Human Health Risk Assessment at a Depleted Uranium Site

Human health risk assessments for depleted uranium are common for Department of Defense (DOD) sites since the metal has various military uses. At a training and experimental site, DU was evaluated in soil in order to make decisions regarding cleanup and future use of the site. At this site, concentrations were found to be protective of human health; DU is less toxic than uranium. Other data important to this decision were the type of receptors likely to be exposed, the amount of time spent by the receptor on-site, the acceptable yearly radiation dose, and other non-radiation associated effects to the kidney. Total uranium concentrations in soil were calculated for the 90th percentile and the 50th percentile. The highest soil concentration used as an exposure point was 3500 ug/g (90th percentile). Short exposure timeframes contributed to the risk results.     

Microbial Community Composition Near Depleted Uranium Impact Points

Military training activities can result in the deposition of depleted uranium (DU) into surface soils. Mechanisms of introduction include the generation of dust from firing and impact as well as the eventual corrosion of projectile fragments and unexploded ordnance. Microorganisms in surface soils have the potential to affect the transport of DU by direct binding of the metal to the cell surface, by altering near field soil chemistry that affects metal solubility, and by microbially influenced corrosion. We investigated the response (in terms of community composition) of a native soil microbiota to the presence of DU in an arid environment. Bacteria in soils outside of the test area were challenged in dilute media with “yellow cake” or U ₃ O ₈ . At concentrations of 200 to 20,000 mg L^{? 1} only species of Bacillus were identified. In situ characterizations (by PLFA analysis) of exposed site soils showed an enrichment in sulfate reducing bacterial (i17:1w7c up 39%) and Bacillus species (a15:0 up 35%) biomarkers. Three types of microbial communities were defined (as PLFA profiles) using exploratory statistics and related to three different levels of DU exposure. The community types were then statistically corresponded to site soil chemistry. Observed differences in site soil chemistry were attributed to munitions firing since enrichments (unexposed to exposed) were observed in the minerals magnesium (increase of ～ 18 mg kg^?1 ), potassium (increase of ～ 46 mg kg^?1 ) and sulfur (increase of ～ 12 mg kg^?1 ), all constituents of munitions residues. Increased concentrations of these minerals corresponded with a community type that was associated with an area of extensive DU round use.     

Corrosion of Depleted Uranium in an Arid Environment: Soil-Geomorphology,SEM/EDS,XRD, and Electron Microprobe Analyses

Corrosion of anthropogenic uranium in natural environments is not well understood, but is important for determining potential health risks and mobility in the environment. A site in the southwestern United States contains depleted uranium that has been weathering for approximately 22 years. Soil-geomorphic, SEM/EDS, XRD, and electron microprobe analyses were conducted to determine the processes controlling the uranium corrosion. Schoepite and metaschoepite are the primary products of corrosion, and occur as silica-cemented, mixed schoepite-metaschoepite/clay/silt aggregates, as schoepite/metaschoepite-only aggregates, or rarely as coatings upon soil grains. Current extraction procedures do not adequately explain the behavior of uranium in alkaline soils when amorphous silica and clay coatings are present. Soil geomorphology and chemistry at this site limit uranium mobility and decreases potential health risks. However, if land-use and/or regional climate changes occur, uranium mobility could increase.     

Investigations on the solubility of corrosion products on depleted uranium projectiles by simulated body fluids and the consequences on dose assessment

Ingestion and inhalation of corrosion products covering weathered penetrators made of depleted uranium (DU) represent potential radiological exposure pathways. In order to study the bioavailability of these corrosion products, their solubility was determined using simulated gastric and pulmonary juices. About 75 and 36% of the uranium in the corrosion products were found to be soluble in simulated gastric and pulmonary juices, respectively. The effective dose coefficient for adults after ingestion was calculated to be 0.61 μSv mg⁻¹ DU. This compares to an effective dose coefficient for an adult of 0.71 μSv mg⁻¹ for DU materials given by the World Health Organization (WHO). The effective dose coefficient for inhalation was calculated to be 3.7 × 10⁻⁶ Sv Bq⁻¹ for workers and 5.3 × 10⁻⁶ Sv Bq⁻¹ for members of the public, respectively, which is between those of particles of Types M and S as defined by the International Commission on Radiological Protection (ICRP). The speciation of the corrosion products was investigated by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The mean oxidation state of uranium was found to be 4.6, which suggests that the uranium in the corrosion products consists of a mixture of U(IV) and U(VI) species.     

Physicochemical and Mineralogical Characterization of Uranium-Contaminated Soils

Physicochemical and mineralogical properties of the contaminants should be taken into account to decide a remediation strategy for a given radionuclide because development and optimization of soil remedial technologies are based on physicochemical and mineralogical separation techniques. The objectives of this study are to (1) demonstrate how a priori physicochemical and mineralogical characterization of soil contaminants can direct the development of remediation strategies and their performance evaluation for soil treatments and (2) understand the nature of uranium contamination and its association with the soil matrix by chemical extractions. This study examined two U-contaminated sites (K311 and K1300) at the DOE K-25 site, presently located at East Tennessee Technology Park, Oak Ridge, Tennessee. Uranium concentrations of the soils ranged from 1499 to 216,413 Bq kg^?1 at both sites. Scanning electron microscopy with backscattered electron spectroscopy and X-ray diffraction analysis showed that the dominant U phases are U oxides (schoepite), U-Ca-silicate (uranophane) and U silicate (coffinite) from the K311 site soils, whereas U-Ca-oxide and U-Ca-phosphate dominate in the K1300 site soils. Sodium carbonate/bicarbonate leaching was effective on the K1300 site soils, whereas citric acid leaching is effective on the K311 site soils. Sequential leaching showed that the majority of the uranium in the contaminated soils was contained in carbonate minerals (45%) and iron oxides (40%). Conventional leaching showed that citric acid treatment was most effective on the K311 site soils, whereas the sodium carbonate/ bicarbonate treatment was most effective on the K1300 site soils.     

Ecological Risk Assessment of Radiological Exposure to Depleted Uranium in Soils at a Weapons Testing Facility

The potential for unacceptable risks to biota from radiological exposure to depleted uranium (DU) in soils was evaluated at two sites where DU weapons testing had been conducted in the past. A screening risk assessment was conducted to determine if measured concentrations of DU-associated radionuclides in site soils exceed radionuclide levels considered protective of biota. While concentrations of individual radionuclides did not exceed acceptable levels, total radionuclide concentrations could result in potentially unacceptable doses to exposed biota. Thus, a receptor-specific assessment was conducted to estimate external and internal radiological doses to vegetation and wildlife known or expected to occur at the sites. Wildlife evaluated included herbivores, omnivores, and top-level predators. Internal dose estimates to wildlife considered exposure via fugitive dust inhalation and soil and food ingestion; root uptake was the primary exposure route evaluated for vegetation. Total doses were compared with acceptable dose levels of 1.0 and 0.1 rad/day for vegetation and wildlife, respectively, with potentially unacceptable risks indicated for doses exceeding these levels. All estimated doses were below or approximated acceptable levels, typically by an order of magnitude or more. These results indicate that current levels of DU in soils do not pose unacceptable radiological risks to biota at the sites evaluated.     

宁夏典型天然草地土壤团聚体稳定性及其有机碳分布特征

土壤团聚体作为土壤结构的基本单元和土壤有机碳存在的重要场所,对维系土壤质量和生态环境可持续发展具有重要作用。为探究宁夏天然草地土壤团聚体稳定性及其有机碳分布特征,以宁夏4种典型的天然草地（草甸草原、温性草原、草原化荒漠和荒漠草原）为研究对象,系统开展研究。结果表明：草甸草原、温性草原和草原化荒漠各粒级机械团聚体和水稳性团聚体含量均呈现随粒径减小而先减小后增大趋势,荒漠草原机械团聚体含量呈现随粒径减小而先减小后增大的趋势,水稳性团聚体含量呈现随粒径减小逐渐增大的趋势;且草甸草原和温性草原机械稳定性和水稳性团聚体在0-10 cm、10-20 cm和20-40 cm 3个土层均以>0.25 mm大团聚体为主,草原化荒漠和荒漠草原水稳性团聚体均以<0.25 mm的微团聚体为主。4种草地类型机械团聚体和水稳性团聚体MWD和GMD,以及各粒级土壤团聚体有机碳含量均表现为草甸草原和温性草原显著高于草原化荒漠和荒漠草原。草甸草原和温性草原在3个土层深度均以>0.25 mm的大团聚体对有机碳的贡献率最高,分别达到43.86%、59.26%、58.89%和58.02%、54.03%、57.15%;草原化荒漠和荒漠草原在3个土层深度,均以<0.25 mm的微团聚体贡献率高,分别达到了60.37%、55.86%、54.33%和75.61%、78.34%、78.74%。结果表明：草甸草原和温性草原较草原化荒漠和荒漠草原土壤团聚体稳定性更高,更有利于土壤有机碳累积。     

Neurotoxicity of depleted uranium

Depleted uranium (DU) is a byproduct of the enrichment process of uranium for its more radioactive isotopes to be used in nuclear energy. Because DU is pyrophoric and a dense metal with unique features when combined in alloys, it is used by the military in armor and ammunitions. There has been significant public concern regarding the use of DU by such armed forces, and it has been hypothesized to play a role in Gulf War syndrome. In light of experimental evidence from cell cultures, rats, and humans, there is justification for such concern. However, there are limited data on the neurotoxicity of DU. This review reports on uranium uses and its published health effects, with a major focus on in vitro and in vivo studies that escalate concerns that exposure to DU might be associated with neurotoxic health sequelae.     

Brain accumulation of depleted uranium in rats following 3- or 6-month treatment with implanted depleted uranium pellets

Depleted uranium (DU) is used to reinforce armor shielding and increase penetrability of military munitions. Although the data are conflicting, DU has been invoked as a potential etiological factor in Gulf War syndrome. We examined regional brain DU accumulation following surgical implantation of metal pellets in male Sprague-Dawley rats for 3 or 6 mo. Prior to surgery, rats were randomly divided into five groups: Nonsurgical control (NS Control); 0 DU pellets/20 tantalum (Ta) pellets (Sham); 4 DU pellets/16 Ta pellets (Low); 10 DU pellets/10 Ta pellets (Medium); 20 DU pellets/0 Ta pellets (High). Rats were weighed weekly as a measure of general health, with no statistically significant differences observed among groups in either cohort. At the conclusion of the respective studies, animals were perfused with phosphate-buffered saline, pH 7.4, to prevent contamination of brain tissue with DU from blood. Brains were removed and dissected into six regions: cerebellum, brainstem (pons and medulla), midbrain, hippocampus, striatum, and cortex. The uranium content was measured in digested samples as its ²³⁸U isotope by high-resolution inductively coupled plasma-mass spectrometry. After 3 mo postimplantation, DU significantly accumulated in all brain regions except the hippocampus in animals receiving the highest dose of DU (p<0.05). By 6 mo, however, significant accumulation was measured only in the cortex, midbrain, and cerebellum (p<0.01). Our data suggest that DU implanted in peripheral tissues can preferentially accumulate in specific brain regions.     

Leaching of depleted uranium in soil as determined by column experiments

The basic features of the leachability of depleted uranium (DU) projectiles in soil was investigated by using 12 projectiles (145–294 g DU) and 16 columns installed in an air-conditioned laboratory. Two soils widely distributed in Europe, a sandy-loamy cambisol and a silty-loamy luvisol, were filled into the columns (3.3 kg dry soil each). The effluents of all columns were collected weekly during the observation period of 1 year. In 648 samples, ²³⁵U and ²³⁸U were determined by inductively coupled plasma mass spectrometry. The leaching rates of ²³⁸U from natural uranium were in general about 0.01 μg week^-1 or smaller, while those of ²³⁸U from the DU munitions varied considerably and reached values of up to 100 μg week^-1, for the different columns. In total, about 0.3 μg natural uranium corresponding to 20 ppm of its inventory in the soil was leached during the observation period. From the projectiles, an average of about 50 μg DU were leached corresponding to 18 ppm of the corroded DU mass (about 1.6% of the mean initial DU mass of the projectiles). Assuming that corrosion and leaching continue as observed, the mobilisation of ²³⁸U from DU munitions will last, on an average, for thousands of years in the soils investigated, while the munitions themselves will have been corroded after a much shorter time. It is proposed to use, for the investigated soil types, the mean leaching rates of the six columns with projectiles for transport calculations of ²³⁸U to the groundwater and, thus, for a better risk assessment of the water-dependent uptake pathways of DU.     

Composition and vertical distribution patterns of the microarthropod fauna in a Negev desert soil

The faunal composition and changes in the vertical distribution patterns of soil mites and other microarthropods were described and monitored over an 18-h period at a site in the Negev desert of southern Israel. There was an overwhelming predominance of prostigmatid mites (55%) compared with Cryptostigmata (33%) in the collections. Specific determinations on the Cryptostigmata indicated that taxa, which could be identified as Mediterranean, made a sizeable contribution to this fauna. Microarthropod densities in general, and those of Prostigmata, Cryptostigmata and Mesostigmata in particular, compared favourably with those recorded from other arid desert sites in N. America and Australia. Prior to the sampling period which commenced at 6 p.m., the site was exposed to the drying effects of the Khamsin wind. Microarthropod populations were mainly located at depths below 6 cm during the following 18-h period, and this may be interpreted as an avoidance of the arid conditions obtaining at the surface, particularly during the hours from 6 p.m. to midnight. Soil temperatures remained low after midnight, but the relative humidity above the soil increased to 90% and there may have been some internal dew formation in the soil surface horizon at this time. There is some evidence of an upward movement of prostigmatid and cryptostigmatid mites as a response to increasing levels of humidity in the surface horizon during this period. We suggest that this study confirms the findings of Whitford et al. (1981) that soil microarthropods are sensitive to changes in soil moisture characteristics which operate on a diurnal scale.     

贫铀经口慢性染毒对小鼠肠道菌群多样性的影响

目的观察贫铀经口慢性染毒对小鼠肠道菌群多样性的影响。方法通过将不同剂量的贫铀混入饲料中饲养小鼠,以小鼠肝脏和肾脏铀含量作为判断贫铀在动物体内蓄积的指标,建立贫铀经121慢性染毒小鼠模型,观察各组小鼠之间的体重变化,对各组小鼠进行基于细菌16SrRNAV6－V8区的PCR－DGGE分析。结果食入贫铀的各组小鼠肝脏和肾脏铀含量显著高于对照组（P〈0．05）,各组小鼠体重差异无统计学意义（P〉0．05）,各组小鼠V6－V8IXDGGE图谱的丰富度和多样性指数差异均无统计学意义（P〉0．05）。结论贫铀经日慢性染毒对小鼠肠道菌群多样性无显著影响。     

贫铀的体内外毒性及流行病学研究进展

贫铀在工业和军事中广泛应用,尤其是贫铀武器在战争中的大量消耗,使其化学毒性和放射毒性越来越受到重视。了解贫铀的毒性,对于贫铀防护及解毒药物的研究具有重要意义。本文从细胞、动物、辐射流行病学调查三个层面,对近年来有关贫铀毒性研究的新进展进行了综述。细胞毒性实验探索出了研究贫铀放射毒性新的实验方法及氧化应激损伤可能的分子机制,而动物实验提供了贫铀危害肾脏、骨骼及神经系统等新的研究结果,同时流行病学调查调查也发现了部分贫铀毒性的阳性证据。     

Leukemic transformation of hematopoietic cells in mice internally exposed to depleted uranium

Depleted uranium (DU) is a dense heavy metal used in military applications. During military conflicts, US military personnel have been wounded by DU shrapnel. The health effects of embedded DU are unknown. Published data from our laboratory demonstrated that DU exposure in vitro can transform immortalized human osteoblast cells (HOS) to the tumorigenic phenotype. Results from our laboratory have also shown that DU is genotoxic and mutagenic in cultured human cells. Internalized DU could be a carcinogenic risk and concurrent alpha particle and heavy metal toxic effects complicate this potential risk. Anecdotal reports have suggested that DU can cause leukemia. To better assess this risk, we have developed an in vivo leukemogenesis model. This model involves using murine hematopoietic cells (FDC-P1) that are dependent on stimulation by granulocyte-macrophage colony stimulating factor (GM-CSF) or interleukin 3 (IL-3) and injected into mice to produce myeloid leukemia. Although immortalized, these cells are not tumorigenic on subcutaneous inoculation in mice. Intravenous injection of FDC-P1 cells into DU-implanted DBA/2 mice was followed by the development of leukemias in 76% of all mice implanted with DU pellets. In contrast, only 12% of control mice developed leukemia. Karyotypic analysis confirmed that the leukemias originated from FDC-P1 cells. The growth properties of leukemic cells from bone marrow, spleen, and lymph node were assessed and indicate that the FDC-P1 cells had become transformed in vivo. The kidney, spleen, bone marrow, muscle, and urine showed significant elevations in tissue uranium levels prior to induction of leukemia. These results demonstrated that a DU altered in vivo environment may be involved in the pathogenesis of DU induced leukemia in an animal model.     

Long-term corrosion and leaching of depleted uranium (DU) in soil

Corrosion and leaching of depleted uranium (DU) was investigated for 3 years using six DU munitions (145–264 g DU) each buried in a column with a soil core of about 3.3 kg dry soil mass. The columns were installed in an air-conditioned laboratory. Each week they were irrigated and ²³⁸U was determined in the effluents by inductively coupled plasma mass spectrometry. In addition, ²³⁵U was measured occasionally to assure that the ²³⁸U was predominantly from the DU munition. On average, 14.5 g corresponding to 7.9% of the initial DU mass was corroded after 3 years, indicating an increased corrosion as compared to the first year of observation. The leaching rates increased much stronger than the corrosion rates by factors of more than 100, resulting in a mean total amount of leached ²³⁸U of 13 mg as compared to 0.03 mg after the first year. Uranium species identified in the seepage water by time-resolved laser-induced fluorescence spectroscopy were mainly hydroxo and carbonate compounds, while those in the corroded material were phosphate compounds. It is concluded that the dramatic increase of the leaching and its large temporal variability do not allow any extrapolation for the future. However, the high ²³⁸U concentrations observed in the seepage water highlight the need for further investigations on the transport of ²³⁸U through soil, in particular with regard to the potential future ²³⁸U contamination of groundwater in areas affected by DU weapons.     

Soil microbial communities in the zone of uranium deposits of the Central Aldan (South Yakutia)

Specific features of soil microbial colonies in industry-affected mountainous-taiga permafrost landscapes in the El’kon uranium ore district on the territory of South Yakutia are revealed: a high number of ecological trophic groups of microorganisms (2.0 × 10³ ?7.6 × 10⁷ cells/g), comparable to the density of microbes in meadow steppe soils of Central Yakutia and a special nature of their distribution over the soil profile depending on the uranium content of the soil. In the soil of a uranium-contaminated pit, the number of individuals in all examined groups of microorganisms increases with a decrease in uranium content to 161 ppm. In the remaining samples of this pit, the disappearance of microorganisms or their decline by one or two orders of magnitude with increasing uranium content of the soil is observed. A different situation is with microorganisms in the soil of native landscape: Their numbers remain there high over the entire soil profile. Estimated correlations between the number of individuals of the main ecological trophic groups of microorganisms and factors such as uranium content, temperature, and humidity of soil shows that the relationship with the concentration of this radionuclide was strongly negative (r = ?0.6) in the radiation-contaminated alluvial soil, while a strict relationship between the number of microorganisms and soil temperature was revealed for the uncontaminated soil (r = ±1).     

Fine scale measurement and mapping of uranium in soil solution in soil and plant-soil microcosms, with special reference to depleted uranium

Background and aims

Residues from use of depleted uranium (DU) munitions pose a lasting environmental impact through persistent contamination of soils. Consequently, an understanding of the factors determining the fate of DU in soil is necessary. An understudied factor is the interaction of root exudates with DU. This study describes the use of ‘Single-Cell-Sampling-and-Analysis’ (SiCSA) for the first time in soil and investigates the effects of root exudates on DU dissolution.

Methods

Soil solutions from soil and plant-soil microcosms containing DU fragments were sampled and analysed using SiCSA and capillary electrophoresis/ICP-MS for organic acids and uranium.

Results

Nanolitre volumes of soil solution were sampled and analysed. Soils with DU fragments but no citrate addition showed low uranium concentrations in contrast to those with added citrate. Lupin root exudation gave concentrations up to 8 mM citrate and 4.4 mM malate in soil solution which solubilised DU fragments yielding transient solution concentrations of up to 30 mM.

Conclusions

Root exudates solubilise DU giving high localised soil solution concentrations. This should be considered when assessing the environmental risk of DU munitions. The SiCSA method was used successfully in soil for the first time and enables investigations with high spatial and temporal resolution in the rhizosphere.

轮牧方式对荒漠草原土壤团聚体及有机碳特征的影响

合理的草地轮牧方式对草原的科学管理具有重要意义.以宁夏荒漠草原为研究对象,对围封禁牧、连续放牧和二区、四区及六区轮牧下0~30 cm土层土壤团聚体分布特征、稳定性、有机碳含量及其贡献率进行了研究.结果表明: 除围封禁牧草地以机械稳定性大团聚体为主外,其他处理的土壤水稳性团聚体均以微团聚体为主;增加轮牧分区有利于表层土壤水稳性团聚体含量的保持及大团聚体含量增加.机械稳定性团聚体分形维数在连续放牧下最大,增加轮牧分区则呈现减小趋势,但水稳性团聚体分形维数无明显变化规律;团聚体平均重量直径(MWD)及几何平均直径(GMD)在禁牧草地最大,且随着轮牧分区的增加而增大;MWD和GMD与微团聚体含量呈显著负相关.水稳定性大团聚体有机碳含量以六区轮牧和围封禁牧较高,二区轮牧和连续放牧较低;试验区微团聚体有机碳对土壤有机碳含量贡献率较高,但0~20 cm土层中,轮牧分区越多则大团聚体有机碳贡献率越高.从土壤团聚体及其有机碳特征考虑,六区轮牧为研究区荒漠草原最适宜的轮牧方式.     

Wildfire reduces carbon dioxide efflux and increases methane uptake in ponderosa pine forest soils of the southwestern USA

Severe wildfire may cause long-term changes in the soil-atmosphere exchange of carbon dioxide and methane, two gases known to force atmospheric warming. We examined the effect of a severe wildfire 10?years after burning to determine decadal-scale changes in soil gas fluxes following fire, and explored mechanisms responsible for these dynamics. We compared soil carbon dioxide efflux, methane uptake, soil temperature, soil water content, soil O horizon mass, fine root mass, and microbial biomass between a burned site and an unburned site that had similar stand conditions to the burned site before the fire. Compared to the unburned site, soil carbon dioxide efflux was 40% lower and methane uptake was 49% higher at the burned site over the 427-day measurement period. Soil O horizon mass, microbial biomass, fine root mass, and surface soil water content were lower at the burned site than the unburned site, but soil temperature was higher. A regression model showed soil carbon dioxide efflux was more sensitive to changes in soil temperature at the burned site than the unburned site. The relative importance of methane uptake to carbon dioxide efflux was higher at the burned site than the unburned site, but methane uptake compensated for only 1.5% of the warming potential of soil carbon dioxide efflux at the burned site. Our results suggest there was less carbon available at the burned site for respiration by plants and microbes, and the loss of the soil O horizon increased methane uptake in soil at the burned site.     

Root biomass distribution of planted <Emphasis Type="Italic">Haloxylon ammodendron</Emphasis> in a duplex soil in an oasis: desert boundary area

Duplex soils, consisting of a sandy surface soil (A-horizon) and silty-clay subsoil (B-horizon), occur in a boundary area between oasis and desert in northwestern China and create a challenging habitat for restoration of plant growth. We conducted an experiment in a 10-year-old H. ammodendron plantation forest to determine the influence of physical properties of duplex soil on water infiltration and plant root growth. We used a trenching method to assess root biomass, and classified roots into two diameter classes: fine (<2 mm) and coarse (>2 mm). Following a 26.7 mm rain event, water infiltrated to the B- horizon; further deep percolation was hindered by low hydraulic conductivity, so that B horizon remained at high available soil moisture for an extended period of time. Root biomass increased rapidly in, or very close to the B horizon, especially for coarse roots. The subsoil formed a barrier to root penetration, but may also reflect the accumulation of water resources at the boundary between the A- and B-horizon. Shoot growth and root distribution, shrub height and canopy area, and total root biomass were negatively correlation with depth to the B horizon, and that was reflected by quadratic functions. We conclude that the texture and structure of duplex soils influenced the soil environment for water infiltration and storage, indicating that the B-horizon underlying sand in duplex soils is advantageous for the growth, and development of planted sand-stabilizing vegetation. These results have important implications for sustainable development of sand-fixing plantations in desert ecosystems.