Changes in sulfur metabolism in mouse brains following radon inhalation

Kanzaki, Norie; Sakoda, Akihiro; Kataoka, Takahiro*; Sun, L.*; Tanaka, Hiroshi; Otsu, Iwao*; Yamaoka, Kiyonori*

International Journal of Environmental Research and Public Health, 19(17), p.10750_1 - 10750_14, 2022/09

https://doi.org/10.3390/ijerph191710750

Reactive sulfur species (RSS) involve oxidative stress deeply and contribute anti-inflammatory effect, but no studied have focused on RSS changes after irradiation. In this study, we comprehensively analyzed the metabolites, focusing on RSS in mouse brain following radon inhalation. The ratio of oxidized glutathione to reduced glutathione and proportion of RSS in GSH or cysteine increased by radon inhalation. The sulfur ion might bind to GSH or cysteine chemically under conditions of oxidative stress, even at very low-dose exposure. We performed the overall assessment of high-dimensional data by applying machine learning and showed the specific characteristics of the effects by the exposure conditions. Our results suggested that RSS could produce a biological defense against oxidative stress following radon inhalation.

Radon solubility and diffusion in the skin surface layer

Sakoda, Akihiro; Ishida, Tsuyoshi*; Kanzaki, Norie; Tanaka, Hiroshi; Kataoka, Takahiro*; Mitsunobu, Fumihiro*; Yamaoka, Kiyonori*

International Journal of Environmental Research and Public Health, 19(13), p.7761_1 - 7761_12, 2022/07

https://doi.org/10.3390/ijerph19137761

In specific situations such as bathing in a radon spa, where the radon activity concentration in thermal water is far higher than that in air, it has been revealed that radon uptake via skin can occur and should be considered for more precise dose evaluation. The primary aim of the present study was to numerically demonstrate the distribution as well as the degree of diffusion of radon in the skin, with a focus on its surface layers (i.e., stratum corneum). We made a biokinetic model that included diffusion theory at the stratum corneum, and measured radon solubility in the stratum corneum to get a crucial parameter. The implementation of the model suggested that the diffusion coefficient in the stratum corneum was as low as general radon-proof sheets. The depth profile of radon in the skin was found to be that after a 20-minute immersion in water, the radon activity concentration at the top surface skin layer was approximately 1000 times higher than that at the viable skin layer. The information on the position of radon as a radiation source would contribute to special dose evaluation where specific target cell layers are assumed for the skin.

Dosimetry of radon progeny deposited on skin in air and thermal water

Sakoda, Akihiro; Ishimori, Yuu; Kanzaki, Norie; Tanaka, Hiroshi; Kataoka, Takahiro*; Mitsunobu, Fumihiro*; Yamaoka, Kiyonori*

Journal of Radiation Research (Internet), 62(4), p.634 - 644, 2021/07

https://doi.org/10.1093/jrr/rrab030

It is held that the skin dose from radon progeny is not negligibly small and that introducing cancer is a possible consequence under normal circumstances, while there are a number of uncertainties in terms of related parameters such as activity concentrations in air, target cells in skin, skin covering materials, and deposition velocities. Meanwhile, an interesting proposal emerged in that skin exposure to natural radon-rich thermal water as part of balneotherapy can produce an immune response to induce beneficial health effects. The goal of the present study was to obtain generic dose coefficients with a focus on the radon progeny deposited on the skin in air or water in relation to risk or therapeutic assessments. We thus first estimated the skin deposition velocities of radon progeny in the two media based on data from the latest human studies. Using the optimized velocities, skin dosimetry was then performed under different assumptions regarding alpha-emitting source position and target cell (i.e., basal cells or Langerhans cells). Furthermore, the impact of the radon progeny deposition on effective doses from all exposure pathways relating to "radon exposure" was assessed using various possible scenarios. It was found that in both exposure media, effective doses from radon progeny inhalation are one to four orders of magnitude higher than those from the other pathways. In addition, absorbed doses on the skin can be the highest among all pathways when the radon activity concentrations in water are two or more orders of magnitude higher than those in air.

Methodology for simple spot measurement of equilibrium equivalent radon concentration

Sakoda, Akihiro; Ishimori, Yuu; Kanzaki, Norie; Tanaka, Hiroshi

Radiation Protection Dosimetry, 191(4), p.383 - 390, 2020/10

https://doi.org/10.1093/rpd/ncaa176

Estimation of the effective inhalation dose of short half-life radon progeny requires the quantification of radon equilibrium equivalent activity concentrations (EEC). The aim of the present study is to develop new methodology that focuses on spot measurements to determine EEC from single gross alpha counts and determine an optimized protocol. The core of the approach is to measure alpha particles over time when the radon progeny attached to the sampling filter are significantly disintegrated. The calibration curve of single counts to EEC is theoretically deduced and validated by a comparison test. The advantage of the present method is its minimal requirements, including the use of common instruments and simple sampling, alpha counting, and analysis procedures. This approach offers an option for radon practitioners working in a variety of fields, as well as the possibility for non-experts to easily measure EEC.

Study of biokinetics of radon progeny with thoron progeny as the isotope tracer

Sakoda, Akihiro; Kanzaki, Norie; Tanaka, Hiroshi; Kataoka, Takahiro*; Yamaoka, Kiyonori*

Nihon Kenko Kaihatsu Zasshi, (40), p.90 - 94, 2019/06

https://doi.org/10.32279/jjhr.40.0_90

no abstracts in English

Measurements of radon activity concentration in mouse tissues and organs

Ishimori, Yuu; Tanaka, Hiroshi; Sakoda, Akihiro; Kataoka, Takahiro*; Yamaoka, Kiyonori*; Mitsunobu, Fumihiro*

Radiation and Environmental Biophysics, 56(2), p.161 - 165, 2017/05

https://doi.org/10.1007/s00411-017-0682-9

In order to investigate the biokinetics of inhaled radon, radon concentrations in mouse tissues and organs were determined after mice had been exposed to about 1 MBq/m of radon in air. Radon concentrations in mouse blood and in other tissues and organs were measured with a liquid scintillation counter and with a well-type HP Ge detector, respectively. Radon concentration in mouse blood was 0.4100.016 Bq/g when saturated with 1 MBq/m of radon concentration in air. In addition, average partition coefficients obtained were 0.740.19 for liver, 0.460.13 for muscle, 9.090.49 for adipose tissue, and 0.220.04 for other organs. With these results, a value of 0.414 for the blood-to-air partition coefficient was calculated by means of our physiologically based pharmacokinetic model. The time variation of radon concentration in mouse blood during exposure to radon was also calculated. All results are compared in detail with those found in the literature.

Analysis of variations in observed ambient dose rates due to rainfall or snowfall at JAEA Ningyo-toge

Tanaka, Hiroshi; Sakoda, Akihiro; Ando, Masaki; Ishimori, Yuu

Hoken Butsuri, 51(2), p.107 - 114, 2016/06

https://doi.org/10.5453/jhps.51.107

Ambient dose rates are continuously monitored in Ningyo-toge Environmental Engineering Center, Japan Atomic Energy Agency. The present study discussed the variations in ambient dose rates, observed from April 2014 to March 2015, due to snowfall as well as rainfall. It is much snowy as one of climatic features in this area. Rain or snow was sampled for a certain period in the day of interest (17 cases in total), and then the concentration of radon progeny was measured. With the measured data, the variation in ambient dose rate was calculated considering the accumulation of the radon progeny on the ground. As a whole, this calculation was found to reasonably reproduce the time trends of observed dose rates, except for four cases. Based on the backward trajectory analysis, it was explained that the discrepancy in two cases out of the four was induced by changes of radon progeny concentration in precipitation around sampling period. It was suggested that the other two cases were caused by the run-off of rain from the ground surface.

Animal study on biological responses by radon inhalation making use of waste rock which contains feeble activity of uranium, 2; (Joint research)

Ishimori, Yuu; Sakoda, Akihiro; Tanaka, Hiroshi; Mitsunobu, Fumihiro*; Yamaoka, Kiyonori*; Kataoka, Takahiro*; Etani, Reo*

JAEA-Research 2015-024, 41 Pages, 2016/03

JAEA-Research-2015-024.pdf:3.11MB

Okayama University and the Japan Atomic Energy Agency (JAEA) have carried out the collaborative study of physiological effects of inhaled radon for the low-dose range. Main assignments were as follows. Based on the clinical knowledge, Misasa Medical Center (Okayama University Hospital) clarified the issues that should be addressed. Graduate School of Health Sciences (Okayama University) supervised the research and studied the biological responses. The JAEA made the development and control of a facility for radon inhalation experiments and the investigation of biokinetics and exposure doses of radon. From 2009 to 2013, the following results were obtained. (1) Literature on drinking effects of radon hot spring water was surveyed to determine the present tasks. (2) Under the present experimental conditions, drinking of hot spring water into which radon was intentionally introduced using the equipment in the facility did not have significant effects on mice. (3) Inhibitory effects of antioxidant pre-supplements (Vitamins C and E) and radon pre-inhalation on hepatic or renal oxidative damage were examined to make the comparison. (4) In order to discuss biological responses quantitatively following radon inhalation, the biokinetics of inhaled radon were studied. (5) Some exposure routes due to inhalation of radon or its progeny were modeled to calculate organ doses in mice.

New result in the production and decay of an isotope, 113 of the 113th element

Morita, Kosuke*; Morimoto, Koji*; Kaji, Daiya*; Haba, Hiromitsu*; Ozeki, Kazutaka*; Kudo, Yuki*; Sumita, Takayuki*; Wakabayashi, Yasuo*; Yoneda, Akira*; Tanaka, Kengo*; et al.

Journal of the Physical Society of Japan, 81(10), p.103201_1 - 103201_4, 2012/10

https://doi.org/10.1143/JPSJ.81.103201

An isotope of the 113th element, 113, was produced in a nuclear reaction with a Zn beam on a Bi target. We observed six consecutive decays following the implantation of a heavy particle in nearly the same position in the semiconductor detector, in extremely low background condition. The fifth and sixth decays are fully consistent with the sequential decays of Db and Lr both in decay energies and decay times. This indicates that the present decay chain consisted of 113, Rg (Z = 111), Mt (Z = 109), Bh (Z = 107), Db (Z = 105), and Lr (Z = 103) with firm connections. This result, together with previously reported results from 2004 and 2007, conclusively leads the unambiguous production and identification of the isotope 113, of the 113th element.

Performance of the first Japanese large-scale facility for radon inhalation experiments with small animals

Ishimori, Yuu; Mitsunobu, Fumihiro*; Yamaoka, Kiyonori*; Tanaka, Hiroshi; Kataoka, Takahiro*; Sakoda, Akihiro*

Radiation Protection Dosimetry, 146(1-3), p.31 - 33, 2011/07

https://doi.org/10.1093/rpd/ncr100

A radon test facility for small animals was developed in order to increase the statistical validity of differences of the biological response in various radon environments. This paper illustrates the performances of that facility, the first large-scale facility of its kind in Japan. The facility has a capability to conduct approximately 150 mouse-scale tests at the same time. The apparatus for exposing small animals to radon has six animal chamber groups with five independent cages each. Different radon concentrations in each animal chamber group are available. Because the first target of this study is to examine the in vivo behavior of radon and its effects, the major functions to control radon and to eliminate thoron were examined experimentally. Additionally, radon progeny concentrations and their particle size distributions in the cages were also examined experimentally to be considered in future projects.