Adsorption-desorption of 241Am(Ⅲ) on montmorillonite colloids and quartz sand: Effects of pH, ionic strength, colloid concentration and grain size

Clay colloids in the subsurface environment have a strong adsorption capacity for radionuclides, and the mobile colloids will carry the nuclides for migration, which would promote the movability of radionuclides in the groundwater environment and pose a threat to the ecosphere. The investigations of the adsorption/desorption behaviors of radionuclides in colloids and porous media are significant for the evaluation of the geological disposal of radioactive wastes. To illustrate the adsorption/desorption behaviors of 241Am(Ⅲ) in Na-montmorillonite colloid and/or quartz sand systems at different pH (5, 7 and 9), ionic strengths (0, 0.1 and 5 mM), colloid concentrations (300 and 900 mg/L), nuclide concentrations (500, 800, 1100 and 1400 Bq/mL) and grain sizes (40 and 60 mesh), a series of batch sorption-desorption experiments were conducted. Combining the analysis of the physical and chemical properties of Na-montmorillonite with the Freundlich model, the influencing mechanism of different controlling factors is discussed. The experimental results show that the adsorption/desorption behaviors of 241Am(Ⅲ) in Na-montmorillonite colloid and/or quartz sand strongly are influenced by the pH value and ionic strength of a solution, the colloid concentration as well as quartz sand grain size. The adsorption and desorption isotherms within all the experimental conditions could be well-fitted by the Freundlich model and the correlation coefficients (R2) are bigger than 0.9. With the increase in pH, the adsorption partition coefficient (Kd) at 241Am(Ⅲ)-Na-montmorillonite colloid two-phase system and 241Am(Ⅲ)-Na-montmorillonite colloid-quartz sand three-phase system presents a trend which increases firstly followed by decreasing, due to the changes in the morphology of Am with pH. The Kd of 241Am(Ⅲ) adsorption on montmorillonite colloid and quartz sand decreases with increasing in ionic strength, which is mainly attributed to the competitive adsorption, surface complexation and the reduction of surface zeta potential. Additionally, the Kd increases with increasing colloid concentrations because of the increase in adsorption sites. When the mean grain diameter changes from 0.45 to 0.3 mm, the adsorption variation trends of 241Am(Ⅲ) remain basically unchanged. The research results obtained in this work are meaningful and helpful in understanding the migration behaviors of radionuclides in the underground environment.

Preparation and related properties of geopolymer solidified uranium tailings bodies with various fibers and fiber content

Uranium tailing ponds are a potential major source of radioactive pollution. Solidification treatment can control the diffusion and migration of radioactive elements in uranium tailings to safeguard the surrounding ecological environment. A literature review and field investigation were conducted in this study prior to fabricating 11 solidified uranium tailing samples with different proportions of PVA fiber, basalt fiber, metakaolin, and fly ash, and the weight percentage of uranium tailings in the solidified body is 61.11%. The pore structure, volume resistivity, compressive strength, radon exhalation rate variations, and U(VI) leaching performance of the samples were analyzed. The pore size of the solidified samples is mainly between 1 and 50 nm, the pore volume is between 2.461 and 5.852 × 10^-2 cm³/g, the volume resistivity is between 1020.00 and 1937.33 Ω·m, and the compressive strength is between 20.61 and 36.91 MPa. The radon exhalation rate is between 0.0397 and 0.0853 Bq·m^-2·s^-1. The cumulative leaching fraction of U(VI) is between 2.095 and 2.869 × 10^-2 cm, and the uranium immobilization rate is between 83.46 and 85.97%. Based on a comprehensive analysis of the physical and mechanical properties, radon exhalation rates, and U(VI) leaching performance of the solidified samples, the basalt fiber is found to outperform PVA fiber overall. The solidification effect is optimal when 0.6% basalt fiber is added.

Kinetics of uranium(VI) lability and solubility in aerobic soils

Uranium may pose a hazard to ecosystems and human health due to its chemotoxic and radiotoxic properties. The long half-life of many U isotopes and their ability to migrate raise concerns over disposal of radioactive wastes. This work examines the long-term U bioavailability in aerobic soils following direct deposition or transport to the surface and addresses two questions: (i) to what extent do soil properties control the kinetics of U speciation changes in soils and (ii) over what experimental timescales must U reaction kinetics be measured to reliably predict long-term of impact in the terrestrial environment? Soil microcosms spiked with soluble uranyl were incubated for 1.7 years. Changes in U^VI fractionation were periodically monitored by soil extractions and isotopic dilution techniques, shedding light on the binding strength of uranyl onto the solid phase. Uranyl sorption was rapid and strongly buffered by soil Fe oxides, but U^VI remained reversibly held and geochemically reactive. The pool of uranyl species able to replenish the soil solution through several equilibrium reactions is substantially larger than might be anticipated from typical chemical extractions and remarkably similar across different soils despite contrasting soil properties. Modelled kinetic parameters indicate that labile U^VI declines very slowly, suggesting that the processes and transformations transferring uranyl to an intractable sink progress at a slow rate regardless of soil characteristics. This is of relevance in the context of radioecological assessments, given that soil solution is the key reservoir for plant uptake.

A case study on the correlation between radon and multiple geophysicochemical properties of soils in G island, Korea, and effects on the bacterial metabolic behaviors

This study was conducted to assess the natural radiation intensity of radon observed from 'G' islands and its effects against Bacillus pumilus, predominantly found throughout the field survey. The physicochemical properties and microbial characteristics were simultaneously investigated and compared. From these studies, it was confirmed that the areal distribution of radon concentration varied from 920 Bq/m³ to 3367 Bq/m³ depending on the soil depth, lithology, or geophysicochemical properties (including pH, moisture content, and grain size) inherently subject to each location. Particularly, the slightly acidic (pH < 6) and low-fertility soil with a higher level of radon concentration exceeding 3000 Bq/m³ had a considerably low level of bacterial density. In contrast, the fertile soil of a relatively middle level of radon radioactivity revealed a much larger bacterial community density, dominated by Bacillus spp., Pseudomonas sp., Paenarthrobacter sp., and Microbacterium sp. Furthermore, the monitored metabolic activity and growth of Bacillus pumilus against the various radon exposure conditions clearly indicated that radon could be considered as the potential ecological risk to natural environmental habitats of microbial soil biota.

Critical insight and indication on particle size effects towards uranium release from uranium mill tailings: Geochemical and mineralogical aspects

Uranium (U) is both chemically toxic and radioactive. Uranium mill tailings (UMTs) are one of the most important sources of U contamination in the environment, wherein the mechanisms that control U release from UMTs with different granularities have not yet been well understood. Herein, the release behaviours and underlying release mechanisms of U from UMTs with five different particle size fractions (<0.45, 0.45-0.9, 0.9-2, 2-6 and 6-10 mm) were studied with a well-defined leaching test (ANS 16.1) combined with geochemical and mineralogical characterizations. The results showed that the most remarkable U release unexpectedly emerged from UMT_{2-6 mm}; in contrast, the smallest particle size UMT_{<0.45 mm} contributed to the least U release. The predominant mechanism of U release from UMT_{2-6 mm} was the oxidative dissolution of U-bearing sulfides, while abundant gypsum present in UMT_{<0.45 mm} inhibited U release. The study highlights the importance of combined geochemical and mineralogical investigation when performing leaching tests of mineral-containing hazardous materials such as UMTs with consideration of particle size effects. The findings also indicate that elevating the content of gypsum and avoiding the oxidation of sulfides can effectively help immobilize and minimize the residual U release from the UMTs.

Quantification of U, Th and specific radionuclides in coal from selected coal fired power plants in South Africa

Most of South Africa’s energy is derived from the combustion of coal in pulverized coal-fired power plants (CFPP). However, when compared with the rest of the world, limited information regarding the main radioactive elements (U and Th) and specific radionuclides of interest (K⁴⁰, Ra²²⁶ and Th²³²) from South African CFPP is available in the public domain. This paper aims to quantify the U, Th and specific radionuclides found in the coal used in selected South African CFPP in comparison to world averages found in literature. The U and Th concentrations were obtained by ICP-MS. The main radionuclides, K⁴⁰, Ra²²⁶ and Th²³⁸, were quantified using gamma spectrometry. The U concentration and Th concentrations for the coal used in all the power plants was above the world average of 1.9 mg/kg and 3.2 mg/kg respectively. The coals with the highest Th content originated from the Mpumalanga power plant, while the U content in the Freestate power plant samples was the highest of the three. The concentrations of the K⁴⁰ were between 88.43±10.75–110.76±8.92 Bq/kg, which are in-line with world averages of 4–785 Bq/kg. Similarly, the Ra²²⁶ and Th²³² values were between 21.69±2.83–52.63±4.04 Bq/kg and 19.91±1.24–22.97±1.75 Bq/kg respectively, which are also in line with the world averages of 1–206 Bq/kg and 1–170 Bq/kg respectively. Radiological hazard indices such as radium equivalent (Ra_eq); external hazard index (H_ex) and internal hazard index (H_in), that were estimated from these average radionuclide concentrations were less than the prescribed values found in literature. This indicated that no significant health risk was posed by the coal being used from these coal fields.

Determination of distribution coefficient of uranium from physical and chemical properties of soil

Uranium is a long lived radioactive element which is naturally present in minute concentrations in igneous, sedimentary and metamorphic rocks. These rocks when subjected to weathering results in the formation of soil which also has traces of uranium. Distribution coefficient (K_d) is a crucial parameter in environmental assessment which is used to predict the interaction and transport of uranium in groundwater. The objective of the study is to estimate the K_d of uranium in soils and to develop a relation between this and the soil parameters. Seven rock samples and twenty three soil samples were collected during this study. The K_d of rock samples of different grain sizes where determined and the soil samples were analysed for electrical conductivity, pH, grain size, bulk density, particle density, porosity, calcium carbonate, cation exchange capacity and K_d. The K_d of the soil increases with increase in soil pH up to 6, after which it gradually decreases. Multiple regression analysis was performed to quantify the effect of various soil parameters on soil K_d and equations were statistically significant. Thus, soil K_d in a region could be predicted using limited soil properties with such statistically significant equations.

Effect of DTPA on europium sorption onto quartz - Batch sorption experiments and surface complexation modeling

Sorption of radionuclides on mineral surfaces retards their migration in the environment of a repository. Presence of organic ligands, however, affects sorption and consequently influences their transport behavior. In this study, we quantify the sorption of Eu(III) onto quartz surfaces as a function of pH in the absence and presence of diethylenetriaminepentaacetic acid (DTPA). Batch sorption experiments show a pH-dependent sorption of Eu(III) on quartz. The presence of DTPA results in slightly higher sorption of Eu(III) at neutral to slightly acidic pH and considerably lower sorption at alkaline conditions. Sorption experiments were simulated using the Diffuse Double Layer Model (DDLM) with single sorption sites (≡QOH) and monodentate surface complexation. The reactions were established based on the aqueous speciation calculation under the experimental conditions, and the thermodynamic constants of surface reactions were obtained and refined by numerical optimization. Results of surface complexation modeling show the formation of a surface species ≡QOHEuDTPA^2-, explaining the elevated sorption of Eu(III) at neutral to slightly acidic pH. In contrast, dissolved EuDTPA^2- complex species are present at alkaline pH, resulting in an enhanced mobility of Eu(III).

Uranium sequestration in sediment at an iron-rich contaminated site at Oak Ridge, Tennessee via. bioreduction followed by reoxidation

This study evaluated uranium sequestration performance in iron-rich (30 g/kg) sediment via bioreduction followed by reoxidation. Field tests (1383 days) at Oak Ridge, Tennessee demonstrated that uranium contents in sediments increased after bioreduced sediments were re-exposed to nitrate and oxygen in contaminated groundwater. Bioreduction of contaminated sediments (1200 mg/kg U) with ethanol in microcosm reduced aqueous U from 0.37 to 0.023 mg/L. Aliquots of the bioreduced sediment were reoxidized with O₂, H₂O₂, and NaNO₃, respectively, over 285 days, resulting in aqueous U of 0.024, 1.58 and 14.4 mg/L at pH 6.30, 6.63 and 7.62, respectively. The source- and the three reoxidized sediments showed different desorption and adsorption behaviors of U, but all fit a Freundlich model. The adsorption capacities increased sharply at pH 4.5 to 5.5, plateaued at pH 5.5 to 7.0, then decreased sharply as pH increased from 7.0 to 8.0. The O₂-reoxidized sediment retained a lower desorption efficiency at pH over 6.0. The NO₃^--reoxidized sediment exhibited higher adsorption capacity at pH 5.5 to 6.0. The pH-dependent adsorption onto Fe(III) oxides and formation of U coated particles and precipitates resulted in U sequestration, and bioreduction followed by reoxidation can enhance the U sequestration in sediment.

Large-scale experimental investigations of specified granular fill materials for radon mitigation by active and passive soil depressurisations

A series of large-scale experimental tests were performed to examine the flow behaviour of the T1 Struc and T2 Perm specified granular fill materials with active and passive depressurisations. Granular materials were compacted and tested at various compacted thicknesses. Compaction works were performed using a field compactor and compaction degrees of the materials were found to be higher than those induced by a standardised small-scale compactor. The air permeability (k_ah) values of the materials were obtained with active depressurisation. It was found that the overall trend of k_ah tended to decrease with the increase in the compacted thickness of the materials and were found to be compatible with those determined by the small-scale test apparatus. Results from passive depressurisation tests indicated that the rotating cowls performed the best, followed by a static open pipe and a pipe with a cap.

Experimental study of the effect of water level and wind speed on radon exhalation of uranium tailings from heap leaching uranium mines

Water level and wind speed have important influences on radon release in particle-packing emanation media. Based on radon migration theory in porous media under three water level conditions, an experimental setup was designed to measure the surface radon exhalation rate of uranium tailings from heap leaching uranium mine at different water levels and wind speeds. When the water level was at 0.3 m (overlying depth 0.05 m), radon transfer velocities at the gas-liquid interface were also measured at different wind speeds. Results show that when the water level was equal to or lower than the surface of the sample, the radon exhalation rate increased with increasing wind speed and decreased with increasing water level. When the water level was higher than the surface of the sample, radon exhalation rate of the water surface increased with increasing surface wind speed. The wind speed, however, was less influential on the radon exhalation rate as the depth of the overlying water increased, with a dramatic decrease in radon release. That said, at different wind speeds, radon transfer velocities at the gas-liquid interface were consistent with literature. On the other hand, changes in wind speed had significant influences on the radon transfer velocity at the gas-liquid interface, with the effect less pronounced at higher wind speeds.

Assessment of radionuclide transfer factors and transfer coefficients near phosphate industrial areas of South Tunisia

The activity concentrations of naturally occurring and anthropogenic radionuclides in agriculture soils as well as in several food products at four locations within the phosphate area of South Tunisia were investigated. Soil-to-plant transfer factors as well as feed-to-animal products transfer coefficients were determined for the first time for the region. Activity concentrations of ⁴⁰K, ²¹⁰Pb, ²²⁶Ra, ²²⁸Ra and ¹³⁷Cs in soils of agriculture fields were lower than worldwide average values. The soil-to-plant transfer factors (TFs) for ⁴⁰K in leafy vegetables were higher than those in fruit vegetables. Soil-to-grass transfer factor (F_v) values were in the following order: ⁴⁰K > ²¹⁰Pb > ²²⁶Ra. The grass-to-milk transfer coefficient (F_m) values for ⁴⁰K and ²¹⁰Pb ranged between 2 × 10^-3 and 4 × 10^-3(day L^-1). The concentration ratios for the animal products (CR_milk-feed, CR_meat-feed and CR_egg-feed) varied in the ranges of 2 × 10^-2-4 × 10^-2 L kg^-1, 1 × 10^-2-2 × 10^-1 (L kg^-1) and 5 × 10^-2-1 (L kg^-1)for ⁴⁰K, ²¹⁰Pb and ²²⁶Ra, respectively. Transfer parameters determined in the present study were compared with those reported in International Atomic Energy Agency reports and other published values. The absorbed gamma dose rate in air and the external hazard index associated with these natural radionuclides were computed to assess the radiation hazard of radioactivity in this region, and the results indicated that these areas are within set safety limits.

Sorption of U(VI) onto natural soils and different mineral compositions: The batch method and spectroscopy analysis

This research studied the sorption behavior of uranium(VI) onto two different kinds of soils: surface soil and undersurface soil that taken from the depth of 30 m undersurface. The soil samples were collected from a low and medium-level radioactive waste disposal site in the southwest of China. The effects of pH, solid-liquid ratio and contact time on the adsorption behavior were studied by batch adsorption method. The experiment results show that the mineral composition of soil and the speciation of U in natural groundwater are two main influencing factors. Muscovite and clinochlore, two of the main minerals of soil samples, dominate the sorption behavior of uranium onto natural soils at weak acidic and near neutral pH range. Under neutral and weak alkaline conditions, the thermodynamic calculation results show that Ca²⁺ and CO₃^2- have significant influence on the species of uranium in aqueous solution. The U sorption reduced sharply due to the formation of the CaUO₂(CO₃)₃^2- (aq) complex. This work provides a better insight of the sorption behavior of uranium onto natural soils, and gives an in-depth understanding about the influence of aqueous and surface speciation.

Effects of zeolite and vermiculite addition on exchangeable radiocaesium in soil with accelerated ageing

Soil amendments with zeolite and vermiculite were expected to prevent radiocaesium (¹³⁷Cs) dissolution and uptake from the soil by plants. In this study, we investigated how zeolite and vermiculite added to soil influence the radiocaesium fixation with ageing. Zeolite and vermiculite were mixed with soil (1 wt%) before or after the addition of carrier-free caesium-137 (¹³⁷Cs) to soils with different radiocaesium interception potential (RIP), which is related to the capacity of the soil to fix trace radiocaesium. Then, the soils were exposed for repeated wet and dry cycles to accelerate ¹³⁷Cs immobilization, and its extractability by 1 mol L^-1 ammonium acetate was determined before and after 30 dry and wet cycles. Before accelerated ageing (i.e before dry and wet cycles), when ¹³⁷Cs was adsorbed on the soil before the addition of the amendments, the addition of zeolite and vermiculite caused a decrease in the amount of exchangeable ¹³⁷Cs in low-RIP soils but an increase in the amount of exchangeable ¹³⁷Cs in high-RIP soils. The amount of exchangeable ¹³⁷Cs was significantly decreased after accelerated ageing regardless of the application of amendments. However, radiocaesium fixation with accelerated ageing was partly inhibited by the addition of zeolite, regardless of the RIP values. The ¹³⁷Cs adsorbed on highly selective sites in zeolite is exchangeable by 1 mol L^-1 ammonium acetate. Thus, because a portion of the ¹³⁷Cs is selectively adsorbed on highly selective sites in zeolite, the redistribution of ¹³⁷Cs to frayed edge site followed by ageing-induced fixation was likely limited. However, when ¹³⁷Cs was adsorbed on the soil before the addition of the amendments, the addition of zeolite and vermiculite had little influence on the amount of exchangeable ¹³⁷Cs. In conclusion, the use of realistic doses of zeolite and vermiculite as agricultural amendments is not effective in enhancing the immobilization of radiocaesium in soil.

Enhanced radiocesium uptake by rice with fermented bark and ammonium salt amendments

There are ongoing problems with radioactive cesium (Cs) contaminated agricultural soil after the Fukushima Daiichi Nuclear Power Plant accident. In this study, the behavior of Cs uptake by rice plants grown in soil sprayed with fermented bark amendment (FBA) was investigated. In rice cultivation by pot, the application of FBA resulted in the acceleration of Cs uptake by rice plants. This might be related to the reduction of oxidation reduction potential in the soil caused by spraying FBA. Also, when 0.1 wt% ammonium sulfate was used as a fertilizer in Cs-contaminated soil, the bioconcentration factor (BCF) of Cs taken up into rice straw was 1.4-times higher than that in soil sprayed with FBA. The Cs uptake effect was further enhanced by the combination of 1 wt% FBA with 0.1 wt% ammonium sulfate to soil where the BCF was enhanced to 1.8-times higher than that in soil sprayed with FBA alone. The enhanced uptake into rice was likely because of accelerated uptake of leachable forms of Cs based on the cation-exchange to NH₄⁺ in soil; this was confirmed by the Cs fractionation by sequential extraction procedures. The phytoremediation capability of rice is considered to be lower than that of commonly used phytoremediation plants, but supplementation with FBA and ammonium salt could enhance Cs accumulation even for low-efficiency phytoremediation plants.

Behavior of 36Cl in agricultural soil-plant systems: A review of transfer processes and modelling approaches

This article aims to review up-to-date knowledge and data acquired on ³⁶Cl transfers to terrestrial soil-plant systems, evaluate the existing modelling approaches and identify priorities for future model improvements. This update has revealed the existence of fairly recent studies, whose results could be used for improving the modelling approaches which have been developed over the last decade. The priority areas include the consideration of the dry deposition process and the transfer of both gaseous and aerosol ³⁶Cl to plants. The consideration of secondary processes such as the synthesis/mineralization of organochlorines and plant biomass litterfall is not recognized as a priority issue when assessing the impact of gaseous discharges. It was also identified that additional experimental studies had to be conducted to improve the understanding of the processes governing stable Cl and ³⁶Cl dynamics in other terrestrial ecosystems (field crops, vegetables, grass) than forest environments on which most of the reported knowledge and data are reviewed.

Studies of particle size distribution of Non-Exchangeable Organically Bound Tritium activities in the soil around Qinshan Nuclear Power Plant

The NE-OBT (Non-Exchangeable Organically Bound Tritium) in the soil plays a significant role in tritium migration and transformation. In order to further understand the NE-OBT activity in the soil, the particle size, vertical profile and spatial distribution of the NE-OBT activities in the soil were determined around the Qinshan Nuclear Power Plant (NPP) in China. The experimental results indicated that the NE-OBT preferred to concentrate in the soil particle sizes of 53-250 μm within the soil depth of 5 cm-25 cm. The NE-OBT activity showed significantly vertical variations, however, its largest activity did not appear at the surface soil (0-5 cm). Meanwhile, the NE-OBT had a significant spatial distribution, its activity decreased with the increasing distance from the NPP, especially from the HWRs. In this study, the NE-OBT activities have no significant relationship to the organic matter content in the soil. But the vertical profile distribution of the NE-OBT activity has a strong correlation with the NE-OBT/HTO ratio in the soil, which reflect the capability of living organisms converting HTO into NE-OBT. According to these analyses, we supposed that the NE-OBT in the soil may be derived from the microbial transformation of HTO.

Uranium adsorption and subsequent re-oxidation under aerobic conditions by Leifsonia sp. - Coated biochar as green trapping agent

It has generally been assumed that the immobilization of U(VI) via polyphosphate accumulating microorganisms may present a sink for uranium, but the potential mechanisms of the process and the stability of precipitated uranium under aerobic conditions remain elusive. This study seeks to explore the mechanism, capacity, and stability of uranium precipitation under aerobic conditions by a purified indigenous bacteria isolated from acidic tailings (pH 6.5) in China. The results show that over the treatment ranges investigated, maximum removal of U(VI) from aqueous solution was 99.82% when the initial concentration of U(VI) was 42 μM, pH was 3.5, and the temperature was with 30 °C much higher than that of other reported microorganisms. The adsorption mechanism was elucidated via the use of SEM-EDS, XPS and FTIR. SEM-EDS showed two peaks of uranium on the surface. A plausible explanation for this, supported by FTIR, is that uranium precipitated on the biosorbent surfaces. XPS measurements indicated that the uranium product is most likely a mixture of 13% U(VI) and 87% U(IV). Notably, the reoxidation experiment found that the uranium precipitates were stable in the presence of Ca²⁺ and Mg²⁺, however, U(IV) is oxidized to U(VI) in the presence of NO₃^- and Na⁺ ions, resulting in rapid dissolution. It implies that the synthesized Leifsonia sp. coated biochar could be utilized as a green and effective biosorbent. However, it may not a good choice for in-situ remediation due to the subsequent re-oxidation under aerobic conditions. These observations can be of some guiding significance to the application of the bioremediation technology in surface environments.

Assessment of natural radionuclides mobility in a phosphogypsum disposal area

The phosphogypsum (PG) stacks located at Huelva (SW Spain) store about 100 Mt of PG, and covers a surface of 1000 ha. It has been very well established in many studies that this waste contains significant U-series radionuclides concentrations, with average activity concentrations rounding the 650, 600, 400 and 100 Bq kg^-1 for ²²⁶Ra, ²¹⁰Po, ²³⁰Th and ²³⁸U, respectively. However, the radionuclide transfer from this repository into the environment by the aquatic pathway will depend on the mobility of each radionuclide. The mobility of the natural radionuclides (U-isotopes, Th-isotopes, 226Ra, and 210Po) contained in the PG piles were evaluated by using the optimized BCR sequential extraction procedure (BCR "Community Bureau of Reference"). The radionuclides were measured in the liquid fractions by alpha-particle spectrometry with semiconductor PIPS detectors. In addition, to validate the obtained results, waters from different locations of the PG piles (pore-water, perimeter channel and edge outflow leachates) were taken and the alpha emitter radionuclides determined. Uranium presents the highest mobility, being its total mobile fraction in the PG around 70%, while 210Po and 226Ra present an intermediate mobility of (around 50% and 30%, respectively). And finally, the Th-isotopes have very low mobility (mobile fraction < 5%), being fixed to the residual fraction. It is noteworthy that this behaviour has been also found in the water samples taken from the stacks, demonstrating that this sequential leaching operational methodology is a useful tool for assessing the release capacity of radionuclides by inorganic wastes.

Radiocesium interaction with clay minerals: Theory and simulation advances Post-Fukushima

Insights at the microscopic level of the process of radiocesium adsorption and interaction with clay mineral particles have improved substantially over the past several years, triggered by pressing social issues such as management of huge amounts of waste soil accumulated after the Fukushima Dai-ichi nuclear power plant accident. In particular, computer-based molecular modeling supported by advanced hardware and algorithms has proven to be a powerful approach. Its application can now generally encompass the full complexity of clay particle adsorption sites from basal surfaces to interlayers with inserted water molecules, to edges including fresh and weathered frayed ones. On the other hand, its methodological schemes are now varied from traditional force-field molecular dynamics on large-scale realizations composed of many thousands of atoms including water molecules to first-principles methods on smaller models in rather exacting fashion. In this article, we overview new understanding enabled by simulations across methodological variations, focusing on recent insights that connect with experimental observations, namely: 1) the energy scale for cesium adsorption on the basal surface, 2) progress in understanding the structure of clay edges, which is difficult to probe experimentally, 3) cesium adsorption properties at hydrated interlayer sites, 4) the importance of the size relationship between the ionic radius of cesium and the interlayer distance at frayed edge sites, 5) the migration of cesium into deep interlayer sites, and 6) the effects of nuclear decay of radiocesium. Key experimental observations that motivate these simulation advances are also summarized. Furthermore, some directions toward future solutions of waste soil management are discussed based on the obtained microscopic insights.

Distribution of natural radionuclides and radon concentration in the riverine environs of Cauvery, South India

Systematic studies were carried out to understand the distribution of natural radionuclides in sediments and radon in water in the riverine environs of Cauvery, one of the major rivers of South India. The activity of radionuclides in the sediment was measured by gamma ray spectrometry. The radon emanation from the sediment was measured by the sealed 'can technique' and the radon in the water was measured using the RAD-7 instrument. The mean values of ⁴⁰ K, ²²⁶Ra, and ²³²Th in the sediment samples were found to be 297.3 ± 4.16 Bq kg^-1, 75.1 ± 2.64 Bq kg^-1, and 85.5 ± 2.62 Bq kg^-1, respectively. The mean activity of radon, radon exhalation rate, and radium content were found to be 135.68 Bq m^-3, 327.1 mBq m^-1 h^-1, and 133.03 mBq kg^-1, respectively. The radon in the water ranged from 0.19 kBq m^-3 to 1.40 kBq m^-3. The hyper pure germanium gamma spectroscopy measured via ²²⁶Ra activity and the radon activity measured by the passive can technique showed good correlation. The mean value of radon in the water was within the internationally recommended level. The sediment was considered safe for the purpose of construction, except for some extreme values, and the water was deemed safe for drinking.

Spatial distribution and lifetime cancer risk due to naturally occurring radionuclides in soils around tar-sand deposit area of Ogun State, southwest Nigeria

Anthropogenically enhanced naturally occurring radionuclides ²³⁸U, ²³²Th and ⁴⁰K present in the tar-sand soil samples were measured by gamma ray spectrometer using a highly shielded NaI (TI) detector with the aim of evaluating the environmental radiological hazards. Mineralogical analysis and characterization was carried out using Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) techniques. The results obtained showed that the average activity concentrations of ²³⁸U, ²³²Th and ⁴⁰K ranges from BDL↔76.00 ± 12.00, BDL↔204.48 ± 13.02 and BDL↔755.6 ± 40.15 Bqkg^-1 respectively. Eleven other radiological and hazard parameters were estimated to know the complete hazardous nature of the samples. The values obtained for radionuclides and all its associated radiological and health hazard parameters were all higher than the world's average set by UNSCEAR. Five different minerals were identified and characterized as major and minor minerals. The mean radionuclides activity concentrations, radium equivalent and dose rate of measured radionuclides were compared with other literature values. RESRAD computer code was used to calculate the probability of excess lifetime cancer incurred by dwellers of the tar-sand deposit site, the level of which was determined to be 2.3 × 10^-3(2310000). Spatial distribution of natural radionuclides in the study area was also investigated for radioactivity disequilibrium. Multivariate statistics were applied to establish the effect of mineralogy on radionuclides activity. Therefore, the tar-sand soil samples are considered to pose serious radiological hazard and cancer risk to human through the multiple routes of exposure and significant soil remediation action need to be taken for future use of the soils.

Uptake and speciation of uranium in synthetic gypsum (CaSO4•2H2O): Applications to radioactive mine tailings

Phosphogypsum formed from the production of phosphoric acid represents by far the biggest accumulation of gypsum-rich wastes in the world and commonly contains elevated radionuclides, including uranium, as well as other heavy metals and metalloids. Therefore, billions-of-tons of phosphogypsum stockpiled worldwide not only possess serious environmental problems but also represent a potential uranium resource. Gypsum is also a major solid constituent in many other types of radioactive mine tailings, which stems from the common usage of sulfuric acid in extraction processes. Therefore, management and remediation of radioactive mine tailings as well as future beneficiation of uranium from phosphogysum all require detailed knowledge about the nature and behavior of uranium in gypsum. However, little is known about the uptake mechanism or speciation of uranium in gypsum. In this study, synthesis experiments suggest an apparent pH control on the uptake of uranium in gypsum at ambient conditions: increase in U from 16 μg/g at pH = 6.5 to 339 μg/g at pH = 9.5. Uranium L₃-edge synchrotron X-ray absorption spectroscopic analyses of synthetic gypsum show that uranyl (UO₂)²⁺ at the Ca site is the dominant species. The EXAFS fitting results also indicate that uranyl in synthetic gypsum occurs most likely as carbonate complexes and yields an average U-O distance ∼0.25 Å shorter than the average Ca-O distance, signifying a marked local structural distortion. Applications to phosphogypsum from the New Wales phosphoric acid plant (Florida, USA) and uranium mine tailings from the Key Lake mill (Saskatchewan, Canada) show that gypsum is an important carrier of uranium over a wide range of pH and controls the fate of this radionuclide in mine tailings. Also, development of new technologies for recovering U from phosphogypsum in the future must consider lattice-bound uranyl in gypsum.

Interaction of niobium with iron-oxide colloids and the role of humic acid

In this work, we report the sorption of Nb on iron oxides and the effect of humic acid. Iron oxides viz. goethite, hematite and magnetite were chemically synthesised and characterised by X-ray diffraction, particle size, surface area and zeta potential measurement. The sorption of Nb on all the three iron oxides was low (∼40%) at pH 1, increased to ∼ 90% at pH 8 and decreased marginally above pH 8. The effect of humic acid on the sorption was very small. Thermodynamic parameters viz. activation energy, enthalpy, entropy, free energy and sticking probability were calculated to understand the mechanism of the sorption process. Although the enthalpy was positive, the free energy change was negative i.e. the sorption was entropy driven process. The sorption followed pseudo-second-order kinetics and sticking probability model indicated that the process was chemisorption. This study is important to understand the probable migration of ⁹⁴Nb (half life 20300 y) during underground storage of radioactive waste.

Forage grasses with lower uptake of caesium and strontium could provide 'safer' crops for radiologically contaminated areas

Substitution of a species or cultivar with higher uptake of an element by one with lower uptake has been proposed as a remediation strategy following accidental releases of radioactivity. However, despite the importance of pasture systems for radiological dose, species/cultivar substitution has not been thoroughly investigated for forage grasses. 397 cultivars from four forage grass species; hybrid ryegrass (Lolium perenne L. x Lolium multiflorum Lam.), perennial ryegrass (Lolium perenne L.), Italian ryegrass (Lolium multiflorum Lam.) and tall fescue (Festuca arundinacea Shreb.); were sampled from 19 field-based breeding experiments in Aberystwyth and Edinburgh (UK) in spring 2013 and analysed for caesium (Cs) and strontium (Sr) concentrations. In order to calculate concentration ratios (CRs; the concentration of an element in a plant in relation to the concentration in the soil), soils from the experiments were also analysed to calculate extractable concentrations of Cs and Sr. To test if cultivars have consistently low Cs and Sr concentration ratios, 17 hybrid ryegrass cultivars were sampled from both sites again in summer 2013 and spring and summer 2014. Tall fescue cultivars had lower Cs and Sr CRs than the other species. Three of the selected 17 hybrid ryegrass cultivars had consistently low Cs CRs, two had consistently low Sr CRs and one had consistently low Cs and Sr CRs. Cultivar substitution could reduce Cs CRs by up to 14-fold and Sr CRs by 4-fold in hybrid ryegrass. The identification of species and cultivars with consistently low CRs suggests that species or cultivar substitution could be an effective remediation strategy for contaminated areas.

No effect of digestate amendment on Cs-137 and Sr-90 translocation in lysimeter experiments

The soil-plant transfer of Cs-137 and Sr-90 in different crops was determined with respect to the present-day amendment practice of using digestate from biogas fermenters. The studies were performed using large lysimeters filled with undisturbed luvisol monoliths. In contrast to the conservative tracer, Br^-, neither of the studied radionuclides showed a significant vertical translocation nor effect of the applied digestate amendment compared to a non-amended control was found. Furthermore, no significant plant uptake was measured for both nuclides in wheat or oat as indicated by the low transfer factors between soil-shoot for Cs-137 (TF 0.001-0.010) and for Sr-90 (0.10-0.51). The transfer into nutritionally relevant plant parts was even lower with transfer factors for soil-grain for Cs-137 (TF 0.000-0.001) and for Sr-90 (0.01-0.06). Hence, the amendment with biogas digestate is unfortunately not an option to further reduce plant uptake of these radionuclides in agricultural crops, but it does not increase plant uptake either.

Pb-210 and Po-210 atmospheric releases via fly ash from oil shale-fired power plants

During high temperature processes in the furnace volatile and semi-volatile elements and radionuclides are partially emitted to the environment, depending on their chemical form in the original fuel, the technological set-up of the combustion system, and the prevailing combustion conditions. Two of the world's largest oil shale-fired power plants (PPs) have been operational in Estonia from the 1960s, during which time creation of significant environmental emissions and waste containing naturally occurring radionuclides has occurred. Pb-210 and ²¹⁰Po are considered natural radionuclides with the highest emission rates from PPs and possess elevated potential radiation exposure risks to humans and the environment. These radionuclides have the highest activity concentration values in fine ash fractions, especially in fractions remaining below 2.5 μm. To determine the activity concentrations of ²¹⁰Pb and ²¹⁰Po in the PPs' outlet, sampling was conducted from boilers operating on pulverized fuel (PF) technology with novel integrated desulphurization (NID) system and bag filters as well as with electrostatic precipitators (ESPs). The ²¹⁰Pb and ²¹⁰Po activity concentrations remained around 300 Bq kg^-1 for the NID system compared to 60-80 Bq kg^-1 in the ESP system. The dominant ash fraction in both systems was PM2.5, constituting over 50% of the fly ash mass collected from the outlet. The authors estimate that the total atmospherically emitted activity for the modernized PPs remains dominantly below 1% of the activity that is inserted via fuel. The implementation of higher efficiency purifications systems has significantly reduced the negative effect of these PPs. Based on annually emitted fly ash and boilers' working hours, the ²¹⁰Pb and ²¹⁰Po activity released relative to energy production were up to 68.3 kBq GWh_el^-1 for ²¹⁰Pb and 64.6 kBq GWh_el^-1 for ²¹⁰Po. These values are 1 to 2 orders of magnitude lower compared to the situation in the 1980s. These findings represent the first publicly available quantitative results estimating the ²¹⁰Po emissions from large oil shale-fired PPs.

Stabilisation/solidification of 137Cs-contaminated soils using novel high-density grouts: γ-ray shielding properties, contaminant immobilisation and a γRS index-based approach for in situ applicability

In this work, γ-ray shielding and Cs immobilisation performances of high-density magnetite (MG) and iron powder (IP) in Portland cement (PC) based-S/S treatment were investigated. Experimental results were elaborated using a γ-radiation shielding (γRS) index-based approach for assessing the effectiveness of in situ S/S of ¹³⁷Cs-contaminated soils. Main results reveal that the replacement of PC by MG or IP (up to 50%) leads to a marked increase (up to about 4-fold) in the γ-ray shielding performance, whereas a further material addition decreases the S/S shielding performance. The highest γRS index of ∼26% (662 keV) was found in the case of IP addition (33.3%). The use of MG-mixes allows reaching slightly slower γRS index jointly with the highest Cs-immobilisation of 97.8%. In this case, calculation shows a maximum ¹³⁷Cs-contamination level successfully treatable by in situ S/S up to ∼2.9 or ∼14.5 kBq kg^-1 for the realistic or low probability scenario, respectively, highlighting the possibility to remediate a very wide range of real contamination. Findings show MG - PC S/S as the best choice and could provide a basis for decision-making of S/S remediation of ¹³⁷Cs-contaminated sites.

Chemical fractionation of radium-226 in NORM contaminated soil from oilfields

Contamination of soil with ²²⁶Ra is a common problem in the oilfields, leading to costly remediation and disposal programmes. The present study focuses on the chemical fractionation and mobility of ²²⁶Ra in contaminated soils collected from an oilfield using a three-step sequential extraction procedure (BCR). The total activity concentrations of ²²⁶Ra in contaminated soils were measured and found to be in the range from 1030 ± 90 to 7780 ± 530 Bq kg^-1, with a mean activity concentration of 2840 ± 1840 Bq kg^-1. The correlation between the total concentration of ²²⁶Ra and soil properties, mainly pH, LOI, C_org, clay and Ca, was investigated using the principal component analysis method (PCA). The chemical fractionation of ²²⁶Ra was studied using the sequential extraction method (BCR). The highest fraction of ²²⁶Ra (27-65%) was found to be in the acid-reducible fraction, which suggests that ²²⁶Ra is mainly bound to FeMn oxides. The BCR method showed that high percentages of ²²⁶Ra were found to be in mobile soil phases (between 45 and 99%). Consequently, groundwater contamination could occur due to the remobilization of ²²⁶Ra from soils under normal environmental conditions. However, the obtained results could be useful to reduce the volume of NORM wastes generated from the oilfields and decision-making process for final treatment and disposal of NORM-contaminated soil.

Fractal Theory and Field Cover Experiments: Implications for the Fractal Characteristics and Radon Diffusion Behavior of Soils and Rocks

Radon diffusion and transport through different media is a complex process affected by many factors. In this study, the fractal theories and field covering experiments were used to study the fractal characteristics of particle size distribution (PSD) of six kinds of geotechnical materials (e.g., waste rock, sand, laterite, kaolin, mixture of sand and laterite, and mixture of waste rock and laterite) and their effects on radon diffusion. In addition, the radon diffusion coefficient and diffusion length were calculated. Moreover, new formulas for estimating diffusion coefficient and diffusion length functional of fractal dimension d of PSD were proposed. These results demonstrate the following points: (1) the fractal dimension d of the PSD can be used to characterize the property of soils and rocks in the studies of radon diffusion behavior; (2) the diffusion coefficient and diffusion length decrease with increasing fractal dimension of PSD; and (3) the effectiveness of final covers in reducing radon exhalation of uranium tailings impoundments can be evaluated on the basis of the fractal dimension of PSD of materials.

Open charcoal chamber method for mass measurements of radon exhalation rate from soil surface

Radon exhalation rate from the soil surface can serve as an important criterion in the evaluation of radon hazard of the land. Recently published international standard ISO 11665-7 (2012) is based on the accumulation of radon gas in a closed container. At the same time since 1998 in Russia, as a part of engineering and environmental studies for the construction, radon flux measurements are made using an open charcoal chamber for a sampling duration of 3-5 h. This method has a well-defined metrological justification and was tested in both favorable and unfavorable conditions. The article describes the characteristics of the method, as well as the means of sampling and measurement of the activity of radon absorbed. The results of the metrological study suggest that regardless of the sampling conditions (weather, the mechanism and rate of radon transport in the soil, soil properties and conditions), uncertainty of method does not exceed 20%, while the combined standard uncertainty of radon exhalation rate measured from the soil surface does not exceed 30%. The results of the daily measurements of radon exhalation rate from the soil surface at the experimental site during one year are reported.

Plutonium Content in Soil Fractions of Various Sizes and Estimation of the Risks of the Chernobil Nuclear Power Plant Zone

Based on the data from the literature the authors analyzed the methods used for the estimation of the risks of plutonium-contaminated areas. The analysis was based on the published data on the measured plutonium concentrations in the air and soil. To calculate plutonium concentrations in the near-surface air layer above the contaminated area a modification of the method of the load estimation from the mass was proposed: instead of the average plutonium specific activity in soil the authors suggested the use of the soil coefficient which consists of the sum of specific activities of every respirable fraction (size 0.05 to 10 μm) multiplied by the percentage of its activity in the total activity of the soil sample. Verification of the proposed method on independent data showed that the calculated values approached the measured ones.

Effectiveness of Protective Activities for Rehabilitation of the Forage Lands in Russia and Belarus Contaminated as a Result of the Chernobyl Accident

Regularities of changes in the content of (137)Cs in green fodder during the remote period after the CNPP accident depending on application of agro-technical and agrochemical activities are analyzed. It is revealed that the use of mineral fertilizers reduces receipt of (137)Cs from the soil to forage and further to a food chain. It is also established that agrochemical activities are more effective than agro-technical ones.

Effects of long-term radionuclide and heavy metal contamination on the activity of microbial communities, inhabiting uranium mining impacted soils

Ore mining and processing have greatly altered ecosystems, often limiting their capacity to provide ecosystem services critical to our survival. The soil environments of two abandoned uranium mines were chosen to analyze the effects of long-term uranium and heavy metal contamination on soil microbial communities using dehydrogenase and phosphatase activities as indicators of metal stress. The levels of soil contamination were low, ranging from 'precaution' to 'moderate', calculated as Nemerow index. Multivariate analyses of enzyme activities revealed the following: (i) spatial pattern of microbial endpoints where the more contaminated soils had higher dehydrogenase and phosphatase activities, (ii) biological grouping of soils depended on both the level of soil contamination and management practice, (iii) significant correlations between both dehydrogenase and alkaline phosphatase activities and soil organic matter and metals (Cd, Co, Cr, and Zn, but not U), and (iv) multiple relationships between the alkaline than the acid phosphatase and the environmental factors. The results showed an evidence of microbial tolerance and adaptation to the soil contamination established during the long-term metal exposure and the key role of soil organic matter in maintaining high microbial enzyme activities and mitigating the metal toxicity. Additionally, the results suggested that the soil microbial communities are able to reduce the metal stress by intensive phosphatase synthesis, benefiting a passive environmental remediation and provision of vital ecosystem services.

Remediation of radiocesium-contaminated liquid waste, soil, and ash: a mini review since the Fukushima Daiichi Nuclear Power Plant accident

The radiation contamination after the Fukushima Daiichi Nuclear Power Plant accident attracts considerable concern all over the world. Many countries, areas, and oceans are greatly affected by the emergency situation other than Japan. An effective remediation strategy is in a highly urgent demand. Though plenty of works have been carried out, progressive achievements have not yet been well summarized. Here, we review the recent advances on the remediation of radiocesium-contaminated liquid waste, soil, and ash. The overview of the radiation contamination is firstly given. Afterwards, the current remediation strategies are critically reviewed in terms of the environmental medium. Special attentions are paid on the adsorption/ion exchange and electrically switched ion exchange methods. Finally, the present review outlines the possible works to do for the large-scale application of the novel remediation strategies.

Estimation of radon emanation coefficient for representative soils in Okinawa, Japan

Radon ((222)Rn) emanation coefficients for the representative soils distributed in Okinawa Island, Japan, have been estimated empirically. Arithmetic means of the emanation coefficients for dry and moist conditions were calculated to be 0.19 and 0.29, respectively. In Okinawa, the soils are traditionally classified into three types, namely the dark red soils, the residual regosols and the red and yellow soils. The dark red soils have relatively high coefficients. The residual regosols and the red and yellow soils have relatively low coefficients. To investigate the variable factor of the emanation coefficients, analyses of radioactive elements and physical properties have also been performed on the soils. For the dark red soils, the contents of the fine particle and the (226)Ra are relatively higher than those for the other soils. Based on these results, it is suggested that the variation in the radon emanation coefficient is mainly regulated by the (226)Ra concentration, the particle sizes and the water contents of the soils.

Soil features and indoor radon concentration prediction: radon in soil gas, pedology, permeability and 226Ra content

This work aims at relating some physicochemical features of soils and their use as a tool for prediction of indoor radon concentrations of the Metropolitan Region of Belo Horizonte (RMBH), Minas Gerais, Brazil. The measurements of soil gas radon concentrations were performed by using an AlphaGUARD monitor. The (226)Ra content analysis was performed by gamma spectrometry (high pure germanium) and permeabilities were performed by using the RADON-JOK permeameter. The GEORP indicator and soil radon index (RI) were also calculated. Approximately 53 % of the Perferric Red Latosols measurement site could be classified as 'high risk' (Swedish criteria). The Litholic Neosols presented the lowest radon concentration mean in soil gas. The Perferric Red Latosols presented significantly high radon concentration mean in soil gas (60.6 ± 8.7 kBq m(-3)), high indoor radon concentration, high RI, (226)Ra content and GEORP. The preliminary results may indicate an influence of iron formations present very close to the Perferric Red Latosols in the retention of uranium minerals.

Evidence for Hydroxamate Siderophores and Other N-Containing Organic Compounds Controlling (239,240)Pu Immobilization and Remobilization in a Wetland Sediment

Pu concentrations in wetland surface sediments collected downstream of a former nuclear processing facility in F-Area of the Savannah River Site (SRS), USA, were ∼2.5 times greater than those measured in the associated upland aquifer sediments; similarly, the Pu concentration solid/water ratios were orders of magnitude greater in the wetland than in the low-organic matter content aquifer soils. Sediment Pu concentrations were correlated to total organic carbon and total nitrogen contents and even more strongly to hydroxamate siderophore (HS) concentrations. The HS were detected in the particulate or colloidal phases of the sediments but not in the low molecular weight fractions (<1000 Da). Macromolecules which scavenged the majority of the potentially mobile Pu were further separated from the bulk mobile organic matter fraction ("water extract") via an isoelectric focusing experiment (IEF). An electrospray ionization Fourier-transform ion cyclotron resonance ultrahigh resolution mass spectrometry (ESI FTICR-MS) spectral comparison of the IEF extract and a siderophore standard (desferrioxamine; DFO) suggested the presence of HS functionalities in the IEF extract. This study suggests that while HS are a very minor component in the sediment particulate/colloidal fractions, their concentrations greatly exceed those of ambient Pu, and HS may play an especially important role in Pu immobilization/remobilization in wetland sediments.

Iodide uptake by negatively charged clay interlayers?

Understanding iodide interactions with clay minerals is critical to quantifying risk associated with nuclear waste disposal. Current thought assumes that iodide does not interact directly with clay minerals due to electrical repulsion between the iodide and the negatively charged clay layers. However, a growing body of work indicates a weak interaction between iodide and clays. The goal of this contribution is to report a conceptual model for iodide interaction with clays by considering clay mineral structures and emergent behaviors of chemical species in confined spaces. To approach the problem, a suite of clay minerals was used with varying degrees of isomorphic substitution, chemical composition, and mineral structure. Iodide uptake experiments were completed with each of these minerals in a range of swamping electrolyte identities (NaCl, NaBr, KCl) and concentrations. Iodide uptake behaviors form distinct trends with cation exchange capacity and mineral structure. These trends change substantially with electrolyte composition and concentration, but do not appear to be affected by solution pH. The experimental results suggest that iodide may directly interact with clays by forming ion-pairs (e.g., NaI(aq)) which may concentrate within the interlayer space as well as the thin areas surrounding the clay particle where water behavior is more structured relative to bulk water. Ion pairing and iodide concentration in these zones is probably driven by the reduced dielectric constant of water in confined space and by the relatively high polarizability of the iodide species.

Predicting radiocaesium sorption characteristics with soil chemical properties for Japanese soils

The high variability of the soil-to-plant transfer factor of radiocaesium (RCs) compels a detailed analysis of the radiocaesium interception potential (RIP) of soil, which is one of the specific factors ruling the RCs transfer. The range of the RIP values for agricultural soils in the Fukushima accident affected area has not yet been fully surveyed. Here, the RIP and other major soil chemical properties were characterised for 51 representative topsoils collected in the vicinity of the Fukushima contaminated area. The RIP ranged a factor of 50 among the soils and RIP values were lower for Andosols compared to other soils, suggesting a role of soil mineralogy. Correlation analysis revealed that the RIP was most strongly and negatively correlated to soil organic matter content and oxalate extractable aluminium. The RIP correlated weakly but positively to soil clay content. The slope of the correlation between RIP and clay content showed that the RIP per unit clay was only 4.8 mmol g(-1) clay, about threefold lower than that for clays of European soils, suggesting more amorphous minerals and less micaceous minerals in the clay fraction of Japanese soils. The negative correlation between RIP and soil organic matter may indicate that organic matter can mask highly selective sorption sites to RCs. Multiple regression analysis with soil organic matter and cation exchange capacity explained the soil RIP (R(2)=0.64), allowing us to map soil RIP based on existing soil map information.

Returning land contaminated as a result of radiation accidents to farming use

An assessment is given of the possibility of sorbents based on natural aluminosilicates (glauconite and clinoptilolite) being used for remediation of radioactively contaminated land with the aim of returning it to farming use. A comparative study of selectivity and reversibility of radiocaesium and radiostrontium sorption by natural aluminosilicates as well as by modified ferrocyanide sorbents based on these aluminosilicates was made. It was found that surface modification of aluminosilicates by ferrocyanides increases the selectivity of synthesized sorbents to caesium by 100-1000 times, increases sorption capacity and makes caesium sorption almost irreversible, whereas, selectivity of these sorbents to strontium radionuclides remains approximately the same as for natural aluminosilicates. The caesium distribution coefficient for mixed nickel-potassium ferrocyanide on glauconite is 10((5.0±0.6)) L kg(-1), the static exchange capacity (SEC) is 63 mg g(-1); for mixed nickel-potassium ferrocyanide based on clinoptilolite caesium distribution coefficients in various concentration ranges are 10((7.0±1.0)), 10((5.7±0.4)) and 10((3.2±0.7)) L kg(-1), total SEC was 500 mg g(-1). Caesium leaching by various leaching solutions from saturated mixed nickel-potassium ferrocyanide based on clinoptilolite was lower than 2%; from saturated mixed nickel-potassium ferrocyanide based on glauconite it was 1.5-14.6%. Ferrocyanide sorbents, based on glauconite and clinoptilolite are recommended for remediation of land, contaminated by caesium as a result of the Fukushima accident in Japan. Use of these sorbents should decrease the transfer of caesium to agricultural vegetation up to a factor of 20.

Radon transport: laboratory and model study

In order to exploit radon profiles for geophysical purposes and also to estimate its entry indoors, it is necessary to study its transport through porous soils. The great number of involved parameters and processes affecting the emanation of radon from the soil grains and its transport in the source medium has led to many theoretical and/or laboratory studies. The authors report the first results of a laboratory study carried out at the Radioactivity Laboratory of the Department of Physics and Astronomy (University of Catania) by means of a facility for measuring radon concentrations in the sample pores at various depths under well-defined and controlled conditions of physical parameters. In particular, radon concentration vertical profiles extracted in low-moisture samples for different advective fluxes and temperatures were compared with expected concentrations, according to a three-phase transport model developed by Andersen (Risø National Laboratory, Denmark), showing, in general, a good agreement between measurements and model calculations.

Temporal variability of radon in a remediated tailing of uranium ore processing--the case of Urgeiriça (central Portugal)

Radon monitoring at different levels of the cover of the Urgeiriça tailings shows that the sealing is effective and performing as desired in terms of containing the strongly radioactive waste resulting from uranium ore processing. However, the analysis of the time series of radon concentration shows a very complex temporal structure, particularly at depth, including very large and fast variations from a few tens of kBq m(-3) to more than a million kBq m(-3) in less than one day. The diurnal variability is strongly asymmetric, peaking at 18 h/19 h and decreasing very fast around 21 h/22 h. The analysis is performed for summer and for a period with no rain in order to avoid the potential influence of precipitation and related environmental conditions on the radon variability. Analysis of ancillary measurements of temperature, relative humidity, wind speed and wind direction, as well as atmospheric pressure reanalysis data shows that the daily averaged radon concentration in the taillings material is anti-correlated with the atmospheric pressure and that the diurnal amplitude is associated with the magnitude of atmospheric pressure daily oscillations.

Geochemical association of Pu and Am in selected host-phases of contaminated soils from the UK and their susceptibility to chemical and microbiological leaching

Understanding the biogeochemical behaviour and potential mobility of actinides in soils and groundwater is vital for developing remediation and management strategies for radionuclide-contaminated land. Pu is known to have a high Kd in soils and sediments, however remobilization of low concentrations of Pu remains a concern. Here, some of the physicochemical properties of Pu and the co-contaminant, Am, are investigated in contaminated soils from Aldermaston, Berkshire, UK, and the Esk Estuary, Cumbria, UK, to determine their potential mobility. Sequential extraction techniques were used to examine the host-phases of the actinides in these soils and their susceptibility to microbiological leaching was investigated using acidophilic sulphur-oxidising bacteria. Sequential extractions found the majority of (239,240)Pu associated with the highly refractory residual phase in both the Aldermaston (63.8-85.5 %) and Esk Estuary (91.9-94.5%) soils. The (241)Am was distributed across multiple phases including the reducible oxide (26.1-40.0%), organic (45.6-63.6%) and residual fractions (1.9-11.1%). Plutonium proved largely resistant to leaching from microbially-produced sulphuric acid, with a maximum 0.18% leached into solution, although up to 12.5% of the (241)Am was leached under the same conditions. If Pu was present as distinct oxide particles in the soil, then (241)Am, a decay product of Pu, would be expected to be physically retained in the particle. The differences in geochemical association and bioleachability of the two actinides suggest that this is not the case and hence, that significant Pu is not present as distinct particles. These data suggest the majority of Pu in the contaminated soils studied is highly recalcitrant to geochemical changes and is likely to remain immobile over significant time periods, even when challenged with aggressive "bioleaching" bacteria.

Use of combined microscopic and spectroscopic techniques to reveal interactions between uranium and Microbacterium sp. A9, a strain isolated from the Chernobyl exclusion zone

Although uranium (U) is naturally found in the environment, soil remediation programs will become increasingly important in light of certain human activities. This work aimed to identify U(VI) detoxification mechanisms employed by a bacteria strain isolated from a Chernobyl soil sample, and to distinguish its active from passive mechanisms of interaction. The ability of the Microbacterium sp. A9 strain to remove U(VI) from aqueous solutions at 4 °C and 25 °C was evaluated, as well as its survival capacity upon U(VI) exposure. The subcellular localisation of U was determined by TEM/EDX microscopy, while functional groups involved in the interaction with U were further evaluated by FTIR; finally, the speciation of U was analysed by TRLFS. We have revealed, for the first time, an active mechanism promoting metal efflux from the cells, during the early steps following U(VI) exposure at 25 °C. The Microbacterium sp. A9 strain also stores U intracellularly, as needle-like structures that have been identified as an autunite group mineral. Taken together, our results demonstrate that this strain exhibits a high U(VI) tolerance based on multiple detoxification mechanisms. These findings support the potential role of the genus Microbacterium in the remediation of aqueous environments contaminated with U(VI) under aerobic conditions.

Plutonium sorption and desorption behavior on bentonite

Understanding plutonium (Pu) sorption to, and desorption from, mineral phases is key to understanding its subsurface transport. In this work we study Pu(IV) sorption to industrial grade FEBEX bentonite over the concentration range 10(-7)-10(-16) M to determine if sorption at typical environmental concentrations (≤10(-12) M) is the same as sorption at Pu concentrations used in most laboratory experiments (10(-7)-10(-11) M). Pu(IV) sorption was broadly linear over the 10(-7)-10(-16) M concentration range during the 120 d experimental period; however, it took up to 100 d to reach sorption equilibrium. At concentrations ≥10(-8) M, sorption was likely affected by additional Pu(IV) precipitation/polymerization reactions. The extent of sorption was similar to that previously reported for Pu(IV) sorption to SWy-1 Na-montmorillonite over a narrower range of Pu concentrations (10(-11)-10(-7) M). Sorption experiments with FEBEX bentonite and Pu(V) were also performed across a concentration range of 10(-11)-10(-7) M and over a 10 month period which allowed us to estimate the slow apparent rates of Pu(V) reduction on a smectite-rich clay. Finally, a flow cell experiment with Pu(IV) loaded on FEBEX bentonite demonstrated continued desorption of Pu over a 12 day flow period. Comparison with a desorption experiment performed with SWy-1 montmorillonite showed a strong similarity and suggested the importance of montorillonite phases in controlling Pu sorption/desorption reactions on FEBEX bentonite.

Plutonium(IV) sorption to montmorillonite in the presence of organic matter

The effect of altering the order of addition in a ternary system of plutonium(IV), organic matter (fulvic acid, humic acid and desferrioxamine B), and montmorillonite was investigated. A decrease in Pu(IV) sorption to montmorillonite in the presence of fulvic and humic acid relative to the binary Pu-montmorillonite system, is attributed to strong organic aqueous complex formation with aqueous Pu(IV). No dependence on the order of addition was observed. In contrast, in the system where Pu(IV) was equilibrated with desferrioxamine B (DFOB) prior to addition of montmorillonite, an increase in Pu(IV) sorption was observed relative to the binary system. When DFOB was equilibrated with montmorillonite prior to addition of Pu(IV), Pu(IV) sorption was equivalent to the binary system. X-ray diffraction and transmission electron microscopy revealed that DFOB accumulated in the interlayer of montmorillonite. The order of DFOB addition plays an important role in the observed sorption/desorption behavior of Pu. The irreversible nature of DFOB accumulation in the montmorillonite interlayer leads to an apparent dependence of Pu sorption on the order of addition in the ternary system. This work demonstrates that the order of addition will be relevant in ternary systems in which at least one component exhibits irreversible sorption behavior.

[Migration in soil and accumulation in plants of peaceful nuclear explosion products in Perm region]

The data on the migration capacity in soil and accumulation of 238Pu, 239, 240Pu, 137Cs and 90Sr by plants in the area of a peaceful nuclear explosion located in the taiga zone are presented. The influence of the soil parameters on the distribution and transformation forms of the radionuclides in the podzolic soil profile was studied. The major amounts of man-made radionuclides were found in the matter of the ground lip. The accumulation parameters of pollutants by plants were the highest for the leaves, young branches and conifer of trees.

[Effect of soil microflora on 137Cs transition to plants]

The impact of certain types of microorganisms on 137Cs transfer from the substrate into the plant was analyzed in the experiment on artificial mediums. It was found that certain types of microorganisms could either reduce or increase the ratio of 137Cs transfer from the substrate to the plant. It is shown that this property is independent of the localization of the microorganism on the surface of the root, for all the analyzed bacteria belonging to the rhizospheric group. Azotobacter chroococcum UKM B-6003 stimulated the radionuclide transfer to plants up to 1.5 times, while the best bacteria for reducing its accumulation is Burkholderia sp IMER-B1 -53 - 1.3 times in comparison with the control. It was shown that the strain Bacillus megaterium UKM B-5724 from the collection of the Institute of Microbiology and Virology of NASU has a high ability to accumulate radionuclides.

Physical properties, structure, and shape of radioactive Cs from the Fukushima Daiichi Nuclear Power Plant accident derived from soil, bamboo and shiitake mushroom measurements

We conducted an elution experiment with contaminated soils using various aqueous reagent solutions and autoradiography measurements of contaminated bamboo shoots and shiitake mushrooms to determine the physical and chemical characteristics of radioactive Cs from the Fukushima Daiichi Nuclear Power Plant accident. Based on our study results and data in the literature, we conclude that the active Cs emitted by the accident fell to the ground as granular non-ionic materials. Therefore, they were not adsorbed or trapped by minerals in the soil, but instead physically adhere to the rough surfaces of the soil mineral particles. Granular Cs* can be transferred among media, such as soils and plants. The physical properties and dynamic behavior of the granular Cs* is expected to be helpful in considering methods for decontamination of soil, litter, and other media.