Modelling radiocaesium transfer and long-term changes in reindeer

Steep declines in radioactive caesium after 30 years of monitoring alpine plants in mountain areas of central Norway

The Chernobyl accident exposed large areas of northern Europe to radiocaesium (137Cs). We investigated temporal and spatial variation in concentrations of radiocaesium among five functional groups of alpine plants at two mountain areas in central Norway over a 31-year period from 1991 to 2022. Average concentrations of radiocaesium were initially high in lichens and bryophytes at around 4600-6400 Bq/kg dry weight during 1991-1994 but then decreased dramatically over three decades to current concentrations of <200 Bq/kg for all plant groups in 2019-2022. The effective half-life of radiocaesium was estimated to be 4-6 years in lichens and mosses, 7-13 years in herbaceous plants, and 22-30 years in woody plants, which were less than the physical half-life of 30.2 years. Concentrations of radiocaesium were greater at the nutrient-poor site than at the nutrient-rich site, probably due to greater deposition levels at higher elevations and the geographical pattern of the deposition. Functional groups of plants differed with higher concentrations among non-vascular than vascular plants. Common heather Calluna vulgaris was unusual among woody plants with high concentration of radiocaesium, especially in the new shoots. Our new estimates of concentrations and dynamics of radiocaesium for alpine plants in natural environments will be useful for modelling herbivore exposure and evaluating potential impacts on wildlife and human health.

Chemical availability of fallout radionuclides in cryoconite

Atmospheric deposition on glaciers is a major source of legacy fallout radionuclides (FRNs) accumulating in cryoconite, a dark granular material with surface properties that efficiently bind FRN contaminants (specifically 137Cs; 210Pb; 241Am). Cryoconite-bound FRNs in glaciers can be released when they interact with and are transported by glacial meltwater, resulting in the discharge of amassed particulate contaminants into aquatic and terrestrial environments downstream. The environmental consequences of FRN release from the cryosphere are poorly understood, including impacts of cryoconite-sourced FRNs for alpine food chains. Consequently, there is limited understanding of potential health risks to humans and animals associated with the consumption of radiologically-contaminated meltwater. To assess the chemical availability of cryoconite-adsorbed FRNs we used a three-stage sequential chemical extraction method, applied to cryoconite samples from glaciers in Sweden and Iceland, with original FRN activity concentrations up to 3300 Bq kg-1 for 137Cs, 10,950 Bq kg-1 for unsupported 210Pb (210Pbun) and 24.1 Bq kg-1 for 241Am, and orders of magnitude above regional backgrounds. Our results demonstrate that FRNs attached to cryoconite are solubilized to different degrees, resulting in a stage-wise release of 210Pbun involving significant stepwise solubilization, while 137Cs and 241Am tend to be retained more in the particulate phase. This work provides an insight into the vulnerability of pristine glacial environments to the mobilization of FRN-contaminated particles released during glacier melting, and their potential impact on glacial-dependent ecology.

Time dependence of 137Cs contamination in wild Japanese monkeys after the Fukushima Daiichi nuclear accident

Over the 10 years immediately after the Fukushima Daiichi nuclear accident, we measured the changes in the muscle ¹³⁷Cs concentration (Bq/kg) of wild Japanese monkeys living in Fukushima City, which is located approximately 70 km from the Fukushima Daiichi Nuclear Power Plant. The muscle¹³⁷Csconcentration, which was observed at a maximum of 13,500 Bq/kg immediately after the accident, had decreased to several hundred Bq/kg 10 years later. The muscle ¹³⁷Cs concentration was significantly related to the soil contamination levels (10,000-30,000, 30,000-60,000, 60,000-100,000, and 100,000-300,000 Bq/m²), sex, age class (immature, mature), body weight (> 5000 g, 5000-10,000 g, < 10,000 g), and seasons (the cold period from December to April, the warm period from May to November).The value of muscle ¹³⁷Cs concentration and the aggregated transfer factor (T_ag: calculated by dividing muscle ¹³⁷Cs concentration [Bq/kg] by soil ¹³⁷Cs deposition density at the capture site [Bq/m²]) apparently decreased with time for several years. However, post hoc pairwise comparisons showed no difference from 2017 to 2020, and the accumulation of ¹³⁷Cs in muscle may continue for some time.

Modeling the Dynamic Behavior of Radiocesium in Grazing Reindeer

Radiocesium contamination in Norwegian reindeer and the factors influencing contamination levels have been studied for more than 50 years, providing significant amounts of data. Monitoring contamination in reindeer is of utmost importance for reindeer husbandry and herders in Norway and will need to be studied for many years because of the persistent contamination levels due to the 1986 Chernobyl fallout. This paper presents a novel dynamic model that takes advantage of the large data sets that have been collected for reindeer monitoring to estimate ¹³⁷Cs in reindeer meat at any given time. The model has been validated using detailed ¹³⁷Cs data from one of the herds most affected by the fallout. The model basis includes detailed ¹³⁷Cs soil data from aerial surveys, GPS-based knowledge of reindeer migration, and local soil-to-vegetation ¹³⁷Cs transfer information. The validation exercise shows that the model satisfactorily predicts both short- and long-term changes in ¹³⁷Cs concentrations in reindeer meat and suggests that the model will be a useful tool in estimating seasonal changes and evaluating possible remedial actions in case of a future fallout event.

Effective and environmental half-lives of radiocesium in game from Poland

For the first time changes in the ¹³⁷Cs activity in game throughout Poland, including its most contaminated part known as the Opole Anomaly, were analyzed. Due to its long physical half-life, ¹³⁷Cs continuously demonstrates high activity both in soil and biota. The species of game mammals, along with forest fruit and mushrooms, tend to accumulate this radionuclide, becoming one of the main sources of secondary contamination in people. In this study the ¹³⁷Cs activity in roe deer, wild boar and red deer muscle tissue samples, within the years of 1986-2019, were studied. The effective and environmental half-lives were determined for each of the mentioned species for four regions including NE Poland and the Opole Anomaly placed in SW Poland. In all examined species at least two different phases of changes in the ¹³⁷Cs activity were distinguished, therefore the values of effective half-lives for the researched period since the Chernobyl accident do not correspond with the values from within last ten years. It was proven for the first time that within the anomalous area, featuring the highest values of gamma surface activity in Poland, the ¹³⁷Cs activity increases with time in the muscle tissues of all three species. No intraspecies, nor interspecies differences of ¹³⁷Cs activity among the studied species were found. In the light of the collected data, monitoring game considering the ¹³⁷Cs activity appears to be valid, as, due to not completely clear trophic dependencies, this radionuclide currently increased its migration to the game species despite passing its physical half-life period.

Caesium-137 in mountain flora with emphasis on reindeer's diet - Spatial and temporal trends

The present study summarizes three decades of studies on ¹³⁷Cs transfer to various species of lichens, graminoids, herbs and woody plants across a ~3000 km² area used as mountain pasture for reindeer and other ruminants. The investigation comprised of field studies covering the period 2011-2016, and a compilation of studies and data for the preceding period (1986-2010). Altogether, more than 700 individual vegetation samples were considered. For lichens, relatively fast decrease in contamination levels was observed during the first decade after the Chernobyl fallout (ecological half-time of about 3 years). For later years there seems to be a continuous re-contamination which results in a "steady state" where time-trends are mainly governed by physical decay of ¹³⁷Cs. For green plants, decline in transfer factors (TF) (i.e. the ratio between activity concentration in vegetation and activity density in soil) during the period 1986-2012 was not as pronounced as for lichens: Some species showed significant decrease with time, while others did not. 25-30 years after the Chernobyl accident, ¹³⁷Cs levels in lichens and green plants were significantly dependent on the levels in soil (R² between 0.53 and 0.57), but there were also some significant differences in transfer between sampling sites. Moreover, marked variability in TFs was found between different plant species growing at the same site, whereas such differences were not found for reindeer lichens.

Exploring taxonomic and phylogenetic relationships to predict radiocaesium transfer to marine biota

One potentially useful approach to fill data gaps for concentration ratios, CRs, is based upon the hypothesis that an underlying taxonomic and/or phylogenetic relationship exists for radionuclide transfer. The objective of this study was to explore whether these relationships could be used to explain variation in the transfer of radiocaesium to a wide range of marine organisms. CR data for ¹³⁷Cs were classified in relation to taxonomic family, order, class and phylum. A Residual Maximum Likelihood (REML) mixed-model regression modelling approach was adopted. The existence of any patterns were then explored using phylogenetic trees constructed with mitochondrial COI gene sequences from various biota groups and mapping the REML residual means onto these trees. A comparison of the predictions made using REML with blind datasets allowed the efficacy of the procedure to be tested. The only significant correlation between predicted and measured activity concentrations was revealed at the taxonomic level of order when comparing REML analysis output with data from the Barents Sea Region. For this single case a correlation 0.80 (Spearman rank) was derived which was significant at the 0.01 level (1-tailed test) although this was not the case once a (Bonferroni) correction was applied. The application of the REML approach to marine datasets has met with limited success, and the phylogenetic trees illustrate complications of using predictions based on values from different levels of taxonomic organization, where predicted values for the order level can mask the values at lower taxonomic levels. Any influence of taxonomy and phylogeny on transfer is not immediately conspicuous and categorizing marine organisms in this way is limited in providing a potentially robust prognostic extrapolation tool. Other factors may plausibly affect transfer to a much greater degree in marine systems, such as quite diverse life histories and different diets, which may confound any phylogenetic pattern.

Impacts on the terrestrial environment in case of a hypothetical accident involving the recovery of the dumped Russian submarine K-27

Objects containing radioactivity have been routinely dumped in Arctic waters near NW Russia up until the 1990s. One of the most radioactive objects in this region, the nuclear submarine K-27, was dumped in Stepogovo Fjord and contained spent nuclear fuel (SNF). Although the two K-27 submarine reactors were mothballed before dumping, concerns about the potential long term risks of contamination remain and plans to retrieve and decommission K-27 exist. In this article, human dose and environmental impact aseessments are presented for two possible future scenarios involving: (1) an ingress of water into a reactor in situ leading to a spontaneous chain reaction (SCR) and (2) an on-board fire when SNF is being removed at the mainland decommissiong site at Gremhika Bay on the Kola Peninsula. Assessments have been completed using conservative assumptions, focusing on possible effects to Norwegian territory. Atmospheric transport and deposition of radioactivity was modelled near field and regionally, using appropriate models, whilst human doses and environmental exposures were modelled using a standard IAEA approach and the ERICA tool, respectively. Results indicate that large areas of Norwegian territory could be affected by fallout from the Gremhika scenario, especially in the north, though at levels two orders of magnitude lower than those observed after the Chernobyl accident. Potential doses, primarily due to ground shine, to a critical group of personnel on-site at Stepogovo resulting from a SCR could require preventative measures based on ICRP recommendations (20-100 mSv). Doses to non-human biota in Norway for the Gremhika scenario would be negligible, typical of background dose rates for terrestrial organisms.

Measurements of cesium in Arctic beluga and caribou before and after the Fukushima accident of 2011

Concern from northern communities following the Fukushima Daiichi nuclear accident of March 2011 has prompted a reassessment of the safety of their traditional foods with respect to radioactivity levels. To this end, a study was conducted to measure the levels of radionuclides in Arctic caribou (Rangifer tarandus) and beluga (Delphinapterus leucas). The main radionuclide of concern is cesium-137, which is easily transferred through the lichen-caribou food chain. Previous studies have been conducted on the cesium-137 levels in Canadian caribou herds from 1958 to 2000, allowing researchers to determine the amount of cesium-137 in caribou specifically attributable to atmospheric weapons testing and the Chernobyl nuclear accident in 1986. In this study, samples of lichens, mushrooms, caribou, beluga and beluga prey collected before and after the Fukushima accident were analyzed for radioactivity levels. Samples were processed and measured using gamma ray spectroscopy to identify the radionuclides present and determine the radioactivity concentration. Both calibration standards and Monte Carlo simulations were used to determine the efficiency of the detectors for the samples, taking into account differences in individual sample sizes as well as matrices. In particular, a careful analysis of the atomic composition of lichens and mushrooms was performed to ensure the efficiencies for these sample types were correct. A comparison of the concentrations from before and after the accident indicated that there was no increase in radioactivity as a result of the atmospheric plume from the Fukushima accident. Some cesium-137, likely attributable to fallout from atmospheric weapons testing of the 1950s and 1960s (since there was no cesium-134 measured in the samples), was measured in the post Fukushima caribou and beluga whale samples; however, this amount was determined to be insignificant for any radiological concern (9.1 ± 1.8 and 0.63 ± 0.23 Bq kg^-1 ww respectively). The activity concentrations of cesium-137 was about 200 times smaller than that of natural radioactive potassium in the beluga samples. Both the caribou and beluga results showed that these foods continue to be a healthy food choice for northern Canadians with respect to radioactivity, and this result has been communicated to the nearby northern communities and stakeholders.

Averted doses to Norwegian Sámi reindeer herders after the Chernobyl accident

The Chernobyl fallout is an enduring challenge to reindeer husbandry in Norway, and South Sámi reindeer herders in central and southern Norway are as contaminated by (137)Cs as inhabitants close to Chernobyl. Therefore, Norwegian authorities continuously recommend to these reindeer herders the use of countermeasures to reduce their intake of (137)Cs. In this study, the authors have applied data on contamination levels in reindeer, results of dietary surveys, and whole body monitoring data in low and high contaminated areas to estimate the effectiveness of countermeasures and resulting averted doses to the reindeer herders. In the most contaminated area, the various countermeasures applied reduced radiocesium ingestion doses during 1986-2009 by about 73%, to an integrated dose of about 17 mSv. However, to comply with the recommended (137)Cs ingestion dose limit of 1 mSv y(-1), the study indicates that reindeer herders in the most contaminated areas will need to carry on with their countermeasures for another 10-15 y. Furthermore, the study indicates that whole body monitoring is an important tool to assess individual doses and countermeasure effectiveness in long-term management of a contamination situation and that such monitoring may be required to reach long-term reference levels.

Cesium-137 monitoring using lichens from W. Macedonia, N. Greece

(137)Cs content in lichens and substrate (soil, bark) collected from W. Macedonia, Greece was measured 20 years after the Chernobyl reactor accident. Archive material from previous collections was also used for comparison and a diachronic estimation of the radio-contamination status. A gradual decrease was detected which depended on various factors such as the collected species, location, growth rate and substrate. Maximum accumulation capacity of (137)Cs was observed in epilithic lichens in comparison to epigeic or epiphytic ones. Furthermore, foliose or crustose lichens such as Parmelia sulcata, Xanthoria parietina, Xanthoria calcicola, Xanthoparmelia somloensis were more contaminated than filamentose at the same biotope. Among filamentose or fruticose species those with large surface area to biomass ratio e.g. Usnea sp. showed also greater accumulation capacity. Autoradiography revealed an amount of (137)Cs distributed more or less uniformly in lichen thalli. The high (137)Cs activities found in lichens 20 years after Chernobyl suggest that these primitive plants are effective, suitable and inexpensive biological detectors of the distribution and burden of fallout radionuclide fallout pattern.