the varve counting. The model results showed that the ²¹⁰Pb deposition has been constant over the last 80 years and no effect of climate change to the ²¹⁰Pb deposition was observed.

Biometric traits of onion (Allium cepa L.) exposed to 137Cs and 243Am under hydroponic cultivation

To elucidate the features of bioaccumulation and phytotoxic effects of long-lived artificial radionuclides, a hydroponic experiment was carried out with the cultivation of onion (Allium cepa L.) in low-mineralized solutions spiked with ¹³⁷Cs (250 kBq L^-1) or ²⁴³Am (9 kBq L^-1). After the 27-day growth period, ≈70% of ¹³⁷Cs and ≈14% of ²⁴³Am were transferred from the solutions to onion biomass with transfer factor values ≈ 400 and ≈ 80, respectively. Since the bioaccumulation of both radionuclides mainly took place in the roots of onion (77% ¹³⁷Cs and 93% ²⁴³Am of the total amount in biomass), edible organs - bulbs and leaves - were protected to some extent from radioactive contamination. At the same time, the incorporation of the radionuclides into the root tissues caused certain changes in their biometric (geometric and mass) traits, which were more pronounced under the ²⁴³Am-treatment of onion. Exposure to ²⁴³Am significantly reduced the number, length, and total surface area of onion roots by 1.3-2.6 times. Under the influence of ¹³⁷Cs, the dry-matter content in roots decreased by 1.3 times with a corresponding increase in the degree of hydration of the root tissues. On the whole, the data obtained revealed the specific features of ¹³⁷Cs and ²⁴³Am behaviour in "hydroponic solution - plant" system and suggested that biometric traits of onion roots could be appropriate indicators of phyto(radio)toxicity.

A Review of the Occurrence of Alpha-Emitting Radionuclides in Wild Mushrooms

Alpha-emitting radioisotopes are the most toxic among all radionuclides. In particular, medium to long-lived isotopes of the heavier metals are of the greatest concern to human health and radiological safety. This review focuses on the most common alpha-emitting radionuclides of natural and anthropogenic origin in wild mushrooms from around the world. Mushrooms bio-accumulate a range of mineral ionic constituents and radioactive elements to different extents, and are therefore considered as suitable bio-indicators of environmental pollution. The available literature indicates that the natural radionuclide 210Po is accumulated at the highest levels (up to 22 kBq/kg dry weight (dw) in wild mushrooms from Finland), while among synthetic nuclides, the highest levels of up to 53.8 Bq/kg dw of 239+240Pu were reported in Ukrainian mushrooms. The capacity to retain the activity of individual nuclides varies between mushrooms, which is of particular interest for edible species that are consumed either locally or, in some cases, also traded on an international scale. The effective radiation dose from the ingestion of this food can reportedly range from 0.033 µSv/kg dw to 26.8 mSv/kg and varies depending on the country. Following pollution events, such consumption may expose consumers to highly radiotoxic decay particles produced by alpha emitters.

Artificial (137Cs) and natural (40K) radioactivity and total potassium in medicinal fungi from Yunnan in China

Evaluated has been radioactive contamination with ¹³⁷Cs in parallel to occurrence of ⁴⁰K and total K in 31 species of medicinal mushrooms from Yunnan, China. We chose species that were not previously studied. The activity concentrations of ¹³⁷Cs in the medicinal fungi in this study were low. The maximum values were 54 ± 4 Bq kg^-1 dry biomass (db) in caps and 48 ± 5 Bq kg^-1 db in stipes of saprotrophic fungus Gerronema xanthophyllum from the family of Tricholomataceae. Mushrooms with relatively higher activity concentrations of ⁴⁰K were among the non-polypore species but certain species from the genus Ganoderma such as G. applanatum, G. capense, G. philippii and G. sinense showed ⁴⁰K in the higher range of 900 ± 240 to 1400 ± 340 Bq kg^-1 db. The concentrations of total K in the fungal materials in this study were in the range from 2.9 ± 6.5 g kg^-1 db in Fomes rufolaccatus to 110 ± 6 g kg^-1 db in G. xanthophyllum. The species studied, which represented both some popular wood-decaying polypore fungi but also terrestrial forms from the herbal medicine of China, can be considered as little contaminated with ¹³⁷Cs and potentially good source of leachable K in extract and decoction or as a powdered form in capsules.

137Cs activity concentration in mushrooms from the Bobrůvka river valley

In the 2017-2018 mushrooming seasons at the (Bohemian-Moravian Highlands near Dolní­ Roží­nka) a total of 505 mushrooms belonging to 9 species were collected, and analyzed by gamma spectrometry for 137Cs activity. The maximum 137Cs activity of 575 Bq.kg-1 was detected in Boletus edulis species, what in native state, is just below the allowed limit. In contrast, in mushroom Imleria badia, which is reported to be associated with the highest cumulative capability from all fungi species, detected activity level was only 316 Bq. kg-1. However, differences in mean contamination values were not significant due to high variability. It was shown, that activity concentration is not dependent on the weight (size) of Imleria badia. Our results also confirmed generally well known lower 137Cs activity in the Russula species representatives belonging to the group of gills or lamella bearing mushrooms.

137Cs and 40K in Cortinarius caperatus mushrooms (1996-2016) in Poland - Bioconcentration and estimated intake: 137Cs in Cortinarius spp. from the Northern Hemisphere from 1974 to 2016

Cortinarius caperatus grows in the northern regions of Europe, North America and Asia and is widely collected by mushroom foragers across Europe. This study shows that in the last three decades since the Chernobyl nuclear accident, C. caperatus collected across much of Northern Poland exhibited high activity concentrations of radiocaesium (¹³⁷Cs) - a long-lived radionuclide. The mushroom appears to efficiently bioconcentrate ¹³⁷Cs from contaminated soil substrata followed by sequestration into its morphological parts such as the cap and stipe which are used as food. The gradual leaching of ¹³⁷Cs into the lower strata of surface soils in exposed areas are likely to facilitate higher bioavailability to the mycelia of this species which penetrate to relatively greater depths and may account for the continuing high activity levels noticed in Polish samples (e.g. activity within caps in some locations was still at 11,000 Bq kg^-1 dw in 2008 relative to a peak of 18,000 in 2002). The associated dietary intake levels of ¹³⁷Cs have often exceeded the tolerance limits set by the European Union (370 and 600 Bq kg^-1 ww for children and adults respectively) during the years 1996-2010. Human dietary exposure to ¹³⁷Cs is influenced by the method of food preparation and may be mitigated by blanching followed by disposal of the water, rather than direct consumption after stir-frying or stewing. It may be prudent to provide precautionary advice and monitor activity levels, as this mushroom continues to be foraged by casual as well as experienced mushroom hunters.

137Cs and 40K concentration ratios (CRs) in annual and perennial plants in the Caspian coast

This research attempted to investigate the plant/soil concentration ratios (CRs) of ¹³⁷Cs and ⁴⁰K in plants that grow on the Anzali Lagoon of the Caspian coast, Iran. The activity concentrations of ¹³⁷Cs and ⁴⁰K were measured in soil samples, annual plants (Echinochloa crus-galli, Digitaria sanguinalis, and Trifolium repens), and perennial plants (Phragmites australis, and Cynodon dactylon). The relationship of activity concentration with soil particle density, and pH of soil samples, CR, and ¹³⁷Cs/⁴⁰K discrimination factor (DF) were determined. The activity concentration of ¹³⁷Cs in the soil, annual plants, and perennial plants ranged between 12- and 124 (Bq/kg dry weight), 2- and 17 (Bq/kg dw), and 2 - and 14 (Bq/kg dw), respectively. The geometric mean (GM) values of DF in annual and perennial plants were 0.57 and 0.55, respectively. The CR for ¹³⁷Cs and ⁴⁰K varied as a non-linear relation in annual plants and perennial plants. This study showed that the CRs for ¹³⁷Cs in annual plants were higher than the CRs for perennial plants.

Artificial 137Cs and natural 40K in mushrooms from the subalpine region of the Minya Konka summit and Yunnan Province in China

A study on ¹³⁷Cs pollution and activity concentrations of ⁴⁰K in mushrooms of the genera Cortinarius, Leccinum, Russula, Tricholoma, Tylopilus, and Xerocomus from two neighboring regions in southwest China in 2010-2013 revealed different patterns of pollution with ¹³⁷Cs, which seemed to be highly dependent on climate conditions. Tricholoma matsutake was collected in Yunnan before and after the Fukushima Dai-ichi nuclear accident and showed similar contamination with ¹³⁷Cs. Mushrooms from the elevation of 2800-3480 m above sea level on the east slope of Minya Konka and forest topsoil showed higher contamination with ¹³⁷Cs than mushrooms from the highlands of Yunnan. In detail, the activity concentration of ¹³⁷Cs in caps of mushrooms from Minya Konka were in the range 62 ± 6-280 ± 150 Bq kg^-1 dry biomass and from Yunnan at < 4.4-83 ± 3 Bq kg^-1 dry biomass. The climate in the region of the Minya Konka is much colder than in Yunnan, which seems to favor deposition of ¹³⁷Cs at higher altitudes from global atmospheric circulation. The activity concentration of ⁴⁰K in mushrooms and soils highly exceeded that of ¹³⁷Cs. The assessed annual effective doses for ¹³⁷Cs in 1 kg of consumed mushrooms of the genera Leccinum and Xerocomus in Yunnan were low, i.e., in the range < 0.0043-0.049 ± 0.004 μSv, while those for ⁴⁰K were 0.26 ± 0.02-0.81 ± 0.09 μSv.

Radionuclides in mushrooms and soil-to-mushroom transfer factors in certain areas of China

Activity concentrations of ²³⁸U, ²²⁶Ra, ²²⁸Ra, ¹³⁷Cs and ⁴⁰K in 64 mushroom samples collected in China from Yunnan, Fujian and Heilongjiang Provinces, were measured. Gamma-ray emissions were determined by using high-purity germanium (HPGe) γ spectrometry. The range of concentrations (Bq kg^-1 dry weight) for ²³⁸U, ²²⁶Ra, ²²⁸Ra, ¹³⁷Cs and ⁴⁰K in all investigated mushroom samples were from 0.12 to 12, 0.05 to 7.5, 0.14 to 14, MDC(<0.01) to 339, and 396 to 1880, respectively. Activity concentrations of ¹³⁷Cs in mushrooms showed some variation between species sampled at the same site. To calculate soil to mushroom transfer factors, levels of radionuclide in 15 paired soil samples and mushrooms were also investigated. The median transfer factors for ²³⁸U, ²²⁶Ra, ²²⁸Ra, ¹³⁷Cs and ⁴⁰K were 8.32 × 10^-2, 3.03 × 10^-2, 6.69 × 10^-2, 0.40 and 1.19, respectively. The results were compared with values of other areas.

Ingestion intakes of 137Cs by the Czech population: Comparison of different approaches

Ingestion intakes of ¹³⁷Cs of the Czech population were calculated in two different ways - either from the measured activity of ¹³⁷Cs in components of food in combination with statistical data about consumption rates or from retention of ¹³⁷Cs in the human body obtained by whole body counting or calculated from daily urinary excretion of ¹³⁷Cs. Data from the time period since 1986 to 2015 are used. The daily ingestion intake was about 25 Bq d^-1 in 1986 and is around 0.1 Bq d^-1 at present. Both approaches of ingestion intake calculation have their advantages and disadvantages. Ingestion intake calculated from ¹³⁷Cs body content was assumed to be the most accurate as it requires fewer assumptions than the calculation from food consumption. However, calculation of ¹³⁷Cs intake from food consumption is an important tool for prediction doses after the release of radionuclides into environment. The best agreement exceeding the intakes from urine measurement 5 times at maximum was achieved when intakes calculated from food also included products from the natural environment. Without this, the ingestion intake could be under-predicted seriously up to 6 times, especially in the longer time after the release of ¹³⁷Cs into environment. Ingestion intakes up to 11 Bq d^-1 in a group of people with significant consumption of game meat containing elevated activity of ¹³⁷Cs activity were included as a special case. Various groups of foodstuffs had varying effects on the total committed effective dose from ¹³⁷Cs. Dose estimates for the Czech population from ¹³⁷Cs ingestion intake achieved 80 μSv in 1986 and not more than 2 μSv currently and were similar to those incurred by the population of neighbouring countries.

Radioactivity in mushrooms from selected locations in the Bohemian Forest, Czech Republic

¹³⁷Cs is one of the most important radionuclides released in the course of atmospheric nuclear weapon tests and during accidents in nuclear power plants such as that in Chernobyl, Ukraine, or Fukushima, Japan. The aim of this study was to compare ¹³⁷Cs and ⁴⁰K concentrations in particular species of mushrooms from selected locations in the Bohemian Forest (Czech: Šumava), Czech Republic, where a considerable contamination from the Chernobyl accident had been measured in 1986. Samples were collected between June and October 2014. Activities of ¹³⁷Cs and ⁴⁰K per dry mass were measured by means of a semiconductor gamma spectrometer. The ¹³⁷Cs values measured range from below detection limit to 4300 ± 20 Bq kg^-1, in the case of ⁴⁰K from 910 ± 80 to 4300 ± 230 Bq kg^-1. Differences were found between individual locations, due to uneven precipitation in the course of the movement of the radioactive cloud after the Chernobyl accident. There are, however, also differences between individual species of mushrooms from identical locations, which inter alia result from different characteristics of the soil and depths of mycelia. The values measured are compared with established limits and exposures from other radiation sources present in the environment. In general, it can be stated that the values measured are relatively low and the effects on the health of the population are negligible compared to other sources of ionizing radiation.

Turnover of 137Cs in 'soil-tree' system: An experience of measuring the isotope flows in a Siberian conifer forest

Little attention has been paid to the uptake of ¹³⁷Cs in natural forests under low levels of the isotope fallout when no immediate ecological danger presents. Here we present the extended assessments of the soil-to-plant and canopy-to-litter flows of ¹³⁷Cs recently evaluated in a native Siberian forested area. The area undergoes a typical after-fire long term succession, with light-conifer upper story being followed by undergrowth of Siberian fir and other dark-conifer species. The one-year-old needles of Siberian fir were found to accumulate the largest concentration of the isotope, 4.10 Bq/kg oven-dry weight during the first growth season, as compared with older needles that accumulated 4.67 Bq/kg oven-dry weight in 2-3 years of growth. Based on these data an approach was developed that, hypothetically, can allow one to estimate the ¹³⁷Cs activity concentration in soil solutions. Direct activity measurements in the soil solutions were not possible. The isotope activity in soil solutions was estimated to be 0.0061-0.0105 Bq/L. Based on the original data from the litter fall the annual flow of the isotope from the upper canopy to on-ground litter was found to be 0.42-0.84 Bq/m². The amount of ¹³⁷Cs that returns yearly back from canopy with falling litter was estimated to be 0.012-0.015% of the total soil isotope content. A combination of the estimations obtained in our study with the values of global ¹³⁷Cs fallout allowed us to assess the ages (the time of formation) of horizons of the soils in the area.

The Time-Dependent Transfer Factor of Radiocesium from Soil to Game Animals in Japan after the Fukushima Dai-ichi Nuclear Accident

Since the Fukushima Dai-ichi accident, monitoring of tissues from hunted game animals ensures compliance with the standard food limits for radionuclides in Japan. We quantified the transfer of (137)Cs from contaminated land to game animals using the Aggregated transfer factor (Tag = activity concentration in meat [Bq kg(-1) fw]/amount in soil [Bq m(-2)]) of (137)Cs for Asian black bear, wild boar, sika deer, green pheasant, copper pheasant and wild duck, collected between 2011 and 2015. Open data sources were used from Fukushima, Miyagi, Ibaraki, Tochigi, and Gunma prefectures. Our initially compiled data showed that the maximum reported (137)Cs activity concentration in wild boar after the Fukushima Dai-ichi accident were lower than those reported after the Chernobyl accident. The geometric mean Tag values (m(2)kg(-1) fw) of (137)Cs in 2015 for Asian black bear, wild boar, sika deer and copper pheasant were similar (1.9-5.1) × 10(-3) while those for green pheasant and wild duck were about 1 order of magnitude lower at (1.0-2.2) × 10(-4). Effective half-lives were 1.2-6.9 y except for sika deer and copper pheasant where no decreases were found. In contrast to the Chernobyl accident, no seasonal change occurred in the meat (137)Cs activity concentrations of the wild animals during the study period.

(137)Cs distributions in soil and trees in forest ecosystems after the radioactive fallout - Comparison study between southern Finland and Fukushima, Japan

The nuclear accidents at Chernobyl and Fukushima released large amounts of (137)Cs radionuclides into the atmosphere which spread over large forest areas. We compared the (137)Cs concentration distribution in different parts of two coniferous forest ecosystems (needle litter, stems and at different depths in the soil) over short and long term periods in Finland and Japan. We also estimated the change in (137)Cs activity concentrations in needle and soil between 1995 and 2013 in Southern Finland based on the back-calculated (137)Cs activity concentrations. We hypothesized that if the (137)Cs activity concentrations measured in 1995 and 2013 showed a similar decline in concentration, the (137)Cs activity concentration in the ecosystem was already stable in 1995. But if not, the (137)Cs activity concentrations were still changing in 2013. Our results showed that the vertical distribution of the (137)Cs fallout in the soil was similar in Hyytiälä and Fukushima. The highest (137)Cs concentrations were observed in the uppermost surface layers of the soil, and they decreased exponentially deeper in the soil. We also observed that (137)Cs activity concentrations estimated from the samples in 1995 and 2013 in Finland showed different behavior in the surface soil layers compared to the deep soil layer. These results suggested that the (137)Cs nuclei were still mobile in the surface soil layers 27 years after the accident. Our results further indicated that, in the aboveground parts of the trees, the (137)Cs concentrations were much closer to steady-state when compared to those of the surface soil layers based on the estimated declining rates of (137)Cs concentration activity in needles which were similar in 1995 and 2013. Despite its mobility and active role in the metabolism of trees, the (137)Cs remains in the structure of the trees for decades, and there is not much exchange of (137)Cs between the heartwood and surface layers of the stem.

The influence of biotic and abiotic factors on (137)Cs accumulation in higher fungi after the accident at Chernobyl NPP

Levels of soil contamination with (137)Cs, the belonging of fungi to a certain ecological group, the localization depth of the main part of mycelium in soil are the primary factors influencing the value of (137)Cs specific activity in higher fungi after the accident at Chernobyl NPP. It has been found that the value of (137)Cs specific activity in fungi of one species could vary by more than 10 times during a vegetation period. A correlation between the changes of (137)Cs content in fungi during the vegetation period and the amount of precipitates during various periods preceding the collection of samples has not been determined. An assumption has been proposed stating dependence between peculiarities of mycelium growth during the vegetation period and the changes of (137)Cs specific activity in fungi.

Transfer factors and effective half-lives of (134)Cs and (137)Cs in different environmental sample types obtained from Northern Finland: case Fukushima accident

The Fukushima NPP accident caused a small but detectable cesium fallout in northern Finland, of the order of 1 Bq/m(2). This fallout transferred further to soil, water, flora and fauna. By using modern HPGe detector systems traces of (134)Cs from the Fukushima fallout were observed in various samples of biota. In northern Finland different types of environmental samples such as reindeer meat, berries, fish, lichens and wolf were collected during 2011-2013. The observed (134)Cs concentrations varied from 0.1 Bq/kg to a few Bq/kg. By using the known (134)Cs/(137)Cs ratio observed in Fukushima fallout the increase of the Fukushima accident to the (137)Cs concentrations was found to vary from 0.06 % to 6.9 % depending on the sample type. The aggregated transfer factors (Tag) and effective half-lives (Teff) for (134)Cs and (137)Cs were also determined and then compared with known values found from earlier studies which are calculated based on the fallout from the Chernobyl accident. Generally, the Tag and Teff values determined in this study were found to agree with the values found in the earlier studies. The Teff values were sample-type specific and were found to vary from 0.91 to 2.1 years for (134)Cs and the estimates for (137)Cs ranged between 1.6 and 19 years. Interestingly, the ground lichens had the longest Teff whereas the beard lichen had the shortest. In fauna, highest Tag values were determined for wolf meat ranging between 1.0 and 2.2 m(2)/kg. In flora, the highest Tag values were determined for beard lichens, ranging from 1.9 m(2)/kg to 3.5 m(2)/kg.

Spatial patterns and ratios of ¹³⁷Cs, ⁹⁰Sr, and Pu isotopes in the top layer of undisturbed meadow soils as indicators for contamination origin

Spatial distribution of activity concentrations of (137)Cs, (90)Sr, and (239,240)Pu in the top layer of undisturbed meadow soils was compared between two regional transects across Lithuania: one in the SW region, more affected by the Chernobyl radioactive fallout, and the other in the NE region. Radiochemical, γ-, α-, β-, and mass spectrometric methods were used to determine the radionuclide activity. Our results validate that higher activity concentrations in the top soil layer were present in the SW region, despite the fact that sampling was performed after 22 years of the Chernobyl Nuclear Power Plant (NPP) accident. Using the activity concentration ratio (137)Cs/(239,240)Puglobal, the contribution of the Chernobyl NPP accident to the total radiocesium activity concentrations in these meadow soils was evaluated and found to be in the range of 6.5-59.1%. Meanwhile, the activity concentration ratio (238)Pu/(239,240)Pu showed that Chernobyl-derived Pu occurred at almost half of the sampling sites. The locations with maximal values of 47% of Chernobyl-derived Pu material were close to northeastern Poland, where deposition of most of non-volatile radioisotopes from the Chernobyl plume was determined.

137Cs and 40K in some traditional herbal teas collected in the mountain regions of Serbia

Herbal teas are an important part of traditional medicine in Serbia. The objective of the present study was to determine the activity concentrations of (40)K and (137)Cs in herbal tea, using the gamma spectroscopy method. The samples were collected during the period 2011-2012 in three mountain regions in Western and Central Serbia. The activity concentrations of (40)K and (137)Cs were found to be in the range of 130-1160 and 0.7-124 Bq kg(-1), respectively. The average annual effective dose equivalents from ingestion of (40)K and (137)Cs for an adult person consuming one cup of herbal tea daily were found to be 588.4-5250.2 nSv for (40)K and 4.0-706.1 nSv for (137)Cs. Our investigation showed that the herbal teas originating from Maljen, Zlatibor and Tara mountains are radiologically safe for human consumption.