Plutonium In Soils Research Articles

Plutonium distribution in sequentially extracted phases of arable and uncultivated soils

The aim of this study was to determine the distribution of alpha-emitting plutonium isotopes from arable and uncultivated soils. The effect of soils cultivation on plutonium fractionation and mobility was studied using the sequential extraction technique (modified Tessier’s method). Soil samples were collected from the surface layer in the selected points. By means of reagents with increasing leaching power, the fractions were separated: readily available, carbonate bound, sesquioxide (Fe/Mn) bound and organically bound as well as residual. The content of 239+240Pu in the fractions was determined by alpha spectrometry. The sequential analysis showed that in the case of uncultivated soils, 67% of Pu was combined with organic matter, 15% was permanently bound to the matrix, but only 4% was associated with the available fraction, and 2% with the carbonate one. Arable soils revealed a different distribution: 36% of Pu was combined with the organic fraction, only 7% was bound permanently but as much as 9% was bound with the available fraction, and 11% with the carbonate one. It was proved that plutonium is bound mostly by organic matter (67% Pu—uncultivated and 36%—arable soils), however, the amounts of Pu combined with the labile fractions (ion-exchange and carbonate) are approximately 4 times higher for the arable soils than for uncultivated ones. This proves that soil cultivation can lead to the launch of plutonium in soil and its transition to more accessible forms which can cause a radiological risk.

Local and global trace plutonium contributions in fast breeder legacy soils

Trace-level plutonium in the environment often comprises local and global contributions, and is usually anthropogenic in origin. Here, we report estimates of local and global contributions to trace-level plutonium in soil from a former, fast-breeder reactor site. The measured 240Pu/239Pu ratio is anomalously low, as per the reduced 240Pu yield expected in plutonium bred with fast neutrons. Anomalies in plutonium concentration and isotopic ratio suggest forensic insight into specific activities on site, such as clean-up or structural change. Local and global 239Pu contributions on-site are estimated at (34 ± 1)% and (66 ± 3)%, respectively, with mass concentrations of (183 ± 6) fg g−1 and (362 ± 13) fg g−1. The latter is consistent with levels at undisturbed and distant sites, (384 ± 44) fg g−1, where no local contribution is expected. The 240Pu/239Pu ratio for site-derived material is estimated at 0.05 ± 0.04. Our study demonstrates the multi-faceted potential of trace plutonium assay to inform clean-up strategies of fast breeder legacies.

Accurate Determination of Plutonium in Soil by Tandem Quadrupole ICP-MS with Different Sample Preparation Methods

Accurate Determination of Plutonium in Soil by Tandem Quadrupole ICP-MS with Different Sample Preparation Methods

Sequential determination of uranium and plutonium in soil and sediment samples by borate salts fusion

This study describes a rapid method for sequential determination of uranium and plutonium isotopes in soil and sediment samples and its application to the study of Anthropocene sedimentary records. Different pretreatment methods have been tested (open-vessel digestion, borate salts fusion and NaOH salt fusion) achieving the complete dissolution of the sample in case of fusion methods. LiBO2 and Li2B4O7 (80/20) flux was finally selected because a higher amount of sample can be analyzed (up to 5 g). Moreover, separation steps with extraction chromatographic resin UTEVA were optimized. Average recoveries obtained for uranium and plutonium were acceptable, 59% and 72% respectively, and relative bias were below ± 15%. The time to complete the separation is approximately 11 h without ashing the samples and, consequently, it can be used in emergencies.

Sequential extraction as a tool for mobility studies of radionuclides and metals in soils and sediments

Abstract To assess the long term environmental impact of radioactive contamination of ecosystems, information on source terms including radionuclide speciation, mobility and biological uptake is of high importance. The speciation of radionuclides deposited or occurring naturally depends on source term and release scenario characteristics, transport and dispersion mechanisms and ecosystem properties. If mobile species are present, ecosystem transfer is relatively fast, whereas the ecosystem transfer is delayed if radionuclides are present as particles or incorporated in mineral lattices. This paper discusses cases showing important factors influencing the mobility of different radionuclides and metals. As examples can be given: the difference between 137Cs and 90Sr from Chernobyl fallout and stable Cs and Sr in the soil showing that the fallout has not reached a steady state and therefore shows different mobility properties, thus the time since contamination is important. the presence of organic matter affect the mobility of plutonium in soils and sediments even though the source term is the same. physical properties (i.e. pH, OM, clay content, grain sice etc.) is important to interpret mobility data between similar sites. the influence of industrial activity on radionuclides and metals shows that any man-made activity might change the mobility.

Plutonium in Soils from Northeast China and Its Potential Application for Evaluation of Soil Erosion

Surface and soil core samples from northeast China were analyzed for Pu isotopes. The measured 240Pu/239Pu atomic ratios and 239 + 240Pu/137Cs activity ratios revealed that the global fallout is the dominant source of Pu and 137Cs at these sites. Migration behavior of Pu varying with land type and human activities resulted in different distribution of Pu in surface soils. A sub-surface maximum followed by exponential decline of 239 + 240Pu concentrations was observed in an undisturbed soil core, with a total 239 + 240Pu inventory of 86.9 Bq/m2 and more than 85% accumulated in 0 ~ 20 cm layers. While only half inventory of Pu was obtained in another soil core and no sub-surface maximum value occurred. Erosion of topsoil in the site should be the most possible reason for the significantly lower Pu inventory, which is also supported by the reported 137Cs profiles. These results demonstrated that Pu could be applied as an ideal substitute of 137Cs for soil erosion study in the future.

Modeling aeolian transport of soil-bound plutonium: considering infrequent but normal environmental disturbances is critical in estimating future dose

Dose assessments typically consider environmental systems as static through time, but environmental disturbances such as drought and fire are normal, albeit infrequent, events that can impact dose-influential attributes of many environmental systems. These phenomena occur over time frames of decades or longer, and are likely to be exacerbated under projected warmer, drier climate. As with other types of dose assessment, the impacts of environmental disturbances are often overlooked when evaluating dose from aeolian transport of radionuclides and other contaminants. Especially lacking are predictions that account for potential changing vegetation cover effects on radionuclide transport over the long time frames required by regulations. A recently developed dynamic wind-transport model that included vegetation succession and environmental disturbance provides more realistic long-term predictability. This study utilized the model to estimate emission rates for aeolian transport, and compare atmospheric dispersion and deposition rates of airborne plutonium-contaminated soil into neighboring areas with and without environmental disturbances. Specifically, the objective of this study was to utilize the model results as input for a widely used dose assessment model (CAP-88). Our case study focused on low levels of residual plutonium found in soils from past operations at Los Alamos National Laboratory (LANL), in Los Alamos, NM, located in the semiarid southwestern USA. Calculations were conducted for different disturbance scenarios based on conditions associated with current climate, and a potential future drier and warmer climate. Known soil and sediment concentrations of plutonium were used to model dispersal and deposition of windblown residual plutonium, as a function of distance and direction. Environmental disturbances that affected vegetation cover included ground fire, crown fire, and drought, with reoccurrence rates for current climate based on site historical patterns. Using site-specific meteorology, accumulation rates of plutonium in soil were modeled in a variety of directions and distances from LANL sources. Model results suggest that without disturbances, areas downwind to the contaminated watershed would accumulate LANL-derived plutonium at a relatively slow rate (<0.01 Bq m−2 yr−1). However, model results under more realistic assumptions that include environmental disturbances show accumulation rates more than an order-of-magnitude faster. More generally, this assessment highlights the broader need in radioecology and environmental health physics to consider infrequent but normal environmental disturbances in longer-term dose assessments.

Concentration and characterization of plutonium in soils of Hubei in central China

To study the Pu concentration and isotope ratio distributions present in China, the 239+240Pu total activities and 240Pu/ 239Pu atom ratios in core soil samples from Hubei Province in central China were investigated using Accelerator Mass Spectrometry (AMS). The activities ranged from 0.019 to 0.502 mBq g −1 and the 239+240Pu inventories of 45 and ∼55 Bq m −2 agree well with that expected from global fallout. The 240Pu/ 239Pu atom ratios in the soil ranged from 0.172 to 0.220. The ratios are similar to typical global fallout values. Hence, any close-in fallout contribution from the Chinese nuclear weapons tests, mainly conducted in the 1970s, must have either been negligible or had a similar 240Pu/ 239Pu ratio to that of global fallout. The top 10 cm layer of the soil contributes ∼90% of the total inventory and the maximum concentrations appeared in the 2–4 cm or 4–6 cm layers. It is suggested that climatic conditions and organic content are the two main factors that affect the vertical migration of plutonium in soil.

Vertical migration of 134Cs bearing soil particles in arid soils: implications for plutonium redistribution

Vertical migration of plutonium in soils at the Waste Isolation Pilot Plant (WIPP) and the Rocky Flats Environmental Technology Site (RFETS) was evaluated based on observed 134Cs migration in soil column experiments. After applying 134Cs-labeled soil particles to the surfaces of large, undisturbed soil cores collected from each site, resulting soil columns were subjected to experimental cycles of irrigation plus drying (treatment columns) or to cycles of irrigation only (control columns). Mean losses of 134Cs inventory from soil surfaces were 3.1 ± 0.6% cycle −1 and 0.7 ± 0.6% cycle −1 respectively for RFETS treatment and control columns. WIPP columns had mean respective losses of 1.3 ± 1.2% cycle −1 and 0.5 ± 0.2% cycle −1. Bulk transport of labeled soil particles through soil cracks was an important process in RFETS soils, accounting for 64–86% of total 134Cs migration. Colloidal transport processes governed migration in WIPP soils.

Lanthanide phosphate interferences in actinide determination using inductively coupled plasma mass spectrometry

The determination of actinides at low levels using ICP-MS can be interfered by polyatomic ions appearing at the same nominal mass-to-charge ratio. In this work, interferences initially found when analysing plutonium in soil and sediment samples were identified as lanthanide phosphates and the formation of these species examined. It was found that high sample gas flow rates and low rf powers enhanced the formation of lanthanide phosphates. All lanthanides studied (La, Ce, Pr and Nd) formed phosphates, albeit to various extents and of slightly different compositions. Furthermore, the lanthanide phosphate formation was verified by introducing the source of phosphorus, hydroxyethylidene diphosphonic acid (HEDPA), in an 18O enriched water solution. This experiment also revealed that the HEDPA is essentially completely dissociated in the plasma and that the interfering species are most likely formed during ion extraction.

Determination of Plutonium in Soil by ICP‐MS After CCC Preseparation

Environmental plutonium was determined by ICP‐MS after countercurrent chromatography (CCC) preseparation with 20% tri‐n‐octylamine in toluene as stationary phase. The matrix elements, thorium and uranium, were eluted by using 7.5 mol/L nitric acid, 10 mol/L hydrochloric acid, and 3 mol/L nitric acid, respectively, and the plutonium was quantitatively stripped by using 0.025 mol/L oxalic acid–0.15 mol/L nitric acid. The spectral interferences due to the tailing of adjacent actinoids, polyatomic ion, and the matrix effect were depleted after the sample was subjected to the CCC preseparation because uranium and thorium were well separated with decontamination factors of 104 and 105, respectively; the memory effect could be eliminated effectively with a solution with the same composition of plutonium eluant. Isotopic dilution was used to determine ultra‐trace 239Pu using 242Pu as the spike. The limit of detection of 239Pu is 6 fg (27 attomoles), and the limit of determination is 25.5 fg for soil. The depth profile of 239Pu was revealed with maximum 239Pu concentrations of ∼0.08 × 10−12 g/g (0.3 femtomole per g) in Xi'an and ∼1.6 × 10−12 g/g (6.7 femtomole per g) in Gansu, China. The ratio of 240Pu/239Pu in the soil sampled from Gansu differs from the mean value of the global fallout, indicating a different origin.

Excess plutonium in soil near the Nevada Test Site, USA

Two soil profiles were collected from undisturbed areas near the Nevada Test Site (NTS). The activity of 137Cs in the surface layer of the downwind Queen City Summit profile is three times higher than at the upwind site at Searchlight, NV (41.1±0.6 mBq/g vs. 13.0±0.4 mBq/g), and the 239,240Pu activity is 100 times greater (51±2 mBq/g vs. 0.52±0.03 mBq/g). An examination of the literature suggests that the 137Cs/ 239,240Pu and the 239,240Pu/ 238Pu activity ratios in soils and sediments from the northern hemisphere, due to fallout from atmospheric atomic weapons testing, have generalized values of 36±4 and 30±4, respectively (as of 1 July 1995). Deviations from these values may indicate possible contamination by sources other than fallout. Data from the surface soil of the downwind Queen City Summit profile yield a 137Cs/ 239,240Pu ratio of 0.81±0.02 and a 239,240Pu/ 238Pu ratio of 78±6. Clearly, an increase in 239,240Pu relative to 137Cs or 238Pu can account for these observations. There is compelling evidence that this “excess” 239,240Pu came from activities at the NTS during the aboveground testing of nuclear devices, more than likely from safety tests, some 40 years ago, and/or during the interim by the wind-driven resuspension of contaminated surface soil on the NTS and its transport off-site. Moreover, the two concentration profiles show that high percentages of both of these elements are retained for decades in the upper few centimeters of soil in Nevada's desert environment.

Pu and Am determination in the environment—method development

A high resolution inductively coupled plasma mass spectrometric (HR-ICP-MS) method for the determination of plutonium isotopes, Am and the 240Pu/239Pu isotope ratio utilising modification of Pu-02-RC Plutonium in Soil Samples, Pu-03-RC Plutonium in Soil Residue—Total Dissolution Method, Pu-11-RC Plutonium Purification—Ion Exchange Technique, Pu-12-RC Plutonium and/or Americium in Soil or Sediments, HASL-300 was developed. Total plutonium concentrations (239+240Pu) measured in environmental samples by this HR-ICP-MS method were in good agreement with recommended data obtained from a-spectrometry. It was achieved the decreasing of the time to analyze the samples over than 33%.

Anthropogenic plutonium in soils of the Ural Region

The Pu content and distribution in soils of certain territories of the Ural region located in zones of nuclear accidents and regular operation of power reactor facilities are studied. The maximum content of 239;240Pu isotopes (up to 5000 Bc/m2) was revealed in soils of the central axis of the East Ural radioactive contamination at a distance of 30 km from the accident point. Regular gas-aerosol releases from the PO “Mayak” plants appreciably contribute to contamination of the neighboring territories. It is shown that almost 1012 Bc of 239;240Pu was released in the environment as a result of two nuclear accidents in 1957 and 1967. The nonuniform terrestrial plutonium contamination (from 200 to 5000 Bc/m2) is noted within the expected central axis of the Totsk radioactive trail. The contribution of the Beloyarsk nuclear power plant to the soil contamination in the fall-out zone of the aerosol emission plume is estimated on the basis of an analysis of the 238Pu/239;240Pu isotope ratio.

Study on geochemical association of plutonium in soil using sequential extraction procedure

Three kinds of soil, collected in various places (in northwestern and southeastern Poland and near Chernobyl) were used as a subject of sequential extraction and plutonium distribution study. The modified method of Tessier was applied to separate readily available, carbonate, organic, Fe/Mn oxide and residual fractions. Plutonium isotope activity in soil as well as in particular separated fractions was determined by means of alpha spectrometry. The method of plutonium separation and purification for alpha-spectrometric measurements was modified according to the chemical properties of the extracted fraction. It was found that the major part (about 90%) of 239,240Pu is bound to organic and Fe/Mn oxide fractions (in uncultivated soil samples of northwestern Poland and Chernobyl). In soil samples coming from river valley (southeastern Poland) almost equal amounts of plutonium are distributed between the available, organic and residual fractions.

Plutonium in soil from Dolon near the Semipalatinsk nuclear test site

The plutonium activities (238Pu and 239,240Pu) of soil samples from the village of Dolon, located close to the Semipalatinsk Nuclear Test Site in Kazakhstan, were measured and compared with the 90Sr and 137Cs activities. Depth profiles of 239,240Pu were determined for four of the nine sampling sites. The 239,240Pu areal deposition at the nine sites is in the range of 140 to 9700 Bq m-2. For all samples, the 239,240Pu yield after destruction of the soil matrix is significantly higher than after extracting with 8 M HNO3 indicating that 239,240Pu originates mainly from local fallout. The fraction of 239,240Pu not leached with 8 M HNO3 is assumed to be associated with fused silicates.

Analysis of plutonium in soil samples

Procedures for analysis of plutonium in soil samples were developed using anion exchange as a purification technique. Special attention was paid to removing impurities of 228Th which interferes in 238Pu determination by alpha spectrometry. Two anion-exchange methods were compared. The determination of plutonium in soil involves the conversion of soil samples to acid-soluble form. Two methods for the extraction of plutonium from a natural reference soil were compared. The first method (a direct digestion in nitric acid) is suitable for the determination of plutonium in large amounts of sample. The second method involves microwave digestion of soil (5 g) with a mixture of HNO3, HCl and HF, and is suitable for saving time in routine determinations. Activities calculated with a reference soil matrix were in good agreement with the reference value. The microwave digestion method was applied in a study of different soil samples, and recoveries ranged between 20% and 50%.

Concentrations and spatial distribution of plutonium in the terrestrial environment of the Marshall Islands

Measurements of plutonium in the terrestrial environment of the Marshall Islands are one indicator of the degree of environmental contamination from nuclear weapons testing. Moreover, the spatial pattern of environmental plutonium concentrations is indicative of the pattern of total radionuclide deposition from all of the nuclear tests. Measurements of plutonium ( 239+240Pu) to discern the spatial pattern of deposition and the degree of contamination were made in soil samples collected from 1990 through 1993 at all 29 of the atolls which form the archipelago of the Marshall Islands. Measured concentrations ranged over nearly five orders of magnitude though the difference between the highest observed values and the estimated global fallout contribution was about four orders of magnitude. A strong gradient of increasing concentration of plutonium in soil was noted with increasing latitude between 9 and 11.5 oN. The pattern of contamination and latitudinal increase was similar to that for 137Cs. Global fallout deposition of plutonium was estimated from two different data sets. Measurements of environmental plutonium in nearly 650 soil samples from the Marshall Islands are summarized and compared to estimates of the global fallout deposition. The ratio of 239+240Pu in the soil to 137Cs in the soil over a 1000 km distance was also examined to determine if there was evidence for fractionation, i.e. differential deposition. It was found that the plutonium/cesium (Pu/Cs) ratio varied considerably with distance from the Bikini test site, decreasing with increasing distance. The ratio of Pu/Cs was found to decrease about 133 times over the 1000 km distance.

Distribution of plutonium among soil phases near a Subsurface Disposal Area in Southeastern Idaho, USA

The physicochemical association of plutonium in soil near the Subsurface Disposal Area (SDA) at the Idaho National Engineering and Environmental Laboratory (INEEL) has been determined using selective sequential extraction techniques. Our results suggest that plutonium in surface soils is associated primarily with the hydrous oxide coatings of the soil (37±5.3%). Appreciable amounts of plutonium were also removed with the organic matter (22±2.8%) and carbonates (13±3.1%). On the other hand it appears that plutonium association with the soluble and exchangeable components of the soil is relatively small (>4.0%). The remainder of plutonium (21±4.7%) is tightly bound to the refractory silicate residue of the soil. Relatively little plutonium is available for physicochemical mobilization from the soil under the present prevailing conditions of the INEEL site.

A three-dimensional spatial model of plutonium in soil near Rocky Flats, Colorado.

The horizontal and depth distribution of plutonium was measured in soil east of the Rocky Flats Environmental Technology Site (formerly the Rocky Flats Plant) near Denver, Colorado, during 1992-1994. The study area was centered on the eastern plume of plutonium contamination and included transects extending from 0.2 km east of the primary origin of the contamination (the 903 Pad) to distances of up to 19 km northeast, east, southeast and south-southeast of the 903 Pad. Soil was collected in 3 cm layers down to 21 cm at exponentially increasing distances along the four transects. Plutonium concentrations decreased rapidly with depth, distance from the 903 Pad, and angle from due east. Depth distributions were independent of distance and angle from the 903 Pad, and our profile model can be used to adjust to a common basis, historical measurements made from sampling to different depths. Based on a total of approximately 1,400 independent measurements, mathematical functions were developed to describe the distance, directional, and depth relationships. These equations, combined with soil density and rock measurements, provided a new method to estimate the plutonium concentration or total deposition per unit area anywhere within the study area. Total deposition per unit area measurements at 50 sites provided an independent test of the model's predictive accuracy. Sampling coefficients of variation based on replicate samples at the main sampling locations averaged 33%, but ranged from 12 to 98%. The analytical measurement coefficient of variation averaged 8%. Mean 0-3 cm soil concentrations of (239,240)Pu among 10 Front Range "background" and 11 community locations near Rocky Flats were 2.1 and 2.3 Bq kg(-1), respectively.