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Purpose: To study the environmental radiation effects of wild animals after the Fukushima Dai-ichi nuclear power plant accident, we assessed effects on hematopoietic progenitor cells (HPCs) in large Japanese field mice ( Apodemus speciosus )., Materials and Methods: A. speciosus were collected from three contaminated sites and control area. The air dose-rates at the control and contaminated areas were 0.96 ± 0.05 μGy/d (Hirosaki), 14.4 ± 2.4 μGy/d (Tanashio), 208.8 ± 31.2 μGy/d (Ide), 470.4 ± 93.6 μGy/d (Omaru), respectively. We investigated possible DNA damage and pro-inflammatory markers in the bone marrow (BM) cells. The colony-forming potential of BM cells was estimated by the number of HPC colony-forming cells. Radiation-induced genomic instability (RIGI) in HPCs was also analyzed by quantifying delayed DNA damage in CFU-GM clones., Results: Although no significant differences in DNA damage and inflammation markers in BM cells from control and contaminated areas, the number of HPC colonies exhibited an inverse correlation with air dose-rate. With regard to RIGI, no significant differences in DNA damage of CFU-GM clones between the mice from the control and the three contaminated areas., Conclusions: Our study suggests that low dose-rate radiation of more than 200 Gy/d reduced HPCs, possibly eliminating genomically unstable HPCs.

Purpose: After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in Japan on March 11 2011, the surroundings became contaminated with radionuclides. To understand the possible biological effects after chronic low dose-rate radiation in contaminated areas of Fukushima, we assessed the effects in large Japanese field mice ( Apodemus speciosus ) by means of chromosome aberration analysis., Materials and Methods: We collected A. speciosus in five sites around Namie Town, Fukushima (contaminated areas) and in two sites in Hirosaki City, Aomori (control areas, 350 km north of FDNPP) from autumn 2011 to 2013. The number of mice captured and ambient dose-rates were as follows: high ( n  = 11, 10.1-30.0 µGy h -1 ), moderate ( n  = 10, 5.7-15.6 µGy h -1 ), low ( n  = 12, 0.23-1.14 µGy h -1 ) and control ( n  = 20, 0.04-0.07 µGy h -1 ). After spleen extraction from rodents, spleen cell culture was performed to obtain metaphase spreads. Chromosome aberrations were assessed on Giemsa-stained metaphase spreads., Results: Although the mice in the contaminated areas were chronically exposed, there was no radiation-specific chromosome aberrations observed, such as dicentric chromosomes and rings. Some structural aberrations such as gaps and breaks were observed, and these frequencies decreased annually in mice from Namie Town., Conclusion: These findings suggest that chromosome aberration analysis is useful to evaluate and monitor radiation effects in wild animals.

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., (© 2020 Wiley-VCH GmbH.)

We investigated the internal contamination by radioactive cesium associated with the FDNPP accident, in the testes or uterus and ovaries of free-roaming cats ( Felis silvestris catus ), which were protected by volunteers in the Namie Town, Fukushima. A total of 253 samples (145 testes and 108 uterus and ovaries) obtained from adult cats and 15 fetuses from 3 pregnant female cats were measured. Free-roaming cats in Namie Town had a higher level of radioactive contamination in comparison to the control group in Tokyo, as the 134 Cs + 137 Cs activity concentration ranged from not detectable to 37,882 Bq kg -1 in adult cats. Furthermore, the radioactivity in the fetuses was almost comparable to those in their mother's uterus and ovaries. The radioactivity was also different between several cats protected in the same location, and there was no significant correlation with ambient dose-rates and activity concentrations in soil. Moreover, radioactive cesium levels in cats decreased with each year. Therefore, it is likely that decontamination work in Namie Town and its surroundings could affect radioactive cesium accumulation, and thus possibly reduce the internal radiation exposure of wildlife living in contaminated areas. It is hence necessary to continue radioactivity monitoring efforts for the residents living in Namie Town.

In this study we analyzed the effect of chronic and low-dose-rate (LDR) radiation on spermatogenic cells of large Japanese field mice ( Apodemus speciosus ) after the Fukushima Daiichi Nuclear Power Plant (FNPP) accident. In March 2014, large Japanese field mice were collected from two sites located in, and one site adjacent to, the FNPP ex-evacuation zone: Tanashio, Murohara and Akogi, respectively. Testes from these animals were analyzed histologically. External dose rate from radiocesium (combined 134 Cs and 137 Cs) in these animals at the sampling sites exhibited 21 μGy/day in Tanashio, 304-365 μGy/day in Murohara and 407-447 μGy/day in Akogi. In the Akogi group, the numbers of spermatogenic cells and proliferating cell nuclear antigen (PCNA)-positive cells per seminiferous tubule were significantly higher compared to the Tanashio and Murohara groups, respectively. TUNEL-positive apoptotic cells tended to be detected at a lower level in the Murohara and Akogi groups compared to the Tanashio group. These results suggest that enhanced spermatogenesis occurred in large Japanese field mice living in and around the FNPP ex-evacuation zone. It remains to be elucidated whether this phenomenon, attributed to chronic exposure to LDR radiation, will benefit or adversely affect large Japanese field mice.

Radionuclide concentrations in environmental samples such as surface soils, plants and water were evaluated by high purity germanium detector measurements. The contribution rate of short half-life radionuclides such as (132)I to the exposure dose to residents was discussed from the measured values. The highest values of the (131)I/(137)Cs activity ratio ranged from 49 to 70 in the environmental samples collected at Iwaki City which is located to the south of the F1-NPS. On the other hand, the (132)I/(131)I activity ratio in the same environmental samples had the lowest values, ranging from 0.01 to 0.02. By assuming that the (132)I/(131)I activity ratio in the atmosphere was equal to the ratio in the environmental samples, the percent contribution to the thyroid equivalent dose by (132)I was estimated to be less than 2%. Moreover, the contribution to the thyroid exposure by (132)I might be negligible if (132)I contamination was restricted to Iwaki City.