Global Fallout Research Articles

Evaluation of soil erosion rates in the hilly-gully region of the Loess Plateau in China in the past 60 years using global fallout plutonium

Soil erosion strongly threatens the sustainability of natural ecosystems over the world, especially in the Loess Plateau in China, where has suffered severe soil erosion along with extensive land reclamation and deforestation from the 1950s to the 1970s. The large-scale vegetation restoration practices are supposed to be effective for reducing soil erosion, but the quantitative evaluation of soil erosion, particularly the response of land utilization types and vegetation coverage changes on the mitigation of soil degradation is still not well understood. Plutonium isotopes in soil cores collected from the forest, grassland slope, apple orchard, and cornfield in a typical watershed in the hilly-gully region of the Loess Plateau were analyzed to estimate the soil erosion rates in different land-use types. Widespread soil erosion at rates of 5.1–40.5 t/ha/yr. in this region in the past six decades was estimated. The influences of human activities in the past decades, type of land utilization, level of vegetation coverage, and terrain on the soil erosion in this region were discussed, and the accumulation of the eroded soil in the study sites was explored. Different types of land utilization showed diverse soil erosion rates (forest (slight) < grassland (light) < apple orchard ≈ cornfield (moderate)), indicating that natural vegetation rehabilitation, particularly restoring forest with high vegetation coverage is a practically effective conservation measure for soil erosion control; convex micro-topography on sloping fields is critical in alleviating soil loss by depositing eroded soil.

The properties and health hazards from early nuclear weapon fallout: The Castle Bravo incident revisited

Early fallout is defined as the fallback to the earth’s surface of radioactive particles shortly after a nuclear detonation (often arbitrarily defined within 24 h). At the difference of wide spreading global fallout, early fallout mainly consists of larger particles that are often visible. The initial mixture is rich in short- and very short-lived radionuclides associated with a very high initial activity that decreases rapidly (in 7 h, the dose rate is reduced by 90%). The main danger of early fallout results from external irradiation by highly penetrating gamma-radiation that may cause acute radiation sickness. Only in the case of the thyroid, internal irradiation by the incorporation of radioiodine may prevail. The bombings of Hiroshima and Nagasaki are examples of airbursts with many fatalities by prompt effects (blast, burns, and initial ionizing radiations), but they produced little fallout. The nuclear test code-named Castle Bravo on the Marshall Islands (1954) did not have casualties by its blast, thermal or initial radiation effects, but the inhabitants of the nearby islands and the crew of a Japanese fisherboat (Lucky Dragon) were affected by large amounts of fallout. For the inhabitants of the Rongelap Atoll, the average dose from external irradiation was assessed at 1.6 Gy. From a clinical point of view, based on hematological data using the METREPOL classification system, the acute radiation syndrome can be categorized as mild (H1). Blood transfusions were not required, and antibiotics were not administered for prophylaxis or therapy of infections related to irradiation. The equivalent dose received by the thyroid resulted mainly from internal irradiation with 7.6 Gy. The major late effects were thyroid abnormalities, including thyroid failure, nodules, and malignant tumors. The 23 Japanese crewmen seem to have been irradiated by higher doses (2.9 Gy). Compared to the hematological data of the Rongelap victims, the evolution pattern over time is quite similar. Still, the absolute values of the cell counts are lower, and on average, the acute radiation syndrome can be categorized as rather moderate (H2). Considering the individual cases, data show a large interindividual variability, and the clinical severity category ranges from “no alterations” (H0) to severe (H3). Victims were treated with repeated blood transfusions and antibiotics. Several of them developed jaundice, and one of them died six months after the incident showing symptoms compatible with subacute liver failure. A radiochemical organ analysis revealed that only the bones were clearly contaminated with fission products. In the 1990s, many surviving crewmen were diagnosed with hepatitis C, incurred probably from blood transfusions that were often contaminated at the time, and died from hepatocellular carcinomas. Thyroid dysfunctions were not reported. The Castle Bravo case permits to study the health hazards resulting from early fallout independently from the prompt effects of a nuclear detonation. The prevailing external irradiation was confirmed, except for the thyroid with a higher dose resulting from radioiodine incorporation mainly caused by ingestion. As shown for the Japanese fishermen, the risks incurred by medical treatments must be carefully weighed against the benefits of the therapeutic intervention. The cause of death of the only short-term fatality is not fully elucidated, but is consistent with liver failure due to transfusion hepatitis rather than radiation effects.

MILEs Multimedia Intentional Learning Ecosystems (MILEs)

Background: Recent developments in flexible learning and online teaching due to the global COVID-19 pandemic have sought to link the attributes of high-quality instruction with social constructivists’ theories to provide an ethical compass for navigating sustainable Multimedia Intentional Learning Ecosystems (MILES). Despite lingering doubts about the design and implementation of such ecosystems, belief in the perceived benefits motivates educators to persist.&#x0D; Objectives: Research about methodology has revealed contradictory results that have not broken new pedagogical ground. Despite looking good on paper, the effectiveness and real-world utility of such guiding principles are often difficult to assess because the principles do not facilitate the development of self-efficacy.&#x0D; Methods: Initially, the proposed methodology was of a follow-up sample web survey. However, such a survey would suffer because only a snapshot would be captured. Consequently, the web survey evolved into a non-equivalent pretest-posttest control group Internet quasi-experiment.&#x0D; Result and Conclusion: Teaching staff with traditional, minimal or no online teaching experience should not have to be reliant on trial and error to learn about how to teach effectively post the global COVID-19 endemic. There is little use in knowing what instructional technology has to offer unless educators are confident to step forward knowing when, where and how to best use instructional technology to support learning.&#x0D; Major Takeaways: The validation of DLISt7 by factor analysis to promote the use of the concept as a toolkit for educators coming to terms with or transitioning to flexible learning and online teaching in response to the global COVID-19 fallout.&#x0D; Background: Recent developments in flexible learning and online teaching due to the global COVID-19 pandemic have sought to link the attributes of high-quality instruction with social constructivists’ theories to provide an ethical compass for navigating sustainable Multimedia Intentional Learning Ecosystems (MILES). Despite lingering doubts about the design and implementation of such ecosystems, belief in the perceived benefits motivates educators to persist.&#x0D; Objectives: Research about methodology has revealed contradictory results that have not broken new pedagogical ground. Despite looking good on paper, the effectiveness and real-world utility of such guiding principles are often difficult to assess because the principles do not facilitate the development of self-efficacy.&#x0D; Methods: Initially, the proposed methodology was of a follow-up sample web survey. However, such a survey would suffer because only a snapshot would be captured. Consequently, the web survey evolved into a non-equivalent pretest-posttest control group Internet quasi-experiment.&#x0D; Result and Conclusion: Teaching staff with traditional, minimal or no online teaching experience should not have to be reliant on trial and error to learn about how to teach effectively post the global COVID-19 endemic. There is little use in knowing what instructional technology has to offer unless educators are confident to step forward knowing when, where and how to best use instructional technology to support learning.&#x0D; Major Takeaways: The validation of DLISt7 by factor analysis to promote the use of the concept as a toolkit for educators coming to terms with or transitioning to flexible learning and online teaching in response to the global COVID-19 fallout.

Retrospective determination of fallout radionuclides and 236U/238U, 233U/236U and 240Pu/239Pu atom ratios on air filters from Vienna and Salzburg, Austria

137Cs and 241Pu (via 241Am) concentrations were measured γ-spectrometrically on air filters from the early 1960s (mainly from 1964–66) from Vienna, Austria, and an alpine station in Salzburg, Austria. Accelerator mass spectrometry (AMS) was used to determine 240Pu/239Pu, 236U/238U and 233U/236U atom ratios as well as 236U, 239Pu and 240Pu atom concentrations. The maximum 236U/238U atom ratio of these unique undisturbed global fallout samples was (1.19 ± 0.31) × 10−5 in spring 1964. The 233U/236U atom ratios were found within (0.15–0.49) × 10−2 and indicate that the weapons tests of the early 1960s can be excluded as 233U source. The 236U/239Pu atom ratios were calculated in the range of 0.22–0.48.

Super‐Droplet Method to Simulate Lagrangian Microphysics of Nuclear Fallout in a Homogeneous Cloud

AbstractNuclear detonations produce hazardous local and global particles or fallout. Predicting fallout size, chemical components, and location is necessary to inform officials and determine immediate guidance for the public. However, existing nuclear detonation fallout models prescribe the particle size distributions based on limited observations. In this work, we apply the super‐droplet method, which is a numerical modeling technique developed for cloud microphysics, to simulate size distributions of particles in a mushroom cloud formed post‐detonation of a nuclear device. We model fallout formation and evolution with homogeneous nucleation and condensation of a single species and a Monte Carlo coagulation algorithm. We verify the numerical methods representing coagulation and condensation processes against analytical test problems. Additionally, we explore several scenarios for the integral system mass and yield in equivalent kilotons (kt) of TNT (trinitrotoluene). The fallout size distribution median diameter dpg follows a scaling law based on the integral system mass mv0 kg and yield Y kt: nm. We test the effect of cloud turbulence, enhanced nucleation and growth, and vapor volatility with a sensitivity study. The range in median diameter predictions for simulations of historical tests performed over the Pacific encompass the measurements of particles sampled from the cloud caps. Predicted median particle size ranges up to 217, 123, 86, and 35 nm for historical tests with yields of 0.2, 0.7, 2, and 10 Mt, respectively. This work can be expanded in many different directions to build a more predictive model for fallout formation.

Historical changes of 236U/238U and 235U/238U isotopic ratios in Tokyo Bay from the 1960s to the 2000s

We examine the historical changes of 236U/238U and 235U/238U in a sediment core collected in Tokyo Bay and elucidate the anthropogenic sources of uranium in the 1960s–2000s. Uranium-236 was detected in samples deposited in the 1960s–2000s, and the 236U/238U ratio of the sediment core shows peak values in the 1970s. The 235U/238U isotopic ratios in samples deposited in the early 1960s are almost identical to that of natural uranium, implying that the 236U might have originated from global fallout. A decrease in 235U/238U was observed in the late 1960s–2000s, suggesting that depleted uranium from nuclear fuel reprocessing increased the 236U/238U ratios in the sediment. The 236U/238U values in sediments from the 1980s–2000s were lower than those in the 1970s but considerably higher than those in the 1960s, suggesting that the main source of depleted uranium still remains around Tokyo Bay. Our results demonstrated that the depleted uranium released in the 1970s should be considered as an important end-member when using uranium isotopic ratios as environmental tracers in closed aquatic environments around industrial cities.

Spatio-temporal distribution of 239+240Pu in sediments of the China sea and adjacent waters

Data of 239+240Pu activities and 240Pu/239Pu atom ratios in surface and core sediments of the China Sea and adjacent waters were collected. We examine a dataset of 239+240Pu activities and 240Pu/239Pu ratios determined from surface sediments at 516 sites and 84 core sediment mainly across the China Sea and adjacent waters. For the first time the spatial distributions of the 239+240Pu activities, the 240Pu/239Pu ratios and the Pacific Proving Ground (PPG) fraction in the China Sea and adjacent waters are fully presented at the same time. Four types of typical 239+240Pu distribution with depth are commonly summarized: non-peak, pseudo single peak, single peak and multi peaks, which are based on the comprehensive analysis of the vertical distribution of 239+240Pu in 84 sediment cores that had been studied in the China Sea and adjacent waters. Their occurrence probability are ∼15%, ∼4%, ∼67% and ∼11%, respectively. This is the dominant Pu source in seawater which was transported by the North Equatorial Current and Kuroshio Current and its extension into the China Sea and adjacent waters first from east to west, then from south to north. A sea area to the northeast of Taiwan Island and the Okinawa Trough, shows high 239+240Pu activities and 240Pu/239Pu atom ratios spatial distribution trends, which are related to the intrusion of the Kuroshio Current carrying 239+240Pu from the PPG nuclear weapon tests. The used two end-member mixing model suggests that global fallout and PPG close-in fallout are the main sources of Pu in most of the investigate areas. As the 240Pu/239Pu of global fallout is relatively constant, the change of 240Pu/239Pu ratios in surface sediments of the China Sea and adjacent waters are mainly controlled by the PPG close-in fallout input.

The Sedimentation Rate in the Crimean Hypersaline Lake Aktashskoye Estimated Using the Post-Chernobyl Artificial Radionuclide 90Sr as a Radiotracer

Artificial 90Sr is one of the most important long-lived radionuclides of global radioactive fallout from the atmosphere after the testing of nuclear weapons and the accident at the Chernobyl Nuclear Power Plant in 1986. In addition to fallout from the atmosphere, secondary radioactive contamination of Crimea was mainly from the Dnieper River and the North Crimean Canal, which occurred until 2014. 90Sr was used as the optimal radiotracer for estimating the rate of sedimentation in the Crimean hypersaline lake. Its vertical distribution in the bottom sediments was assessed. In the core of the bottom sediments, the detectable activity of 90Sr in layers 0–1.5 cm and 16.7–21.9 cm was absent, and it was determined again in the layer of 15.5 cm, which was associated with atmospheric fallout of the radionuclide after the Chernobyl NPP accident. There were well-isolated peaks of specific activity in layers at a depth of 4.6 and 13.3–14.3 cm. The calculated rate of sedimentation varied within 0.5–1.5 cm year−1: the minimum rate corresponded to the period 1971–2017, and the highest rate corresponded to the period 1954–1971.

Distribution of Anthropogenic 129I in the Western South China Sea and Its Application for Tracing the Sources and Movement of Pollution.

Anthropogenic 129I has been dispersed all over the world and could be utilized as an oceanographic tracer based on its conservative nature in the ocean. The first datasets of 129I and 127I were obtained by analysis of seawater of 36 water columns collected in the western South China Sea during August-September 2018. The measured 129I concentrations decreased with depth from (0.93-1.61) × 107 atoms/L in the upper 200 m to (0.04-0.14) × 107 atoms/L at 1500 m, indicating a clear anthropogenic source in the upper layer, mainly originated from the global fallout. The riverine input of the deposited 129I on the catchment area of the Mekong River is an important source besides the direct deposition in the seas. The water mass with high 129I from the Mekong River water moves to the east at 11°N by the North Nansha Current in the surface layer (2-25 m). The exponentially decreasing 129I level with depth indicates that the vertical dispersion of 129I from the upper to the lower layer was mainly through slow diffusion, and the deep water at more than 1500 m was not significantly contaminated by the upper layer water at least in the past 70 years.

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.

Understanding source terms of anthropogenic uranium in the Arctic Ocean – First 236U and 233U dataset in Barents Sea sediments

This work reports the first dataset of 236U and 233U in sediment cores taken from the Barents Sea, with the aim to better understand the source terms of anthropogenic uranium in the Arctic region. Concentrations of 236U and 233U along with 137Cs, and 233U/236U atomic ratio were measured in six sediment profiles. The cumulative areal inventories of 236U and 233U obtained in this work are (3.50–12.7) × 1011 atom/m2 and (4.92–21.2) × 109 atom/m2, with averages values of (8.08 ± 2.93) × 1011 atom/m2 and (1.08 ± 0.56) × 1010 atom/m2, respectively. The total quantities of 236U and 233U deposited in the Barents Sea bottom sediments were estimated to be 507 ± 184 g and 7 ± 3 g, respectively, which are negligible compared to the total direct deposition of 236U (6000 g) and 233U (40–90 g) from global fallout in the Barents Sea. The integrated atomic ratios of 233U/236U ranging in (0.98–1.57) × 10−2 reflect the predominant global fallout signal of 236U in the Barents Sea sediments and the highest reactor-236U contribution accounts for 30 ± 14 % among the six sediment cores. The reactor-236U input in the Barents Sea sediments is most likely transported from the European reprocessing plants rather than related to any local radioactive contamination. These results provide better understanding on the source term of anthropogenic 236U in the Barents Sea, prompt the oceanic tracer application of 236U for studying the dynamics of the Atlantic-Arctic Ocean and associated climate changes. The 236U-233U benchmarked age-depth profiles seem to match reasonably well with the reported input function history of radioactive contamination in the Barents Sea, indicating the high potential of anthropogenic 236U-233U pair as a useful tool for sediment dating.

Удельная активность и особенности вертикальной миграции стронция-90 в торфянике Мурманской области

The peatlands of the Arctic territories are repositories of radioactive contaminations. The physicochemical properties, specific activity and features of vertical migration of 90Sr in the peat profile of the Murmansk region have been studied. A correlation matrix was compiled according to the studied indicators. The factor that determines the localization of 90Sr in peat has been established. The sources of isotope for the region were determined.&#x0D; The reaction of the peat medium is acidic (4.2 ≤ pHwater ≤ 4.9; 3.6 ≤ pHsalt ≤ 4.1). The ash content of peat is medium and high (5.2 % ≤ Ash ≤ 28 %). The share of organic matter in the peat profile is more than 70 %. The upper part of the profile is saline (soluble salts&gt;0.3%). The share of carbonates in the peat profile is insignificant (0.42–0.83 %).&#x0D; 90Sr activity (0.55–7.7 Bq/kg) was recorded in each peat sample. The activity of the technogenic radionuclide is below the established permissible norm and within the range typical for all Russian soils. The 90Sr isotope is localized in the upper layers of the profile and at a depth of more than 16 cm. The localization of 90Sr in peat layers is due to the content of water-soluble salts (r = 0.85). The main sources of the isotope for the Murmansk region are past global fallout from nuclear tests, the Chernobyl accident and current local fallout from nuclear fuel facilities.

Plutonium isotopes in the North Western Pacific sediments coupled with radiocarbon in corals recording precise timing of the Anthropocene

Plutonium (Pu) has been used as a mid-twentieth century time-marker in various geological archives as a result of atmospheric nuclear tests mainly conducted in 1950s. Advancement of analytical techniques allows us to measure 239Pu and 240Pu more accurately and can thereby reconstruct the Pacific Pu signal that originated from the former Pacific Proving Grounds (PPG) in the Marshall Islands. Here, we propose a novel method that couples annual banded reef building corals and nearshore anoxic marine sediments to provide a marker to precisely determine the start of the nuclear era which is known as a part of the Anthropocene. We demonstrate the efficacy of the methods using sediment obtained from Beppu Bay, Japan, and a coral from Ishigaki Island, Japan. The sedimentary records show a clear Pu increase from 1950, peaking during the 1960s, and then showing a sharp decline during the 1970s. However, a constantly higher isotope ratio between 239Pu and 240Pu suggest an additional contribution other than global fallout via ocean currents. Furthermore, single elevations in 240Pu/239Pu provide supportive evidence of close-in-fallout similar to previous studies. Coral skeletal radiocarbon displays a clear timing with the signatures supporting the reliability of the Beppu Bay sediments as archives and demonstrates the strength of this method to capture potential Anthropocene signatures.

Estimation of Atlantic Water transit times in East Greenland fjords using a 233U-236U tracer approach

Water mass composition and transit times of outflowing waters from the Arctic Ocean can reflect changes of polar climate and ocean circulation upstream. In this study we apply a novel approach using anthropogenic uranium tracers (233U and 236U), combined with salinity, and nutrients (nitrate and phosphate) to estimate transit times of waters from the Atlantic passing through the Arctic and into East Greenland fjords. In Polar Surface Water (PSW, typically found in surface ~150 m of the fjords) the dominant source of 236U is European reprocessing plants (63%) while in Arctic Atlantic Water (AAW, typically directly below PSW in these fjords) it is much less (26%) and the 236U signal is dominated by the global fallout contribution. Here we isolate the 236U signal from reprocessing plants using 236U/233U ratios and use the temporal development in 236U discharges to estimate transit times for Atlantic Water entering the Arctic Ocean and exiting as either PSW or AAW on the Greenland Shelf. PSW, which flows into the fjords from the shelf, has a transit time of between 6 and 14 years from the Arctic entrance (Barents Sea Opening, 74°N, 19°E). The transit time of AAW, which is entrained into upwelling subglacial discharge in the inner parts of the fjords, is in the order of 24–25 years since entrance in the Barents Sea. The findings indicate the potential of this novel 233U-236U approach to trace Atlantic Water circulation in the Arctic Ocean. The method offers independent transit time estimates to compare with circulation models and indicates the potential time lag between documented recent change in properties of water leaving the Arctic Ocean and the upstream processes contributing to these changes.

Radioactivity concentration measurements in fish and shellfish samples from the west coast of Canada after the Fukushima nuclear accident (2011–2018)

Radioactive contamination of the Pacific Ocean following the Fukushima nuclear accident has raised public concern about seafood safety, particularly in coastal Indigenous communities. To address this, Health Canada and partners have collected and analyzed a total of 621 samples of commonly consumed salmon, ground fish, and shellfish from the Canadian west coast from 2011 to 2018. While the vast majority of the 137Cs and 134Cs levels were below the Minimum Detectable Concentration (MDC, typically 0.7–1.0 Bq kg−1 fw for a 6 h counting), further examination of 19 fish samples revealed 137Cs concentrations of 0.17–0.53 Bq kg−1 fw with an average value and uncertainty (k = 1) of 0.29 ± 0.02 Bq kg−1 fw. Of these, only two samples were found to have trace levels of 134Cs likely derived from the Fukushima accident. The global fallout contribution from atmospheric nuclear weapons testing to the observed 137Cs in these two samples was determined to be 0.26 ± 0.08 Bq kg−1 fw (49 ± 14%) and 0.12 ± 0.02 Bq kg−1 fw (24 ± 4%) for collection years 2015 and 2016, respectively. The annual average level of 137Cs in fish and shellfish was also determined by spectral summation for collection years 2014–2018. In fish, 137Cs levels determined through spectral summation were relatively constant (0.18–0.25 Bq kg−1 fw) with an average value and uncertainty of 0.21 ± 0.02 Bq kg−1 fw. By contrast, 38 shellfish samples (bivalves) were measured and revealed no radiocesium or other anomalies in either tissue or shell. In all, measurements over eight years showed that the radioactivity in fish and shellfish was dominated by natural radionuclides and that the level of anthropogenic radionuclides, as indicated by the radioactive cesium content, remained small. An upper bound for ingested dose from 137Cs was determined to be approximately 0.26 μSv per year, far below the worldwide average annual effective dose of 2400 μSv from exposure to natural background radiation. We can therefore conclude that fish, such as salmon, ground fish, and shellfish from the Canadian west coast are of no radiological health concern despite the Fukushima Dai-ichi nuclear accident of 2011.

High-resolution records of cesium, plutonium, americium, and uranium isotopes in sediment cores from Swiss lakes

The Aare river system in Switzerland, with two nuclear power plants on the banks of the river, and its intermediate lakes and reservoirs, provides a unique opportunity to analyze the contribution of different sources to the radioactive contamination. Sediment cores were collected from two lakes and a reservoir, all connected by the river Aare. In order to study the influence of the Chernobyl accident, one sediment core was collected from a lake in the southern part of Switzerland. The sediment cores were sliced and analyzed with gamma ray spectrometry. Plutonium, americium, and uranium were extracted radiochemically, and their concentrations were measured with a sector field ICP-MS. The uranium isotope ratios were further measured with a multi collector ICP-MS. The maximum 137Cs activity from the Chernobyl accident and the Pu and 137Cs activities associated to the 1963 global fallout maximum were well identified in sediments from all three lakes. High-resolution records of plutonium isotopes in the zone of the sediments corresponding to the period of maximum fallout from the atmospheric nuclear weapon testing showed distinct fingerprints, depending on the different test activities. Pu isotope ratios could be used to detect non-global fallout plutonium. The ratio 241Am/241Pu was used to determine the age of the plutonium. Despite of very low 241Pu and 241Am concentrations, the calculated plutonium production dates seemed to be reasonable for the sediment layers corresponding to the NWT tests. The calculated production date of the plutonium in the upper most 15 cm of the sediment core seemed to be younger. The reason for this could be additional non-global fallout plutonium. For the lake sediments, natural ratios for 235U/238U and enriched or depleted ratios for 234U/238U were measured, depending on the lake. A small increase of the 236U/238U ratio could be recognized for the NWT zone in all three lakes and, for Lake Lugano, a further distinct increase in the Chernobyl layer.

Sources and Variability of Plutonium in Chinese Soils: A Statistical Perspective with Moving Average

We investigated the different sources and their corresponding impact areas of Pu in Chinese surface soils to illustrate the state-of-the-art of the sources, levels and distributions of 240Pu/239Pu atom ratios as well as 239+240Pu activity concentrations in China. For the first time a moving average strategy in combination with statistical analysis was employed to partition geographic areas in China based on the reported 240Pu/239Pu atom ratio and 239+240Pu concentration data from public literature. During the partitioning, the median (MED) of the dataset was basically employed as a criteria in place of the commonly used arithmetic average (AM). Concisely, three areas were partitioned according to the different influences of Pu from the Lop Nor (LNTS) and Semipalatinsk (STS) test sites and the global fallout. The partitioned Ternary area (80° E–105° E, 35° N–50° N) was supposed to have multiple sources of Pu including the STS and LNTS besides the global fallout, which was characterized with slightly lower 240Pu/239Pu atom ratios (MED = 0.174) as well as elevated 239+240Pu concentrations (MED = 0.416 mBq/g). Meanwhile, the Binary area (35° N–45° N, 100° E–115° E) was considered to have received the extra contribution from the high-yield nuclear tests at the LNTS besides the global fallout, resulting in the highest 240Pu/239Pu atom ratios (MED = 0.200) across China. The remaining area was marked as the Unitary area, where it only received the exclusive contribution of global fallout. Furthermore, through the statistical analysis of the 240Pu/239Pu data in the Unitary area, we recommended a value of 0.186 ± 0.021 (AM ± SD) as a representative or area-specific 240Pu/239Pu atom ratio baseline to characterize the global fallout derived Pu in Chinese soils.

Plutonium isotopes in the Qinghai-Tibet Plateau: Sources, distribution, and their environmental behaviors

Due to the high radiotoxicity in high concentrations, plutonium isotopes have drawn high attentions in the consideration of radiation risk, their sources, level, environmental behaviors, including deposition, retention and migration behaviors. However, such research in the Qinghai-Tibet Plateau is still missing, where is deemed as an environmental sensitive area. 239,240Pu in surface soil collected from the Qinghai-Tibet Plateau were determined for the first time in this work. The concentrations of 239,240Pu are in the range of 0.0176–1.95 Bq/kg, falling into the reported ranges in the background areas from the similar latitude belt. The 240Pu/239Pu atomic ratio range was measured to be 0.146–0.225, which is similar with the global fallout values. Both indicate that the global fallout is the major source of plutonium in this region, and the low plutonium level will not cause any radiation risk so far. Based on the statistical analysis of the possible parameters (organic content, moisture content, average annual precipitation, altitudes, topography and human activity), the large variations of 239,240Pu concentrations were mainly attributed to the retention process related factors including soil organic content and human activity disturbances. While, the deposition related factors including the average annual precipitation, altitudes, topography made insignificant influence on the spatial distribution of 239,240Pu concentrations due to the low 239,240Pu concentrations in atmosphere, less wet deposition amount and insignificant re-suspended amount. The highest 239,240Pu concentrations of 0.805–1.95 Bq/kg were mainly due to the good retention condition in the sampling sites with higher soil organic content and less human activity disturbances.

Global fallout Pu isotopes, 137Cs and 237Np records in the sediments of Lake Xingkai and their response to environmental changes in the catchment

Plutonium (Pu) isotopes, neptunium-237 (237Np) and cesium-137 (137Cs) in the environment have emerged as important tools for promoting geochemical studies. To elucidate their source terms, deposition process, and the geochemical behavior, as well as their response to catchment environmental changes in lacustrine environment, 239, 240Pu, 137Cs and 237Np were determined for the first time in a sediment core collected from the Lake Xingkai. The 240Pu/239Pu atom ratios (0.163–0.178) in all sediment samples corresponded well with the typical global fallout value of ∼0.18, indicating that there were no other significant radioactive source inputs. The activity concentrations of 239+240Pu, 137Cs, and 237Np were 0.010–1.030 Bq kg−1, 6.4–30.1 Bq kg−1, and (0.020–2.195) × 10−3 Bq kg−1, respectively. They presented similar vertical distribution patterns, with a typical global fallout peak (15–16 cm) corresponding to the year of 1964. On the other hand, the 237Np/239Pu atom ratios exhibited a wide range (0.207–1.306), and showed a trend of increasing values with depth, implying different geochemical behaviors of these two elements. Using the advection-dispersion equation model (ADE), the obtained apparent dispersion coefficient of 237Np (0.58 ± 0.09 cm2 yr−1) was higher than that of 239+240Pu (0.38 ± 0.07 cm2 yr−1), indicating that Np has greater mobility than Pu. The total global fallout inventories of 239+240Pu, 137Cs, and 237Np were 145, 4592, and 0.291 Bq m−2, respectively. Approximately 46% of the total global fallout was derived from riverine input, indicating that severe soil erosion occurred in the catchment of Lake Xingkai in the past decades.

Biomonitoring of Pu isotopes in liver of North Pacific giant octopus (Enteroctopus dofleini) collected off the Rokkasho Nuclear Fuel Reprocessing Plant, western North Pacific margin

Concentrations of 239+240Pu and 240Pu/239Pu atom ratios were determined in liver samples of North Pacific giant octopus (Enteroctopus dofleini) collected off the Rokkasho Nuclear Fuel Reprocessing Plant (RNFRP) to understand the bioaccumulation of Pu in the octopus liver, to provide Pu data before full commercial operation of the reprocessing plant, and to identify the sources of Pu isotopes in the studied liver samples. Mean 239+240Pu concentration was 6.3 ± 3.1 mBq/kg-wet, which was within the previously reported concentration ranges in liver of the Japanese common squid and in hepatopancreas of red queen and snow crabs. The 240Pu/239Pu atom ratios ranged from 0.223 to 0.252 with a mean ratio of 0.234 ± 0.009, which was noticeably greater than the mean global fallout ratio of ~0.18. These ratios reflected a mixture of global fallout Pu from atmospheric nuclear weapons testing and close-in fallout Pu from the Pacific Proving Grounds (PPG). The relative percentage of the PPG close-in fallout Pu to global fallout was calculated to be 39.6 ± 6.7%. The liver of the NPG octopus is an excellent bioindicator for biomonitoring of Pu pollution. Data on 239+240Pu concentrations and 240Pu/239Pu atom ratios in liver of the NPG octopus collected in the vicinity of the RNFRP will provide powerful keys for continuous biomonitoring of Pu pollution and for distinguishing the potential sources of Pu after the plant begins full commercial operation.