(90)Sr in teeth of cattle abandoned in evacuation zone: Record of pollution from the Fukushima-Daiichi Nuclear Power Plant accident

Direct Quantification of Attogram Levels of Strontium-90 in Microscale Biosamples Using Isotope Dilution-Thermal Ionization Mass Spectrometry Assisted by Quadrupole Energy Filtering

Although thermal ionization mass spectrometry (TIMS) has been employed for the high-precision analysis of isotope ratios, direct quantification of artificial mono-nuclide in the environment is difficult by even using isotope dilution (ID) due to the coexistence of the great magnitude of natural stable nuclides or isobars. In traditional TIMS and ID-TIMS, a sufficient amount of stable Sr doped on a filament is required to realize a stable and adequate ion-beam intensity (i.e., thermally ionized beams). However, the background noise (BGN) at m/z 90, detected by an electron multiplier, disturbs ⁹⁰Sr analysis at low concentration levels due to peak tailing of a significant ⁸⁸Sr ion beam dependent on the ⁸⁸Sr-doping amount. Here, TIMS assisted by quadruple energy filtering was successfully employed for the direct quantification of attogram levels of an artificial monoisotopic radionuclide strontium-90 (⁹⁰Sr) in microscale biosamples. Direct quantification was achieved by integrating the ID quantification of natural Sr and simultaneous ⁹⁰Sr/⁸⁶Sr isotope ratio analysis. Additionally, the measurement amount calculated by the combination of the ID and intercalibration was corrected for the net result amount of ⁹⁰Sr by subtracting dark noise and the detected amount derived from the survived ⁸⁸Sr, which are equivalent with the BGN intensity at m/z 90. Background correction revealed that the detection limits were in the range of 6.15 × 10^-2-3.90 × 10^-1 ag (0.31-1.95 μBq), depending on the concentration of natural Sr in a 1 μL sample, and the quantification of 0.98 ag (5.0 μBq) of ⁹⁰Sr in 0-300 mg/L of natural Sr was successful. This method could analyze small sample quantities (1 μL), and the quantitative results were verified against authorized radiometric analysis techniques. Furthermore, the amount of ⁹⁰Sr in actual teeth was successfully quantified. This method will be a powerful tool for measuring ⁹⁰Sr in the measurement of micro-samples, which are required to assess and understand the degree of internal radiation exposure.

Detection limit of electron spin resonance for Japanese deciduous tooth enamel and density separation method for enamel-dentine separation

Electron spin resonance (ESR) dosimetry is one of the most powerful tools for radiation dose reconstruction. The detection limit of this technique using human teeth is reported to be 56 mGy or 67 mGy; however, the absorbed dose of Fukushima residents after the Fukushima Daiichi Nuclear Power Plant (FNPP) accident was estimated to be lower than this detection limit. Our aim is to assess the absorbed radiation dose of children in Fukushima Prefecture after the accident; therefore, it is important to estimate the detection limit for their teeth. The detection limit for enamel of deciduous teeth of Japanese children separated by the mechanical method is estimated to be 115.0 mGy. The density separation method can effectively separate enamel from third molars of Japanese people. As we have collected thousands of teeth from children in Fukushima, the present technique may be useful to examine their external absorbed dose after the FNPP accident.

A summary of environmental radioactivity research studies by members of the Japan Society of Nuclear and Radiochemical Sciences

Many scientists who are members of the Japan Society of Nuclear and Radiochemical Sciences have been involved in academic activities in response to the Fukushima Daiichi Nuclear Power Plant accident. Projects had been implemented that include determining radionuclides in environmental samples, identifying the distribution of radionuclides by large-scale soil monitoring, tracing radionuclide discharge time series, clarifying environmental dynamics of radionuclides, etc. For the last 10 years, these results have been shared and discussed in annual workshops partly sponsored by the society. This review summarizes the studies yielding these results, and they include reconstruction of the 131I distribution on soil by long-lived 129I analysis, reconstruction of the radioactive plume transport, identification of biological resuspension sources, discovery and characterization of cesium particles, and parameterization of the environmental behavior of radiocesium for dose assessment.

A part per trillion isotope ratio analysis of 90Sr/88Sr using energy-filtered thermal ionization mass spectrometry

Strontium-90 is a major radioactive nuclide released by nuclear accidents and discharge waste. Input of such radioactive nuclide into earth surface environment causes potential threat of long-term internal exposure when taken up by organism. Rapid and precise measurement of ⁹⁰Sr in variety of environmental sample is important to understand the distribution and dynamics of ⁹⁰Sr in the local environment after the accident and to assess the effect of radioactive nuclide inputs on bodies. However, previous ⁹⁰Sr measurement techniques have drawbacks such as long measurement times for radiometry and high detection limits for mass spectrometry. Here we present a technique to accurately measure a significantly small amount of ⁹⁰Sr in natural environmental samples using an energy-filtered thermal ionization mass spectrometry. Our technique achieved a ⁹⁰Sr detection limit of 0.23 ag, which corresponds to a ⁹⁰Sr activity of 1.2 µBq. The detection limit was lowered by two orders of magnitude compared with the previous mass spectrometric ⁹⁰Sr analyses. The ability of our technique will expand the applicability of mass spectrometric ⁹⁰Sr survey not only to the rapid ⁹⁰Sr survey upon nuclear accidents but also to study a long-term environmental diffusion of radioactive materials using size-limited environmental and biological samples.

Synthesis of β-Ca2P2O7 as an Adsorbent for the Removal of Heavy Metals from Water

In the present work, beta-calcium pyrophosphate (β-Ca2P2O7) was investigated as a potential adsorbent for the removal of heavy metal ions from water. Single-phase β-Ca2P2O7 powders were synthesized by a simple, scalable and cost-effective wet precipitation method followed by annealing at 800 °C, which was employed for the conversion of as-precipitated brushite (CaHPO4∙2H2O) to β-Ca2P2O7. Physicochemical properties of the sorbent were characterized by means of X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR), thermal analysis (TGA/DSC), scanning electron microscopy (SEM) and low temperature adsorption–desorption of nitrogen (BET method). The synthesized powders consisted of porous plate-like particles with micrometer dimensions. Specific surface area calculated by the BET method was found to be 7 m2 g−1. For the estimation of sorption properties, the aqueous model solutions containing different metal ions (Al3+, Cd2+, Co2+, Cu2+, Fe2+, Mn2+, Ni2+, Pb2+, Sn2+, Sr2+ and Zn2+) were used. The adsorption test revealed that β-Ca2P2O7 demonstrates the highest adsorption capacity for Pb2+ and Sn2+ ions, while the lowest capacity was observed towards Sr2+, Ni2+ and Co2+ ions. The optimal pH value for the removal of Pb2+ ions was determined to be 2, which is also related to the low solubility of β-Ca2P2O7 at this pH. The adsorption capacity towards Pb2+ ions was calculated as high as 120 mg g−1.

Radioactivity and radionuclides in deciduous teeth formed before the Fukushima-Daiichi Nuclear Power Plant accident

The Fukushima-Daiichi Nuclear Power Plant (FNPP) accident in March of 2011 released substantial amounts of radionuclides into the environment. We collected 4,957 deciduous teeth formed in children before the Fukushima accident to obtain precise control data for teeth formed after the accident. Radioactivity was measured using imaging plates (IP) and epidemiologically assessed using multivariate regression analysis. Additionally, we measured 90Sr, 137Cs, and natural radionuclides which might be present in teeth. Epidemiological studies of IP showed that the amount of radioactivity in teeth from Fukushima prefecture was similar to that from reference prefectures. We found that artificial radionuclides of 90Sr and 137Cs, which were believed to have originated from past nuclear disasters, and natural radionuclides including 40 K and daughter nuclides in the 238U and 232Th series contributed to the generation of radioactivity in teeth. We also found no evidence to suggest that radionuclides originating from the FNPP accident significantly contaminated pre-existing teeth. This is the first large-scale investigation of radioactivity and radionuclides in teeth. The present findings will be indispensable for future studies of teeth formed after the FNPP accident, which will fall out over the next several years and might be more contaminated with radionuclides.

Morphological reproductive characteristics of testes and fertilization capacity of cryopreserved sperm after the Fukushima accident in raccoon (Procyon lotor)

Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, we have established an archive system of livestock and wild animals from the surrounding ex-evacuation zone. Wildlife within the alert zone have been exposed to low-dose-rate (LDR) radiation for a long continuous time. In this study, we analysed the morphological characteristics of the testes and in vitro fertilization (IVF) capacity of cryopreserved sperm of racoons from the ex-evacuation zone of the FDNPP accident. The radioactivity of caesium-137 (137 Cs) was measured by gamma-ray spectrometry, and the measured radioactivity concentration was 300-6,630 Bq/kg in the Fukushima raccoons. Notably, normal spermatogenesis was observed in the seminiferous tubules of the testes, with the germinal epithelium composed of a spermatogenic cell lineage with no evident ultrastructural alterations; freeze-thawing sperm penetration ability was confirmed using the interspecific zona pellucida-free mouse oocytes IVF assays. This study revealed that the chronic and LDR radiation exposure associated with the FDNPP accident had no adverse effect on the reproductive characteristics and functions of male raccoons.

Dose Reconstruction Using Electron Paramagnetic Resonance Dosimetry on Tooth Enamel From Wild Boar Living in the Fukushima Exclusion Zone

The goal of the study was to establish characteristics of Japanese wild boar tooth enamel in the dose region of 0.25-2.0 Gy and to reconstruct external absorbed doses to wild boar native to the Fukushima exclusion zone using electron paramagnetic resonance dosimetry. The significance of Japanese wild boar in their ecosystem and their position within the trophic hierarchy make the wild boar a species of particular importance and therefore, the focus of this study. Dose response linearity and variability of enamel originating from various wild boar were investigated. Radiation dose response of Japanese wild boar tooth enamel in the range of 0.25-2.0 Gy was found to be linear, and the average variation in dose response between teeth originating from the same boar specimen was nearly 30%. No statistically significant difference in dose response was found based on sex of the boar or in permanent molar teeth of boar of differing ages. Electron paramagnetic resonance absorbed doses to boar tooth enamel were successfully reconstructed using the calibration curve method and converted into estimates of absorbed dose to soft tissue with large associated confidence intervals. The critical level dose value for the calibration curve was 1.0 Gy and the detection limit dose was 1.8 Gy, suggesting that this method would be more beneficial for boar with lifetime absorbed doses greater than 1.0 Gy. The method of reconstructing external absorbed doses using electron paramagnetic resonance dosimetry with tooth enamel from Japanese wild boar as dosimeters has proven to be a viable method which can be used to reconstruct absorbed doses to wildlife in accident-stricken areas in the absence of alternative dosimetry.

Intestinal Bacteria as Powerful Trapping Lifeforms for the Elimination of Radioactive Cesium

In March 2011, an accident at the Fukushima Daiichi Nuclear Power Plant led to major problems, including the release of radionuclides such as Cesium (Cs)-137 into the environment. Ever since this accident, Cs-137 in foods has become a serious problem. In this study, we determined the concentration of Cs-137 in the feces, urine, and ruminal contents of cattle and demonstrated the possibility of its elimination from the body by intestinal bacteria. The results revealed a high Cs-137 concentration in the feces; in fact, this concentration was higher than that in skeletal muscles and other samples from several animals. Furthermore, intestinal bacteria were able to trap Cs-137, showing an uptake ratio within the range of 38–81% in vitro. This uptake appeared to be mediated through the sodium–potassium (Na⁺-K⁺) ion pump in the bacterial cell membrane. This inference was drawn based on the fact that the uptake ratio of Cs-137 was decreased in media with high potassium concentration. In addition, it was demonstrated that intestinal bacteria hindered the trapping of Cs-137 by the animal. Cattle feces showed high concentration of Cs-137 and intestinal bacteria trapped Cs-137. This study is the first report showing that intestinal bacteria contribute to the elimination of Cs-137 from the body.

A review of measurement methodologies and their applications to environmental 90Sr

The high fission yield product ⁹⁰Sr has been released into the environment in large amounts due to nuclear weapon tests, nuclear power plant accidents, and nuclear fuel reprocessing industries. It is a long half-life radionuclide (28.9 y), with serious consequences to human health; hence, it is desirable to perform routine monitoring of ⁹⁰Sr in environmental samples. Many ⁹⁰Sr radiometric methods have been developed in the past decades, which generally require complicated separation and purification steps with a relatively long analytical time. Moreover, some nominally rapid methods usually have high method detection limits, making them unsuitable for the environmental samples with ultra-low ⁹⁰Sr levels. In this review, some rapid and practical methods for ⁹⁰Sr routine monitoring are summarized. Different sample pretreatments and major purification procedures for ⁹⁰Sr developed in recent years, such as variable digestion methods and extraction chromatography using Sr resin or DGA resin, are especially described. Additionally, four conventional and widely used β spectrometric and mass spectrometric methods are demonstrated. Finally, ⁹⁰Sr evaluations focusing on contaminated soil and seawater samples collected after the Fukushima Daiichi Nuclear Power Plant accident, and ⁹⁰Sr application as tracers for environmental behavior are also reviewed.

A Brief Review-EPR Dosimetry and the Use of Animal Teeth as Dosimeters

The technique of electron paramagnetic resonance dosimetry using tooth enamel was established in the late 1960s, and considerable research has been conducted to learn more about the benefits of using human teeth as dosimeters for the purpose of retrospective dose reconstruction. Comparatively few studies have been done which have investigated animal teeth for the same purpose. The potential exists for utilizing animal teeth as dosimeters to reconstruct doses received by a species, as well as by humans. Animals investigated in electron paramagnetic resonance studies included cows, rats, mice, dogs, pigs, rhesus monkeys, goats, reindeer, walruses, bison, polar foxes, moose, and polar bears. Much has been determined regarding the characteristics of animal teeth, and overall the use of animal teeth for electron paramagnetic resonance dosimetry appears to be a viable means of estimating external dose. Although much has been learned from animal studies, there remain unanswered questions related to electron paramagnetic resonance dosimetry and the use of animal teeth as electron paramagnetic resonance dosimeters. This article summarizes the findings of animal electron paramagnetic resonance studies and outlines what is still unknown.

Estimation of concentration of radionuclides in skeletal muscle from blood, based on the data from abandoned animals in Fukushima

The damage caused by the earthquake on 11 March, 2011 resulted in a serious nuclear accident in Japan. Due to the damage to the Fukushima Daiichi Nuclear Power Plant (FNPP), large amounts of radioactive substances were released into the environment. In particular, one of the largest safety concerns is radioactive cesium (¹³⁴Cs and ¹³⁷Cs). Due to the FNPP nuclear accident, a 20 km area was restricted from human activity, and various types of domestic animals were left in the zone. We collected the organs and tissues from sacrificed animals to obtain scientific data to evaluate the internal deposition of radioactive compounds. At first, we found there is a strong correlation between blood ¹³⁷Cs and organ ¹³⁷Cs with data from 44 cattle, indicating that skeletal muscle is the target organ of deposition of radioactive cesium. Second, we analyzed the relationship between blood ¹³⁷Cs and muscle ¹³⁷Cs within relatively lower radioactive concentration, suggesting that estimation of concentration of ¹³⁷Cs is possible from blood concentration of ¹³⁷Cs. Finally, we developed computer software to estimate the muscle ¹³⁷Cs concentration from blood samples. Our study contributes to the food safety of livestock products.

90Sr specific activity of teeth of abandoned cattle after the Fukushima accident - teeth as an indicator of environmental pollution

⁹⁰Sr specific activity in the teeth of young cattle that were abandoned in Kawauchi village and Okuma town located in the former evacuation areas of the Fukushima-Daiichi Nuclear Power Plant (FNPP) accident were measured. Additionally, specific activity in contaminated surface soils sampled from the same area was measured. (1) All cattle teeth examined were contaminated with ⁹⁰Sr. The specific activity, however, varied depending on the developmental stage of the teeth during the FNPP accident; teeth that had started development before the accident exhibited comparatively lower values, while teeth developed mainly after the accident showed higher values. (2) Values of ⁹⁰Sr-specific activity in teeth formed after the FNPP accident were higher than those of the bulk soil but similar to those in the exchangeable fraction (water and CH₃COONH₄ soluble fractions) of the soil. The findings suggest that ⁹⁰Sr was incorporated into the teeth during the process of development, and that ⁹⁰Sr in the soluble and/or leachable fractions of the soil might migrate into teeth and contribute to the amount of ⁹⁰Sr in the teeth. Thus, the concentration of ⁹⁰Sr in teeth formed after the FNPP accident might reflect the extent of ⁹⁰Sr pollution in the environment.

Calcium-deficient Hydroxyapatite as a Potential Sorbent for Strontium

A calcium (Ca)-deficient hydroxyapatite was investigated for its potential to remove Sr²⁺ from environmentally relevant water. We conducted sorption tests on solutions containing magnesium ion (Mg²⁺) and calcium ion (Ca²⁺) as competing cations at a strontium ion (Sr²⁺) concentration of 0.05 mmol/L. The Ca-deficient hydroxyapatite maintained a high Sr²⁺ sorption ratio of above 80% in the presence of Mg²⁺ and Ca²⁺ at the concentrations between 0.1 and 1.0 mmol/L, whereas the stoichiometric hydroxyapatite showed a lower ratio even in the presence of small amounts of Mg²⁺ and Ca²⁺ (72% for Mg²⁺ and 51% for Ca²⁺ at 0.1 mmol/L). For solutions with various Sr²⁺ concentrations between 0.01 and 10 mmol/L, Ca-deficient hydroxyapatite exhibited a higher Sr²⁺ sorption ratio than stoichiometric hydroxyapatite. The bonding states of Sr²⁺ on the Ca-deficient hydroxyapatite were evaluated by extended X-ray absorption fine structure measurements. The results indicated that there are specific sorption sites in Ca-deficient hydroxyapatite where Sr²⁺ is stably and preferentially immobilized.