Contribution of close-in fallout from the French atmospheric tests in inventories of 137Cs, 241Am and plutonium (238, 239, 240) in Gambier Islands (French Polynesia) - Signatures of stratospheric fallout in the Southern Hemisphere

The inventories of ¹³⁷Cs (503 ± 34 Bq.m^-2), ²⁴¹Am (11.3 ± 1.2 Bq.m^-2), ²⁴¹Pu (33.7 ± 3.4 Bq.m^-2), ²³⁸Pu (6.82 ± 0.87 Bq.m^-2) and ^239+240Pu (113.0 ± 5.9 Bq.m^-2), sum of ²³⁹Pu (100 ± 11 Bq.m^-2) and ²⁴⁰Pu (14.5 ± 1.7 Bq.m^-2), in the Gambier archipelago (23°S) of the French Polynesia, are well higher the global fallout at this latitude, in unequal proportions for the different radionuclides. (²⁴⁰Pu/²³⁹Pu)_AR (AR: atomic ratio) of 0.0394 ± 0.0062, and (²⁴¹Pu/²³⁹Pu)_AR of (2.03 ± 0.39)10^-4, confirm that the overwhelmingly dominant source of these radionuclides comes from local fallout during the 1970s of the French atmospheric tests of Moruroa and Fangataufa located nearly 400 km from Gambier. The signatures of the local fallout were deduced from the excess of its inventory in ¹³⁷Cs and from the mixing lines established from the signatures of the global fallout, some of the test sites and the isotopic ratios measured in Gambier. Signatures obtained are 2.0 ± 0.4 for ¹³⁷Cs/^239+240Pu, 0.045 ± 0.008 for ²³⁸Pu/^239+240Pu, 0.031 ± 0.009 for ²⁴¹Am/^239+240Pu, 0.092 ± 0.027 for ²⁴¹Pu/^239+240Pu, 0.0163 ± 0.0049 for (²⁴⁰Pu/²³⁹Pu)_AR, (0.78 ± 0.23)10^-4 for (²⁴¹Pu/²³⁹Pu)_AR. The concordance of the mixing lines of the [(²⁴⁰Pu/²³⁹Pu)_AR, (²⁴¹Pu/²³⁹Pu)_AR] and the linear regression of these ratios measured in the stratosphere (40°S) during the 1970s, indicates that the signatures of the close-in deposition are also those of the stratospheric injections of the French tests. The signatures of stratospheric fallout in the Southern Hemisphere were evaluated by considering that the fission energy of these injections represents 11% and that of the Northern Hemisphere represents 89% and that the isotopic ratios of stratospheric injections remained the same over the period 1970-1974. The activity ratios deducted are 21.9 ± 0.1 in ¹³⁷Cs/^239+240Pu, 0.11 ± 0.05 in ²³⁸Pu/^239+240Pu, 1.03 ± 0.12 in ²⁴¹Pu/^239+240Pu and 0.35 ± 0.04 in ²⁴¹Am/^239+240Pu. The associated atom ratios are 0.157 ± 0.011 for (²⁴⁰Pu/²³⁹Pu)_AR and (8.33 ± 0.48)10^-4 for (²⁴¹Pu/²³⁹Pu)_AR. These signatures appear to be consistent with the results of the inventories at Hiva Oa, located more than 1,000 km north of both French test sites, and with those found in the Australian continent, in regions not impacted by UK-test debris. The proportions of close-in tropospheric fallout from the French tests are about 90% in Gambier. They represent a proportion in the inventories of 40% for the ¹³⁷Cs, 60% for ²⁴¹Am and in the range between 80 and 90% for Pu isotopes.

Characterization of radioactive particles from the Dounreay nuclear reprocessing facility

Radioactive particles originating from nuclear fuel reprocessing at the United Kingdom Atomic Energy Authority's Dounreay Facility were inadvertently released to the environment in the late 1950s to 1970s and have subsequently been found on site grounds and local beaches. Previous assessments of risk associated with encountering a particle have been based on conservative assumptions related to particle composition and speciation. To reduce uncertainties associated with environmental impact assessments from Dounreay particles, further characterization is relevant. Results of particles available for this study showed variation between Dounreay Fast Reactor (DFR) and Materials Test Reactor (MTR) particles, reflecting differences in fuel design, release scenarios, and subsequent environmental influence. Analyses of DFR particles showed they are small (100-300 μm) and contain spatially correlated U and Nb. Molybdenum, part of the DFR fuel, was identified at atomic concentrations below 1%. Based on SR-based micrometer-scale X-ray Absorption Near Edge Structure spectroscopy (μ-XANES), U may be present as U(IV), and, based on a measured Nb/U atom ratio of ~2, stoichiometric considerations are commensurable with the presence of UNb₂O₇. The MTR particles were larger (740-2000 μm) and contained U and Al inhomogeneously distributed. Neodymium (Nd) was identified in atomic concentrations of around 1-2%, suggesting it was part of the fuel design. The presence of U(IV) in MTR particles, as indicated by μ-XANES analysis, may be related to oxidation of particle surfaces, as could be expected due to corrosion of UAl_x fuel particles in air. High ²³⁵U/²³⁸U atom ratios in individual DFR (3.2 ± 0.8) and MTR (2.6 ± 0.4) particles reflected the presence of highly enriched uranium. The DFR particles featured lower ¹³⁷Cs activity levels (2.00-9.58 kBq/particle) than the MTR (43.2-641 kBq ¹³⁷Cs/particle) particles. The activities of the dose contributing radionuclides ⁹⁰Sr/⁹⁰Y were proportional to ¹³⁷Cs (⁹⁰Sr/¹³⁷Cs activity ratio ≈ 0.8) and particle activities were roughly proportional to the size. Based on direct beta measurements, gamma spectrometry, and the VARSKIN6 model, contact dose rates were calculated to be approximately 74 mGy/h for the highest activity MTR particle, in agreement with previously published estimates.

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.

More surprises in the global greenhouse: Human health impacts from recent toxic marine aerosol formations, due to centennial alterations of world-wide coastal food webs

Reductions of zooplankton biomasses and grazing pressures were observed during overfishing-induced trophic cascades and concurrent oil spills at global scales. Recent phytoplankton increments followed, once Fe-, P-, and N-nutrient limitations of commensal diazotrophs and dinoflagellates were also eliminated by respective human desertification, deforestation, and eutrophication during climate changes. Si-limitation of diatoms instead ensued during these last anthropogenic perturbations of agricultural effluents and sewage loadings. Consequently, ~15% of total world-wide annual asthma trigger responses, i.e. amounting to ~45 million adjacent humans during 2004, resulted from brevetoxin and palytoxin poisons in aerosol forms of western boundary current origins. They were denoted by greater global harmful algal bloom [HAB] abundances and breathing attacks among sea-side children during prior decadal surveys of asthma prevalence, compiled here in ten paired shelf ecosystems of western and eutrophied boundary currents. Since 1965, such inferred onshore fluxes of aerosolized DOC poisons of HABs may have served as additional wind-borne organic carriers of toxic marine MeHg, phthalate, and DDT/DDE vectors, traced by radio-iodine isotopes to potentially elicit carcinomas. During these exchanges, as much as 40% of mercury poisonings may instead have been effected by inhalation of collateral HAB-carried marine neurotoxic aerosols of MeHg, not just from eating marine fish. Health impacts in some areas were additional asthma and pneumonia episodes, as well as endocrine disruptions among the same adjacent humans, with known large local rates of thyroid cancers, physician-diagnosed pulmonary problems, and ubiquitous high indices of mercury in hair, pesticides in breast milk, and phthalates in urine.

Micro-analytical characterisation of radioactive heterogeneities in samples from Central Asian TENORM sites

The present work focuses on the use of micro-analytical techniques to demonstrate the heterogeneous distribution of radionuclides and metals in soils collected at Former Soviet Union mining sites in Central Asia. Based on digital autoradiography, radionuclides were heterogeneously distributed in soil samples collected at the abandoned uranium mining sites Kurday, Kazakhstan, Kadji Sai, Kyrgyzstan and Taboshar, Tajikistan. Using electron microscopy interfaced with X-ray microanalysis submicron - mm-sized radioactive particles and rock fragments with U, As, Se and toxic metals on the surfaces were identified in Kurday and Kadji Sai samples. Employing scanning and tomographic (3D) synchrotron radiation based micro-X-ray fluorescence (μ-SRXRF) and synchrotron radiation based micro-X-ray diffraction (μ-SRXRD) allowed us to observe the inner structure of the particles without physical sectioning. The distribution of elements in virtual crosssections demonstrated that U and a series of toxic elements were rather heterogeneously distributed also within individual radioactive TENORM particles. Compared to archived data, U in Kadji Sai particles was present as uraninite (U4O9+y or UO2+x) or Na-zippeite ((Na4(UO2)6[(OH)10(SO4)3]·4H2O), i.e. U minerals with very low solubility. The results suggested that TENORM particles can carry substantial amount of radioactivity, which can be subject to re-suspension, atmospheric transport and water transport. Thus, the potential radioecological and radioanalytical impact of radioactive particles at NORM and TENORM sites worldwide should be taken into account. The present work also demonstrates that radioecological studies should benefit from the use of advanced methods such as synchrotron radiation based techniques.

Plutonium isotopes as tracers for ocean processes: a review

Since the first nuclear weapons tests in the 1940s, pulsed inputs of plutonium isotopes have served as excellent tracers for understanding sources, pathways, dynamics and the fate of pollutants and particles in the marine environment. Due to the well-defined spatial and temporal inputs of Pu, the long half-lives of (240)Pu and (239)Pu and its unique chemical properties, Pu is a potential tracer for various physical and biogeochemical ocean processes, including circulation, sedimentation and biological productivity, and hence a means of assessing the impacts of global climate change. Due to the source dependency of the Pu isotopic signature, plutonium isotopes are beginning to be exploited as tools for the evaluation and improvement of regional and global ocean models that will enhance understanding of past and future changes in the oceans. This paper addresses the major sources of Pu and the physical and biogeochemical behaviour in the marine environment. Finally, the use of Pu isotopes as tracers for various oceanic processes (e.g. water mass transport, particle export, and sedimentation) is considered.

Determination of plutonium in environmental samples by AMS and alpha spectrometry

Environmental samples from nuclear weapons test sites at the atolls of Mururoa and Fangataufa (French Polynesia, south Pacific) have been analyzed for their content of plutonium isotopes by applying the independent techniques of decay counting (Alpha Spectrometry) and accelerator mass spectrometry (AMS). Here, we propose the combination of both techniques which results in a maximum of information on the isotopic signature of Pu in environmental samples. Plutonium was chemically separated from the bulk material by anion exchange. (242)Pu was used as an internal standard for both AMS and alpha spectrometry. The samples for alpha spectrometry were prepared by micro-precipitation with NdF(3). After alpha spectrometry, the samples were reprocessed for AMS. Pu was co-precipitated with Fe(OH)(3) and finally, solid samples were prepared. At the VERA (Vienna Environmental Research Accelerator) facility, the various Pu isotopes were separated by their isotopic masses and quantified by the AMS technique. A good agreement of the results obtained from the AMS measurements was found with those obtained from Alpha Spectrometry. Overall, the data agree on average within 10% of each other. Isotope ratios for (238)Pu, (239)Pu and (240)Pu can be extracted from our investigations. Alpha spectrometry delivers data for the (238)Pu and the combination of ((239+240))Pu concentrations in those samples. In addition, the AMS technique provides information on the individual concentrations of (240)Pu and (239)Pu.