¹³⁵Cs/¹³⁷Cs Isotopic Ratio as a New Tracer of Radiocesium Released from the Fukushima Nuclear Accident

Since the Fukushima Daiichi nuclear power plant (FDNPP) accident in 2011, intensive studies of the distribution of released fission products, in particular ¹³⁴Cs and ¹³⁷Cs, in the environment have been conducted. However, the release sources, that is, the damaged reactors or the spent fuel pools, have not been identified, which resulted in great variation in the estimated amounts of ¹³⁷Cs released. Here, we investigated heavily contaminated environmental samples (litter, lichen, and soil) collected from Fukushima forests for the long-lived ¹³⁵Cs (half-life of 2 × 10⁶ years), which is usually difficult to measure using decay-counting techniques. Using a newly developed triple-quadrupole inductively coupled plasma tandem mass spectrometry method, we analyzed the ¹³⁵Cs/¹³⁷Cs isotopic ratio of the FDNPP-released radiocesium in environmental samples. We demonstrated that radiocesium was mainly released from the Unit 2 reactor. Considering the fact that the widely used tracer for the released Fukushima accident-sourced radiocesium in the environment, the ¹³⁴Cs/¹³⁷Cs activity ratio, will become unavailable in the near future because of the short half-life of ¹³⁴Cs (2.06 years), the ¹³⁵Cs/¹³⁷Cs isotopic ratio can be considered as a new tracer for source identification and long-term estimation of the mobility of released radiocesium in the environment

Chromosomal Aberrations in Wild Mice Captured in Areas Differentially Contaminated by the Fukushima Dai-Ichi Nuclear Power Plant Accident

Following the Fukushima Dai-ichi Nuclear Power Plant accident, radiation effects on nonhuman biota in the contaminated areas have been a great concern. The induction of chromosomal aberrations in splenic lymphocytes of small Japanese field mice (<i>Apodemus argenteus</i>) and house mice (<i>Mus musculus</i>) inhabiting Fukushima Prefecture was investigated. In mice inhabiting the slightly contaminated area, the average frequency of dicentric chromosomes was similar to that seen in mice inhabiting a noncontaminated control area. In contrast, mice inhabiting the moderately and heavily contaminated areas showed a significant increase in the average frequencies of dicentric chromosomes. Total absorbed dose rate was estimated to be approximately 1 mGy d^–1 and 3 mGy d^–1 in the moderately and heavily contaminated areas, respectively. Chromosomal aberrations tended to roughly increase with dose rate. Although theoretically, the frequency of chromosomal aberrations was considered proportional to the absorbed dose, chromosomal aberrations in old mice (estimated median age 300 days) did not increase with radiation dose at the same rate as that observed in young mice (estimated median age 105 days)