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

Spectroscopic and dosimetric comparison of tooth enamel separation methods for EPR retrospective dosimetry

Precise estimation of individual radiation dose utilizing biomaterials (fingernail, bone, and tooth) is very challenging due to their complex sample processing. Despite, tooth enamel, the most mineralized tissue of tooth is used for this purpose due to its high radiation sensitivity and ability to produce radiation induced long lived CO2- radicals. However, human teeth are not always available, and invasive nature of sample collection adds to the complexity making dose estimation difficult. In such cases, animal teeth (goat, cow, and moose) can be used as a substitute for human teeth due to comparable enamel sensitivity. Moreover, separation of enamel from dentine is a crucial step towards accurate dose estimation from irradiated teeth. In this work, Indian goat teeth were used as it was readily available to us and the comparison of goat enamel sensitivity to radiation was found to be within ∼7.4 % that of human. The enamel samples were separated following two chemical methods; (1) density separation using sodium polytungstate, (2) alkaline denaturation using NaOH and the quality was compared based on their purity and radiation sensitivity. Combined results of spectroscopic characterization using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman analysis authenticated the crystallinity and purity of the separated enamel samples. The radiation sensitivity of separated enamel samples was compared by electron paramagnetic resonance (EPR) analysis as a part of dosimetric characterization. The suitability of both the samples for retrospective dosimetry and epidemiological studies was checked by validating the dose estimated from separated enamel samples with standard alanine/EPR dosimeter.

Ultrastructural Analysis of Large Japanese Field Mouse (Apodemus speciosus) Testes Exposed to Low-Dose-Rate (LDR) Radiation after the Fukushima Nuclear Power Plant Accident

Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, great attention has been paid to the impact of chronic low-dose-rate (LDR) radiation exposure on biological systems. The reproductive system is sensitive to radiation, with implications connected to infertility. We investigated the testis ultrastructure of the wild large Japanese field mouse (Apodemus speciosus) from three areas contaminated after the FDNPP accident, with different levels of LDR radiation (0.29 µSv/h, 5.11 µSv/h, and 11.80 µSv/h). Results showed good preservation of the seminiferous tubules, comparable to the unexposed animals (controls), except for some ultrastructural modifications. Increases in the numerical density of lipid droplet clusters in spermatogenic cells were found at high levels of LDR radiation, indicating an antioxidant activity rising due to radiation recovery. In all groups, wide intercellular spaces were found between spermatogenic cells, and cytoplasmic vacuolization increased at intermediate and high levels and vacuolated mitochondria at the high-level. However, these findings were also related to the physiological dynamics of spermatogenesis. In conclusion, the testes of A. speciosus exposed to LDR radiation associated with the FDNPP accident showed a normal spermatogenesis, with some ultrastructural changes. These outcomes may add information on the reproductive potential of mammals chronically exposed to LDR radiation.

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 low-cost photo-evaporation inorganic membrane preparation and treatment of the simulated high salinity radioactive waste water

Solar-driven desalination is an energy-saving and environmentally benign wastewater treatment technology. A method of in situ self-reduction of graphene oxide (rGO) by cheap geopolymer was introduced, and a photo evaporation membrane device (rGOPGC) for treatment of the simulated high salt liquid radioactive waste (HSLRW) was prepared in the present study. Compared with other rGO based photo evaporation membrane materials, geopolymer matrix has the advantages of low cost, reductant free, simple preparation process and mild conditions. After desalination of simulated seawater, the concentrations of Na⁺, K⁺, Ca²⁺ and Mg²⁺ ions reached the WHO standard, and the removal rates of radioactive I^-, Cs⁺ and Sr²⁺ in the simulated high salinity wastewater reached 99.62%, 99.71% and 99.99% respectively; The evaporation rate of rGOPGC remained stable at 1.5 kg/m²/h after 16 cycles in high salinity environment. There was no obvious salt accumulation on the upper surface of the device, indicating its high stability. Furthermore, the evaporation performance at high temperature near the nuclear power plant (NPP) waste water was simulated and tested. Under one solar intensity and 35 °C ambient temperature, the evaporation rate of 1.75 kg/m²/h and the evaporation efficiency of 98.51% were achieved. The results indicated that the rGOPGC device is potential in the concentration evaluation of HSLRW.