Determination of 236 U in environmental samples by single extraction chromatography coupled to triple-quadrupole inductively coupled plasma-mass spectrometry

Simultaneous Measurement of Trace Levels of Hg, As, Sb, and Bi in Coastal Seawater with a Multichannel Chemical Vapor Generation Atomic Fluorescence Spectrometer

Trace levels of Hg, As, Sb, and Bi in coastal seawater have been simultaneously detected by a laboratory-built multichannel chemical vapor generation coupled to an atomic fluorescence spectrometer. The system was configured with a built-in electrochemical H2 generator as the fuel supplier to replace chemical H2 produced by the oxidation of potassium borohydride under acidic conditions in traditional instruments. The electrochemical H2 generator not only isolated the atomization process from the chemical vapor injection process but also improved the stability of atomization, excitation, and fluorescence emission in the hydrogen flame, making it easier to optimize conditions for CVG while introducing evaporating multielement vapors. Calibrations were obtained using a mixed standard solution of Hg(II), As(III), Sb(III), and Bi(III). The addition of KBr to a 3% (v/v) HCl solution was selected as the preservative to ensure the stability of 0.10 μg/L Hg(II) in a multielement standard solution for at least 15 days while also preserving μg/L levels of As(III), Sb(III), and Bi(III) stable. The method detection limits (LOD, 3σ) were 0.001, 0.015, 0.010, and 0.005 μg/L for Hg, As, Sb, and Bi, respectively. The relative standard deviations (RSD, n = 7) of the standard spiked seawater samples were 3.2% (0.020 μg/L Hg), 1.2% (0.50 μg/L As), 1.0% (0.50 μg/L Sb), and 3.5% (0.050 μg/L Bi), respectively. The recoveries of seawater samples spiked with different salinities were in the range of 84.5%(Sb)-114%(Hg). The system has been successfully applied to the simultaneous analysis of the four elements in the seawater samples collected from Xiamen Bay, Southeast China.

Determination of uranium isotopes in marine sediments and seawaters by SF ICP-MS after rapid chemical separation using TK200 resin

This work provided a novel analytical procedure for rapid and precise uranium isotopic determination in marine sediment and seawater, using a new type of extraction resin, TK200 resin, in combination with microwave digestion (for marine sediments), Fe(OH)₃ co-precipitation (for seawater), and single collector sector field-inductively coupled plasma mass spectrometry (SF ICP-MS) measurement. The removal ability of TK200 extraction chromatography for the interfering elements (IEs) Hg, Pb, Th, Pt, Tl, and the matrix rare earth elements (REEs) was carefully investigated. High decontamination factors (DFs) were obtained for IEs and REEs. Accurate quantification of uranium isotope ratios was accomplished based on a "double-cycle" ICP-MS measurement method. The analytical method was optimized and validated with isotopic standards (IRMM-187), matrix-containing certified reference marine sediments (IAEA-384, IAEA-385, and IAEA-412), and seawater reference material (IAEA-443). A stable chemical recovery of ~ 90% was obtained for both types of marine environmental samples, and the method showed great efficiency with a total analytical time of less than 6 h. The proposed procedure was validated following ISO/IEC 17025 guidelines. The important factors affecting the isotope ratio results (instrument background, procedural blank, memory effects, peak tailing, mass discrimination, dead time, and hydride interferences) were considered in the estimation of combined uncertainties. This work provides an alternative way for the determination of trace uranium isotope ratios and can be applied in the emergency monitoring of nuclear accidents and marine environmental analysis.

Deciphering sources of U contamination using isotope ratio signatures in the Loire River sediments: Exploring the relevance of 233U/236U and stable Pb isotope ratios

A broad range of contaminants has been recorded in sediments of the Loire River over the last century. Among a variety of anthropogenic activities of this nuclearized watershed, extraction of uranium and associated activities during more than 50 years as well as operation of several nuclear power plants led to industrial discharges, which could persist for decades in sedimentary archives of the Loire River. Highlighting and identifying the origin of radionuclides that transited during the last decades and were recorded in the sediments is challenging due to i) the low concentrations which are often close or below the detection limits of routine environmental surveys and ii) the mixing of different sources. The determination of the sources of anthropogenic radioactivity was performed using multi-isotopic fingerprints (²³⁶U/²³⁸U, ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb) and the newly developed ²³³U/²³⁶U tracer. For the first time ²³³U/²³⁶U data in a well-dated river sediment core in the French river Loire are reported here. Results highlight potential sources of contamination among which a clear signature of anthropogenic inputs related to two accidents of a former NUGG NPP that occurred in 1969 and 1980. The ²³³U and ²³⁶U isotopes were measured by recent high performance analytical methods due to their ultra-trace levels in the samples and show a negligible radiological impact on health and on the environment. The determination of mining activities by the use of stable Pb isotopes is still challenging probably owing to the limited dissemination of the Pb-bearing material marked by the U-ore signature downstream to the former U mines.

A review of anthropogenic radionuclide 236U: Environmental application and analytical advances

²³⁶U is an anthropogenic radionuclide that is produced from nuclear reactions of ²³⁵U(n, γ) and ²³⁸U(n, 3n). It has gained extensive attention in the field of environment, geology, nuclear emergency, and nuclear forensics. Due to the unique physical and chemical character and the distinct fingerprint character from different sources, ²³⁶U has been successfully applied in the environmental tracer, nuclear material source appointment, and environmental assessment. Until now, few reviews were published about the database, application, and the latest analytical technology development of ²³⁶U. In this review, the ²³⁶U concentration and ²³⁶U/²³⁸U isotope ratio were summarized, and the data were classified into four categories, including soil and seawater samples affected by global fallout and nuclear incidents. Furthermore, the development of environmental application and pretreatment methods were also summarized. The advanced pretreatment technology using alkali fusion and flow injection was especially discussed to introduce the development of a rapid analytical method. Finally, the research challenge and direction of ²³⁶U were proposed for further research, such as the tracer application combining ²³⁶U with other radionuclides in the terrestrial environment and the precise analysis of minor isotopes in ultra-trace uranium samples. We hope this review will help scholars to have a deep research on the analysis and application of ²³⁶U.

Temporal change of 236U/238U and 235U/238U isotopic ratios in atmospheric deposition in Tokyo and Akita from 1963 to 1979

We examine the temporal changes of ²³⁶U/²³⁸U and ²³⁵U/²³⁸U in atmospheric deposition from samples collected in Tokyo and Akita from 1963 to 1979 and elucidate the spatial distribution and historical changes of the anthropogenic sources of uranium in Japan. The ²³⁶U/²³⁸U ratio of atmospheric deposition in Tokyo peaked in 1963 and again during the 1970s, while the corresponding ²³⁵U/²³⁸U ratios of atmospheric deposition during the second peak period were lower than that of natural uranium. The ²³⁶U/²³⁸U ratios of atmospheric deposition in Akita samples peaked in 1963. The ²³⁵U/²³⁸U ratios in Akita samples were almost identical to that of the natural uranium ratios. These results suggest that the peak of ²³⁶U/²³⁸U in 1963 corresponds to what is recognized as representative for global fallout. The increase of ²³⁶U/²³⁸U and the decrease of ²³⁵U/²³⁸U observed simultaneously in the 1970s indicate that depleted uranium has subsequently been released into the environment around Tokyo. The cumulative deposition density of ²³⁶U for atmospheric fallout samples collected in Tokyo from 1968 to 1979 is an order of magnitude larger than that of the global fallout, suggesting that the depleted uranium in the 1970s is a major component of ²³⁶U in Tokyo and should be considered as an end-member when using ²³⁶U as an environmental tracer in the industrial city. This knowledge can facilitate future research using ²³⁶U as an effective environmental tracer.

Determination of Nd isotopic composition in seawater using newly developed solid phase extraction and MC-ICP-MS

Determination of neodymium (Nd) isotopic composition in seawater is useful for tracing water masses and geochemical cycles for lithogenic elements in the ocean. A new separation procedure for determination of the Nd isotopic composition of in seawater samples was developed that offers enhanced sample throughput and improved measurement reliability. The procedure consists of conventional Fe hydroxide coprecipitation, solid phase extraction using DGA chelating resin column chromatography, and Ln Resin column chromatography to preconcentrate samples. High selectivity in HNO₃ medium and elution by low concentration HCl medium for Nd are characteristics of extraction using DGA Resin®, and they allowed an evaporation step to be omitted between the chromatographic steps. These chromatographic steps, using DGA Resin to separate REEs and Ln Resin® to remove Sm, were refined from a previous study. The procedural blank value of Nd was obtained as 2 pg (n = 6) from 3 L of water samples. Chemical yield of Nd from 3 L of seawater ranged within 90-95%. The developed procedure was combined with multiple collector-ICP-MS and applied to analysis of vertical seawater samples obtained from the western subarctic gyre of the North Pacific Ocean, where ε_Nd ranged from -1.29 ± 0.42 at the surface to -3.80 ± 0.41 at 4000 m depth. These results were validated by comparing them with results obtained by the conventional method verified in the GEOTRACES inter-calibration program.

A rapid, automated system for the separation, preconcentration and measurement of 90Sr, and U, Am and Pu isotopes

An online separation and preconcentration method, using an automated flow injection setup and solid phase extraction followed by ICP-MS/MS, was developed for the analysis of ⁹⁰Sr, and U, Am and Pu isotopes in various liquid sample matrices. The radionuclide analytes were separated from interferences and complex matrices using DGA-branched resin and Sr resin, then specific gases were used in the reaction/collision cell in the ICP-MS/MS to measure the different analytes. The system requires smaller sample volumes (10 mL), less sample preparation and shorter processing time (46 min per sample) compared to traditional radiometric and other MS techniques. Based on a 10 mL sample, the limits of detection were 1.48 pg L^-1 (8257 mBq L^-1) for ⁹⁰Sr, 1.75 pg L^-1 (0.40 mBq L^-1) for ²³⁴U, 0.65 pg L^-1 (77.65 mBq L^-1) for ²⁴¹Am, and 0.56 pg L^-1 (1.25 mBq L^-1) for ²³⁹Pu when all target analytes were measured in one analysis. The analytical figures of merit were evaluated for a range of sample matrices including lake water, seawater and urine and were comparable to those reported in the literature. This online system thus provides a novel, fully automated analytical tool with faster analysis time, smaller sample requirements, minimum sample preparation, low detection limits and the flexibility to handle single and multiple measurements of various radionuclides.

Background and fingerprint characteristics of anthropogenic 236U and137Cs in soil and road dust samples collected from Beijing and Zhangjiakou, China

²³⁶U has attracted more attention as an environmental tracer in recent years. However, in-depth study of ²³⁶U in terrestrial environments is still rare in China. Data on ²³⁶U and ¹³⁷Cs concentrations in soil and road dust samples collected from Beijing and Zhangjiakou, China were obtained to demonstrate the background and distinct characteristics of anthropogenic ²³⁶U and ¹³⁷Cs. ²³⁶U and ¹³⁷Cs were detected in the range of (1.10-7.90) × 10⁷ atoms g^-1 and below the method limits of detection to 5.30 Bq kg^-1. A clear characteristic was observed in road dust, where ²³⁶U concentrations increased with decreasing of sample particle size. Soil samples showed an irregular characteristic, but the highest ²³⁶U concentrations were observed in particle size fraction of <0.053 mm in both samples. This phenomenon was caused by U chemical properties, higher specific surface areas and organic compounds in fine particles. Anthropogenic radionuclides fingerprint characteristics in <0.053 mm samples were specially discussed. ²³⁶U/²³⁸U atom ratios were detected in the range of (0.627-3.38) × 10^-8. A weak correlation between anthropogenic ²³⁶U and natural U isotopes were observed. The intermediate correlation between ²³⁶U and ¹³⁷Cs indicated somewhat distinct migration behavior of these two radionuclides in soil after release to the environment. The released amount of ²³⁶U from global fallout during the period of atmospheric nuclear weapons testing was roughly estimated to be 1300 ± 448 kg. These results could be used as fingerprint information for anthropogenic ²³⁶U migration behavior and tracer application in environment.

Determination of ultra-low 236U in environment samples using ICP-MS/MS measurement and chemical separation

²³⁶U in the environment mainly originates from human nuclear activities. Based on the unique properties of uranium, ²³⁶U can be used as a powerful tracer for investigation of oceanographic and environmental processes. This requires sensitive measuement of ²³⁶U in various environmental samples. Due to the ultra-low radioactive level of ²³⁶U in the environment, its measurement is only possible by mass spectrometry. Because of the low atomic ratio of ²³⁶U/²³⁵U down to 10^-7-10^-5 in the environment, the interferences of ²³⁵U¹H⁺ and peak tailings of ²³⁵U and ²³⁸U are critical challenges in the measurement of ²³⁶U by ICP-MS. This work developed a sensitive ICP-MS/MS method for measurement of ultra-low ²³⁶U by employing reaction cell technique and sequential quadrupole mass separators. By using 0.6 mL min^-1 CO₂ - 7 mL min^-1 helium as collision/reaction gas to convert U⁺ and UH⁺ to UO⁺, the interferences of UH⁺ (UOH⁺/UO⁺ ratio) were significantly reduced to less than 2.4 × 10^-7. A minimum detectable ²³⁶U/²³⁸U ratio of 3.0 × 10^-10 was achieved, which is one order of magnitude better than reported values. By using collision focusing with helium in the reaction cell and APEX sample introduction system, the measurement sensitivity for ²³⁶U (²³⁶UO⁺) was improved to 7.5 × 10⁶ cps ppb^-1. In combination with an effective chemical separation of uranium from sample matrix and interferences using total borate fusion following extraction chromatography with UTEVA resin, a detection limit of 7.2 × 10^-16 g g^-1 for ²³⁶U was achieved. The developed method was verified by analysis of certified reference materials and by comparison with AMS measurement method. Soil samples collected from Northwest China were successfully analyzed. ²³⁶U/²³⁸U ratios down to 9 × 10^-10 were measured in these samples, and the sources of ²³⁶U in different sits were discussed.

First dataset of 236U and 233U around the Greenland coast: A 5-year snapshot (2012-2016)

We report the first combined dataset of ²³⁶U and ²³³U in the Greenland marine environment during the period of 2012-2016. Results are discussed in terms of time evolution and spatial distribution of ²³⁶U concentration, and atomic ratios of ²³⁶U/²³⁸U and ²³³U/²³⁶U. ²³⁶U concentrations along the Greenland coast are distributed within a relatively narrow range of (0.7-12.9) × 10⁷ atom/L, corresponding to ²³⁶U/²³⁸U atomic ratios of (1.1-15.5) × 10^-9. The ²³³U/²³⁶U atomic ratios obtained vary from 0.12 × 10^-2 to 1.16 × 10^-2, with the majority distributed in the range of (0.2-0.7) × 10^-2. We applied ²³³U/²³⁶U and ²³⁶U/²³⁸U atomic ratios in a binary mixing model to identify possible ²³⁶U source terms. The results indicate that anthropogenic ²³⁶U and ²³³U in Greenland surface seawater originated from the direct global fallout (DGF) and the Sellafield and La Hague reprocessing plants (RP) is diluted by a third endmember, mostly likely natural ocean water (NOW), containing marginal ²³⁶U and ²³³U. A preliminary estimation of the source terms of ²³⁶U using ²³³U/²³⁶U atomic ratios indicate that, for both eastern and western Greenland seawater, contributions from global fallout (GF) constitute about 30% of ²³⁶U. The dominating source for ²³⁶U, i.e. 70 %, is associated to reactor ²³⁶U including discharges from RP and local reactor input in the Arctic Ocean.

Pushing Limits of ICP-MS/MS for the Determination of Ultralow 236U/238U Isotope Ratios

Determination of uranium isotope ratios is of great expedience for assessing its origin in environmental samples. In particular, the ²³⁶U/²³⁸U isotope ratio provides a powerful tool to discriminate between the different sources of uranium (uranium ore, geochemical background, and uranium from anthropogenic activities). However, in the environment, this ratio is typically below 10^-8. This low abundance of ²³⁶U and the presence in large excess of major isotopes (mainly ²³⁸U and ²³⁵U) complicates the accurate detection of ²³⁶U signal by mass spectrometry and thus highly sensitive analytical instruments providing high abundance sensitivity are required. This work pushes the limits of triple quadrupole-based ICP-MS technology for accurate detection of ²³⁶U/²³⁸U isotope ratios down to 10^-10, which is so far mainly achievable by AMS. Coupled with an efficient desolvating module, N₂O was used as the reaction gas in the collision reaction cell of the ICP-MS/MS. This configuration allows a significant decrease of the uranium polyatomic interferences (²³⁵UH⁺ ions) and an accurate determination of low ²³⁶U/²³⁸U isotope ratios. This new methodology was successfully validated through measurements of certified reference material from 10^-7 to 10^-9 and then through comparisons with AMS measurement results for ratios down to 10^-10. This is the first time that ²³⁶U/²³⁸U isotope ratios as low as 10^-10 were determined by ICP-MS/MS. The possibility of measuring low ²³⁶U/²³⁸U isotope ratios can offer a large variety of geochemical applications in particular for the determination of uranium sources in the environment.

236U and radiocesium in river bank soil and river sediment in Fukushima Prefecture, after the Fukushima Daiichi Nuclear Power Plant accident

Almost 8 years after the Japanese Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, data for ²³⁶U and ²³⁶U/²³⁸U have mainly remained limited to only a few heavily contaminated samples. In the present study, activities of ²³⁶U, ¹³⁴Cs, and ¹³⁷Cs, along with ²³⁴U, ²³⁵U, ²³⁸U, in 15 river bank soil and 10 river sediment samples, were measured by ICP-MS/MS and γ spectrometry. The ¹³⁴Cs activities and ¹³⁴Cs/¹³⁷Cs activity ratios (decay-corrected to March 11, 2011) in these 15 river bank soil samples were from 74.8 to 3.88 × 10⁵ Bq kg^-1 and from 0.944 to 1.02, respectively; and in these 10 river sediment samples were from 87.1 to 1.86 × 10⁵ Bq kg^-1 and from 0.904 to 0.990, respectively. The ²³⁶U activities and ²³⁶U/²³⁸U atom ratios in these soil samples were in the respective ranges of (0.139-17.6) × 10^-5 Bq kg^-1 and (0.259-3.83) × 10^-8; and in these sediment samples were in the respective ranges of (0.884-27.0) × 10^-5 Bq kg^-1 and (1.12-5.04) × 10^-8. For one river sediment core sample, ¹³⁴Cs and ²³⁶U activities decreased with the depth indicating ¹³⁴Cs and ²³⁶U accumulated in the river sediment with time. Unlike ¹³⁴Cs, no clear evidence of FDNPP accident-derived ²³⁶U has been found in this study, although further monitoring is encouraged to establish the background database on ²³⁶U/²³⁸U for its potential application as a tracer in environmental studies.

Reconstruction of uranium and plutonium isotopic signatures in sediment accumulated in the Mano Dam reservoir, Japan, before and after the Fukushima nuclear accident

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in Japan resulted in a major release of radionuclides into the environment. Compared to other radionuclides, few studies have investigated the fate of actinides in the environment. Accordingly, this research investigates the Pu composition in soil samples collected in paddy fields before and after the accident. Furthermore, the vertical distributions of Pu and U isotopic signatures, along with ¹³⁷Cs activities, were measured in a sediment core collected in the Mano Dam reservoir, in the Fukushima Prefecture. Changes in the relative contributions of the major actinide sources (global fallout or FDNPP derived fallout) were investigated in sediment deposited in the reservoir. The distinct peak observed for all Pu isotope ratios (²⁴⁰Pu/²³⁹Pu, ²⁴¹Pu/²³⁹Pu and ²⁴²Pu/²³⁹Pu) and for ¹³⁷Cs concentrations in the sediment core was attributed to the Fukushima fallout, and coincided with the maximum atomic contribution of only 4.8 ± 1.0% of Pu from the FDNPP. Furthermore, ²³⁶U/²³⁸U ratios measured in the sediment core remained close to the global fallout signature indicating there was likely no U from the FDNPP accident detected in the sediment core. More research is required on the environmental dynamics of trace actinides in landscapes closer to the FDNPP where there are likely to be greater abundances of FDNPP-derived Pu and U.

Determination of the geographical origin of marine mussels (Mytilus spp.) using 143Nd/144Nd ratios

Geographical traceability of marine bivalves is critical to guarantee their quality and safeguard the interest of both consumers and producers. The neodymium isotopic ratio (¹⁴³Nd/¹⁴⁴Nd) of the coastal water mainly reflects the geology of its neighboring watershed, displaying the distinct and systematic variability at high level of geographical detail and thereby shedding light on its potential as a geochemical tracer. For the first time, the present study investigated the utility and robustness of ¹⁴³Nd/¹⁴⁴Nd archived in mytilid mussel shells for geographical traceability purposes. The reproducibility of ¹⁴³Nd/¹⁴⁴Nd ratios maintained in mussels shells from the same cohort demonstrates that the Nd isotopic ratio meets the major requirement for an ideal geochemical tracer, i.e., the biologically induced variation should be rather minimal. The distribution and variability of mussel shell ¹⁴³Nd/¹⁴⁴Nd patterns were subsequently mapped along the Japanese and Chinese coastal waters. Neodymium isotopes of mussel shells record ¹⁴³Nd/¹⁴⁴Nd variations among local regions and between the two countries, which are rather compatible with the ages and lithology of the continental bedrocks. These findings highlight the great potential of ¹⁴³Nd/¹⁴⁴Nd for tracing the geographical origin of marine bivalves.

First report on global fallout 236U and uranium atom ratios in soils from Hunan Province, China

More nuclear power plants continue to be built in China. Due to its long half-life, radiotoxicity and potential application as an environmental tracer, ²³⁶U is one of the most important artificial radionuclides deserving more study since activity data are important for risk assessment. However, the ultra-trace activity of ²³⁶U and its dilution by natural uranium isotopes make it difficult to distinguish its sources and there are only limited global fallout ²³⁶U data for present in Chinese environmental samples. In order to understand the background levels for uranium isotopes, especially ²³⁶U, and clarify their sources, inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) was applied to analyze uranium isotopes in 48 soil samples from Hunan Province, China. The ²³⁴U, ²³⁵U, ²³⁸U and ²³⁶U concentrations were measured as 9.91-33.7, 0.312-1.43, 6.63-28.7 Bq kg^-1 and (1.61-21.3) × 10⁷ atoms g^-1, while, the ²³⁶U/²³⁸U, ²³⁴U/²³⁸U and ²³⁵U/²³⁸U atom ratios were (0.470-4.91) × 10^-8, (5.10-9.31) × 10^-5, and (7.11-7.82) × 10^-3, respectively. The uranium isotopic fractionation may be due to irrigation of the agricultural lands where the samples were collected. Considering the facts that neither previous nuclear tests nor nuclear accidents had occurred in Hunan Province and the present ²³⁶U/²³⁸U atom ratios were included in the range of global fallout values in other areas, it may be concluded that ²³⁶U in soils from Hunan Province is mainly from global fallout. To the best of the authors' knowledge, the presence of global fallout ²³⁶U in soil samples from China has been confirmed for the first time, and these values may be useful as background data for risk assessment in the future.

Application of synchrotron radiation and other techniques in analysis of radioactive microparticles emitted from the Fukushima Daiichi Nuclear Power Plant accident-A review

During the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, large amounts of radioactive materials were released into the environment. Among them, a large proportion of the radionuclides, such as Cs, entered into the environment as radioactive microparticles (RMs). In recent years, the characterization of RMs based on synchrotron radiation (SR) techniques has been reported, since their physical and chemical properties played an important role in evaluating the chemical reactions and physical changes that occurred when the nuclear material meltdowns took place. In this review, we summarize separation and measurement technologies used in studies of RMs, and we emphasize the application of SR-based techniques in the characterization of RMs. We report research progress, including information for elemental composition, isotopic distribution, radioactivity, and formation processes. Also, we compare the RMs from the FDNPP and the Chernobyl Nuclear Power Plant accidents. The SR-based technologies offer great improvement in the resolution and precision compared to conventional technologies, such as X-ray fluorescence and X-ray diffraction.

Presence of 236U and 239,240Pu in soils from Southern Hemisphere

²³⁶U, ²³⁹Pu and ²⁴⁰Pu are present in soils mainly as a result of the local- and global-fallout from the atmospheric nuclear weapons tests carried out mainly in the 1950's and 1960's. In this work we provide new data on the presence of ²³⁶U and ^239,240Pu in surface soils (i.e. up to 5 cm depth) from Chile and Africa. The results were obtained by low-energy Accelerator Mass Spectrometry (AMS). In the case of the Chilean samples, ²³⁶U/²³⁹Pu atom ratios show a high variability and are in general higher than the reported value for the global fallout in the Northern Hemisphere, ranging from 0.2 to 1.5. The ²³⁶U atomic concentrations range from 3.5 × 10⁶ to 9.1 × 10⁶ atoms/g, and are at least two orders of magnitude lower than the reported values in the Northern Hemisphere. The measured ²⁴⁰Pu/²³⁹Pu atom ratio in soils from South-Africa and Mozambique are of about 0.17, in agreement with the expected one for global-fallout at those coordinates. To best knowledge of the authors the present work is the first publication on ²³⁶U concentrations and ²³⁶U/²³⁹Pu atom ratios in soils from South-America and Africa.

A review of measurement methodologies and their applications to environmental 90Sr

The high fission yield product ⁹⁰Sr has been released into the environment in large amounts due to nuclear weapon tests, nuclear power plant accidents, and nuclear fuel reprocessing industries. It is a long half-life radionuclide (28.9 y), with serious consequences to human health; hence, it is desirable to perform routine monitoring of ⁹⁰Sr in environmental samples. Many ⁹⁰Sr radiometric methods have been developed in the past decades, which generally require complicated separation and purification steps with a relatively long analytical time. Moreover, some nominally rapid methods usually have high method detection limits, making them unsuitable for the environmental samples with ultra-low ⁹⁰Sr levels. In this review, some rapid and practical methods for ⁹⁰Sr routine monitoring are summarized. Different sample pretreatments and major purification procedures for ⁹⁰Sr developed in recent years, such as variable digestion methods and extraction chromatography using Sr resin or DGA resin, are especially described. Additionally, four conventional and widely used β spectrometric and mass spectrometric methods are demonstrated. Finally, ⁹⁰Sr evaluations focusing on contaminated soil and seawater samples collected after the Fukushima Daiichi Nuclear Power Plant accident, and ⁹⁰Sr application as tracers for environmental behavior are also reviewed.

Can 129I track 135Cs, 236U, 239Pu, and 240Pu apart from 131I in soil samples from Fukushima Prefecture, Japan?

In the present study, ¹²⁹I activities and ¹²⁹I/¹²⁷I atom ratios were measured in 60 soil samples contaminated by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The ¹²⁷I concentrations, ¹²⁹I activities, and ¹²⁹I/¹²⁷I atom ratios in dry-weight were observed to be 0.121–23.6 mg kg⁻¹, 0.962–275 mBq kg⁻¹, and (0.215–79.3) × 10⁻⁷, respectively. The maximum values of both ¹²⁹I activities and ¹²⁹I/¹²⁷I atom ratios in Japanese soil increased about three orders of magnitude due to this accident. The equation logy = 0.877logx + 0.173 (Pearson’s r = 0.936; x, ¹²⁹I concentration; y, ¹³¹I concentration; decay-corrected to March 11, 2011) instead of a simple constant may be a better way to express the relationship between ¹²⁹I and ¹³¹I in Japanese soil affected by both global fallout and FDNPP accident fallout. In addition, a moderate correlation was observed between ¹²⁹I and ¹³⁵Cs (logy = 0.624logx + 1.01, Pearson’s r = 0.627; x, ¹²⁹I activity; y, ¹³⁵Cs activity). However, ¹²⁹I presented larger fractionations with less volatile radionuclides, such as ²³⁶U, ²³⁹Pu, and ²⁴⁰Pu. These findings indicated ¹³⁵Cs could be roughly estimated from ¹²⁹I or ¹³¹I; this is advantageous as fewer ¹³⁵Cs data are available and ¹³⁵Cs/¹³⁷Cs is being considered a promising tracer during radiocesium source identification.

Isotopic compositions of 236U, 239Pu, and 240Pu in soil contaminated by the Fukushima Daiichi Nuclear Power Plant accident

Six years after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, data for ²³⁶U and ²³⁶U/²³⁸U have remained limited to a few heavily contaminated samples. In the present study, activities of ²³⁶U, ²³⁹Pu, and ²⁴⁰Pu, along with other U isotopes in 46 soil samples both heavily and lightly contaminated by this accident were measured by inductively coupled plasma–mass spectrometry (ICP-MS) and triple-quadrupole ICP-MS. The ²³⁶U activities and ²³⁶U/²³⁸U atom ratios in these soil samples were in the range of (0.469–24.4) × 10⁻⁵ Bq kg⁻¹ and ((0.099–1.35) × 10⁻⁷), respectively. Higher ²⁴⁰Pu/²³⁹Pu atom ratios (0.245–0.312) and ²³⁸Pu/^239+240Pu activity ratios (0.859–1.62) indicated Pu contamination originated from this accident and global fallout in some samples. For those soil samples along with black substances collected along roads in Fukushima Prefecture, high linear correlations were presented between ²³⁶U activities and ^239+240Pu activities (Pearson’s r = 0.755, p < 0.01), and between ²³⁶U activities and ²³⁸Pu activities (Pearson’s r = 0.844, p < 0.01). The analysis of these soil samples confirmed the release of ²³⁶U, although in trace amounts, during the FDNPP accident.

Anthropogenic 236U in Danish Seawater: Global Fallout versus Reprocessing Discharge

This work focuses on the occurrence of ²³⁶U in seawater along Danish coasts, which is the sole water-exchange region between the North Sea-Atlantic Ocean and the Baltic Sea. Seawater collected in 2013 and 2014 were analyzed for ²³⁶U (as well as ²³⁸U and ¹³⁷Cs). Our results indicate that ²³⁶U concentrations in Danish seawater are distributed within a relatively narrow range of (3.6-8.2) × 10⁷ atom/L and, to a certain extent, independent of salinity. ²³⁶U/²³⁸U atomic ratios in Danish seawater are more than 4 times higher than the estimated global fallout value of 1× 10^-9. The levels of ²³⁶U/²³⁸U atomic ratios obtained are comparable to those reported for the open North Sea and much higher than several other open oceans worldwide. This indicates that besides the global fallout input, the discharges from the two major European nuclear reprocessing plants are dominating sources of ²³⁶U in Danish seawater. However, unexpectedly high ²³⁶U/²³⁸U ratios as well as high ²³⁶U concentrations were observed at low-salinity locations of the Baltic Sea. While this feature might be interpreted as a clue for another significant ²³⁶U input in the Baltic Sea, it may also be caused by the complexity of water currents or slow turnover rate.