Fate of 137Cs, 90Sr and 239+240Pu in soil profiles at a water recharge site in Basel, Switzerland

Migration mechanisms of 90Sr and 137Cs on terraces

In order to investigate the impact of environmental conditions on the distribution and migration of 90Sr in the Longji terrace environment, the activity concentrations of 90Sr and 137Cs were determined. The activity concentration ranges of 90Sr and 137Cs in surface soil were 0.15-1.04 Bq/kg and 2.16-6.94 Bq/kg, respectively. These results showed that there was a similar trend between the activity concentration of 90Sr and 137Cs in the surface soil along the runoff path and their activity concentration were influenced by the slope of the terraced terrain. On the other hand, the activity ranges of 90Sr and 137Cs in soil cores were 0.01-2.74 Bq/kg and 0.43-7.19 Bq/kg, respectively. These results indicate that the migration mechanism of 90Sr is different from that of 137Cs. As compared with 137Cs, 90Sr is significantly influenced by the moisture content. In addition, high span of 137Cs/90Sr activity ratios were found in this study, which were attributed to the characteristics of cultivated land and frequent artificial disturbances that intensified the migration of 90Sr.

Fresh Groundwater Discharge as a Major Source of 90Sr into the Coastal Ocean

The behavior and source of 90Sr in the coastal ocean remain uncertain. Here, we investigated the distributions of 90Sr in coastal fresh groundwater, river water, pore water, and seawater in three bays along the southeastern coast of China between 2019 and 2021 and evaluated the potential of submarine groundwater discharge (SGD) as a source of coastal 90Sr. The 90Sr activity in coastal fresh groundwater was higher than that in river water and seawater, while the 90Sr activity in pore water was comparable to that in adjacent seawater. In addition, nonconservative mixing behavior of 90Sr along the salinity gradient between river water and seawater was observed. These observations indicated that fresh SGD may serve as an additional source of 90Sr in coastal seawater. Combining our groundwater 90Sr data with the reported fresh SGD flux data, the estimated fresh SGD-derived 90Sr fluxes into the three bays were comparable to or even higher than those supplied by riverine sources. These results revealed that fresh SGD is a major but overlooked source of 90Sr in the coastal ocean. This subterranean pathway for transport of 90Sr to the coastal ocean should be considered in the monitoring and risk assessment of coastal areas, especially those near nuclear facilities.

Simultaneous determination of actinides and 90Sr in large-size soil and sediment samples

A simultaneous analytical method for sequential separation and determination of actinides and ⁹⁰Sr in large-size environmental samples has been developed. In this method, successive co-precipitation steps were firstly conducted to remove matrix elements, then sequential column separation method was applied for simultaneous separation and purification of actinides and ⁹⁰Sr/⁹⁰Y. By using vacuum box technology, the total analytical time was minimized and batch processing allowed analyzing 12 samples in four days. The activity of ⁹⁰Sr was obtained immediately by measuring its daughter radionuclide (⁹⁰Y) with triple-to-double coincidence ratio (TDCR) Cherenkov counting, while the concentrations of Pu isotopes and ²⁴¹Am could be measured by alpha spectrometry and mass spectrometric techniques. The overall recoveries of Pu, Am, Sr and Y were higher than 70% for the entire procedure, while the recovery ratios of Sr/Y were between 0.95 and 1.04 before chromatographic separation. The developed method was verified using 20 g and 50 g of environmental soil samples spiked with certified reference materials IAEA-384 or IAEA-385 and standard solution of ⁹⁰Sr/⁹⁰Y, and good agreement between the expected values and measured results has been achieved.

90Sr in seawater of the East China Sea: Inventory, new potential source, and environmental implications

⁹⁰Sr is useful for tracing water mass movement in oceans. We collected a suit of seawater samples from the East China Sea (ECS) in the May 2011 to investigate the spatial and vertical distribution of ⁹⁰Sr and to understand its transportation and fate. To understand the sources and transportation of ⁹⁰Sr more clearly, published ¹³⁷Cs data from the same cruise were used to obtain the ⁹⁰Sr/¹³⁷Cs activity ratios. The results showed that ⁹⁰Sr activities were controlled by the circulation system of the ECS, with high values in coastal regions and low values in oceanic waters. The plume with a high ⁹⁰Sr/¹³⁷Cs ratio showed that in late spring, the Changjiang Diluted Water could flow southeastward and extend to 126-127° E, which is farther than the previously known value of 124° E. The high ⁹⁰Sr/¹³⁷Cs ratios (1.35 ± 0.62) and a long effective half-life of ⁹⁰Sr (20.0 ± 0.3 y) in the ECS surface water revealed that ⁹⁰Sr is surplus in comparison with ¹³⁷Cs. However, historical variations in the ⁹⁰Sr/¹³⁷Cs ratio seem to preclude the simple explanation that riverine input causes a ⁹⁰Sr surplus in the ECS. Groundwater discharge with a high ⁹⁰Sr but very low ¹³⁷Cs may be a new potential source. However, it is difficult to quantify the contribution of groundwater discharge at present, and more detailed studies are required in this regard. Additionally, we compiled ⁹⁰Sr and ¹³⁷Cs water column inventory data in the western North Pacific and found that the cumulative fallout onto the ocean was different from that on land in the 20-40° N band.

Hydroxyapatite nanoparticle functionalized activated carbon particle electrode that removes strontium from spiked soils in a unipolar three-dimensional electrokinetic system

Biohazard performance of Sr radionuclide can be significantly magnified by its release from the contaminated sedimentation. In this study, hydroxyapatite nanoparticle-functionalized activated carbon electrode (AC-HAP) was synthesized and stacked to the cathode compartment of the electrokinetic (EK) system to develop a unipolar three-dimensional (3D) electrochemical process for Sr²⁺ removal from spiked soils. Sr²⁺ adsorption by AC-HAP can be fitted by the pseudo-first-order and pseudo-second-order kinetic models and the Langmuir, Freundlich, and Temkin isotherm models. The largest monolayer adsorption capacity of AC-HAP of 69.49 mg g^-1 was evaluated in the pH range of 10-12 and at 40 °C. 3D EK further intensified the adsorption process of AC-HAP and the corresponding Sr²⁺ removal from aqueous environments. Voltage gradients and proposing time had a significant effect on the migration and transmission of Sr²⁺ in the electrolyzer. The influence of competitive ions on Sr²⁺ removal in the stock solutions followed Al³⁺ < Mg²⁺ < K⁺ < Na⁺ < Ca²⁺ while followed Al³⁺ < Na⁺ < K⁺ < Mg²⁺ < Ca²⁺ in 3D EK. The first three cycles for AC-HAP had taken roughly 50% of the reusability percentage. Sr²⁺ removal from spiked samples in 3D EK was achieved by acid dissolution, electromigration, and selective uptake on particle electrode.

Plutonium aided reconstruction of caesium atmospheric fallout in European topsoils

Global nuclear weapon testing and the Chernobyl accident have released large amounts of radionuclides into the environment. However, to date, the spatial patterns of these fallout sources remain poorly constrained. Fallout radionuclides (137Cs, 239Pu, 240Pu) were measured in soil samples (n = 160) collected at flat, undisturbed grasslands in Western Europe in the framework of a harmonised European soil survey. We show that both fallout sources left a specific radionuclide imprint in European soils. Accordingly, we used plutonium to quantify contributions of global versus Chernobyl fallout to 137Cs found in European soils. Spatial prediction models allowed for a first assessment of the global versus Chernobyl fallout pattern across national boundaries. Understanding the magnitude of these fallout sources is crucial not only to establish a baseline in case of future radionuclide fallout but also to define a baseline for geomorphological reconstructions of soil redistribution due to soil erosion processes.

Heavy metals, nitrates and radionuclides in milk of cows depending on their stress resistance

The paper presents the results of studies on the content of cesium, strontium, zinc, cadmium, copper, lead and nitrates in the milk of Ukrainian black-and-white milk breed cows with different resistance to stress. The resistance of cows to stress was determined by concentration of cortisol in the blood one hour after a stress effect. The following factors were stressful: fixation of animals for one hour and pre-selection of blood by a veterinarian for general analysis. The objective of the research was establishing a connection between the different adaptive potential of Ukrainian black-and-white milk breeds and the ability of their bodies to excrete via the milk heavy metal salts, nitrates and radioactive elements which enter the body with food and water. The scientific hypothesis was that the state of pressure which occurs in the body under the influence of stress impairs homeostasis. It can affect the quantity and quality of products, it can cause disorders in the metabolic processes, the synthesis of milk components and introduction of some harmful substances into milk, which are differently accumulated in the body of cows with diverse reactions to stress and can be excreted with milk in at different levels. We established that different resistance of cows to stress can affect the concentration of the investigated harmful substances in milk. Concentration of lead, cadmium, zinc and nitrates was lower in milk of more stress-resistant cows (the first group). Their milk had a lower specific activity of 137Cs and 90Sr. For all the seasons, the reliable results were obtained only for nitrates, and 137Cs and 90Sr – in spring, summer and autumn. Thus, milk of cows with higher resistance to stress is safer in terms of contents of the investigated elements. We have drawn a conclusion that stress can affect the ability of the body to excrete via the milk harmful elements which enter the body with food and water. Perspectives of further research are determining the effect of cows’ stress resistance on the suitability of milk for the production of baby food products.

Modelling the mitigation speeds of 137Cs, 90Sr and 131I in the topsoils and assessment of the radiological hazards

Fate modelling of artificial radionuclides (ARs) in top soils are necessary to assess the radiological effects to population. Among ARs, ¹³⁷Cs, ⁹⁰Sr and ¹³¹I are very important since the large abundances in the environment. In this study, the fates of ¹³⁷Cs, ⁹⁰Sr and ¹³¹I in the surface soil layers were simulated by the soil model which was developed by the Canadian Centre for Environmental Modelling and Chemistry (CEMC). The scenario that ¹³⁷Cs, ⁹⁰Sr and ¹³¹I contaminated in topsoil in the exclusion of Fukushima Daiichi nuclear power plant (NPP) accident was evaluated. The results show the expected time for the minimum hazardous level of exposure. It is 115.5 days after the exposure, when the total effective dose is 1 mSv y^-1 in which 0.46 mSv y^-1 from ingestion and 0.54 mSv y^-1 from gamma exposure. Hazard levels due to exposure progresses are varied in order gamma exposure (82.14%) > ingestion (17.47%) > inhalation (0.39%). The hazard levels from radionuclides are varied in order ¹³⁷Cs (63.34%) > ¹³¹I (33.48%) > ⁹⁰Sr (3.18%).

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.