Development of a Novel Passive Monitoring Technique to Showcase the 3D Distribution of Tritiated Water (HTO) Vapor in Indoor Air of a Nuclear Facility.

Tritiated water (HTO), a ubiquitous byproduct of the nuclear industry, is a radioactive contaminant of major concern for environmental authorities. Although understanding spatiotemporal heterogeneity of airborne HTO vapor holds great importance for radiological safety as well as diagnosing a reactor's status, comprehensive HTO distribution dynamics inside nuclear facilities has not been studied routinely yet due to a lack of appropriate monitoring techniques. For current systems, it is difficult to simultaneously achieve high representativeness, sensitivity, and spatial resolution. Here, we developed a passive monitoring scheme, including a newly designed passive sampler and a tailored analytical protocol for the first comprehensive 3D distribution characterization of HTO inside a nuclear reactor facility. The technique enables linear sampling in any environment at a one-day resolution and simultaneous preparation of hundreds of samples within 1 day. Validation experiments confirmed the method's good metrological properties and sensitivity to the HTO's spatial dynamics. The air in TU Wien's reactor hall exhibits a range of 3H concentrations from 75-946 mBq m-3 in the entire 3D matrix. The HTO release rate estimated by the mass-balance model (3199 ± 306 Bq h-1) matches the theoretical calculation (2947 ± 254 Bq h-1), suggesting evaporation as the dominant HTO source in the hall. The proposed method provides reliable and quality-controlled 3D monitoring at low cost, which can be adopted not only for HTO and may also inspire monitoring schemes of other indoor pollutants.

Disproportionately High Contributions of 60 Year Old Weapons-137Cs Explain the Persistence of Radioactive Contamination in Bavarian Wild Boars.

Radionuclides released from nuclear accidents or explosions pose long-term threats to ecosystem health. A prominent example is wild boar contamination in central Europe, which is notorious for its persistently high 137Cs levels. However, without reliable source identification, the origin of this decades old problem has been uncertain. Here, we target radiocesium contamination in wild boars from Bavaria. Our samples (2019-2021) range from 370 to 15,000 Bq·kg-1 137Cs, thus exceeding the regulatory limits (600 Bq·kg-1) by a factor of up to 25. Using an emerging nuclear forensic fingerprint, 135Cs/137Cs, we distinguished various radiocesium source legacies in their source composition. All samples exhibit signatures of mixing of Chornobyl and nuclear weapons fallout, with 135Cs/137Cs ratios ranging from 0.67 to 1.97. Although Chornobyl has been widely believed to be the prime source of 137Cs in wild boars, we find that "old" 137Cs from weapons fallout significantly contributes to the total level (10-68%) in those specimens that exceeded the regulatory limit. In some cases, weapons-137Cs alone can lead to exceedances of the regulatory limit, especially in samples with a relatively low total 137Cs level. Our findings demonstrate that the superposition of older and newer legacies of 137Cs can vastly surpass the impact of any singular yet dominant source and thus highlight the critical role of historical releases of 137Cs in current environmental pollution challenges.

Uptake of Radionuclides by Bryophytes in the Chornobyl Exclusion Zone.

The "Chernobyl nuclear disaster" released huge amounts of radionuclides, which are still detectable in plants and sediments today. Bryophytes (mosses) are primitive land plants lacking roots and protective cuticles and therefore readily accumulate multiple contaminants, including metals and radionuclides. This study quantifies 137Cs and 241Am in moss samples from the cooling pond of the power plant, the surrounding woodland and the city of Prypiat. Activity concentrations of up to 297 Bq/g (137Cs) and 0.43 Bq/g (241Am) were found. 137Cs contents were significantly higher at the cooling pond, where 241Am was not detectable. Distance to the damaged reactor, amount of original fallout, presence of vascular tissue in the stem or taxonomy were of little importance. Mosses seem to absorb radionuclides rather indiscriminately, if available. More than 30 years after the disaster, 137Cs was washed out from the very top layer of the soil, where it is no more accessible for rootless mosses but possibly for higher plants. On the other hand, 137Cs still remains solved and accessible in the cooling pond. However, 241Am remained adsorbed to the topsoil, thus accessible to terrestrial mosses, but precipitated in the sapropel of the cooling pond.

Development and calibration of a modifiable passive sampler for monitoring atmospheric tritiated water vapor in different environments.

Anthropogenic release of tritium from nuclear facilities is expected to increase significantly in the coming decades, which may cause radiation exposure to humans through the contamination of water and food chains. It is necessary and urgent to acquire detailed information about tritium in various environments for studying its behavior and assessing the potential radiation risk. In the atmosphere, although the passive sampling technique provides a low-cost and convenient way to characterize the dynamics of tritiated water vapor (HTO), a single, simple sampler configuration makes it difficult to collect sufficient and representative samples within the expected period from different environments. In this study, we systematically studied the impacts of sampler configurations on sampling performance and proposed a modifiable sampler design by scaling sampler geometry and adjusting absorbent to achieve different monitoring demands. The samplers were subsequently deployed at five sites in China and Germany for the field calibration and the measured results exhibited a good agreement between the adsorption process obtained in sites corrected with diffusion coefficient and the one calibrated in Shanghai. This suggests the feasibility of predicting sampling performance in the field based on known data. Finally, we developed a strategy for sampler modification and selection in different environments and demonstrated that using easily obtainable environmental data, our sampler can be optimized for any area without any time-consuming preliminary experiments. This work provides a scientific basis for establishing high-resolution atmospheric HTO database and expands the conventional empirical sampler design paradigm by demonstrating the feasibility of using quantitative indices for sampler performance customization.

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.

Determination of Characteristic vs Anomalous 135Cs/137Cs Isotopic Ratios in Radioactively Contaminated Environmental Samples.

A contamination with the ubiquitous radioactive fission product 137Cs cannot be assigned per se to its source. We used environmental samples with varying contamination levels from various parts of the world to establish their characteristic 135Cs/137Cs isotope ratios and thereby allow their distinction. The samples included biological materials from Chernobyl and Fukushima, historic ashed human lung tissue from the 1960s from Austria, and trinitite from the Trinity Test Site, USA. After chemical separation and gas reaction shifts inside a triple quadrupole ICP mass spectrometer, characteristic 135Cs/137Cs isotope signatures (all as per March 11, 2011) were obtained for Fukushima- (∼0.35) and Chernobyl-derived (∼0.50) contaminations, in agreement with the literature for these contamination sources. Both signatures clearly distinguish from the characteristic high ratio (1.9 ± 0.2) for nuclear-weapon-produced radiocesium found in human lung tissue. Trinitite samples exhibited an unexpected, anomalous pattern by displaying a low (<0.4) and nonuniform 135Cs/137Cs ratio. This exemplifies a 137Cs-rich fractionation of the plume in a nuclear explosion, where 137Cs is a predominant species in the fireball. The onset of 135Cs was delayed because of the longer half-life of its parent nuclide 135Xe, causing a spatial separation of gaseous 135Xe from condensed 137Cs, which is the reason for the atypical 135Cs/137Cs fractionation in the fallout at the test site.

Survival of the basidiomycete Schizophyllum commune in soil under hostile environmental conditions in the Chernobyl Exclusion Zone.

Radioactive contamination resulting from major nuclear accidents presents harsh environmental conditions. Inside the Chernobyl exclusion zone, even more than 30 years after the accident, the resulting contamination levels still does not allow land-use or human dwellings. To study the potential of basidiomycete fungi to survive the conditions, a field trial was set up 5 km south-south-west of the destroyed reactor unit. A model basidiomycete, the lignicolous fungus Schizophyllum commune, was inoculated and survival in the soil could be verified. Indeed, one year after inoculation, the fungus was still observed using DNA-dependent techniques. Growth led to spread at a high rate, with approximately 8 mm per day. This shows that also white-rot basidiomycetes can survive the harsh conditions in soil inside the Chernobyl exclusion zone. The unadapted fungal strain showed the ability to grow and thrive in the contaminated soil where both stress from radiation and heavy metals were present.

Radioactive Games? Radiation Hazard Assessment of the Tokyo Olympic Summer Games.

We conducted a comprehensive radiation hazard assessment of the Tokyo Olympic Games (Tokyo 2020, postponed to 2021). Our combined experimental and literature study focused on both external and internal exposure to ionizing radiation for athletes and visitors of the Games. The effective dose for a visit of 2 weeks ranges from 57 to 310 µSv (including flight dose). The main contributors to the dose are cosmic radiation during the flights (approximately 10-81%), inhalation of natural radon (approximately 9-47%), and external exposure (approximately 8-42%). In this complex exposure, anthropogenic radionuclides from the Fukushima nuclear accident (2011) always play a minor role and have not caused a significant increase of the radiological risk compared to pre-Fukushima Japan. Significantly elevated air dose rates were not measured at any of the Tokyo Olympic venues. The average air dose rates at the Tokyo 2020 sites were below the average air dose rates at the sites of previous Olympic Games. The level of radiological safety of foods and water is very high in Japan, even for athletes with increased water and caloric demands, respectively.

Non-natural ruthenium isotope ratios of the undeclared 2017 atmospheric release consistent with civilian nuclear activities.

Understanding the circumstances of the undeclared 2017 nuclear release of ruthenium that led to widespread detections of the radioisotope 106Ru in the Eurasian region, and whether it derives from a civilian or military source, is of major importance for society and future improvements in nuclear safety. Until now, the released nuclear material has merely been studied by analyzing short-lived radioisotopes. Here, we report precise measurements of the stable isotopic composition of ruthenium captured in air filters before, during, and after the nuclear release, and find that the ruthenium collected during the period of the 2017 nuclear release has a non-natural isotopic composition. By comparing our results with ruthenium isotopic compositions of spent nuclear fuels, we show that the release is consistent with the isotopic fingerprints of a civilian Russian water-water energetic reactor (VVER) fuel at the end of its lifetime, and is not related to the production of plutonium for nuclear weapons.

Identification of a chemical fingerprint linking the undeclared 2017 release of 106Ru to advanced nuclear fuel reprocessing.

The undeclared release and subsequent detection of ruthenium-106 (106Ru) across Europe from late September to early October of 2017 prompted an international effort to ascertain the circumstances of the event. While dispersion modeling, corroborated by ground deposition measurements, has narrowed possible locations of origin, there has been a lack of direct empirical evidence to address the nature of the release. This is due to the absence of radiological and chemical signatures in the sample matrices, considering that such signatures encode the history and circumstances of the radioactive contaminant. In limiting cases such as this, we herein introduce the use of selected chemical transformations to elucidate the chemical nature of a radioactive contaminant as part of a nuclear forensic investigation. Using established ruthenium polypyridyl chemistry, we have shown that a small percentage (1.2 ± 0.4%) of the radioactive 106Ru contaminant exists in a polychlorinated Ru(III) form, partly or entirely as ß-106RuCl3, while 20% is both insoluble and chemically inert, consistent with the occurrence of RuO2, the thermodynamic endpoint of the volatile RuO4 Together, these findings present a clear signature for nuclear fuel reprocessing activity, specifically the reductive trapping of the volatile and highly reactive RuO4, as the origin of the release. Considering that the previously established 103Ru:106Ru ratio indicates that the spent fuel was unusually young with respect to typical reprocessing protocol, it is likely that this exothermic trapping process proved to be a tipping point for an already turbulent mixture, leading to an abrupt and uncontrolled release.

Separation of Ultratraces of Radiosilver from Radiocesium for Environmental Nuclear Forensics.

The presence of environmental radiosilver and the investigation of the 108mAg/110mAg isotopic ratio in the aftermath of a nuclear power plant accident provide valuable information on the condition of the control rods of pressurized water reactors. However, the detection of minute amounts of the γ-emitting radiosilver isotopes is often thwarted by the presence of concomitant and dominating γ emitters, primarily 137Cs, which results in increased detection limits in the γ spectra. We developed a rapid and robust separation protocol for trace silver extraction in the presence of overwhelming activities of 137Cs via the autodepostion of silver on a copper plate. This method achieved a quantitative removal of interfering 137Cs in the deposition product and proved to be very efficient (yields >70% for aqueous samples), rapid (results within 4 h), and robust with respect to varying salinities and composition of the water samples. The autodeposition approach is also applicable for organic samples after acid-assisted microwave digestion. By applying the established sequential extraction protocols for soil, the fate of freshly deposited radiosilver and radiocesium in soil was investigated. Silver showed a high affinity to the soil with a pronounced (>90%) accumulation in the residual fraction after the sequential extraction, whereas radiocesium exhibited higher mobility, allowing for the extraction of major fractions in the first extraction steps. The composition of the aqueous contamination matrix (CaCl2 or Ca(NO3)2) had a significant influence on the binding properties of cesium on soil.

Halide ion influence on the formation of nickel nanoparticles and their conversion into hollow nickel phosphide and sulphide nanocrystals.

A dependence of the formation of tri-n-octylphosphine-capped Ni nanocrystals on the presence of halide ions during their synthesis is shown. For the application-oriented synthesis of Ni particles, this information can be crucial. Furthermore, Ni nanoparticles can be converted to nickel phosphide or sulphide by heating them up in the presence of a phosphorus or sulphur source, resulting in either solid or hollow nanocrystals, formed via the nanoscale Kirkendall effect, depending on the synthesis route. By adjusting the Ni crystallite size in the initial nanoparticles via the halide ion concentration the cavity size of the resulting hollow nanocrystals can be tuned, which is otherwise impossible to realise for particles of a similar total diameter by using this process. The synthesised hollow Ni3S2 nanocrystals exhibit a much sharper localised surface plasmon resonance (LSPR) band than all previously presented particles of this material, which is known to show molar extinction coefficients at the LSPR maximum similar to Au. This narrow linewidth could be explained by the nanoparticles' high crystallinity resulting from the Kirkendall process and is interesting for various possible optical applications such as surface-enhanced Raman spectroscopy owing to the low cost of the involved materials compared to the widely used noble metals.

Radionuclides in surface waters around the damaged Fukushima Daiichi NPP one month after the accident: Evidence of significant tritium release into the environment.

Following the Fukushima nuclear accident (2011), radionuclides mostly of volatile elements (e.g., 131I, 134,137Cs, 132Te) have been investigated frequently for their presence in the atmosphere, pedosphere, biosphere, and the Pacific Ocean. Smaller releases of radionuclides with intermediate volatility, (e.g., 90Sr), have been reported for soil. However, few reports have been published which targeted the contamination of surface (fresh) waters in Japan soon after the accident. In the present study, 10 surface water samples (collected on April 10, 2011) have been screened for their radionuclide content (3H, 90Sr, 129I, 134Cs, and 137Cs), revealing partly unusually high contamination levels. Especially high tritium levels (184 ±â€¯2 Bq·L-1; the highest levels ever reported in scientific literature after Fukushima) were found in a puddle water sample from close to the Fukushima Daiichi nuclear power plant. The ratios between paddy/puddle water from one location only a few meters apart vary around 1% for 134Cs, 12% for 129I (131I), and around 40% for both 3H and 90Sr. This illustrates the adsorption of radiocesium on natural minerals and radioiodine on organic substances (in the rice paddy), whereas the concentration differences of 3H and 90Sr between the two waters are mainly dilution driven.

Chemical and radioanalytical investigations of 106Ru-containing air filters from Vienna in 2017: searching for stable element anomalies.

Related to the recent nuclear release of radioactive ruthenium isotopes in fall 2017, we analyzed air filters from Vienna for irregularities in the (stable) elemental composition of particulate matter from this period. Methods were SEM/EDXS and INAA. For comparison, a reference filter from 2007 and blank filters were used. The chemical fingerprint encompassed 28 elements. The results show no indication for a considerable change in the elemental composition of the suspended matter. For example, no anomalies in the abundance of platinum group elements were found. The results suggest that the release of 106Ru had not been accompanied by a release of detectable amounts of (activatable) stable elements.

Radiostrontium transport in plants and phytoremediation.

Radiostrontium is a common product of nuclear fission and was emitted into the environment in the course of nuclear weapon tests as well as from nuclear reactor accidents. The release of 90Sr and 89Sr into the environment can pose health threats due to their characteristics such as high specific activities and easy access in human body due to its chemical analogy to calcium. Radiostrontium enters the human food chain by the consumption of plants grown on sites comprising fission-derived radionuclides. For humans, Sr is not an essential element, but, due to solubility in water and homology with calcium, once interred in the body, it gets deposited in bones and in teeth. This concern has drawn the attention of researchers throughout the globe to develop sustainable treatment processes to remediate soil and water resources. Nowadays, phytoremediation has become a promising approach for the remediation of large extents of toxic heavy metals. Some of the plants have been reported to accumulate Sr inside their biomass but detailed mechanisms at genetic level are still to be uncovered. However, there is inadequate information offered to assess the possibility of this remediation approach. This review highlights phytoremediation approach for Sr and explains in detail the uptake mechanism inside plants.

Characteristics of radiocesium contaminations in mushrooms after the Fukushima nuclear accident: evaluation of the food monitoring data from March 2011 to March 2016.

The monitoring inspection of food after the Fukushima nuclear accident (2011) was essential for ensuring food safety in Japan and reducing the adverse health effects due to incorporation of inacceptable amounts of radionuclides, in particular radiocesium (134Cs and 137Cs). In this study, the mushroom fraction of the governmental data set of the first 5 years after the accident has been analyzed for contamination levels in mushrooms, in particular time trends and radioecological characteristics as well as associated health risks. The analyses show that mycorrhiza mushrooms are much more sensitive for radionuclide uptake than saprobiontic mushrooms (the latter of which include the very popular shiitake mushrooms (Lentinula edodes)). The maximum value reached 31,000 Bq/kg in a sample of apricot milkcaps in 2012. Analysis of the origin of the samples revealed that the origin (in terms of prefecture) of the mushrooms was a less determining factor for the contamination level than the type of mushrooms, as most exceedances in 2012 and thereafter were found outside Fukushima Prefecture. Several dose models were applied to the data to evaluate both worst case and realistic effective committed dose scenarios. The doses were generally rather low due to low consumption rates in the Japanese food basket. In any case, the analysis proved that the food monitoring campaign was highly effective in cutting doses to the public by more than a factor of 10 compared with a hypothetical scenario in which no monitoring had been conducted.

Japanese Food Data Challenge the Claimed Link between Fukushima's Releases and Recently Observed Thyroid Cancer Increase in Japan.

Internal, high-dose exposure with radioiodine is known to increase the risk for thyroid cancer in children and adolescents. Ingestion of contaminated food is generally regarded a dominant route of internal exposure. We analyzed the huge data set of the post-Fukushima food monitoring campaign and deployed a conservative model for the estimation of the doses to the general public in a worst-case scenario. Our data suggest that the committed equivalent ingestion doses to the thyroids of the affected Japanese public, even in the utmost conservative approach, remained below the limit on ingestion of radioiodine in foodstuffs and beverages of 50 mSv (as thyroid equivalent dose). This level of 50 mSv is also the intervention level for the administration of stable iodine, mainly after inhalation. Our study hence suggests that, based on the food data, the internal exposure of Japanese residents was too low to cause a statistically discernible increase in thyroid cancer, even if the contribution from inhalation is taken into account. The data also indicate that the governmental efforts in the food monitoring campaign were successful and cut the thyroid doses to the public by a factor of approximately 3 compared to a scenario without any monitoring.

Mushrooms: from nutrition to mycoremediation.

Mushrooms are well known as important food items. The uses of mushrooms in the cuisine are manifolds and are being utilized for thousands of years in both Oriental and Occidental cultures. Medicinal properties of mushrooms show an immense potential as drugs for the treatment of various diseases as they are rich in a great variety of phytochemicals. In this review, we attempted to encompass the recent knowledge and scientific advancement about mushrooms and their utilization as food or curative properties, along with their natural ability to accumulate (heavy) metals/radionuclides, which leads to an important aspect of bioremediation. However, accumulation of heavy metals and radionuclides from natural or anthropogenic sources also involves potential nutritional hazards upon consumption. These hazards have been pointed out in this review incorporating a selection of the most recently published literature.

Fat tissue is not a reservoir for radiocesium in wild boars.

Meat of wild boars is not only known for high 137Cs activity concentrations but also for the remarkable constancy of these levels. Even decades after the Chernobyl accident, the 137Cs levels in wild boar meat in Central Europe have not declined but even partly increased. In the present study, we investigated an unusual hypothesis for this very unusual phenomenon: may the boars' fat tissue act as a reservoir for radiocesium? We investigated fat and muscle tissues of four wild boars in Western Germany and found that the 137Cs concentrations in fat were in the range of 10-30% of the respective activities in muscle tissue. Hence, the hypothesis was refuted.