Use of Otolith for Detecting Strontium-90 in Fish from the Harbor of Fukushima Dai-ichi Nuclear Power Plant

To clarify the level of contamination with radioactive cesium (radiocesium) discharged from Fukushima Dai-ichi Nuclear Power Plant (FDNPP), three fish species caught in the main harbor of FDNPP were subjected to γ-ray analysis. The concentration of radiocesium in muscle differed among individual fish, even those of similar size of the same species, and showed little relation to the standard length of fish. The maximum concentration of radiocesium (202 kBq/kg wet) was detected from fat greenling samples. A comparison to data from outside the port indicated that the level of radiocesium contamination inside the port was higher than that outside. We found that β-rays were emitted from otoliths of fishes caught in the port of FDNPP. β-ray intensities were correlated with the concentrations of radiocesium in muscles of the three fish species. In Japanese rockfish, the β-ray count rates from otoliths were significantly correlated with the concentration of radiocesium and ⁹⁰Sr in the whole body without internal organs of Japanese rockfish. However, no β-rays were detected from brown hakeling samples collected around FDNPP, suggesting that the detection of β-rays from otoliths may indicate living in the main harbor of FDNPP

Southwest Intrusion of ¹³⁴Cs and ¹³⁷Cs Derived from the Fukushima Dai-ichi Nuclear Power Plant Accident in the Western North Pacific

Enormous quantities of radionuclides were released into the ocean via both atmospheric deposition and direct release as a result of the Fukushima Dai-ichi Nuclear Power Plant (FNPP) accident. This study discusses the southward dispersion of FNPP-derived radioactive cesium (Cs) in subsurface waters. The southernmost point where we found the FNPP-derived ¹³⁴Cs (1.5–6.8 Bq m^–3) was 18°N, 135°E, in September 2012. The potential density at the subsurface peaks of ¹³⁴Cs (100–500 m) and the increased water column inventories of ¹³⁷Cs between 0 and 500 m after the winter of 2011–2012 suggested that the main water mass containing FNPP-derived radioactive Cs was the North Pacific Subtropical Mode Water (NPSTMW), formed as a result of winter convection. We estimated the amount of ¹³⁴Cs in core waters of the western part of the NPSTMW to be 0.99 PBq (decay-corrected on 11 March 2011). This accounts for 9.0% of the ¹³⁴Cs released from the FNPP, with our estimation revealing that a considerable amount of FNPP-derived radioactive Cs has been transported to the subtropical region by the formation and circulation of the mode water