Uranium In Environmental Samples Research Articles

The transfer of irradiated uranium from the Irish Sea coast to the terrestrial environment in Cumbria, UK

Abstract Sea-to-land transfer of irradiated uranium in soil samples was measured along a transect from the Cumbrian coast south of the Windscale Sellafield nuclear site in a NE direction across the Cumbrian coastal plain. Soluble uranium components were extracted by ion exchange chromatography and ratios 236U:238U and 235U:238U were measured using multi-collector ICP-MS. The method employed demonstrated the utility of 236U ratio measurements for the determination of irradiated uranium in environmental samples. The results produced for uranium were like those that have been reported for other fission product and nuclear fuel components that have been shown to be marine in origin. Measured 236U levels were highest close to the seashore and decreased rapidly as an exponential function of distance. The results indicated the absence of depleted uranium, such as might result from the deposition of aerosols generated by the testing of DU munitions at the nearby Eskmeals firing range in all but one sample.

Membrane-Based Electrochemical Detection of Uranium: A Review

The determination of uranium in environmental samples has always been a crucial environmental issue due to its adverse impacts on human life. Electrochemical detection is one of the most suitable methods for directly determining uranium because of its portable instrument and quick response characteristics. The ion-selective membrane in the working electrodes is selectively responsible for uranium transport and separation. This mini-review provides a general overview of the membrane-based ion-selective electrodes in detecting uranium ions reported in the literature. The ion-selective membranes are classified according to their ionophore categories. Furthermore, the limits and outlook are also discussed to provide a reference for further developing membrane-based electrochemical uranium sensors.

Rational designing an azo colorimetric sensor with high selectivity and sensitivity for uranium environmental monitoring

Uranium, a double-edged sword with high-efficiency energy and radioactive toxicity, attracts people to enjoy the advantages by generating power, but at the same time brings potential harm by nuclide migration. Therefore, it is necessary to develop a highly-efficient sensor to monitor uranyl ions in the field. However, the designed processes of the reported sensors are random, time-consuming and difficulty. It is urgent to find a new strategy to rationally, quickly and effectively screen out the required molecule for efficient uranium detection. Herein, with the guidance from the rational design method, the parameter, Egap, was applied to judge the chromatic aberration between the designed PADAP derivate and its uranyl complex. And the optimized structure sensor, 2-((3-bromo-5-(9,9-dioctyl-7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-fluoren-2-yl)-2-pyridylazo)-5-(diethylamino)phenol (abbr. W1H), was screened and successfully synthesized. W1H exhibited significant color change (red to blue) after binding uranyl ions, and its detection limit for uranium was as low as nanomolar. More meaningfully, the coordination mechanism of W1H toward uranium was clarified by theoretical calculation of the electron cloud density distribution, Ebind, and 1H NMR, IR and MS for the first time. With the more excellent uranyl sensitivity, selectivity, and recyclability, W1H and its colorimetric test strip have been applied to the detection of low-concentration uranium in environmental samples around the uranium tailings, providing a useful on-site method to monitor trace uranium in actual samples.

Total reflection X-ray fluorescence analysis of uranium in the presence of competing elements☆

The analysis of uranium in environmental samples, quantified using total reflection X-ray fluorescence (TXRF) analysis, would be adversely affected by the presence of rubidium and strontium in larger amounts than uranium as coexisting elements. This is because the U Lα line at 13.61 keV is close to the Rb Kα line at 13.40 keV and the Sr Kα line at 14.17 keV. Using the U Lβ1 line (instead of the U Lα line), which does not overlap with the peaks of coexisting elements, we will be able to avoid these adverse effects. Since there is no TXRF device that can perform a quantitative analysis of uranium by using the U Lβ1 line, the following modifications were made to the existing device with the intention of rapid on-site analysis. The X-ray tube of the new device has a silver anode instead of a tungsten anode, and the sensitive area of the detector was expanded. In addition, the mechanism for adjusting the position of the sample stage was changed from manual to computerized control. These changes made it possible to screen uranium in environmental samples rapidly on site without chemical separation.

Improvement of bulk analysis technique for uranium in environmental samples with high thorium contents

Multi-channel inductively coupled plasma mass spectrometry and multi-collector ICPMS were used for effective bulk analysis techniques of environmental samples with high thorium contents. A desolvating nebulizer system was adopted to reduce the 232ThH/232Th formation rate, which was evaluated using U/Th mixture solution. A UTEVA-based chemical separation method, with adjustment of the separation parameters for uranium and thorium, allowed for effective separation of uranium. The separation yields for uranium and thorium were estimated from the elution profiles of various U/Th mixture solutions. Bulk analysis of uranium in simulated samples with high thorium contents was performed to validate the improved analytical procedures.

Electrochemical Peptide-Based (E-PB) Sensor for the Detection of Uranium

Metal ion sensing attracts significant attention as many metal ions that are introduced into natural waters as water waste from industrial processes are toxic to humans. Uranium is a radioactive heavy metal naturally present in the environment and largely found in its hexavalent oxidation state as the uranyl ion, UO2 2+. Anthropogenic activities such as mining, milling, and nuclear testing increase the distribution of groundwater contamination and in many regions in the United States contamination exceeds the U.S. Environmental Protection Agency (EPA) Maximum Contamination Level (MCL) of 30 µg/L (126 nM). Therefore, there is a need for developing sensitive, selective, and cost-effective analytical methods capable of identifying and quantifying uranium in environmental samples. In this study, we focus on understanding the interactions between uranium-binding peptides and UO2 2+ as well as exploiting these interactions in the design of electrochemical peptide-based (E-PB) uranium sensors. We are particularly interested in assessing the effect of threonine phosphorylation on uranium binding affinity of peptides. The peptide probe used in the fabrication of the first generation E-PB uranium sensor is a thiolated 12-amino acid peptide probe modified with methylene blue (MB). In the absence of the target, the probe is flexible and the MB current is high; in the presence of the target, the flexibility of the probe is dampened, resulting in a large reduction in the MB current. Our preliminary results show that the sensor is capable of specific detection of UO2 2+ at concentrations substantially lower than the EPA MCL (limit of detection = 10 nM). Like most E-PB sensors, it is also reusable and selective enough to be employed in 50% synthetic aquifer samples. With further optimization, this sensor could find applications in real time detection of uranium in complex environmental samples.

On-line Green Solid Phase Extraction of Trace Rare Earth Elements and Uranium in Environmental Samples and ICP OES Detection

An on-line solid phase extraction (SPE) method using mini column packed with natural sorbent based on cotton roll dyed by quinalizarin was developed for simultaneously pre-concentration of rare earth elements and uranium at trace levels in environmental samples followed by inductively coupled plasma optical emission spectrometry (ICP OES) determination. Various parameters such as sample and eluent flow rate, sample volume and matrix ions on the method efficiency have been investigated. Under the optimized conditions, the limits of detection (LODs, 3σ) for rare earth elements were in the range of 0.002-0.300 µg L-1 and 0.420 µg L-1 for uranium. The relative standard deviation (n = 5) were lower than 6% except for samarium and uranium. The method was successfully applied for determination of trace rare earth elements and uranium in lake, well, tap water and carbonate mineral samples. The accuracy of the proposed method was validated by add-found method and direct analysis by ICP OES. This method has some advantages such as simplicity, rapidity, green chemistry and high sensitivity.

Switchable solvent based liquid phase microextraction of uranium in environmental samples: a green approach

This paper describes a new and green approach for the preconcentration and separation of U(vi) by switchable solvent based liquid phase microextraction (SPS-LPME) and its UV-vis spectrophotometric determination.

Beam-induced oxidation of monomeric U(IV) species

Uranium L(III)-edge X-ray absorption spectroscopy is often used to probe the oxidation state and coordination of uranium in environmental samples, and micrometre-sized beams can be used to spatially map the distribution of uranium relative to other elements. Here a variety of uranium-containing environmental samples are analyzed at both microbeam and larger beam sizes to determine whether reoxidation of U(IV) occurred. Monomeric U(IV), a recently discovered product of U(VI) reduction by microbes and certain iron-bearing minerals at uranium-contaminated field sites, was found to be reoxidized during microbeam (3 µm × 2 µm) analysis of biomass and sediments containing the species but not at larger beam sizes. Thus, care must be taken when using X-ray microprobes to analyze samples containing monomericU(IV).

Fission track–secondary ion mass spectrometry as a tool for detecting the isotopic signature of individual uranium containing particles

A fission track technique was used as a sample preparation method for subsequent isotope abundance ratio analysis of individual uranium containing particles with secondary ion mass spectrometry (SIMS) to measure the particles with higher enriched uranium efficiently. A polycarbonate film containing particles was irradiated with thermal neutrons and etched with 6M NaOH solution. Each uranium containing particle was then identified by observing fission tracks created and a portion of the film having a uranium containing particle was cut out and put onto a glassy carbon planchet. The polycarbonate film, which gave the increases of background signals on the uranium mass region in SIMS analysis, was removed by plasma ashing with 200W for 20min. In the analysis of swipe samples having particles containing natural (NBL CRM 950a) or low enriched uranium (NBL CRM U100) with the fission track–SIMS method, uranium isotope abundance ratios were successfully determined. This method was then applied to the analysis of a real inspection swipe sample taken at a nuclear facility. As a consequence, the range of 235U/238U isotope abundance ratio between 0.0276 and 0.0438 was obtained, which was higher than that measured by SIMS without using a fission track technique (0.0225 and 0.0341). This indicates that the fission track–SIMS method is a powerful tool to identify the particle with higher enriched uranium in environmental samples efficiently.

Sequential automated fusion/extraction chromatography methodology for the dissolution of uranium in environmental samples for mass spectrometric determination

An improved methodology has been developed, based on dissolution by automated fusion followed by extraction chromatography for the detection and quantification of uranium in environmental matrices by mass spectrometry. A rapid fusion protocol (<8 min) was investigated for the complete dissolution of various samples. It could be preceded, if required, by an effective ashing procedure using the M4 fluxer and a newly designed platinum lid. Complete dissolution of the sample was observed and measured using standard reference materials (SRMs) and experimental data show no evidence of cross-contamination of crucibles when LiBO 2/LiBr melts were used. The use of a M4 fusion unit also improved repeatability in sample preparation over muffle furnace fusion. Instrumental issues originating from the presence of high salt concentrations in the digestate after lithium metaborate fusion was also mitigated using an extraction chromatography (EXC) protocol aimed at removing lithium and interfering matrix constituants prior to the elution of uranium. The sequential methodology, which can be performed simultaneously on three samples, requires less than 20 min per sample for fusion and separation. It was successfully coupled to inductively coupled plasma mass spectrometry (ICP-MS) achieving detection limits below 100 pg kg −1 for 5–300 mg of sample.

Determination of total content and isotopic compositions of plutonium and uranium in environmental samples for safeguards purposes by ICP-QMS

The aim of this work was to determine the concentrations and isotopic compositions of plutonium and uranium in environmental samples for safeguards purposes. An analytical method was developed with a plutonium and uranium separation procedure based on extraction chromatography (using 2 mL TEVA and UTEVA columns) and detection with a quadrupole ICP-MS applying an ultra-sonic nebulizer coupled with a membrane desolvation system. Starting from blank swipes, the background equivalent concentration (BEC) was 8 fg for 239Pu and 1 ng 238U. The method was successfully applied to certified reference materials as well as to round robin samples obtained in the framework of the inter-laboratory exercise program, promoted by the Brazilian–Argentine Agency for Accounting and Control of Nuclear Materials (ABACC), together with the US Department of Energy (USDOE). After the introduction of an additional ion-exchange separation step, the methodology was applied to the IAEA-384 sediment reference sample with precise and accurate total plutonium and uranium, 240Pu/ 239Pu, 241Pu/ 239Pu, 234U/ 238U and 235U/ 238U atomic ratio results.

Surface-enhanced Raman spectroscopy for uranium detection and analysis in environmental samples

Techniques for rapid screening of uranium in environmental samples are needed, and this study entails the development of surface-enhanced Raman scattering (SERS) for analyzing uranium in aqueous media with improved sensitivity and reproducibility. A new SERS substrate based on (aminomethyl)phosphonic acid (APA)-modified gold nanoparticles was found to give greater than three orders of magnitude SERS enhancement compared with unmodified bare gold nanoparticles. Intensities of uranyl band at about 830 cm −1 were proportional to the concentrations of uranium in solution, especially at relatively low concentrations (<10 −5 M). A detection limit of ∼8 × 10 −7 M was achieved with a good reproducibility since the measurement was performed directly in dispersed aqueous suspension. Without pretreatment, the technique was successfully employed for detecting uranium in a highly contaminated groundwater with a low pH, high dissolved salts (e.g., nitrate, sulfate, calcium and aluminum) and total organic carbon.

Ion imprinted polymer based sensor for monitoring toxic uranium in environmental samples

In view of the extreme toxicity of uranium and consequent stringent limits fixed by WHO and various national governments, it is essential to monitor the uranium content in the environment which is at ultratrace levels. Conventional ionophore based ion selective electrodes, barring a few, have limitations in terms of sensitivity and selectivity for the above mentioned purpose. We now propose an ion imprinted polymer (biomimetic) based potentiometric sensor by dispersing the uranyl ion imprinted polymer particles in 2-nitrophenyloctyl ether (plasticizer), which is embedded in polyvinyl chloride matrix. The sensor responds to uranyl ion over a wide concentration range of 2.0 × 10 −8 to 1.0 × 10 −2 M. The limit of detection was 2.0 × 10 −8 M. It showed a good selectivity for uranyl ion over alkali, alkaline earth, transition and heavy metal cations. The sensor is successfully tested for the monitoring of toxic uranium in tap and sea water samples.

Use of the Eurachem guide on method validation for determination of uranium in environmental samples

Three analytical methods for determination of uranium in environmental samples by a fluorescence technique have been validated and compared in accordance with the Eurachem Guide on method validation. The first method depends on uranium separation from iron using the mercury anode technique; in the other two methods uranium is separated from iron on an anion exchange column by use of either a solution of hydrochloric acid containing ascorbic acid and hydrazine hydrate or a dilute sulfuric acid solution. Detection limits, repeatability, reproducibility, and recovery coefficient were the main validation characteristics. The results showed that better statistical values can be achieved by using the third method. Control charts for in-house control samples and international intercomparison samples have also shown that the third method is more statistically stable with time. In addition, uncertainties of measurement were estimated and compared for the three methods. It was found that the Eurachem Guide and comparison of quality statistical validation data can be good tools for selection of the appropriate method for an application.

Analysis of uranyl-bearing phases by EXAFS spectroscopy: Interferences, multiple scattering, accuracy of structural parameters, and spectral differences

As part of a larger study of uranium speciation in complex environmental samples, we have collected and analyzed the U LIII-edge extended X-ray absorption fine structure (EXAFS) spectra of nineteen minerals and compounds containing uranium as the uranyl moiety, UO22+. Analysis of seventeen of these spectra yielded structural parameters for uranyl local environments that agree with their published crystal structures; the clarkeite EXAFS spectrum and published crystal structure do not agree, and zellerite lacks a published structure. EXAFS fitting results for clarkeite show significant variability in the local environment of uranium, indicating that this phase is not truly hexagonal. Although zellerite lacks a published structure, its EXAFS spectrum is quite similar to that of rutherfordine, suggesting a similar uranyl local environment, and possibly a related structure. Our analysis of the uranium EXAFS spectra of the nineteen phases indicates that multiple scattering (MS) contributes significant spectral amplitude, especially MS associated with the uranyl moiety and carbonate and phosphate ligands. The signal from MS associated with bidentate carbonate is strong and ubiquitous, even in aqueous UO2(CO3)34-, suggesting that this signal may serve as an indicator of bidentate carbonate binding to uranyl in adsorption complexes. Multiple atomic shells at similar distances, or split atomic shells-both common features in the structure of uranyl-containing phases-produce interferences in the EXAFS spectrum that reduce the accuracy of the analysis. EXAFS-derived interatomic distances do not differ significantly from those derived from XRD, except when spectral interferences cause systematic errors in the analysis. Spectral differences and similarities have been analyzed using statistical methods. Quantitative analysis of the EXAFS spectra of samples containing multiple uranium phases may be complicated by the similarity of spectra from the same or related uranium-containing mineral groups, and by the possibility that two phases may mask the presence of a third. As EXAFS spectroscopy cannot always unambiguously determine the speciation of uranium in environmental samples, other complementary analytical techniques should be employed as well.

Determination of depleted uranium in environmental samples by gamma-spectroscopic techniques

The military use of depleted uranium initiated the need for an efficient and reliable method to detect and quantify DU contamination in environmental samples. This paper presents such a method, based on the gamma spectroscopic determination of 238U and 235U. The main advantage of this method is that it allows for a direct determination of the U isotope ratio, while requiring little sample preparation and being significantly less labor intensive than methods requiring radiochemical treatment. Furthermore, the fact that the sample preparation is not destructive greatly simplifies control of the quality of measurements. Low energy photons are utilized, using Ge detectors efficient in the low energy region and applying appropriate corrections for self-absorption. Uranium-235 in particular is determined directly from its 185.72 keV photons, after analyzing the 235U– 226Ra multiplet. The method presented is applied to soil samples originating from two different target sites, in Southern Yugoslavia and Montenegro. The analysis results are discussed in relation to the natural radioactivity content of the soil at the sampling sites. A mapping algorithm is applied to examine the spatial variability of the DU contamination.

Isotope ratio measurements of spent reactor uranium in environmental samples by using inductively coupled plasma mass spectrometry

As a result of the accident at the Chernobyl nuclear power plant (NPP) the environment was contaminated with spent nuclear fuel. The 236U isotope was used in this study to monitor the spent uranium from nuclear fallout in soil samples collected in the vicinity of the Chernobyl NPP. A rapid and sensitive analytical procedure for uranium isotopic ratio measurement in environmental samples based on inductively coupled plasma quadrupole mass spectrometry with a hexapole collision cell (HEX-ICP-QMS) was developed. Figures of merit for the HEX-ICP-QMS were studied with a plasma-shielded torch using different nebulizers [such as an ultrasonic nebulizer (USN) and a Meinhard nebulizer] for the solution introduction. An 238U + ion intensity of up to 27 000 MHz/ppm in HEX-ICP-QMS with USN was observed by introducing helium into the hexapole collision cell as the collision gas at a flow rate of 10 mL min −1. The formation rate of uranium hydride ions UH +/U + of 2 × 10 −6 was obtained by using USN with a membrane desolvator. The detection limit for 236U in 10 μg L −1 uranium solution was 3 pg L −1corresponding to the limit of 236U/ 238U ratio determination of 3 × 10 −7. In the case of low isotopic abundance of 236U (<10 −5), the measured isotopic ratio in the synthetic mixture was systematically lower than the calculated ratio. The precision of uranium isotopic ratio measurements in 10 μg L −1 laboratory uranium isotopic standard solution was 0.13% ( 235U/ 238U) and 0.33% ( 236U/ 238U) using a Meinhard nebulizer and 0.45% ( 235U/ 238U) and 0.88% ( 236U/ 238U) using an USN. The isotopic composition of all investigated Chernobyl soil samples differed from those of natural uranium; i.e. in these samples the 236U/ 238U ratio ranged from 10 −5 to 10 −3. Results of isotopic ratio measurement by HEX-ICP-QMS in soil samples are in agreement with those obtained by using a double-focusing sector field ICP-MS within experimental errors.

Determination of Traces of Uranium in Environmental Samples Using a Flow Injection System with Amperometric Catalytic Detection

A new method for flow injection analysis (FIA) of traces of uranium by catalytic amperometric detection in nitrate medium is described. Interfering oxygen was removed by in-line degassing. A simple adapter was designed to afford FIA with batch cells comprising a hanging mercury drop electrode. The carrier electrolyte consisted of 10 mM LiNO3 and the electrolyte for the samples was 10 mM HNO3+10 mM LiNO3. The method is simple, rapid (up to 60 injections/h) and precise (RSD=1.0 % for n=10 and CU=80 nM), presenting a LD of 13 pg of U or 3 nM (3 SD). Dissolution of solid samples (rock and soil) was abbreviated by employing a mixture of nitric and hydrofluoric acids in microwave heated closed vessels, followed by liquid-liquid extraction with TBP. Analysis of reference materials and intercomparison with other techniques gave very favorable results.

The determination of uranium in environmental samples using extraction chromatography

Many traditional methods for the determination of actinides in environmental samples have involved several solvent extraction and/or ion exchange steps that separate the radionuclide of interest from the bulk sample matrix. These methods are generally labor-intensive employ hazardous substances and generate considerable volume of toxic wastes. Extraction chromatographic resins have been developed that combine the power and selectivity of solvent extraction with the ease of use of ion exchange chromatographic resin. Some of these extraction chromatographic resins have been developed that will selectively sorb a particular radionuclide or groups of radionuclides from solution. A considerable amount of interest has recently been shown in these resins as they are claimed to be cost-effective in terms of increasing sample throughput, eliminating the need for expensive solvent extractants and being generally safer to handle. One such commercially available resin, U/TEVA.Spec® will selectively absorb uranium and tetravalent actinides such as thorium and plutonium from an acidic nitrate solution. This paper describes the application of U/TEVA.Spec® to the determination of uranium in a range of environmental samples.