Abstract
The disabling of the Fukushima Daiichi Nuclear Power Plant (F1NPP) resulted in the release of radionuclides, including 134Cs and 137Cs, into the air and the ocean. The unpredicted nuclear accident is of global concern for human health and the ecosystem. Although investigations of radionuclides in environments were performed shortly after the accident started, the temporal and spatial impacts and fluctuations on the releasing radionuclides to natural environment remain unclear. I focused on salmon, which migrate from inland to the open ocean globally, to reveal the three-year (May 2011 to February 2014) fluctuations and accumulations of 134Cs and 137Cs from terrestrial to open ocean environments after the F1NPP accident. The 134Cs and 137Cs concentrations in six salmonids exhibited lower temporal variations for three years after the F1NPP accident, suggesting that these radionuclides are widely distributed and these radionuclides remain in the natural environment globally with less convergence. The accumulation patterns were significantly different among the different salmon species. Fluvial (freshwater residence) type salmons exhibited significantly higher accumulation in 134Cs (25.3–40.2 Bq kg−1 in mean) and 137Cs (41.4–51.7 Bq kg−1 in mean) than did the anadromous (sea-run) type salmons (0.64–8.03 Bq kg−1 in mean 134Cs and 0.42–10.2 Bq kg−1 in mean 137Cs) suggesting widespread contamination in terrestrial environments versus the coastal and open ocean environments. Salmonids are the most highly migratory animals and are characterised by their strong tendency to return home to their natal site for reproduction. Salmonids have a potential to be a good indicator as an effective monitoring animal.
Highlights
The Great East Japan Earthquake of magnitude 9.0 on Friday 11 March 2011 caused considerable damage in the region, and the large tsunami it created caused much more
The present study indicates that migration patterns of the different types of salmon can reveal temporal and spatial fluctuations of radiocesium globally, ranging from terrestrial to open ocean environments
The highest concentration of 18,700 Bq/kg in total cesium was found in fluvial O. masou in March 2012, one year after the F1NPP accident, and there were still detectable amounts in salmon of over 100 Bq kg21 (Japanese safety limit) of 134Cs and 137Cs, even three years after the F1NPP incident (Fig. 2)
Summary
The Great East Japan Earthquake of magnitude 9.0 on Friday 11 March 2011 caused considerable damage in the region, and the large tsunami it created caused much more. A 15-m tsunami disabled the power supply and the cooling of three Fukushima Daiichi reactors, causing a nuclear accident at that date. Radioactive contamination following the Fukushima Daiichi Nuclear Power Plant (F1NPP) accident was the most significant artificial radioactive liquid release into the environment ever known, on a short time and space scale basis [1,2,3,4,5]. The amount of radionuclides discharged from the F1NPP immediately after the accident was estimated to be 5–10 PBq to the atmosphere and 3–6 PBq to the sea, the latter being caused by direct leakage of the contaminated cooling water [5,6,7,8]. In Europe, the first signs of the release were detected seven days later, while the first peak of the activity level was observed between 28 March and 30 March 2011 [3]
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