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

Quantifying uranium radio-isotope ratios in riverine suspended particulate matter: Insights into natural and anthropogenic influences in the glacial-fed river system of the NE Tibetan Plateau

The analysis of uranium isotope ratio 235U/238U in environmental media serves as a reliable method to distinguish between natural and anthropogenic sources of uranium, playing a crucial role in assessing the extent of contamination with anthropogenic uranium and disturbances in its biogeochemical cycle. In this study, we focus on the northeastern Tibetan Plateau to examine the atomic ratio of 235U and 238U in riverine suspended particulate matter (SPM) across eight glacial watersheds. Results reveal that the 235U/238U atomic ratio in the suspended load ranges from 0.007247 to 0.007437 (with an average value of 0.00727 ± 0.00003), which closely aligns with the ratio found in natural uranium (0.00725). The highest mean ratio (0.00729 ± 0.00007) is observed in the upper glacial basin of the Ningchan River. Results suggest the negligible influence of isotopically altered in relation to human nuclear activities. When considering different environmental media, such as soil, snow/cryoconite, and riverine suspended particulate matter in the study area, the 235U/238U ratio in surface soil presents the highest values, pointing to a slight enrichment of 235U. This may be attributed to the fact that soil retains the cumulative signals of uranium atmospheric deposition, including the deposition of 235U-enriched airborne particulate matter deposited after atmospheric nuclear tests carried out in the second half of the 20th century. On the contrary, riverine suspended particulate matter and glacial sediments are more influenced by the natural 235U/238U signature under modern environmental conditions. This confirms that the northeastern Tibetan Plateau is still relatively pristine with respect to biogeochemical disturbances related to human activities.

Insights on the distribution and environmental implications of the radio-isotope 235U in surface soils and glaciers of the Tibetan Plateau

Atom ratio between ²³⁵U and ²³⁸U is often used as an indicator of U contamination as the isotopic signature of products generated by the nuclear and military industry significantly vary from the natural isotopic ratio of U. In this study, surface soils and glaciers samples were collected in the Tibetan Plateau (TP) and its surrounding areas and analyzed for U isotopic composition. Results show that the ²³⁵U/²³⁸U atom ratios in the surface soils of the TP ranges from 0.007122 to 0.007615, with an average value of 0.007378 ± 0.00011; while in the snow/ice dust from high-altitude glaciers it ranges from 0.007254 to 0.007687, with an average value of 0.007345 ± 0.000128. These ratios are slightly higher than the typical crustal value, indicating that the TP was affected by an anthropogenic input of ²³⁵U, especially in its northeast and southwest sectors. The variability of our results suggests that the spatial distribution of this contamination is not uniform, pointing to differences in the potential sources and transmission paths of radioactive particles. Combining the knowledge of past tests and activities conducted in the geographic areas around the TP with the knowledge of prevailing winds, we hypothesize that the observed ²³⁵U contamination in the TP surface soils and glaciers may have originated mainly from the previous nuclear related activities in surrounding areas (e.g., north Gobi Desert and South Asia). In addition, the horizontal and vertical wind field around the Tibetan Plateau, as well as the atmospheric aerosol optical thickness data also demonstrated the possible transport paths of the radionuclides, that is, originated from in northern Gobi desert and South Asia and reached the TP crossing the Himalayas.

Occurrence characteristics of uranium mineral-related substances in various environmental media in China: A critical review

The high demand and extensive exploitation of uranium resources resulted in the ubiquity and high detection levels of uranium mineral-related substances in various environment media in China. The potential adverse effects of uranium mineral-related substances on environment and human health have received extensive attention. Therefore, we reviewed the occurrence and spatial distribution of uranium mineral-related substances in various basins and environmental media in China to obtain an overall understanding. We collected information from over 70 papers reporting the occurrence and distribution of uranium mineral-related substances in multiple environments and 183 articles on the genesis of uranium deposits in China from 2001 to 2021. Then the occurrence of uranium mineral-related substances and corresponding correlation in different basins, environmental media and depth ranges were compared in detail. And this review assessed the uranium mineral-related pollution in China based on various environmental quality standards of China, EPA and WHO, and proposed the priority uranium mineral-related heavy metals and radioactive substances based on cluster analysis. This review showed that there were obvious differences in the occurrence characteristics of various uranium mineral-related substances in different environmental media, especially in the surrounding environment of sandstone type and hard rock type uranium deposits. These results will guide us to tackle the challenge of uranium mineral-related pollution in China. The correlation analysis of uranium mineral-related pollutants in different environmental media and the identification of priority pollutants will also provide instructions for us to control uranium mineral-related pollution. Finally, we put forward a series of urgent and practical suggestions on risk management and control of uranium mining according to the current situation of uranium mining environment in China, which is of guiding significance for the realization of "green uranium mining".

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.

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.

Bolete mushroom Boletus bainiugan from Yunnan as a reflection of the geographical distribution of 210Po, 210Pb and uranium (234U, 235U, 238U) radionuclides, their intake rates and effective exposure doses

This pioneering study aimed to determine the activity concentrations of ²¹⁰Po, ²¹⁰Pb and uranium (²³⁴U, ²³⁵U, ²³⁸U) radionuclides in fruit bodies of wild bolete Boletus bainiugan Dentinger and to estimate its edible safety, which may give scientific evidence for the consumption of this species. The analyses were performed using alpha spectrometer after digestion, exchange resins separation and deposition. Measurement data were analysed and interpolation maps reflecting ²¹⁰Po, ²¹⁰Pb and uranium (²³⁴U, ²³⁵U, ²³⁸U) geographical distribution in Yunnan province (China) were presented. In addition, from the perspective of food safety, the possible related effective radiation dose to mushrooms consumers were estimated. The results indicated that ²¹⁰Po, ²¹⁰Pb and uranium (²³⁴U, ²³⁵U, ²³⁸U) radionuclides contents in B. bainiugan were significantly different with respect to geographical distribution, and their possible intake in a part of the region was considerably higher. A very interesting observation was done according to the values of ²³⁵U/²³⁸U activity ratio indicating the occurrence of uranium faction from the global fallout of nuclear weapon tests.

Space-time Bayesian analysis of the environmental impact of a dismissing nuclear power plant

The assessment of the radiological impact of decommissioning activities at a nuclear power plant requires a detailed analysis of the distribution of radionuclides in the environment surrounding it. The present work concerns data of three campaigns carried out during the last twenty years in the plain of the Garigliano river surrounding the Garigliano Nuclear Power Plant (GNPP), which is located in Southern Italy and shut down in 1979. Moreover, some data from surveys held in the eighties, across the Chernobyl accident, have been taken in account. The results for the soil samples, in particular for ¹³⁷Cs and ²³⁶U specific activity, were analyzed for their extension in space and in time. Some of the problems related to the classical analysis of environmental radiological data (non-normal distribution of the values, small number of sample points, multiple comparison and presence of values lesser than the minimum detectable activity) have been overcome with the use of Bayesian methods. The scope of the paper is threefold: (1) to introduce the data of the last campaign held in the Garigliano plain; (2) to insert these data in a larger spatio-temporal frame; (3) to show how the Bayesian approach can be applied to radiological environmental surveys, stressing out its advantages over other approaches, using the data of the campaigns. The results show that radionuclides specific activity in soil is dominated by the natural sources with the contribution of the atmospheric fallout. A detailed study was performed on the ¹³⁷Cs data to evaluate both their statistical distribution and the trend over the space and the time. It results that (i) no new contribution there was in the last decades, (ii) specific activity values of the area surrounding the GNPP are consistent with those obtained in other farther areas, (iii) the effective depletion half-life factor for ¹³⁷Cs is much lower than the half-life of the radionuclide.

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.