Amorphous K-Co-Mo-Sx Chalcogel: A Synergy of Surface Sorption and Ion-Exchange.

Chalcogel represents a unique class of meso- to macroporous nanomaterials that offer applications in energy and environmental pursuits. Here, the synthesis of an ion-exchangeable amorphous chalcogel using a nominal composition of K2CoMo2S10 (KCMS) at room temperature is reported. Synchrotron X-ray pair distribution function (PDF), X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) reveal a plausible local structure of KCMS gel consisting of Mo5+ 2 and Mo4+ 3 clusters in the vicinity of di/polysulfides which are covalently linked by Co2+ ions. The ionically bound K+ ions remain in the percolating pores of the Co-Mo-S covalent network. XANES of Co K-edge shows multiple electronic transitions, including quadrupole (1s→3d), shakedown (1s→4p + MLCT), and dipole allowed 1s→4p transitions. Remarkably, despite a lack of regular channels as in some crystalline solids, the amorphous KCMS gel shows ion-exchange properties with UO2 2+ ions. Additionally, it also presents surface sorption via [S∙∙∙∙UO2 2+] covalent interactions. Overall, this study underscores the synthesis of quaternary chalcogels incorporating alkali metals and their potential to advance separation science for cations and oxo-cationic species by integrating a synergy of surface sorption and ion-exchange.

Removal of CrO42-, a Nonradioactive Surrogate of 99TcO4-, Using LDH-Mo3S13 Nanosheets.

Removal of chromate (CrO42-) and pertechnetate (TcO4-) from the Hanford Low Activity Waste (LAW) is beneficial as it impacts the cost, life cycle, operational complexity of the Waste Treatment and Immobilization Plant (WTP), and integrity of vitrified glass for nuclear waste disposal. Here, we report the application of [MoIV3S13]2- intercalated layer double hydroxides (LDH-Mo3S13) for the removal of CrO42- as a surrogate for TcO4-, from ppm to ppb levels from water and a simulated LAW off-gas condensate of Hanford's WTP. LDH-Mo3S13 removes CrO42- from the LAW condensate stream, having a pH of 7.5, from ppm (∼9.086 × 104 ppb of Cr6+) to below 1 ppb levels with distribution constant (Kd) values of up to ∼107 mL/g. Analysis of postadsorbed solids indicates that CrO42- removal mainly proceeds by reduction of Cr6+ to Cr3+. This study sets the first example of a metal sulfide intercalated LDH for the removal of CrO42-, as relevant to TcO4-, from the simulated off-gas condensate streams of Hanford's LAW melter which contains highly concentrated competitive anions, namely F-, Cl-, CO32-, NO3-, BO33-, NO2-, SO42-, and B4O72-. LDH-Mo3S13's remarkable removal efficiency makes it a promising sorbent to remediate CrO42-/TcO4- from surface water and an off-gas condensate of nuclear waste.

Indigenous earthworms and gut bacteria are superior to chemical amendments in the remediation of cadmium-contaminated seleniferous soils.

The natural selenium (Se)-rich areas in China are generally characterized by high geological background of cadmium (Cd) which poses potential risks to human health. Therefore, immobilization of Cd is the prerequisite to ensure the safe utilization of natural seleniferous soil resources. A pot experiment was conducted to compare the effects of indigenous earthworm (Amynthas hupeiensis) and its gut bacteria (Citrobacter freundii DS strain) on the remediation of Cd-contaminated seleniferous soil with two traditional chemical amendments. The results indicated that earthworms and DS strain decreased DGT-extractable Cd by 25.52 - 41.53% and reduced Cd accumulation in lettuce leaves by 20.83 - 37.50% compared with control through converting the exchangeable Cd (EX-Cd) into residual Cd (RE-Cd) fractions. Overall, earthworms and DS strain were more effective in Cd immobilization, growth and quality promotion, oxidative stress alleviation, Cd accumulation and bioaccessibility reduction in the soil-lettuce-human continuum than biochar and lime. Moreover, all amendments induced the antagonism between Se and Cd through increasing bioavailable Se/Cd molar ratios in soil. However, all the Cd concentrations in lettuce exceeded the maximum permissible limit of Cd for leaf vegetables, indicating that soil amendment alone could not ensure food safety. This study confirmed that biological amendments were superior to chemical amendments in the remediation of Cd-contaminated seleniferous soil.

The Adsorption Characteristics of Uranium(VI) from Aqueous Solution on Leonardite and Leonardite-Derived Humic Acid: A Comparative Study.

The humic substance is a low-cost and effective adsorbent with abundant functional groups in remediating uranium (U) (VI)-contaminated water. In this research study, leonardite together with leonardite-derived humic acid (L-HA) was used to eliminate U(VI) from water under diverse temperatures (298, 308, and 318 K). L-HA showed a higher adsorption volume for U(VI) than leonardite. U adsorption was varied with pH and increased with temperature. The adsorption kinetics of L-HA had a higher determination coefficient (R2) for pseudo-second-order (R2 > 0.993) and Elovich (R2 > 0.987) models, indicating possible chemisorption-assisted adsorption. This was further supported with the activation energies (15.9 and 13.2 kJ/mol for leonardite and L-HA, respectively). Moreover, U(VI) equilibrium adsorption on leonardite was better depicted with the Freundlich model (R2 > 0.970), suggesting heterogeneous U(VI) adsorption onto the leonardite surface. However, U(VI) adsorption onto L-HA followed the Langmuir equation (R2 > 0.971), which implied the dominant role of monolayer adsorption in controlling the adsorption process. Thermodynamic parameters, including standard entropy change (ΔS0 > 0), Gibbs free energy (ΔG0 < 0), and standard enthalpy change (ΔH0 > 0), suggested a spontaneous and endothermal adsorption process. In addition, ionic species negatively affected U(VI) adsorption by leonardite and L-HA.

Toxicity of As in Crassostrea virginica (Gmelin, 1791) from the Northern Gulf of Mexico at the presence of Zn and its antioxidant defense mechanisms.

Reactive oxygen species (ROS) such as the free radicals (e.g. hydroxyl, nitric acid, superoxide) cause damage to lipids, proteins and DNA. Increased production of ROS occurs from pollution. Process of removal or neutralization of ROS is achieved through antioxidants enzyme defense systems and provide homeostasis within biological systems. Aerobic organisms have complex antioxidant systems using enzymatic and non-enzymatic antioxidants to prevent overproduction of ROS. This study examined the toxic effects of arsenic and zinc on Eastern oysters, their interaction and resulting enzymatic responses. Cellular damage as indicated with lipid peroxidation and antioxidant defensive enzyme activities (superoxide dismutase, SOD; glutathione peroxidase, GPX and catalase, CAT) were measured in the hepatopancreas of Eastern oysters exposed to single and combined treatments of arsenic and zinc for 30 days. The results showed either arsenic or zinc exposure significantly increased the lipid peroxidation and triggered antioxidant defenses. Activities of antioxidant enzymes (SOD, GPX and CAT) were markedly elevated upon expose of As or Zn. However, at the presence of Zn, As toxicity expressed as lipid oxidation significantly decreased as well as accordingly decreased activities of antioxidant enzymes. This revealed that the presence of Zn showed a significantly antagonistic effect on arsenic toxicity in Eastern oysters from Northern Gulf of Mexico.

Electrokinetic-enhanced phytoremediation of uranium-contaminated soil using sunflower and Indian mustard.

Electrokinetic-enhanced phytoremediation is an effective technology to decontaminate heavy metal contaminated soil. In this study, we examined the effects of electrokinetic treatments on plant uptake and bioaccumulation of U from soils with various U sources. Redistribution of uranium in soils as affected by planting and electrokinetic treatments was investigated. The soil was spiked with 100 mg kg-1 UO2, UO3, and UO2(NO3)2. After sunflower and Indian mustard grew for 60 days, 1 voltage of direct-current was applied across the soils for 9 days. The results indicated that U uptake in both plants were significantly enhanced by electrokinetic treatments from soil with UO3 and UO2(NO3)2. U was more accumulated in roots than in shoots. Electrokinetic treatments were effective on lowering soil pH near the anode region. Overall, uranium (U) removal efficiency reached 3.4-4.3% from soils with UO3 and uranyl with both plants while that from soil with UO2 was 0.7-0.8%. Electrokinetic remediation treatment significantly enhanced the U removal efficiency (5-6%) from soils with UO3 and uranyl but it was 0.8-1.3% from soil with UO2, indicating significant effects of U species and electrokinetic enhancement on U bioaccumulation. This study implies the potential feasibility of electrokinetic-enhanced phytoremediation of U soils with sunflower and Indian mustard.

Electro-kinetic remediation coupled with phytoremediation to remove lead, arsenic and cesium from contaminated paddy soil.

The objectives of this study were to investigate distribution and solubility of Pb, Cs and As in soils under electrokinetic field and examine the processes of coupled electrokinetic phytoremediation of polluted soils. The elevated bioavailability and bioaccumulation of Pb, As and Cs in paddy soil under an electro-kinetic field (EKF) were studied. The results show that the EKF treatment is effective on lowering soil pH to around 1.5 near the anode which is beneficial for the dissolution of metal(loid)s, thus increasing their overall solubility. The acidification in the anode soil efficiently increased the water soluble (SOL) and exchangeable (EXC) Pb, As and Cs, implying enhanced solubility and elevated overall potential bioavailability in the anode region while lower solubility in the cathode areas. Bioaccumulations of Pb, As and Cs were largely determined by the nature of elements, loading levels and EKF treatment. The native Pb in soil usually is not bioavailable. However, EKF treatment tends to transfer Pb to the SOL and EXC fractions improving the phytoextraction efficiency. Similarly, EKF transferred more EXC As and Cs to the SOL fraction significantly increasing their bioaccumulation in plant roots and shoots. Pb and As were accumulated more in plant roots than in shoots while Cs was accumulated more in shoots due to its similarity of chemical properties to potassium. Indian mustard, spinach and cabbage are good accumulators for Cs. Translocation of Pb, As and Cs from plant roots to shoots were enhanced by EKF. However, this study indicated the overall low phytoextraction efficiency of these plants.

Sunlight-Driven Photothermally Boosted Photocatalytic Eradication of Superbugs Using a Plasmonic Gold Nanoparticle-Decorated WO3 Nanowire-Based Heterojunction.

Superbug infections are currently one of the biggest global health problems in our society. Herein, we report the design of a plasmonic gold nanoparticle (GNP)-decorated WO3 nanowire-based heterojunction for the proficient usage of sunlight-based renewable energy to inactivate 100% superbugs via photothermally boosted photocatalytic action. Additionally, a synergistic photothermal and photocatalytic approach has been used for sunlight-driven complete eradication of carbapenem-resistant Enterobacteriaceae Escherichia coli (CRE E. coli) and methicillin-resistant Staphylococcus aureus (MRSA) superbugs. Interestingly, photocatalytic activity of methylene blue (MB) dye degradation in the presence of 670 nm near-infrared light shows that photothermally boosted photocatalytic performance is much superior to that of only a photocatalytic or photothermal process. The observed higher photocatalytic performance for the heterojunction is because the plasmonic GNP enhanced the absorption capability at 670 nm and increased the temperature of the photocatalyst surface, which reduces the activation energy of the degradation reaction. Similarly, sunlight-driven photocatalytic experiments show 100% degradation of MB after 60 min of sunlight irradiation. Moreover, sunlight-based photocatalytic inactivation of MRSA and CRE E. coli experiments show 100% inactivation after 60 min of light irradiation.

Light-Induced Wavelength Dependent Self Assembly Process for Targeted Synthesis of Phase Stable 1D Nanobelts and 2D Nanoplatelets of CsPbI3 Perovskites.

Despite black cubic phase α-CsPbI3 nanocrystals having an ideal bandgap of 1.73 eV for optoelectronic applications, the phase transition from α-CsPbI3 to non-perovskite yellow δ-CsPbI3 phase at room temperature remains a major obstacle for commercial applications. Since γ-CsPbI3 is thermodynamically stable with a bandgap of 1.75 eV, which has great potential for photovoltaic applications, herein we report a conceptually new method for the targeted design of phase stable and near unity photoluminescence quantum yield (PLQY) two-dimensional (2D) γ-CsPbI3 nanoplatelets (NPLs) and one-dimensional (1D) γ-CsPbI3 nanobelts (NBs) by wavelength dependent light-induced assembly of CsPbI3 cubic nanocrystals. This article demonstrates for the first time that by varying the excitation wavelengths, one can design air stable desired 2D nanoplatelets or 1D nanobelts selectively. Our experimental finding indicates that 532 nm green light-driven self-assembly produces phase stable and highly luminescent γ-CsPbI3 NBs from CsPbI3 nanocrystals. Moreover, we show that a 670 nm red light-driven self-assembly process produces stable and near unity PLQY γ-CsPbI3 NPLs. Systematic time-dependent microscopy and spectroscopy studies on the morphological evolution indicates that the electromagnetic field of light triggered the desorption of surface ligands from the nanocrystal surface and transformation of crystallographic phase from α to γ. Detached ligands played an important role in determining the morphologies of final structures of NBs and NPLs from nanocrystals via oriented attachment along the [110] direction initially and then the [001] direction. In addition, XRD and fluorescence imaging data indicates that both NBs and NPLs exhibit phase stability for more than 60 days in ambient conditions, whereas the cubic phase α-CsPbI3 nanocrystals are not stable for even 3 days. The reported light driven synthesis provides a simple and versatile approach to obtain phase pure CsPbI3 for possible optoelectronic applications.

WO3 Nanowire-Attached Reduced Graphene Oxide-Based 1D-2D Heterostructures for Near-Infrared Light-Driven Synergistic Photocatalytic and Photothermal Inactivation of Multidrug-Resistant Superbugs.

The rapid emergence of superbugs which are resistant to existing antibiotics is becoming a huge global threat to public health, which demands the discovery of next-generation antibacterial agents for combating superbugs. Herein, we report the design of a two-dimensional (2D) reduced graphene oxide (r-GO) and one-dimensional (1D) WO3 nanowire-based photothermal-photocatalytic heterostructure for combating multiantibiotic-resistant Salmonella DT104, carbapenem-resistant Enterobacteriaceae Escherichia coli, and methicillin-resistant Staphylococcus aureus superbugs. In the presence of near-infrared (NIR) light, due to the generation of electrons and holes, the WO3-based heterostructure generates reactive oxygen species by photocatalytic reaction from water and oxygen, which kills superbugs. To enhance the photocatalytic superbug killing efficiency, r-GO has been used for suppressing the recombination of the photoinduced electron-hole pairs. Reported data show that NIR light-driven synergistic photocatalytic-photothermal processes can be used for 100% degradation of methylene blue using a heterostructure-based catalyst, and the photodegradation rate for the heterostructure is much better than the literature data for different types of WO3/GO-based nanocomposites. Experimentally, time-dependent antibacterial efficiency data reveals that the heterostructure can destroy 100% superbugs within 30 min of light exposure via a synergistic photothermal and photocatalytic mechanism, whereas the WO3 nanowire can kill around 35% superbugs only via photocatalytic action only and r-GO can kill 25% superbugs via photothermal action even after 30 min of exposure to light. Systematic time-dependent microscopy and spectroscopy studies reveal that the excellent antisuperbug activities for heterostructures are due to membrane damage, ATP, and DNA/RNA breakage. For possible real-life applications, sun light-based superbug inactivation shows 100% inactivation possible within 250 min of light exposure using 12 mg/mL heterostructures. The reported sun light-driven killing of superbugs provides a simple and versatile platform to combat drug-resistant superbugs.

Accumulation and phytotoxicity of microcystin-LR in rice (Oryza sativa).

Irrigation with eutrophic water containing microcystins-LR (MC-LR) poses a potential risk to crops. However, the accumulation of MC-LR in rice grains and the mechanism of MC-LR-induced inhibition in rice roots are not understood. In this study, we detected the accumulation of MC-LR in rice grains collected from Taihu Lake region. MC-LR could accumulate in rice grains, but the risk evaluation suggested that MC-LR levels in rice grains from Taihu Lake region may not pose a threat to human health currently. In addition, MC-LR with low concentrations did not affect the growth of rice roots. However, MC-LR with high concentrations impeded the rice root morphogenesis by inhibiting root elongation, crown root formation, and lateral root development from primordia. Treatment with high concentrations of MC-LR stimulated the production of reactive oxygen species (ROS) and inhibited the production of nitric oxide (NO) in rice roots. Exogenous NO treatment reversed the inhibition of rice root growth under MC-LR stress. These results indicated that ROS and NO played important roles in the development of rice roots in responding to MC-LR stress.

Developing a novel computer visualization system to simulate the uranium upward transport mechanism: Uranium pollution in arid landscapes.

Uranium (U) is a naturally occurring, radioactive, toxic trace element that poses severe risks to public and environmental health. Depleted uranium (DU) is widely used in military munitions, including penetrators. Our previous studies showed that in arid landscapes, water-soluble U released from corroded DU penetrators that were buried underground were co-transported upwards with water by evaporation-driven capillary action and eventually precipitated on the ground surface. The first objective of this study was to develop a visualization system to simulate this complex U upward transport mechanism involving cyclic capillary wetting-drying cycles. Multiple visual components such as visual elements, canvases, and animations were created using JavaScript, HTML, and CSS programming languages and coordinated to visualize this biogeochemical process in arid ecosystem landscapes. The second objective was to develop an interactive visualization exercise to allow users to study the effect of the type of capillarity solutions on the speed of the U upward transport. This study is significant in the following aspects:•Contributing a clear and comprehensible visualization of the complex U transport mechanism;•Developing a novel visualization coding framework with more advantages in simulating heavy metal upward transport mechanisms than regular software-based simulations; and•Providing educational uses such as an instructional tool in secondary and college STEM classrooms, an outreach material in promoting student interest in STEM topics and raising public awareness of U pollution, and an educational aid for understanding U mobility in order to develop effective heavy metal pollution control and remediation strategies and policies.

Effect of humic acid derived from leonardite on the redistribution of uranium fractions in soil.

Humic acids (HAs) are complex organic substances with abundant functional groups (e.g., carboxyl, phenolic-OH, etc.). They are commonly distributed in the soil environment and exert a double-edged sword effect in controlling the migration and transformation of uranium. However, the effects of HAs on dynamic processes associated with uranium transformation are still unclear. In this study, we used HAs derived from leonardite (L-HA) and commercial HA (C-HA) as exogenous organic matter and C-HA as the reference. UO2, UO3, and UO2(NO3)2 were used as the sources of U to explore the fractionations of uranium in the soil. We also studied the behavior of the HA. The incubation experiments were designed to investigate the effects of HA on the soil pH, uranium fraction transformation, dynamic behavior of exchangeable, weak acid, and labile uranium. The observations were made for one month. The results showed that soil pH decreased for L-HA but increased for C-HA. Under these conditions, uranium tended to transform into an inactive fraction. The dynamic behavior of exchangeable, weak acid, and labile uranium varied with the sources of HA and uranium. This study highlighted that HA could affect soil pH and the dynamic redistribution of U fractions. The results suggest that the sources of HA and U should be considered when using HA as the remediation material for uranium-contaminated soils.

Silicon enhances abundances of reducing microbes in rhizoplane and decreases arsenite uptake by rice (Oryza sativa L.).

Although silicon (Si) transporters-mediated uptake of arsenic (As) by rice roots is well-documented, how Si influences As behaviors in rhizosphere and rhizoplane before As entry into roots is still unclear. Here we used three rice genotypes to explore the effect of silicic acid on the root uptake of As as impacted by chemical and microbial changes in bulk soil, rhizosphere, rhizoplane and endosphere. The results show that exogenous Si decreased root arsenite [As(III)] absorption, which was attributed to Si-mediated alteration of traits in chemical plaque and microbial films on the rhizoplane. The pH, Eh, As and Fe in the porewater were not influenced by Si. However, Si enhanced the concentrations of As(III) (16-49%) and Fe (15-80%) in the rhizoplane while decreasing As(III) concentrations in the roots (19-39%) and grains (22-29%). The diversities and richness of microbes in soils and plants were not affected by Si. The microbial connections were negatively influenced by Si in bulk and rhizosphere soils, but positively impacted in rhizoplane and endosphere. Both the abundance of reducing microbes, Anaeromyxobacter and Geobacteraceae, and the level of As(III) and Fe in rhizoplane were significantly increased by the addition of Si, thereby restraining As(III) from uptake into roots. This study provides new insights into the microbial mechanisms of Si-mediated As uptake by rice.

A comparative study on adsorption of cadmium and lead by hydrochars and biochars derived from rice husk and Zizania latifolia straw.

In this study, hydrochars and biochars were prepared from rice husk (RH) and Zizania latifolia straw (ZL) at various pyrolysis temperatures as absorbents, for removing toxic ions from single and competitive solutions of cadmium (Cd) and/or lead (Pb). The adsorption efficiencies of Cd and Pb in both hydrochars and biochars were lower in the competitive solution than in the single solution, and the absorbents had a stronger affinity for Pb than for Cd. Compared to hydrochars, biochars showed more favorable Cd and Pb adsorption capacities in the single or competitive solutions, and the ZL biochars had the maximum adsorption capacity among them. The SEM and FTIR analyses suggest that the predominant adsorption mechanisms of biochars and hydrochars are surfaces monolayer adsorption, precipitation, complexation, and coordination with π electrons. However, hydrochars derived from ZL exhibited an optimal additional Pb adsorption capacity in the high-level (5 ~ 10 mg L-1 Cd and Pb) competitive solution. This extra Pb adsorption of hydrochars was likely attributed to the Si-O-Si groups and more bumpy structure. Zizania latifolia straw biochar had a huge potential removal of Cd or/and Pb, and applying hydrochars as absorbents was beneficial to the removal of Cd and Pb in polluted solutions.

A laboratory preparation procedure for studying bioaccumulation of U and its subcellular form in earthworms (Diplocardia spp.).

Uranium (U) is a ubiquitous trace element in soils. With increasing in application of U in nuclear energy and nuclear weapon, a large amount of U was dissipated into the environment including soil and water. Earthworm may be an eco-indicator for U bioaccumulation, transformation and transport across the ecosystem. There have been a variety of methods preformed to assess the bioaccumulation of uranium in small organisms such as earthworms, including uranium speciation, subcellular separation, and total U accumulation. All methods require an initial grinding preparation process that allows for the further fractionation of metals and metalloids in earthworms. The slime like mucus that coats the body of a worm presents a challenge in the disintegration and dissolution of the worm body. In order to analyze U subcellular forms, we developed a reliable and effective procedure to grind the worm body into a uniform fine suspension. We conducted a comparative study of disintegration of worms with 3 grinding techniques (agate mortar, liquid nitrogen freezing then agate mortar, and direct sonication) that would assist U subcellular analyses and bioaccumulation. The essences of this new development was as follows:•A scheme for preparation of earthworm samples for investigation of subcellular U forms in earthworms from U.S. army weapon test range soil with various U forms.•The direct sonication of earthworms was found to be the most proficient process in achieving the best preparation for U subcellular analyses with the high precision.

A laboratory simulation to investigate effects of moistures on U distribution among solid phase components in army range soils.

Uranium is a naturally occurring radioactive trace element found in rocks, soils, and coals. U may contaminate groundwater and soil from nuclear power plant operations, spent fuel reprocessing, high-level waste disposal, ore mining and processing, or manufacturing processes. Yuma Proving Ground in Arizona, USA has been used depleted uranium ballistics for 36 years where U has accumulated in this army testing site. The objective of this study is to develop a laboratory scheme on the effects of soil moisture regiments on the distribution and partitioning of U in army range soil among solid phase components to mimic U biogeochemical processes in the field. Three moisture regiments were saturated paste, field capacity, and wetting-drying cycle which covered major scenarios in fields from the wet summer season to the dry winter season. Uranium in soils with different forms of U (UO2, UO3, uranyl, and schoepite) was fractionated into 8 operationally defined solid components with sequential selective dissolution procedure. The essences of this new development were as following:•A scheme was developed for investigation of U distribution, partitioning and transformation among solid phase components in army weapon test range soils with various U forms under 3 soil moisture regimes.•Soil moisture was one of major environmental factors in controlling biogeochemical processes and fates of U in army weapon test site.

Horizontal and Vertical Transport of Uranium in an Arid Weapon-Tested Ecosystem.

Armor-penetrating projectiles and fragments of depleted uranium (DU) have been deposited in soils at weapon-tested sites. Soil samples from these military facilities were analyzed by inductively coupled plasma-optical emission spectroscopy and X-ray diffraction to determine U concentrations and transport across an arid ecosystem. Under arid conditions, both vertical transport driven by evaporation (upward) and leaching (downward) and horizontal transport of U driven by surface runoff in the summer were observed. Upward vertical transport was simulated and confirmed under laboratory-controlled conditions, to be leading to the surface due to capillary action via evaporation during alternating wetting and drying conditions. In the field, the 92.8% of U from DU penetrators and fragments remained in the top 5 cm of soil and decreased to background concentrations in less than 20 cm. In locations prone to high amounts of water runoff, U concentrations were reduced significantly after 20 m from the source due to high surface runoff. Uranium was also transported throughout the ecosystem via plant uptake and wild animal consumption between trophic levels, but with limited accumulation in edible portions in plants and animals.

Distribution and Fractionation of Uranium in Weapon Tested Range Soils.

Uranium is a chemically toxic and radioactive heavy metal. Depleted uranium (DU) is the byproduct of the uranium enrichment process, with a majority of U as uranium-238, and a lower content of the fissile isotope uranium-235 than natural uranium. Uranium-235 is mainly used in nuclear reactors and in the manufacture of nuclear weapons. Exposure is likely to have an impact on humans or the ecosystem where military operations have used DU. Yuma Proving Ground in Arizona, USA has been using depleted uranium ballistics for 36 years. At a contaminated site in the Proving Grounds, soil samples were collected from the flat, open field and lower elevated trenches that typically collect summer runoff. Spatial distribution and fractionation of uranium in the fields were analyzed with total acid digestion and selective sequential dissolution with eight operationally defined solid-phase fractions. In addition to uranium, other trace elements (As, Ba, Co, Cr, Cu, Hg, Mo, Nb, Pd, Pb, V, Zn, Zr) were also assessed. Results show that the trench area in the testing site had a higher accumulation of total U (12.4%) compared to the open-field soil with 279 mg/kg U. Among the eight solid-phase components in the open-field samples, U demonstrated stronger affinities for the amorphous iron-oxide bound, followed by the carbonate bound, and the residual fractions. However, U in the trench area had a stronger binding to the easily reducible oxide bound fraction, followed by the carbonate-bound and amorphous iron-oxide-bound fractions. Among other trace elements, Nb, As, and Zr exhibited the strongest correlations with U distribution among solid-phase components. This study indicates a significant spatial variation of U distribution in the shooting range site. Fe/Mn oxides and carbonate were the major solid-phase components for binding U in the weapon test site.

Laboratory simulation of uranium metal corrosion in different soil moisture regimes.

A novel laboratory simulation system has been developed for the study of the corrosion of uranium metal in soils. Corrosion and transportation of depleted uranium (DU) as the metal undergoes weathering as a buried material within the soil environment. The corrosion of uranium metal in soil was not well understood due to the gas-liquid-solid phase of the soil. This study presents a novel method to investigate the change of uranium species during the process of process of oxidation of metallic uranium in these environments. Compared with other techniques used for the study of environmental corrosion of metals in soils, this method has the advantage of low secondary uranium pollution, no energy consumption, and ease of operation. The simulation system has been used for the following studies: •Simultaneously simulate the corrosion of uranium metal in different soil moisture regimes•Study the influence of biogeochemical factors on the corrosion of uranium metal•Investigate the change of uranium species during oxidation.