Uranium Accumulation Research Articles

Аккумуляция урана и радия-226 дикорастущими растениями и их фиторемедиационный потенциал

The paper presents the results of studying the accumulation of uranium and radium-226 in ca¬nary grass (Phalaris arun-dinacea L.) and sedge (Carex acuta L.) in order to identify their role in the biogeochemical cycles of radionuclides, as well as their phytoremediation potential for use in remediation of radioactive contaminated ter¬ritories. The content of radionuclides in soils has increased as a result of the activity of radium production enterprise in 1930-1950. Uranium content in the studied soil samples varied within 0.83–1.65 μg / g dry weight. Activity concentrations of radium-226 were in the range 1.82–37.6 Bq / g dry weight. The investigated plants were dug up by the roots. The root part was washed from the soil and separated from the aboveground biomass. In both parts of the plants, concentrations of ura-nium and radium-226 were determined. Based on the obtained data, bioconcentration factors (BCF) of radionuclides in both parts of the plants relative to the soil were calculated. Transfer factor TF (root / aboveground part) was also calculated as the ratio of the radionuclide concentrations in the aboveground part of plants and their roots. It was revealed that the accumulation of uranium and radium-226 in the aboveground part of the plants is low, which does not allow us to classify these species as concentrators of the studied radionuclides. BCFs (aboveground parts / soil) for uranium were ranged in 0.02–0.04. In the case of radium-226, BCFs varied from 0.007 to 0.12. The main part of uranium and radium-226 was accumulated in the root system of plants, which served as a barrier for the transfer of radionuclides to their aboveground parts. TFs (aboveground part / root) was 0.17–0.37 for uranium and 0.08–0.29 for radium. The obtained results indicate that canary grass and sedge contribute to the stabilization of uranium and radium in the studied soil and have the potential to be used as phyto-stabilizators for these contaminants.

Uranium Rhizofiltration by Lactuca sativa, Brassica campestris L., Raphanus sativus L., Oenanthe javanica under Different Hydroponic Conditions

Rhizofiltration experiments were conducted using uranium-contaminated groundwater and lettuce (Lactuca sativa), Chinese cabbage (Brassica campestris L.), radish (Raphanus sativus L.), and buttercup (Oenanthe javanica), which are commonly grown and consumed in South Korea. The results of the rhizofiltration experiments with artificial solutions with different initial uranium concentrations (18, 32, 84, 116, 173, and 263 μg/L) show that the uranium accumulation and bioconcentration factor (BCF) of plant roots increase with increasing uranium concentration in the groundwater. Among the four plants, the uranium concentration in the roots of Raphanus sativus L. is 1215.8 μg/g dry weight, with a maximum BCF value of 2692.7. The BCF value of the artificial solutions with various pH values (pH 3, 5, 7, and 9) is the highest under acidic conditions (pH 3) for all four plants. The uranium BCF values based on different hydroponic conditions range from 170.5 to 11580.3 and the results are comparable with those of other studies using similar methods; the highest BCF value was determined for Brassica campestris L. at pH 3. The BCF values of Raphanus sativus L. after the rhizofiltration experiments with genuine groundwater contaminated with uranium are the highest among the four species; that is, 1684.7 and 1700.1 in Oesam-dong and Bugokdong groundwater samples with uranium concentrations of 83 and 173 μg/L, respectively. The results of the scanning electron microscope/electron dispersive X-ray spectroscope analyses show that uranium in contaminated groundwater is adsorbed as a solid phase on the root surface. These results demonstrate that Raphanus sativus L. has a high tolerance to high concentrations of uranium and low pH conditions and a remarkable potential for uranium accumulation.

Analysis of accumulation and phytotoxicity mechanism of uranium and cadmium in two sweet potato cultivars

The purpose of this study was to reveal the accumulation and phytotoxicity mechanism of sweet potato (Ipomoea batatas L.) roots following exposure to toxic levels of uranium (U) and cadmium (Cd). We selected two accumulation-type sweet potato cultivars as experimental material. The varietal differences in U and Cd accumulation and physiological metabolism were analyzed by a hydroponic experiment. High concentrations of U and Cd inhibited the growth and development of sweet potato and damaged the microstructure of root. The roots were the main accumulating organs of U and Cd in both sweet potato. Root cell walls and vacuoles (soluble components) were the main distribution sites of U and Cd. The chemical forms of U in the two sweet potato varieties were insoluble and oxalate compounds, while Cd mainly combined with pectin and protein. U and Cd changed the normal mineral nutrition metabolism in the roots, and also significantly inhibited the photosynthetic metabolism of sweet potatoes. RNA-seq showed that the cell wall and plant hormone signal transduction pathways responded to either U or Cd toxicity in both varieties. The inorganic ion transporter and organic compound transporter in roots of both sweet potato varieties are sensitive to U and Cd toxicity.

Speciation and partitioning of uranium in waterbodies near Ranger Uranium Mine

Environmental contextAs a part of the rehabilitation of Ranger Uranium Mine, Northern Australia, closure criteria for water concentrations of uranium and other contaminants in local waterbodies have been developed. Increased concentrations of uranium in the water column can result in an accumulation of uranium in the sediment and be hazardous to benthic organisms. A uranium partitioning relationship was derived to predict sediment uranium concentrations from water column concentrations. AbstractAfter almost four decades of mineral processing, the Ranger Uranium Mine (RUM) is set to cease operations in 2021. Beyond this period, rehabilitation of the Ranger Project Area (RPA) will continue into 2026. As part of the rehabilitation of RUM, water quality guideline values (WQGVs) for U and other metals in local waterbodies have been developed to protect aquatic organisms from the effects of metal toxicity. However, benthic organisms will also be exposed to U as it partitions from the water column to the sediments. This important component of the ecosystem may then be exposed to increased U concentrations through ingestion and adsorption of U from sediments. As increased concentrations of U in the water column can result in an accumulation of U in sediment, a U partitioning relationship was derived to enable prediction of sediment U concentrations when water column concentrations were at the WQGV. In this work, the effect of U counter ions and dissolved organic carbon on uranium speciation was modelled and demonstrated a high affinity for the formation of uranyl-organic complexes. Uranium partitioning was studied using experimental U-spiked sediment data as well as water/sediment data collected from multiple sites on and adjacent to the RPA. Using a Freundlich isotherm, and a water-column U concentration of 2.8µg L−1 (representing the WQGV), the acid-extractable U in sediment was calculated to be 48mg kg−1, i.e. lower than the interim sediment quality guideline value (SQGV) of 94mg kg−1. This offers assurance that a WQGV implementation of 2.8µg L−1 U will not lead to a level of U accumulation in sediment that will impact benthic communities.

Monitoring metals in South African harbours between 2008 and 2009, using resident mussels as indicator organisms

More than 65% of the South African coastline is threatened as a result of pollution, a large proportion of which is land derived. To date the majority of published data on metal monitoring has been on limited regions or once-off sampling events. In this paper, we present the first data on metal exposure at sites along the eastern seaboard of South Africa in resident brown mussels (Perna perna) from six harbour sites (Cape Town, Durban, East London, Mossel Bay, Port Elizabeth and Richards Bay Harbours) over a two-year period (2008 and 2009). These data do not represent historical or the current metal exposure levels, but rather an indication of the degree of metal exposure fluctuations over two years at the same site. Metal accumulation of aluminium, arsenic, cadmium, cobalt, chromium, copper, iron, manganese, molybdenum, nickel, lead, selenium, strontium, uranium and zinc was determined by thermo-inductive coupled plasma mass spectrophotometry. The results showed marked fluctuations in metal concentrations between years and identified Cape Town, Mossel Bay and Port Elizabeth Harbours as those sites where mussels had the highest metal levels. Statistically significant variations in metal concentrations were observed between the two sampling periods and the six harbours. Metal concentrations decreased from 2008 to 2009, which was largely attributed to changes in ambient metal concentrations, as a result of variable non-point discharges of metals into the harbours and larger-scale oceanographic changes in upwelling events. The results further emphasise the necessity for annual monitoring of the South African marine environment.

Uranium-thorium mineralization process of the Ukrainian shield suture zones and evolution of the composition of depth fluids in Precambrian

Тhe geochemical properties of uranium and thorium and the geological structure of the ore oc currences of the Golovanevskaya and Ingulo-Inguletskaya suture zones are correlated with changes in the composition of mantle melts and fluids in the Archean-Paleoproterozoic. It is shown that the formation of uranium and thorium deposits on the Ukrainian shield became possible in the Proterozoic, when oxidized and acidic melts prevailing in the Archean mantle were replaced by neutral and alkaline water-chloride-potassium. This led to the accumulation of tho rium (to a greater extent) and uranium (to a less extent) in granite magmas of the layer of partial melting of the crust, where they entered as chloride complexes. The ore occurrences of monazite in microcline granites and pegmatites of the Berdichev and Kirovograd complexes formed in the period 2.1-1.9 billion years ago are associated with these processes. The enrichment of crustal centers of melting with uranium occurred most intensively after 2.0 billion years ago (a maximum of 1.8-1.65 billion years ago), when uranyl-carbonate ions entered the crust as a part of mantle carbonate-fluoride-sodium fluids, they were mixed with melts of existing melting centers. A change in the pH of the medium led to the decomposition of complex compounds and the release of the uranyl group, reduction of uranium to U4+ in the presence of graphite and magnetite, and at geochemical barriers with an acid reaction, and the activity of hydroxyl ions ensured the creation of a brannerite structure.

Atomic uranium modified graphdiyne as catalytic material for hydrogen evolution reaction: An interfacial descriptor led mechanistic study

Catalysis operated on supported single metal atom is considered as one of the vital efforts for chemical and energy conversion. Despite the enormous amount of research on single transition metal (TM) enhanced graphdiyne (GDY) material, its modification with slightly depleted uranium remains unexplored. Herein, we conducted relativistic density functional theory (DFT) calculations for the accumulation of atomic uranium inside size-suitable GDY pore. The stability of graphdiyne-uranium (GDY-U) is corroborated in terms of short U–C bond distances (2.34–2.44 Å), with local depletion of charge and greater U(5f)-C(p) molecular orbital overlap. The magnificent structural and electronic properties of GDY-U system qualify it for the investigation of hydrogen evolution reaction (HER). The HER performance of all exposed sites, including central metal atom and four dissimilarly coordinated acetylenic carbons has been examined and compared with that of pure GDY. As the overall HER interfacial descriptor, free energy change of the intermediate state (ΔGH∗) at the central metal surface of GDY-U was found to be most favorable (0.153 eV) amongst all sites and far superior to those of pure GDY. In addition to the uranium surface, the coordinated carbons also show improved HER activity, indicating the enhancement of the system upon metal insertion. The calculated ΔGH∗ of the GDY-U system here is comparable to some of the recently reported GDY-TM materials, suggesting that atomic uranium could be an exceptional alternative for applied common catalysts.

Critical accumulation of fertilizer-derived uranium in Icelandic grassland Andosol

Long-term phosphorus (P) fertilizer application can lead to an accumulation of uranium (U) in agricultural soil, potentially posing risks on the environment and human health. In this study, we found that such risks could be severe in two long-term grasslands (Andosol) in Iceland (Sámstaðir and Geitasandur) after about 50 years of P fertilization. At Sámstaðir, where P fertilizers were applied at an annual rate of 39.3 kg ha−1 year−1, the soil U concentration increased from 0.65 mg kg−1 in the unfertilized soil to 6.9 mg kg−1 in the fertilized surface soil (0–5 cm). At Geitasandur with P fertilization rate at 78.6 kg ha−1 year−1, the soil U concentration reached 15 mg kg−1. The average annual U accumulation rates were 130 and 310 µg kg−1 year−1, respectively. These values were larger, by up to a factor of ten, than any previously reported rates of fertilizer-derived U accumulation. However, the U concentration in one of the applied P fertilizers was 95 mg U kg−1 fertilizer, similar to the median value of those reported in previous studies, and thus unlikely to be the only factor leading to the high U accumulation rates. By contrast, as our Andosols had low bulk density within a range of 0.2 to 0.5 g cm−3, the annual U inputs to the 0–5 cm soil were 19 g ha−1 year−1 and 32 g ha−1 year−1 at the two sites, respectively, within the range of to-date reported values in agricultural systems. In addition, we found that U was mostly retained in the surface soil rather than mobilizing to deeper soil. This was likely due to the fact that the Andosols were rich in organic matter which promoted U retention. Therefore, the observed high U accumulation rates were a result of the combination of (i) the large amounts of the applied P fertilizers and (ii) the soil properties of the Andosols with low bulk density and elevated organic matter content concentrating U in the upper surface soil. Our study shows that agricultural production systems on Andosols may have already suffered from severe U contamination due to P fertilization. We are therefore calling for future checks and regulations on P fertilizer-related soil U accumulation in these and certain comparable agroecosystems.

Holocene Environments of Anomalous Uranium Concentrations in Sediments of Syrytkul Lake (Southern Urals)

The influence of the Holocene sedimentation conditions on uranium accumulation in sediments in Syrytkul Lake has been studied. The comparison of geochemical, palynological, and diatom data has made it possible to reveal the relation between the U concentration (5–89 ppm) in lacustrine sediments and environmental changes over more than 12 cal ka BP. The Late Glacial lake clay is relatively depleted in U. The maximum enrichment in U has been determined for lake sediments accumulated about 11.6–10.3 cal ka BP under climate warming and humidification. It has been concluded that the climate could have affected U accumulation through the catchment vegetation shifts. The dark coniferous forests that spread out after the climate cooling about 4.2 cal ka BP could have contributed to the U decrease.

Origin and stability of uranium accumulation-layers in an Alpine histosol

Uranium (U) accumulation in organic soils is a common phenomenon that can lead to high U concentration in montane wetlands. The stability of the immobilized U in natural wetlands following redox fluctuations and re-oxidation events, however, is not currently known. In this study, we investigated a saturated histosol that had accumulated up to 6000 ppm of U at 30 cm below ground level (bgl). Uranium in the waters feeding the wetland originates from the weathering of surrounding gneiss rocks, a process releasing trace amounts (<3 ppb) of soluble U into nearby streams. Redox oscillations in the first 20 cm bgl led to the accumulation of U, Ca, S in low permeability layers at 30 and 45 cm bgl. XRF measurements along the core showed that U strongly correlates with sulfur (S) and calcium (Ca), but not iron (Fe). We tested the stability of uranium in the histosol over a nine-month laboratory amendment of a large core of the histosol (∅ 30 cm; length 55 cm) with up to 500 ppm nitrate. Nitrate addition was followed by complete nitrate reduction and re-generation of oxidizing Eh conditions in the top 25 cm of the soil without U release to the soil pore waters above background levels (1–2 ppb). Our results demonstrate that, fast reduction of nitrate, sulfate, and Fe(III) occur in the soil without U release. The remarkable stability of sorbed U in the histosol may result from buffering by sulfide and Sn° and/or strong U(IV)-OM or U(VI)-OM enhanced by organic S moieties or bridging complexation by Ca. That U in the soil was immobile under nitrate addition for up to 9 months can inform remediation strategies based on the use of artificial wetlands to limit U mobility in contaminated sites.

Non-critical uranium accumulation in soils of German and Danish long-term fertilizer experiments

Phosphorus (P) fertilizers vary considerably in contents of uranium (U), thus raising concerns regarding U accumulation in agricultural soils. We examined U concentrations in soil from three long-term field experiments with different P fertilizer applications: Rengen (P fertilizer from basic slag, grassland, Germany), Thyrow (P fertilizer from igneous phosphate rocks, arable land, Germany) and Askov (P fertilizer from igneous phosphate rocks, arable land, Denmark). Accumulation rates were low for Rengen (1.3 µg U kg−1 yr−1) and Thyrow (0.6 µg U kg−1 yr−1) in P-treated plots compared with plots without P fertilization. These accumulation rates were ten times lower than those previously reported (mean 17 µg U kg−1 yr−1). Intriguingly, concentrations of acid-extractable U in the Askov topsoil increased from 1923 to 2016, regardless of whether P was added (5.1 µg kg−1 yr−1) or not (4.7 µg kg−1 yr−1). This suggests that at least part of the accumulated U originated from other sources than P fertilizers. Total U concentrations were significantly larger in the period 1985–2016 than in the period 1938–1976 in Askov soil treated with NPK but not in soils without P fertilization. Hence, long-term P fertilizer application did increase the soil U concentrations at Askov, although at a low level.The low U accumulation rates in soils from these German and Danish long-term P fertilization experiments indicate that with current management, the soil U concentration could remain at non-critical levels even on a centennial scale. This is attributed to the historic use of P fertilizers derived from sources with low U content (igneous phosphate rocks from Finland and Kola Peninsula for Askov and Thyrow, respectively, and basic slag for Rengen). Hence, U accumulation due to long-term P fertilization in agricultural soils may be alleviated by using phosphate rocks from low U sources in P fertilizer production.

Physico-chemical conditions controlling the radionuclides mobilisation in various granitic environments

ABSTRACT Nine samples were chemically characterized and radiometrically analyzed for determination of 234U, 238U, 235U, 230Th, 232Th, 226Ra and 40K by γ-ray spectrometer Hyper Purity Germanium (HPGe detector). 238U activity concentrations reach up to 79.78 Bq Kg-1in the altered granites, 1714.11 and 2223.48 Bq Kg-1in the episyenite and pegmatite. Average 234U activity concentrations in the altered granite is 59.26 Bq Kg-1, between 175.88-543.47 Bq Kg-1and 48.19-1102.88 Bq Kg-1in the episyenite and pegmatite, respectively. 232Th activity concentrations vary between 14.16-1024.8 Bq Kg-1in the episyenite, 11.46-240.27 in the pegmatite and reach up to 201.45 Bq Kg-1in the altered granites. 40K activity concentrations range between 4.42-9.15, 2.76-7.34 and 2.68-9.94 Bq Kg-1in the altered granite, episyenite and pegmatite, respectively. 235U activity concentration ranges between 3.74–2.56, 12.45-78.86 and 0.58-102.34 Bq Kg-1 in the altered granite, episyenite and pegmatite, respectively. The studied altered granite, episyenite and pegmatite samples have relatively higher values than recorded in the international standards with the exception of potassium which has lesser amounts. It is demonstrated that pH changes, oxidation-reduction conditions, mineralogical constituents, in addition to alteration processes in these variable granitic environments were the main factors controlling uranium mobilization according to valid processes. The difference in alteration processes and La/Y ratio clarified the presence of more than one event of uranium accumulation and/or leaching in these rocks as confirmed by the presence of uranium accumulation and uranium vacant occurrences. Also, the isotopic ratios of uranium as 238U/235U,234U/235U, 234U/ 238U, 226Ra/ 238U,226Ra/ 230Th, 210Pb/ 226Ra, 230Th/ 238U, 230Th/ 234U with major, trace and rare earth elements were also affected by physico-chemical conditions changes. The present study shows that the samples of episyenite and pegmatite have been affected by leaching-accumulation events in the period from (1 × 105 to ˃2 × 105years).

Removal of U(VI) from Waters by Ultrafiltration Using Dynamic Membranes Formed From Montmorillonite and the Layered Double Hydroxide Zn–Al–EDTA

The use of sorbing additives in removal of U(VI) species from waters by ultrafiltration (UF) has been investigated in long-term studies. Montmorillonite from the Cherkassy field, a natural clay mineral, and Zn–Al–EDTA, a functionalized synthetic layered double hydroxide intercalated with ethylenediaminetetraacetic acid (EDTA), are used as sorbents. The retention coefficient of U(VI) by a UPM-20 membrane in the presence of montmorillonite and Zn–Al–EDTA is 0.88–0.91 and 0.99–0.999, respectively; with no sorbents added, it is lower (0.85–0.89). In the absence of the sorbents, the volume flow rate of uranium-containing waters is at a level of 82–86 dm3/(m2 h), whereas, with the sorbents added, this parameter falls (for both sorbents) to 40–50 dm3/(m2 h). The contribution of sorbents to the UF filtration of uranium-contaminated waters is identified. Basically, the sorbents act as a dynamic membrane, but their contribution depends mainly on their nature and structure rather than the sorption capacity. The dynamic membrane formed from Zn–Al–EDTA is denser and more robust than the one formed from montmorillonite; therefore, the use of Zn–Al–EDTA in UF purification of uranium-contaminated waters provides considerably better and more stable results. Apart from removing uranium, we investigate the possibility of its concentration. Considerable accumulation of uranium in the relatively small concentrate volume is observed over the entire duration of UF purification process. Thus, the use of sorbing additives considerably improves the indicators of U(VI) removal from water by UF, while enabling us to concentrate U(VI) with the possibility of its further processing.

Uranium reduction and isotopic fractionation in reducing sediments: Insights from reactive transport modeling

Uranium concentrations and isotopic ratios (238U/235U, denoted as δ238U) have been used to provide quantitative information about the degree of oxygenation and de-oxygenation of past oceans. The potential to constrain changes in global redox conditions, in contrast to many other proxies that reflect local conditions, is a particular strength of the uranium isotope approach. Because uranium reduction primarily occurs in sediments underlying anoxic water columns rather than in the anoxic water column itself, the removal of uranium in organic-rich shales is the largest lever on seawater δ238U. Accordingly, accumulation and isotopic fractionation are modulated by local variations in productivity, basin connectivity, sedimentation rate, and bottom-water redox conditions. To isolate the processes at the sediment-water interface that control δ238U and uranium accumulation in reducing sediments, we constructed a reactive transport model that couples biogeochemical reactions to diffusive transport and the burial of solutes and minerals.Using the model framework, we test the sensitivity of authigenic uranium isotopic fractionation and accumulation to oxygenation, permeability, sedimentation rate, organic carbon delivery, and basin restriction. Our results demonstrate that these external forcings produce diagnostic patterns in isotopic fractionation. Specifically, the model predicts that authigenic δ238U is sensitive to productivity because of the associated organic carbon burial rate. Moreover, our results suggest that the isotopic offset does not vary significantly due to changing bottom-water O2 concentrations, but the amount of accumulation does—a result that differs from previous estimates. Water column uranium reduction adds additional complexity to the ultimate δ238U value. The predictive patterns derived from model results can offer insight into local depositional conditions, such as sedimentation patterns. Collectively, these effects—including bottom-water redox conditions and related reducing sediments—alter the isotopic signature of the overlying water column according to the authigenic δ238U value and the diffusive fluxes arising from porewater concentration gradients. More broadly, this work provides important new constraints on the major controls on the δ238U of sediments while also supporting its use as a proxy for global marine redox conditions.

~1760 Ma magnetite-bearing protoliths in the Olympic Dam deposit, South Australia: Implications for ore genesis and regional metallogeny

Spatial associations between banded iron formation and iron-oxide Cu-Au (IOCG) style mineralization are well documented in the Gawler Craton (South Australia), but the possible genetic relationships between these two distinct types of mineralization are hitherto unclear. A texturally conspicuous generation of coarse-grained silician magnetite, intergrown with carbonates and quartz, is observed in drillholes intersecting the ‘outer shell’ of the Olympic Dam IOCG-type deposit. This magnetite is characterised by high U-content (~50 ppm), siliceous chemistry, and unusual zonal textures with respect to Si-Fe-nanoprecipitates. Direct dating of this magnetite by laser ablation inductively coupled plasma mass spectrometry yields reproducible 207Pb/206Pb dates (1761 ± 16 Ma) that are significantly older than the granite hosting the deposit (1593 Ma), or the mineralized breccias constituting the Cu-U-Au-Ag resource (~1592–1589 Ma). The older, Fe-rich crustal material can be correlated with the ~1.76–1.74 Ga (meta)sedimentary Wallaroo Group, host to Fe-rich horizons across the Gawler Craton, including locations ~15 km NW of Olympic Dam. A generation of granitic rocks, which intruded bedrock at ~1.75 Ga are present ~30 km NE of Olympic Dam, and likely exsolved hydrothermal fluids that enriched pre-existing magnetite-bearing protoliths in both U and REE. Such material was physically, and likely chemically, incorporated into the ‘outer shell’ at Olympic Dam some ~150 Ma later, during granite uplift along faults. The coincidence between Fe-rich horizons/BIF and ~1750 Ma granitoids may have provided IOCG systems with an additional source of both Fe and U that predates the ~1.59 Ga craton-scale metallogenic event. The uranium concentrations in some South Australian IOCG systems represent major global anomalies in the element. A combination of the fortuitous geological circumstances outlined here, may help explain the highly anomalous accumulation of uranium found at Olympic Dam.

鹿児島県内の農耕地土壌におけるウランの蓄積実態

鹿児島県内の農耕地土壌におけるウランの蓄積実態

Chemical alteration processes for uranium migration and their significance on uranium isotopic ratio changes

ABSTRACT Gabal Abu Garadi area is covered by metasediments, alkali feldspar granites and stream sediments. Geochemically, silicification, desilicification, sericitisation, fluoritisation and Na-metasomatism are the main alteration features of alkali feldspar granites. The activity concentration of 238U in alkali feldspar granites ranged between 1.7 ± 0.1 Bq g−1 and 3.9 ± 0.3 Bq g−1; between 1.7 ± 0.2 Bq g−1 and 9.4 ± 1.4 Bq g−1 for 234U and between 0.012 ± 0.0002 Bq g−1 and 0.09 ± 0.0001 Bq g−1 for 235U. The activity concentration of 228Th ranges between 1.3 ± 0.1 Bq g−1 and 3.6 ± 0.8 Bq g−1; between 1.5 ± 0.2 Bq g−1 and 2.7 ± 0.7 Bq g−1 for 230Th and between 1.8 ± 0.3 Bq g−1 and 4.1 ± 0.4 Bq g−1 for 232Th. The variability in Chemical Index of Alteration (CIA) with U, Th, 230Th/238U and 230Th/234U for the studied altered granite indicates that U and Th concentrations increased with increasing alteration especially in the silicified and desilicified samples. Changes in U, Th, 230Th/238U and 230Th/234U suggest the role of alteration processes in uranium and thorium mobilisation though thorium is geochemically less mobile or immobile. Thorium mobilisation could be controlled by adsorption in the alteration products of Abu Garadi granites such as clay minerals, manganese and iron oxides. In contrast, 230Th/238U and230Th/234U decreased with increasing CIA values suggesting uranium accumulation. 234U/238U ratios were in equilibrium in most samples; this might suggest the effect of severe chemical weathering or alteration processes that leads to the leachability of the two radionuclides (234U, 238U) with the same ratio probably during kaolinisation processes. In contrast, 230Th/238U and230Th/234U>1 were in disequilibrium, suggesting the changes in the physicochemical conditions accompanying the different alteration processes.

Uranium accumulation and its phytotoxicity symptoms in Pisum sativum L.

Environmental contamination by uranium (U) and other radionuclides is a serious problem worldwide, especially due to, e.g. mining activities. Ultimate accumulation of released U in aquatic systems and soils represent an escalating problem for all living organisms. In order to investigate U uptake and its toxic effects on Pisum sativum L., pea plantlets were hydroponically grown and treated with different concentrations of U. Five days after exposure to 25 and 50μMU, P. sativum roots accumulated 2327.5 and5559.16 mgkg-1 of U, respectively, while in shoots concentrations were 11.16 and 12.16mgkg-1, respectively. Plants exposed to both U concentrations showed reduced biomass of shoots and reduced content of photosynthetic pigments (total chlorophyll and carotenoids) relative to control. As a biomarker of oxidative stress, lipid peroxidation (LPO) levels were determined, while antioxidative response was determined by catalase (CAT) and glutathione reductase (GR) activities as well as cysteine (Cys) and non-protein thiol (NP-SH) concentrations, both in roots and shoots. Both U treatments significantly increased LPO levels in roots and shoots, with the highest level recorded at 50μMU, 50.38% in shoots and 59.9% in roots relative to control. U treatment reduced GR activity in shoots, while CAT activity was increased only in roots upon treatment with 25μMU. In pea roots, cysteine content was significantly increased upon treatment with both U concentrations, for 19.8 and 25.5%, respectively, compared to control plants, while NP-SH content was not affected by the applied U. This study showed significant impact of U on biomass production and biochemical markers of phytotoxicity in P. sativum, indicating presence of oxidative stress and cellular redox imbalance in roots and shoots. Obtained tissue-specific response to U treatment showed higher sensitivity of shoots compared to roots. Much higher accumulation of U in pea roots compared to shoots implies potential role of this species in phytoremediation process.

Uranium-series disequilibrium as a tool for tracing uranium accumulation zone in altered granite rocks

ABSTRACT Abu Garadi area is mainly represented by metasediments, alkali feldspar granites and stream sediments. The granitic mass described different degrees of hydrothermal alterations like albitization, greisenisation, hematitisation, silicification and koalinitisation which are mostly restricted to the faults. Uranium mineralisation in these granitic rocks is mainly controlled by the sheared granite parts. Various radionuclides from uranium decay series such as (238U, 234U, 235U, 230Th, 226Ra) and 40K in the altered granite of Abu Garadi area that located in central Eastern Desert, Egypt are used to localise uranium accumulation sites in this pluton. Uranium and Thorium contents indicate that these altered granites have high thorium and high uranium granites. Th/U ratios vary between 0.81 and 5.79 with an average of 2.64, which suggests the presence of these samples in the transitional oxidation-reduction zone as evidenced by Th/U ratios>2 and reduction zone as suggested by Th/U ratios<2, respectively. 238U/235U, 234U/235U, 234U/238U, 230Th/238U, and 226Ra/230Th activity ratios confirm that most samples of Abu Garadi altered granite lie in the U-accumulations zone. All investigated samples clarify that uranium-series disequilibrium is a technique to trace the recent migration of uranium in these altered granites by the characterisation of the oxidation-reduction boundary.

Enhanced phytoremediation of uranium contaminated soil by artificially constructed plant community plots

In order to develop an artificially constructed plant community plot for the enhanced phytoremediation of uranium contaminated soils, three uranium accumulators including Bamboo-willow (Salix sp.), Paspalum scrobiculatum linn and Macleaya cordata were used to construct four artificial plant community plots, and greenhouse experiments were conducted to investigate the bioaccumulation of uranium by the plants and the organic acid content, enzyme activity, and the change of microbial community structure in their rhizosphere soils. The transfer factor (TF) and the total bioaccumulation amount (TBA) of uranium were used to describe remediation efficiencies in this paper. It was found that their remediation efficiencies were in the order Bamboo-willow (Salix sp.)-Paspalum scrobiculatum linn-Macleaya cordata > Bamboo-willow (Salix sp.)-Macleaya cordata > Paspalum scrobiculatum linn-Macleaya cordata > Bamboo-willow (Salix sp.)-Paspalum scrobiculatum linn. The bioaccumulation amount of uranium by each plant in the Bamboo-willow (Salix sp.)-Paspalum scrobiculatum linn-Macleaya cordata community plot was significantly (P < 0.05) higher than that by its single population, the bioaccumulation amounts of uranium by Bamboo-willow (Salix sp.), Paspalum scrobiculatum linn and Macleaya cordata were 0.29, 0.32 and 2.19 mg/plant, respectively, and they were increased by 31.82%, 77.78% and 146.07%, respectively, and the transfer efficiencies by the plants were increased by 150%, 110% and 52.17%, respectively. The interaction between the plants' roots and the microorganisms in the rhizosphere soil of the Bamboo-willow (Salix sp.)-Paspalum scrobiculatum linn-Macleaya cordata community plot resulted in the high content of organic acids such as oxalic acid in the rhizosphere soil of the plant community plot, which was significantly (P < 0.05) higher than that of its single population. The chelation of the organic acids with uranium led to an increase in the proportion of exchangeable uranium in soil solution. In addition, Burkholderia, which is an iron-producing carrier bacterium and can increase the uptake and accumulation of uranium by plants, and Leptolyngbya, which is a plant growth promoting rhizobacteria and can increase the biomass of plants, emerged in the rhizosphere soil of the plant community plot. These may be the mechanisms by which the phytoremediation of the uranium contaminated soils was enhanced by the plant community plot.