Fate of Plutonium at a Former Nuclear Testing Site in Australia

Unveiling threats to glacier biota: Bioaccumulation, mobility, and interactions of radioisotopes with key biological components

Contemporary melting glaciers are considered a secondary source of pollutants including radionuclides. Cryoconite - biogenic sediment on the glacier surface - exhibits high concentrations of natural and anthrophogenic radioisotopes. Understanding the interactions between radioisotopes and organisms is essential for evaluating their potential impact on glacier-related ecosystems. Using a multidimensional approach and intensive sampling (17 glaciers), we investigated the relationships between activity concentrations of 137Cs and 210Pb and various biotic components of cryoconite such as the amount of organic matter, chlorophyll concentration, the ratio of cyanobacteria to all bacteria, and size of cryoconite granules. Additionally, to better understand the bioavailability and fate of radioisotopes in this ecosystem, we measured the uptake ratio of 137Cs, 210Pb, 238Pu, and 239+240Pu in the top consumers, and examined the mobility of radioisotopes by measuring 137Cs and 210Pb activity concentrations after a parallel extraction using media with different specific ion exchange capacities. The activity concentrations of both 137Cs and 210Pb showed a large variability reaching 5.8 kBq kg-1 and 7.2 kBq kg-1, respectively. Their activity concentrations were positively related to the amount of organic matter, however, the 210Pb also increased with the chlorophyll concentration. This might be due to the difference in the deposition of both elements: lead, being deposited constantly, binds also to currently developing communities, while caesium deposition peaked in the 1960s. The mobility analysis revealed that the loosely bound fraction of 210Pb was more strongly related to organic-metallic complexes than 137Cs. Firmly bound radioisotope fractions (anhydrous interlayer sites of minerals) were three times higher for 137Cs than for 210Pb. The median uptake ratios of radioisotopes were determined as 0.07-0.111 for 137Cs, 0.177 for 210Pb, 0.07 for 239+240Pu. Our findings emphasize the importance of organisms in the accumulation of radioisotopes on glaciers and suggest an impact of radionuclides on glacier organisms.

Research progress on the analysis and application of radioactive hot particle

Radioactive hot particle is the particulate form of nuclear material that exists in the environment. The U, Pu, Am, Cs, and other radionuclides isotope in the hot particle contain abundant and accurate fingerprint information, such as the origin and age of the nuclear material. The acquisition and analysis of the key information in the hot particle can be equivalent to the analysis of bulk nuclear material, which could directly reflect the real situation of nuclear activities. Therefore, the single particle analysis of hot particles has become an irreplaceable key technology in nuclear safeguards inspection. The rapid identification, screening, locating, and accurate isotope analysis of hot particles from a large number of particles dispersed in environmental media or on the surface of other materials are one of the most important research field in nuclear emergency. In this review, the research process of the analytical methods for hot particles in the last decade was summarized, including the physical character of hot particles, and the techniques of localization, screening, and extraction of hot particles. Furthermore, we also focused on the mass spectrometry technology for the analysis of hot particle. The advantages and disadvantages of the most used mass spectrometry were summarized. Finally, the research trend for hot particle analysis methods was proposed.

The nature of Pu-bearing particles from the Maralinga nuclear testing site, Australia

The high-energy release of plutonium (Pu) and uranium (U) during the Maralinga nuclear trials (1955–1963) in Australia, designed to simulate high temperature, non-critical nuclear accidents, resulted in wide dispersion µm-sized, radioactive, Pu–U-bearing ‘hot’ particles that persist in soils. By combining non-destructive, multi-technique synchrotron-based micro-characterization with the first nano-scale imagining of the composition and textures of six Maralinga particles, we find that all particles display intricate physical and chemical make-ups consistent with formation via condensation and cooling of polymetallic melts (immiscible Fe–Al–Pu–U; and Pb ± Pu–U) within the detonation plumes. Plutonium and U are present predominantly in micro- to nano-particulate forms, and most hot particles contain low valence Pu–U–C compounds; these chemically reactive phases are protected by their inclusion in metallic alloys. Plutonium reworking was observed within an oxidised rim in a Pb-rich particle; however overall Pu remained immobile in the studied particles, while small-scale oxidation and mobility of U is widespread. It is notoriously difficult to predict the long-term environmental behaviour of hot particles. Nano-scale characterization of the hot particles suggests that long-term, slow release of Pu from the hot particles may take place via a range of chemical and physical processes, likely contributing to on-going Pu uptake by wildlife at Maralinga.

Plutonium Redox Transformation in the Presence of Iron, Organic Matter, and Hydroxyl Radicals: Kinetics and Mechanistic Insights

Plutonium (Pu) redox and complexation processes in the presence of natural organic matter and associated iron can impact the fate and transport of Pu in the environment. We studied the fate of Pu(IV) in the presence of humic acid (HA) and Fe(II) upon reaction with H₂O₂ that may be generated by photochemical and other reactions. A portion of Pu(IV) was oxidized to Pu(V/VI), which is primarily ascribed to the generation of reactive intermediates from the oxidation of Fe(II) and Fe(II)-HA complexes by H₂O₂. The kinetics of Pu(IV) oxidation is pH-dependent and can be described by a model that incorporates Pu redox kinetics with published HA-modified Fenton reaction kinetics. At pH 3.5, the presence of HA slowed Pu(IV) oxidation, while at pH 6, HA accelerated Pu(IV) oxidation in the first several hours followed by a reverse process where the oxidized Pu(V/VI) was reduced back to Pu(IV). Analysis of Pu-associated particle size suggests that Pu oxidation state is a major driver in its complexation with HA and formation of colloids and heteroaggregates. Our results revealed the H₂O₂-driven oxidation of Pu(IV)-HA-Fe(II) colloids with implications to the transient mobilization of Pu(V/VI) in organic-rich redox transition zones.

Differentiating Fukushima and Nagasaki plutonium from global fallout using 241Pu/239Pu atom ratios: Pu vs. Cs uptake and dose to biota

Plutonium (Pu) has been released in Japan by two very different types of nuclear events - the 2011 Fukushima accident and the 1945 detonation of a Pu-core weapon at Nagasaki. Here we report on the use of Accelerator Mass Spectrometry (AMS) methods to distinguish the FDNPP-accident and Nagasaki-detonation Pu from worldwide fallout in soils and biota. The FDNPP-Pu was distinct in local environmental samples through the use of highly sensitive ²⁴¹Pu/²³⁹Pu atom ratios. In contrast, other typically-used Pu measures (²⁴⁰Pu/²³⁹Pu atom ratios, activity concentrations) did not distinguish the FDNPP Pu from background in most 2016 environmental samples. Results indicate the accident contributed new Pu of ~0.4%-2% in the 0-5 cm soils, ~0.3%-3% in earthworms, and ~1%-10% in wild boar near the FDNPP. The uptake of Pu in the boar appears to be relatively uninfluenced by the glassy particle forms of fallout near the FDNPP, whereas the ^134,137Cs uptake appears to be highly influenced. Near Nagasaki, the lasting legacy of Pu is greater with high percentages of Pu sourced from the 1945 detonation (~93% soils, ~88% earthworm, ~96% boar). The Pu at Nagasaki contrasts with that from the FDNPP in having proportionately higher ²³⁹Pu and was distinguished by both ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu atom ratios. However, compared with the contamination near the Chernobyl accident site, the Pu amounts at all study sites in Japan are orders of magnitude lower. The dose rates from Pu to organisms in the FDNPP and Nagasaki areas, as well as to human consumers of wild boar meat, have been only slightly elevated above background. Our data demonstrate the greater sensitivity of ²⁴¹Pu/²³⁹Pu atom ratios in tracing Pu from nuclear releases and suggest that the Nagasaki-detonation Pu will be distinguishable in the environment for much longer than the FDNPP-accident Pu.

Particulate plutonium released from the Fukushima Daiichi meltdowns

Traces of Pu have been detected in material released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March of 2011; however, to date the physical and chemical form of the Pu have remained unknown. Here we report the discovery of particulate Pu associated with cesium-rich microparticles (CsMPs) that formed in and were released from the reactors during the FDNPP meltdowns. The Cs-pollucite-based CsMP contained discrete U(IV)O₂ nanoparticles, <~10 nm, one of which is enriched in Pu adjacent to fragments of Zr-cladding. The isotope ratios, ²³⁵U/²³⁸U, ²⁴⁰Pu/²³⁹Pu, and ²⁴²Pu/²³⁹Pu, of the CsMPs were determined to be ~0.0193, ~0.347, and ~0.065, respectively, which are consistent with the calculated isotopic ratios of irradiated-fuel fragments. Thus, considering the regional distribution of CsMPs, the long-distance dispersion of Pu from FNDPP is attributed to the transport by CsMPs that have incorporated nanoscale fuel fragments prior to their dispersion up to 230 km away from the Fukushima Daiichi reactor site.

Radionuclides in sea turtles at the Montebello Islands former nuclear test sites: Current and historical dose rates for adults and embryos

Radionuclides from 1950s weapons testing at the Montebello Islands, Western Australia, may impact sea turtle embryos incubating within eggs laid in contaminated sands or be taken up into adult body tissues where they can contribute to radiation dose over a turtles' 60+ year lifespan. We measured plutonium in all local samples including turtle skin, bones, hatchlings, eggshells, sea sediments, diet items and beach sands. The amount of Pu in developing embryos/hatchling samples was orders of magnitude lower than that in the surrounding sands. These contaminated sands caused most dose to eggs (external dose from ¹³⁷Cs, ¹⁵²Eu), while most of the dose to adults was from internalised radionuclides (98%). While current dose rates are relatively low, local dose rates were high for about ten years following the 1950s detonations and may have resulted in lethality or health impacts to a generation of turtles that likely carry biomarkers today.

Speciation of Uranium and Plutonium From Nuclear Legacy Sites to the Environment: A Mini Review

The row of 15 chemical elements from Ac to Lr with atomic numbers from 89 to 103 are known as the actinides, which are all radioactive. Among them, uranium and plutonium are the most important as they are used in the nuclear fuel cycle and nuclear weapon production. Since the beginning of national nuclear programs and nuclear tests, many radioactively contaminated nuclear legacy sites, have been formed. This mini review covers the latest experimental, modeling, and case studies of plutonium and uranium migration in the environment, including the speciation of these elements and the chemical reactions that control their migration pathways.

Distribution of artificial radionuclides in particle-size fractions of soil on fallout plumes of nuclear explosions

In this paper are analyzed the artificial radionuclide distributions (¹³⁷Cs, ⁹⁰Sr, ²⁴¹Am, ^239+240Pu) in particle-size fractions of soils from two radioactive fallout plumes at the Semipalatinsk Test Site. These plumes were generated by a low-yield surface nuclear test and a surface non-nuclear experiment with insignificant nuclear energy release, respectively, and their lengths are approximately 3 and 0,65 km. In contrast with the great majority of similar studies performed in areas affected mainly by global fallout where adsorbing radionuclides such as Pu are mainly associated with the finest soil fractions, in this study it was observed that along both analyzed plumes the highest activity concentrations are concentrated in the coarse soil fractions. At the plume generated by the surface nuclear test, the radionuclides are concentrated mainly in the 1000-500 μm soil fraction (enrichment factor values ranging from 1.2 to 3.8), while at the plume corresponding to the surface non-nuclear test is the 500-250 μm soil fraction the enriched one by technogenic radionuclides (enrichment factor values ranging from 1.1 to 5.1). In addition, the activity concentration distributions among the different soil size fractions are similar for all radionuclides in both plumes. All the obtained data are in agreement with the hypothesis indicating that enrichment observed in the coarse fractions is caused by the presence of radioactive particles resulted from the indicated nuclear tests.

Challenges associated with the behaviour of radioactive particles in the environment

A series of different nuclear sources associated with the nuclear weapon and fuel cycles have contributed to the release of radioactive particles to the environment. Following nuclear weapon tests, safety tests, conventional destruction of weapons, reactor explosions and fires, a major fraction of released refractory radionuclides such as uranium (U) and plutonium (Pu) were present as entities ranging from sub microns to fragments. Furthermore, radioactive particles and colloids have been released from reprocessing facilities and civil reactors, from radioactive waste dumped at sea, and from NORM sites. Thus, whenever refractory radionuclides are released to the environment following nuclear events, radioactive particles should be expected. Results from many years of research have shown that particle characteristics such as elemental composition depend on the source, while characteristics such as particle size distribution, structure, and oxidation state influencing ecosystem transfer depend also on the release scenarios. When radioactive particles are deposited in the environment, weathering processes occur and associated radionuclides are subsequently mobilized, changing the apparent K_d. Thus, particles retained in soils or sediments are unevenly distributed, and dissolution of radionuclides from particles may be partial. For areas affected by particle contamination, the inventories can therefore be underestimated, and impact and risk assessments may suffer from unacceptable large uncertainties if radioactive particles are ignored. To integrate radioactive particles into environmental impact assessments, key challenges include the linking of particle characteristics to specific sources, to ecosystem transfer, and to uptake and retention in biological systems. To elucidate these issues, the EC-funded COMET and RATE projects and the IAEA Coordinated Research Program on particles have revisited selected contaminated sites and archive samples. This COMET position paper summarizes new knowledge on key sources that have contributed to particle releases, including particle characteristics based on advanced techniques, with emphasis on particle weathering processes as well as on heterogeneities in biological samples to evaluate potential uptake and retention of radioactive particles.

Whole-organism concentration ratios in wildlife inhabiting Australian uranium mining environments

Wildlife concentration ratios for ²²⁶Ra, ²¹⁰Pb, ²¹⁰Po and isotopes of Th and U from soil, water, and sediments were evaluated for a range of Australian uranium mining environments. Whole-organism concentration ratios (CR_wo-media) were developed for 271 radionuclide-organism pairs within the terrestrial and freshwater wildlife groups. Australian wildlife often has distinct physiological attributes, such as the lower metabolic rates of macropod marsupials as compared with placental mammals. In addition, the Australian CRs_wo-media originate from tropical and semi-arid climates, rather than from the temperate-dominated climates of Europe and North America from which most (>90%) of internationally available CR_wo-media values originate. When compared, the Australian and non-Australian CRs are significantly different for some wildlife categories (e.g. grasses, mammals) but not others (e.g. shrubs). Where differences exist, the Australian values were higher, suggesting that site-, or region-specific CRs_wo-media should be used in detailed Australian assessments. However, in screening studies, use of the international mean values in the Wildlife Transfer Database (WTD) appears to be appropriate, as long as the values used encompass the Australian 95th percentile values. Gaps in the Australian datasets include a lack of marine parameters, and no CR data are available for freshwater phytoplankton, zooplankton, insects, insect larvae or amphibians; for terrestrial environments, there are no data for amphibians, annelids, ferns, fungi or lichens & bryophytes. The new Australian specific parameters will aide in evaluating remediation plans and ongoing operations at mining and waste sites within Australia. They have also substantially bolstered the body of U- and Th-series CR_wo-media data for use internationally.

Comparison of Homogeneous and Particulate Lung Dose Rates For Small Mammals

Small, highly radioactive fragments of material incorporated into metallic matrices are commonly found at nuclear weapons test and accident sites and can be inhaled by wildlife. Inhaled particles often partition heterogeneously in the lungs, with aggregation occurring in the periphery of the lung, and are tenaciously retained. However, dose rates are typically calculated as if the material were homogeneously distributed throughout the entire organ. Here the authors quantify the variation in dose rates for alpha-, beta-, and gamma-emitting radionuclides with particle sizes from 0.01-150 μm (alpha) and 1-150 μm (beta, gamma) and considering three averaging volumes-the entire lung (64 cm), a 10-cm volume of tissue, and a 1-cm volume of tissue. Dose rates from beta-emitting particles (e.g., Sr) were approximately one order of magnitude higher than those from gamma-emitting radionuclides (e.g., Cs). Self-shielding within the particle, which reduces the dose rate to the surrounding tissue, was negligible for gammas and minor for betas. For alpha-emitting particles (e.g., Pu), self-shielding in larger particles is substantial, with >90% of emissions captured within particles of +20 μm diameter; but for smaller sizes of the respirable range of 0.01 to 5 μm, an average of 85% of the energy escapes the particle and is deposited in the surrounding tissues. These data provide more detail on respirable particles, which may remain lodged deep in the lung where they represent a considerable contribution to long-term lung dose rates. For practical dose rate calculation purposes, a graph of particle size vs. dose rates for plutonium-containing hot particles is provided. This study demonstrates one possible approach to dose assessments for biota in environments contaminated by radioactive particles, which may prove useful for those engaged in environmental radioprotection.

Colloid-Facilitated Plutonium Transport in Fractured Tuffaceous Rock

Colloids have the potential to enhance the mobility of strongly sorbing radionuclide contaminants in groundwater at underground nuclear test sites. This study presents an experimental and numerical investigation of colloid-facilitated plutonium transport in fractured porous media to identify plutonium reactive transport processes. The transport parameters for dispersion, diffusion, sorption, and filtration are estimated with inverse modeling by minimizing the least-squares objective function of multicomponent concentration data from multiple transport experiments with the shuffled complex evolution metropolis algorithm. Capitalizing on an unplanned experimental artifact that led to colloid formation, we adopt a stepwise strategy to first interpret the data from each experiment separately and then to incorporate multiple experiments simultaneously to identify a suite of plutonium-colloid transport processes. Nonequilibrium or kinetic attachment and detachment of plutonium-colloid in fractures were clearly demonstrated and captured in the inverted modeling parameters along with estimates of the source plutonium fraction that formed plutonium-colloids. The results from this study provide valuable insights for understanding the transport mechanisms and environmental impacts of plutonium in groundwater aquifers.