Initial Radioactivity Research Articles

Isothermal thermoluminescence dating of speleothem growth – A case study from Bleßberg cave 2, Germany

Speleothems are a key archive of past climatic and environmental changes. 230Th/U dating is the most commonly used method to determine speleothem ages. However, incorporation of non-radiogenic thorium may hamper 230Th/U dating, and samples older than 600 ka also remain out-of-reach. Calcite exhibits a thermoluminescence (TL) signal at 280 °C with a high characteristic saturation dose, and provides significant potential to date carbonate samples over several million years. Hitherto, the application of TL dating for calcite has mainly been hindered by two factors: 1) a spurious TL signal occurring in the high temperature range, and 2) non-uniform dose rate due to U-series disequilibrium. Here we test an isothermal TL (ITL) dating method on a speleothem sample from Bleßberg cave 2, Germany. We show that the ITL signal measured at 240 °C can completely remove the 280 °C TL peak with a negligible TL contribution from the higher temperature range, thus reducing the influence from the spurious signal. The time-dependent dose rate variation can be simulated using the initial radioactivity of 238U, 234U, 230Th and their decay constants. We use the 230Th/U dating method to provide precise and accurate radiometric ages documenting that the speleothem grew between 425.5 ± 5.4 and 320.5 ± 9.7 ka. The ITL ages (421 ± 23 to 311 ± 23 ka) of four subsamples from the speleothem are consistent with the 230Th/U ages at isochronous sampling positions, showing the general reliability of the ITL dating method. ITL dating provides a pathway to construct chronologies for palaeoclimate reconstructions for speleothems beyond the range of the 230Th/U-method and for samples that are unsuitable for U-series dating methods.

A hybrid adsorption / ultrafiltration membrane process for removal of Cs-137 from radioactive wastewater using natural clay adsorbent

The removal of radioactive cesium element (Cs-137) from wastewater is relatively challenging due to its high diffusion coefficient, short hydration radius, and the similarity between its chemical behavior to other alkali metals having high background concentrations, leading to a competition that reduces the removal efficiency of cesium (Cs-137). This study introduces an innovative treatment process using a submerged membrane adsorption hybrid system (SMAHS) using natural Iraqi clay minerals as adsorbents. The operational conditions were studied using the (SMAHS) continuous flow operation in stirred filtration mode experiments. The maximum operational conditions were achieved for the initial radioactivity concentration of Cs-137 at 7201.8 Bq/L, clay dose 1 g/L, the stirring speed at 700 rpm, pH =6, the transmembrane pressure (TMP) under 2 bar, and temperature at 25 °C. The SMAHS rejection percentage of Cs-137 was 93.6 % and the permeate flux was 105.6 L/m2.h at the best operational conditions. This study demonstrates that utilizing raw bentonite which is both environmentally friendly and locally available as an adsorbent in the SMAHS has proven its effectiveness for removing Cs-137 from wastewater. The hybrid method effectively immobilizes radioactive waste by converting it from liquid to solid state, leading to an extended and safer storage time.

Natural radioactivity of the crust as an important factor of the chemical evolution of the early Earth

The long-lived (billions of years) 40K, 235U, 238U, and 232Th isotopes have a high energy capacity and represent a potent internal source of energy. Together with the external action of the Sun, the natural radioactivity was apparently an important component of evolution of the early Earth and development of Earth's life. The decay of isotopes initiated radiation chemical reactions involving water, which were accompanied by the formation of hydrogen and oxygen and the transformation of Earth's inorganic matter into organic compounds, including prebiotic molecules. Water radiolysis in the Earth's crust continuously produces H2, which is now considered as the main electron donor (food) for microorganisms several kilometers below the Earth's surface. Here we calculate the initial radioactivity of the early Earth's crust from the relative abundances of elements and dynamics of variation of the radioactivity and energy release upon the decay of particular radioactive isotopes. The energy released upon the decay of heavy 235U, 238U, and 232Th throughout the existence of the Earth (4.6 billion years) was 4.5 × 1030 J, while the energy released upon the decay of 40K was approximately 1.0 × 1030 J. The energy release per year during the first billion years decreased from 3.0 × 1021 J to 1.5 × 1021 J for heavy isotopes and from 0.70 × 1021 J to 0.45 × 1021 J for 40K. Over the last billion years, the energy decreased approximately threefold. Analysis of the data on the radiation chemical formation of hydrogen in the wet components of the Earth's crust (cements, zeolites, geopolymers, and other) and bottom sediments indicates that hydrogen is formed upon direct action of radiation on water in yields characteristic of pure water. According to calculations, over the past 4 billion years, approximately 1.7 × 1022 M of hydrogen was formed. Furthermore, ∼93 % of H2 was due to the decay of uranium and thorium, while the contribution of 40K did not exceed 7 %. The global rate of hydrogen formation in the Earth's crust is ∼ 1.5 × 1012 mol per year. A mechanism involving ionic and radical products of water radiolysis was proposed to describe the formation of prebiotic molecules (amino acids, sugars, etc.) from carbon-, nitrogen-, and sulfur-containing inorganic compounds.

Localized radiotherapy of solid tumors using radiopharmaceutical loaded implantable system: insights from a mathematical model.

Computational models yield valuable insights into biological interactions not fully elucidated by experimental approaches. This study investigates an innovative spatiotemporal model for simulating the controlled release and dispersion of radiopharmaceutical therapy (RPT) using 177Lu-PSMA, a prostate-specific membrane antigen (PSMA) targeted radiopharmaceutical, within solid tumors via a dual-release implantable delivery system. Local delivery of anticancer agents presents a strategic approach to mitigate adverse effects while optimizing therapeutic outcomes. This study evaluates various factors impacting RPT efficacy, including hypoxia region extension, binding affinity, and initial drug dosage, employing a novel 3-dimensional computational model. Analysis gauges the influence of these factors on radiopharmaceutical agent concentration within the tumor microenvironment. Furthermore, spatial and temporal radiopharmaceutical distribution within both the tumor and surrounding tissue is explored. Analysis indicates a significantly higher total concentration area under the curve within the tumor region compared to surrounding normal tissue. Moreover, drug distribution exhibits notably superior efficacy compared to the radiation source. Additionally, low microvascular density in extended hypoxia regions enhances drug availability, facilitating improved binding to PSMA receptors and enhancing therapeutic effectiveness. Reductions in the dissociation constant (KD) lead to heightened binding affinity and increased internalized drug concentration. Evaluation of initial radioactivities (7.1×107, 7.1×108, and 7.1×109 [Bq]) indicates that an activity of 7.1×108 [Bq] offers a favorable balance between tumor cell elimination and minimal impact on normal tissues. These findings underscore the potential of localized radiopharmaceutical delivery strategies and emphasize the crucial role of released drugs relative to the radiation source (implant) in effective tumor treatment. Decreasing the proximity of the drug to the microvascular network and enhancing its distribution within the tumor promote a more effective therapeutic outcome. The study furnishes valuable insights for future experimental investigations and clinical trials, aiming to refine medication protocols and minimize reliance on in vivo testing.

Cardiac noradrenergic deficiency revealed by 18F-dopamine positron emission tomography identifies preclinical central Lewy body diseases.

In Lewy body diseases (LBDs) Parkinson disease (PD), and dementia with Lewy bodies (DLB), by the time parkinsonism or cognitive dysfunction manifests clinically, substantial neurodegeneration has already occurred. Biomarkers are needed to identify central LBDs in a preclinical phase, when neurorescue strategies might forestall symptomatic disease. This phase may involve catecholamine deficiency in the autonomic nervous system. We analyzed data from the prospective, observational, long-term PDRisk study to assess the predictive value of low versus normal cardiac 18F-dopamine positron emission tomography (PET), an index of myocardial content of the sympathetic neurotransmitter norepinephrine, in at-risk individuals. Participants self-reported risk factor information (genetics, olfactory dysfunction, dream enactment behavior, and orthostatic intolerance or hypotension) at a protocol-specific website. Thirty-four with 3 or more confirmed risk factors underwent serial cardiac 18F-dopamine PET at 1.5-year intervals for up to 7.5 years or until PD was diagnosed. Nine participants had low initial myocardial 18F-dopamine-derived radioactivity (<6,000 nCi-kg/cc-mCi) and 25 had normal radioactivity. At 7 years of follow-up, 8 of 9 with low initial radioactivity and 1 of 11 with normal radioactivity were diagnosed with a central LBD (LBD+) (P = 0.0009 by Fisher's exact test). Conversely, all 9 LBD+ participants had low 18F-dopamine-derived radioactivity before or at the time of diagnosis of a central LBD, whereas among 25 participants without a central LBD only 1 (4%) had persistently low radioactivity (P < 0.0001 by Fisher's exact test). Cardiac 18F-dopamine PET highly efficiently distinguishes at-risk individuals who are diagnosed subsequently with a central LBD from those who are not. gov NCT00775853. Division of Intramural Research, NIH, NINDS.

Strontium-90 pollution can be bioremediated with the green microalga Tetraselmis chui.

Strontium-90 (90Sr) is an artificial radioisotope produced by nuclear fission, with a relatively long half-life of 29 years. This radionuclide is released into the environment in the event of a nuclear incident, posing a serious risk to human and ecosystem health. There is a need to develop new efficient methods for the remediation of 90Sr, as current techniques for its removal have significant technical limitations and involve high energy and economic costs. Recently, several species of green microalgae within the class Chlorodendrophyceae have been found to form intracellular mineral inclusions of amorphous calcium carbonate (ACC), which can be highly enriched in natural (non-radiogenic) Sr. As bioremediation techniques are an attractive option to address radioactive pollution, we investigated the capacity of the unicellular alga Tetraselmis chui (class Chlorodendrophyceae) to sequester 90Sr. The 90Sr uptake capacity of T. chui cells was assessed in laboratory cultures by monitoring the time course of radioactivity in the culture medium using liquid scintillation counting (LSC). T. chui was shown to effectively sequester 90Sr, reducing the initial radioactivity of the culture medium by up to 50%. Thus, this study demonstrates the potential of the microalga T. chui to be used as a bioremediation agent against 90Sr pollution.

Chemical precipitation–based treatment of acidic wastewater generated by chemical decontamination of radioactive concrete

Radionuclide-contaminated concrete can be turned into non-radioactive industrial waste through the sequential application of thermomechanical and chemical treatments. Herein, we examine the removal of 137Cs, 90Sr, and 60Co from complex acidic wastewater generated by chemical treatment, revealing that wastewater radioactivity due to these nuclides can be decreased to below the discharge criteria through the injection of potassium ferrocyanide and co-precipitation with BaSO4. In these processes, the concentration of Fe3+ in the wastewater significantly enhanced the removal of 137Cs via metal-ferrocyanide precipitation with effective hydroxide precipitation for 60Co, whereby additional Fe3+ was needed after the injection of potassium ferrocyanide. In the case of 90Sr, the nuclide formed an isomorphous sulphate by rapidly combining with Ba2+ in the BaSO4 lattice structure before particle growth. Furthermore, a large amount of BaSO4 will be required relatively to separate very low radioactivity of 90Sr, compared with high initial radioactivity. Thus, our work provides guidelines for reducing the volume of radioactive waste generated during nuclear facility decommissioning and should therefore help to decrease decommissioning cost.

Decontamination of actual radioactive wastewater containing 137Cs using bentonite as a natural adsorbent: equilibrium, kinetics, and thermodynamic studies

Batch adsorption treatment using Iraqi bentonite as a natural adsorbent was adopted in this study to decontaminate actual 137Cs radioactive wastewater from the Al-Tuwaitha Nuclear Research Center, located south of Baghdad. The bentonite characterization was applied before and after treatment, using chemical compositions analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer–Emmett–Teller (BET) surface area analysis and Fourier-transform infrared spectroscopy (FT-IR). The batch adsorption mode was applied with the initial radioactivity concentration (1440.5 Bq/L), solid/liquid ratio (1 g/L), pH (6–8), contact time (1.5 h), and temperature (298°K). The adsorption experiments showed a decontamination removal efficiency of about 95.66% of 137Cs. A Freundlich adsorption isotherm model was approved for the adsorption of 137Cs, with a coefficient of determination R2 = 0.998. A pseudo-second-order model fitted well with the adsorption of 137Cs, with R2 = 0.983. The positive value of ΔH° in the thermodynamic results indicated that the adsorption process was endothermic physisorption (ΔH° = 15.01 kJ mol−1), spontaneous and favorable (ΔG° = −7.66 kJ mol−1 K−1), with a very low degree of disorder (ΔS° = 0.076 kJ mol−1 K−1).

Trophic transfer and environmental safety of carbon dots from microalgae to Daphnia

The application of carbon dots (CDs), a novel carbon nanomaterial, is extensive, leading to inevitable CD pollution. However, studies on their environmental fate and related risks to aquatic ecosystems are limited. Here, the trophic transfer of CDs from Chlorella pyrenoidosa to Daphnia magna and their toxic effects on the two organisms were analyzed. 14C-labelling was used to quantify and evaluate the fate of CDs. The results showed that the radioactivity of CDs in water was >80 % of the initial radioactivity, and that water extractable residues were dominant in organisms, with only 3 % or less recovered from the mineralization product 14CO2. The distribution of radioactivity illustrated how the exposure routes changed the fate of CDs in aquatic environments. CD aggregates were found in algal cells and Daphnia intestinal tract, indicating the cellular uptake of CDs in these aquatic organisms. Wall-membrane detachment, cell collapse, and rupture were observed in the ultrastructural investigations of microalgae, whereas pneumatosis cystoides intestinalis was observed in the ultrastructural investigations of D. magna. CD exposure affected the growth and chlorophyll content of C. pyrenoidosa as well as the feeding behavior, oxidative stress system, digestive system, and symbiotic bacteria of D. magna. The toxicity of CDs is also affected by the route of exposure. These findings suggest that dietary exposure to CDs was more likely to cause environmental risk and adverse effects than aqueous exposure, and the environmental risks associated with CDs should not be underestimated.

Post-substitution of magnesium at CaI of nano-hydroxyapatite surface for highly efficient and selective removal of radioactive 90Sr from groundwater

We have modified the ion-exchange affinity of nano-Hydroxyapatite (Ca5(PO4)3OH, HAP) surface for the rapid and selective adsorption of 90Sr from groundwater. The modification was achieved by the post-substitution of cations (Na+, Mg2+, Cu2+, Ba2+, Fe3+, and Al3+) for parent Ca2+ within surface structure of HAP. The diffraction patterns of modified HAP showed a slight shift of the (002) peak between 25° and 27° 2θ depending the ionic radius of the substituted cation. Magnesium substituted HAP, Mg-HAP, exhibited the highest removal efficiency (>95%) for 10 ppm of Sr2+, which is attributable to the higher ion-exchange affinity of substituted Mg2+ than parent Ca2+ toward Sr2+. The results of various analyses revealed that Mg substitution dominantly occurred at the CaI site of HAP, which enabled the Mg-HAP to adsorb Sr2+ at both of CaI and CaII sites whereas bare HAP could adsorb Sr2+ mainly at CaII site. Adsorption isotherms and the kinetics of Mg-HAP for Sr2+ were evaluated using a bi-Langmuir isotherm and a pseudo-second-order kinetic model, which demonstrated the Mg-HAP exhibited the highest adsorption capacity (64.69 mg/g) and fastest adsorption kinetics (0.161–1.714 g/(mg·min)) than previously modified HAPs. In the presence of competing cations at circumneutral pHs, the enhanced performance of the Mg-HAP led to a greater than 97% reduction of 90Sr (initial radioactivity = 9500 Bq/L) within 1 h. The distribution coefficient of Mg-HAP was 1.3–6.6 × 103 mL/g while that of bare HAP was 1.2–6.6 × 102 mL/g. The findings in the present study highlight that the ion-exchange affinity of CaI and CaII sites on HAP surface plays a key-role in 90Sr uptake. The proposed modification method can simply increase the affinity of HAP surface, therefore, this work can further improve the deployment of an in situ remediation technology for 90Sr contaminated groundwater, i.e., Mg-HAP-based permeable reactive barrier.

Efficiency of marketable decontamination agent and graphene oxide on 99mTc and 131I spillages in nuclear medicine department

Dealing with open sources of radioactive substances in nuclear medicine is a daily task since contamination due to radioactive spills may happen frequently. Proper and safe decontamination management is a vital procedure. However, regular purchase of decontamination agents incurs high costs and might be toxic due to their chemical properties. The purpose of this study is to compare graphene oxide, which is an environmentally friendly carbon-based material and marketable decontamination agent, in decontaminating radioactive spillage. Samples of pure 99mTc and 131I from the laboratory were spilled on a petri dish. The spill was immediately decontaminated with a marketable decontamination agent swab and varying concentrations of graphene oxide swab. The initial radioactivity of each swab containing 99mTc and 131I was measured using a dose calibrator. The absorbance spectra of each sample were analysed using an ultraviolet-visible spectrophotometer. The morphology image of graphene oxide was observed under field emission scanning electron microscope. For decontamination using a marketable decontamination agent, the radioactivity of 131I was slightly higher, whereas that of 99mTc was slightly lower than the high concentration of graphene oxide. The absorbance spectra of 99mTc and 131I that had been decontaminated using graphene oxide were observed at a range of 200 nm to 250 nm due ???* to the transition.

Mass Interception Fractions and Weathering Half-lives of Iodine-131 and Radiocesium in Leafy Vegetables Observed after the Fukushima Daiichi Nuclear Power Plant Accident

Background: This study was carried out to provide environmental transfer parameter values to estimate activity concentrations of these radionuclides in agricultural crops when direct contamination occurred.Materials and Methods: Mass interception fractions (&lt;i&gt;F&lt;sub&gt;B&lt;/sub&gt;&lt;/i&gt;s) and weathering half-lives (&lt;i&gt;T&lt;sub&gt;w&lt;/sub&gt;&lt;/i&gt;s) of 131I and radiocesium were calculated using openly available monitoring data obtained after the Fukushima Daiichi Nuclear Power Plant accident. &lt;i&gt;F&lt;sub&gt;B&lt;/sub&gt;&lt;/i&gt; is the ratio between the initial radioactivity concentration of a radionuclide retained by the edible part of the plant (Bq‧ kg-1 fresh weight [FW]) and the amount of deposited radionuclide in that area (Bq‧m-2). &lt;i&gt;T&lt;sub&gt;w&lt;/sub&gt;&lt;/i&gt; values can be calculated using activity concentrations of crops decreased with time after the initial contamination.Results and Discussion: Calculated &lt;i&gt;F&lt;sub&gt;B&lt;/sub&gt;&lt;/i&gt; and &lt;i&gt;T&lt;sub&gt;w&lt;/sub&gt;&lt;/i&gt; values for 131I and radiocesium were mostly obtained for leafy vegetables. The analytical results showed that there was no difference of &lt;i&gt;F&lt;sub&gt;B&lt;/sub&gt;&lt;/i&gt;s between 131I and radiocesium by t-test; geometric mean values for leafy vegetables cultivated under outdoor conditions were 0.058 and 0.12 m2 ‧ kg-1 FW, respectively. Geometric mean &lt;i&gt;T&lt;sub&gt;w&lt;/sub&gt;&lt;/i&gt; value of 131I in leafy vegetables grown under outdoor conditions was 8.6 days, and that of radiocesium was 6.6 days; there was no significant difference between &lt;i&gt;T&lt;sub&gt;w&lt;/sub&gt;&lt;/i&gt; values of these radionuclides by Wilcoxon rank sum test.Conclusion: There was no difference between 131I and radiocesium for &lt;i&gt;F&lt;sub&gt;B&lt;/sub&gt;&lt;/i&gt;s and &lt;i&gt;T&lt;sub&gt;w&lt;/sub&gt;&lt;/i&gt;s. By using these factors, we would be able to carry out a rough estimation of the activity concentrations of 131I and radiocesium in the edible part of leafy crops when a nuclear accident occurred.

Influence of Tubificidae Limnodrilus and electron acceptors on the environmental fate of BDE-47 in sediments by (14)C-labelling

2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) was difficult to degrade in sediments. In this study, the environmental behavior of BDE-47 with/without the effect of benthos (Tubificidae Limnodrilus) and electron acceptors in sediments was investigated using C-14 tracer. Generally, extractable residues of BDE-47 were dominant in sediment and posed high environment risk. The amount of non-extractable residues (NERs) accounted for 39.0% of initial radioactivity in oxic sediments was significantly higher than those in anoxic sediments (17.6%). Most of NERs were localized in the humin fraction and presented as sequestrated forms. Under oxic conditions, the present of Limnodrilus significantly increased the proportion of NERs in sediment. Limnodrilus accumulated 34.2% of initial radioactivity. Under anoxic conditions, the addition of iron (Ⅲ) [Fe(III)], sulfate and nitrate reduced the environmental risk of BDE-47 with the increase of NERs formation, while manganese (IV) [Mn(IV)] addition had no effect on the formation of NERs. The present of Limnodrilus and electron acceptors promoted the production of metabolites. Meanwhile, BDE-47 changed the microbial community structure of sediments. These findings indicated that the environmental behavior and risk of BDE-47 was affected by benthos and electron acceptors, and the high proportion of sequestrated NERs posed high bioactivity and toxic threat to ecological environment.

Liquid Metal Flow Studied by Positron Emission Tracking

To improve the properties of castings, a new technique to observe the fluid flow and study the motion of oxygen-bearing inclusions has been developed. This new technique, Positron Emission Particle Tracking (PEPT), enabled a single radioactive tracer particle, moving inside a liquid metal casting, to be tracked with an accuracy of some millimeters, depending on the properties of the liquid metal and the mold. These novel experiments give promising results to observe the liquid metal flow and locate the tracked particle in a casting. Experiments have shown that various particle sizes (200 to 600 μm presented here) can be used to observe the liquid metal flow, if the particle has sufficiently initial radioactivity. Different sizes of particles are considered and their radioactivity compared in terms of their usefulness for tracking in flowing liquid aluminum according to the specific surface area.

Transforaminal and systemic diffusion of an active agent from a zinc oxide eugenol-based endodontic sealer containing hydrocortisone-in an in vivo model.

This study aimed to quantify in vivo the release of hydrocortisone acetate (HCA) contained in a zinc oxide eugenol-based endodontic sealer, in various tissues. Roots of human teeth, shaped with One Shape single file and sealed with Endomethasone N, previously radiolabelled with tritium (3H-HCA), were implanted in the back of 24 mice. Mice were sacrificed at 2, 8, 24, and 48h to evaluate and quantify the amount of radioactivity in subcutaneous tissues surrounding the apex (periapical-like) of the implanted teeth, blood, spleen, kidneys, liver, and urine. Radioactivity was released from the apex of the tooth into the periapical-like tissues with a peak measured at 2h post-implantation (2.25% of the initial radioactivity/g). This quantity decreased significantly over time between 2h and each time points. Radioactivity was still measured up to 48h in the periapical-like tissues (0.42% of the initial radioactivity). The same pattern of kinetic was observed for all organs. The total quantity of radioactivity significantly decreased over time from 4.36% measured 2h post-implantation to 0.74% at 48h. Finally, about 10% of the initial radioactivity from Endomethasone N used to fill the root canal was retrieved after 48h in the urine. This study demonstrated that radioactive-HCA from Endomethasone N can diffuse through the apex of the root canal and follow a classical pharmacokinetics. This mouse model shows that radioactive-HCA can diffuse through the apex and do not accumulate in periapical-like tissues and organs.

Fate of 2,4,6-Tribromophenol in Soil Under Different Redox Conditions.

Fate of 2,4,6-tribromophenol (TBP) in environmental matrices is obscure. We used 14C-tracer to investigated mineralization, transformation, and non-extractable residue (NER)-formation of TBP in a soil under continuously oxic, continuously anoxic, and anoxic-oxic alteration conditions. In all cases, TBP rapidly dissipated, mineralized to CO2, and formed NERs in the soil. Considerable amounts of transformation products (2-12%) were detected during the incubation. Marked mineralization (13-26%) indicated that soil microorganisms used TBP as their energy source. About 62-70% of the initial radioactivity was transformed into NERs, being mainly attributed to binding to humic and fulvic acid fractions. TBP transformation was significantly faster under oxic conditions than under anoxic conditions, and was boosted when the soil redox changed from anoxic to oxic state. The results provide new insights into fate of TBP in soil and suggest the importance to evaluate the stability of NERs for risk assessment of TBP in soil.

The bioaccumulation, elimination, and trophic transfer of BDE-47 in the aquatic food chain of Chlorella pyrenoidosa-Daphnia magna

As a persistent organic pollutant, 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) has been widely detected in aquatic environments. However, studies on the fate and transfer of BDE-47 in the aquatic food chain remain scarce. In this study, we investigated the bioaccumulation and elimination of BDE-47 in Chlorella pyrenoidosa, as well as the trophic transfer and biomagnification of BDE-47 in the “C. pyrenoidosa-Daphnia magna” food chain, using C-14 radioactive tracer technology. After 96 h of BDE-47 exposure, the algae accumulated 88.98% ± 0.59% of the initial radioactivity from the medium, and 36.09% ± 9.22% of the accumulated residues in the algae occurred in the form of bound residues. During 96 h of elimination, only 13% ± 0.50% of accumulated radioactivity in the algae was released into the medium. After 24 h of exposure, D. magna accumulated 35.99% ± 2.55% of the initial radioactivity via water filtration from the medium, and 31.35% ± 1.92% of the accumulated radioactivity in D. magna occurred as bound residues. However, D. magna accumulated 66.89% ± 2.37% of the accumulated radioactivity in the algae via food uptake from the contaminated algae, with a high portion of radioactivity observed as bound residues (83.40% ± 0.97% of accumulated radioactivity in D. magna). This indicated a reduction in the environmental risk of BDE-47. There was obvious biomagnification in the food chain between C. pyrenoidosa and D. magna (biomagnification factors, BMFs>1), resulting in environmental hazard transfer in the aquatic food chain. However, no metabolite was found during the exposure experiment, and further studies should be carried out to investigate the intrinsic mechanisms of the trophic transfer of BDE-47, especially in multilevel food chains. Therefore, this study elucidated the effect of dietary uptake on the bioaccumulation of BDE-47 in D. magna and provided new insight for future analysis regarding the bioaccumulation and biomagnification of organic pollutants in the food chain.

Selective removal of radiocesium from micaceous clay for post-accident soil decontamination by temperature-controlled Mg-leaching in a column

The effective and efficient removal of radioactive Cs from contaminated soil is highly urgent for the nuclear post-accident remediation. In present study, we achieved rapid Cs desorption from both a typical micaceous clay (i.e., vermiculitized biotite, VB) and actually contaminated soil by high-speed ion exchange through temperature-controlled continuous leaching with Mg-solutions in a column reactor. Cs-sorbed VB was firstly employed as a soil surrogate to explore the macro-Cs desorption process and micro-mechanism in detail. Results showed that VB sandwiched the adsorbed Cs to its interlayers within collapsed structure (10.7 Å) and prevent Cs release even by abundant extraction with H2O at 250 °C or Mg2+ at 25 °C. However, Mg2+-extracted Cs desorption boosted significantly with elevating temperatures and 100 % of sorbed-Cs was removed from Cs-VB leached above 150 °C. Further structural and composition analysis of the leached specimen ensured that solvated Mg2+ preferentially entered into Cs+-collapsed interlayers at 150 °C than K+-interlayers above 200 °C, leading to prior complete Cs removal over K from VB at lower temperatures. By contrast, the Cs-contaminated soil reduced by ∼39 % but ∼82 % of its initial radioactivity after equally leaching with same volumes of Mg2+-solution at 150 and 200 °C, respectively. These temperature-controlled Cs desorption validated that radioactive Cs in actual soil indeed be tightly trapped by micaceous clays nearly in the Cs-K co-collapsed interlayers, to which its extraction by other cations can conditionally occur above enough high leaching temperatures. These superior features would inspire new insights for the design of novel practical technologies for treatment and decontamination of the nuclear post-accident soils.

Internal radiation dose estimation using multiple D-shuttle dosimeters for positron emission tomography (PET): A validation study using NEMA body phantom.

Internal radiation dosimetry plays an important role in ensuring the safe use of positron emission tomography (PET) technology and is a legal requirement in most countries. We propose a new technique to estimate the internal radiation dose in PET studies by means of multiple D-shuttle dosimeters attached on the body surface of the patient. Radioactivity in a source organ was estimated iteratively using measurements from multiple D-shuttle dosimeters with a maximum-likelihood expectation-maximization (MLEM) algorithm with dose response from a source to a D-shuttle dosimeter computed by Monte Carlo simulation. To validate our technique, we performed a phantom study using a National Electrical Manufacturers Association (NEMA) body phantom. The fillable compartments (torso cavity and six spheres) of the phantom were filled with 18 F-FDG mixed with pure water using an 800:1 sphere-to-background radioactivity concentration ratio. The radioactivity concentrations present in the torso cavity and six spheres were 0.00165 MBq/mL and 1.32 MBq/mL, respectively. The initial radioactivities of the torso cavity and six spheres (treated as source organs) were 15.9 MBq (torso cavity), 34.7 MBq (37 mm sphere), 15.1 MBq (28 mm sphere), 7.27 MBq (22 mm sphere), 3.26 MBq (17 mm sphere), 1.54 MBq (13 mm sphere), and 0.697 MBq (10 mm sphere). Eleven D-shuttle dosimeters were attached to the NEMA body phantom surface to obtain information on body surface dose and a mathematical NEMA body phantom has been modeled in the Heavy Ion Transport Code System (PHITS) Monte Carlo simulation code. Radioactivity was estimated in 2 min intervals over a 110-min total dose time using our proposed technique. A significant correlation (R2 = 0.992) was found between actual radioactivity and estimated radioactivity at every 2 min interval for each source organ. The estimated initial radioactivity (mean with standard deviation) was 16.5 ± 0.311 MBq (torso cavity), 33.0 ± 0.624 MBq (37 mm sphere), 15.7 ± 0.189 MBq (28 mm sphere), 7.11 ± 0.738 MBq (22 mm sphere), 4.17 ± 0.083 MBq (17 mm sphere), 1.48 ± 0.469 MBq (13 mm sphere), and 0.865 ± 0.313 MBq (10 mm sphere), which were very close to the actual initial radioactivity measurements for each source organ. The phantom study showed that our technique worked successfully. This technique could be used to estimate internal radiation dosimetry in a clinical PET study.

Decontamination of radioactive wastewater by two-staged chemical precipitation

Abstract This article presented two-staged chemical precipitation for radioactive wastewater decontamination by using chemical agents. The total amount of radioactive wastewater was 35 m3, and main radionuclides were Cs-137, Cs-134, and Co-60. Initial radioactivity concentration of the liquid waste was 2264, 17, and 9 Bq/L for Cs-137, Cs-134 and Co-60, respectively. Potassium ferrocyanide, nickel nitrate, and ferrum nitrate were selected as chemical agents at high pH levels 8–10 according to the laboratory jar tests. After the process, radioactivity was precipitated as sludge at the bottom of the tank and decontaminated clean liquid was evaluated depending on discharge limits. By this precipitation method decontamination factors were determined as 66.5, 8.6, and 9 for Cs-137, Cs-134, and Co-60, respectively. By using the potassium ferrocyanide, about 98% of the Cs-137 was removed at pH 9. At the bottom of the tank, radioactive sludge amount from both stages was totally 0.98 m3. It was transferred by sludge pumps to cementation unit for solidification. By chemical processing, 97.2% of volume reduction was achieved. The potassium ferrocyanide in two-staged precipitation method could be used successfully in large-scale applications for removal of Cs-137, Cs-134, and Co-60.