North Pacific Anadromous Fish Commission

Technical Report 17

Table of Contents

Radioactive Cesium in the North Pacific after the Fukushima Dai-ichi Nuclear Power Plant Accident

Authors: 
Hideki Kaeriyama

Abstract Excerpt: The Great East Japan Earthquake and consequent giant tsunami on 11 March 2011 resulted in serious damage to the Fukushima Dai-ichi Nuclear Power Plant (FNPP). Radioactive cesium (134Cs and 137Cs) was then released into the ocean through atmospheric deposition and as direct releases. As is a concern for the fisheries community, the contamination level of fisheries products is the most important issue. The monitoring of the concentration of radioactive materials (mostly radioactive cesium and iodine) in fisheries products started immediately after the accident. The standard limit, 100 Bq kg-1 for the sum of radioactive cesium (134Cs + 137Cs), was set as the safe limit for food (https://www.mhlw.go.jp/english/topics/2011eq/dl/new_standard.pdf). This standard limit ensures that the lifetime effect of radioactive materials in fish is sufficiently low as to be safe even when a person continues to eat the fish—one milli-sievert or less per year. The monitoring results of radioactive cesium for fisheries products are published on the Fisheries Agency Japan website (https://www.jfa.maff.go.jp/e/inspection/index.html). Soon after the accident, ~40% of tested samples exceeded the standard limit. After that, the concentrations of radioactive cesium in fisheries products decreased rapidly, and very limited samples (< 10%) have exceeded the standard limit since FY2012. More recently, only 0.01% of inspected samples recorded more than 100 Bq kg-1 during FY2019 and FY2020. Such a rapid decrease of radioactive cesium in marine organisms is reflected by the presence of radioactive cesium in the environment they inhabit, such as seawater and seabed sediment. Generally, cesium is a conservative element and mostly occurs in the dissolved phase in the marine environment. The distribution of radioactive cesium as a dissolved phase is fundamentally important to assess how the FNPP accident affects the oceanic environment.

*This is the first paragraph of an extended abstract. Download the full abstract below.

DOI:
https://doi.org/10.23849/npafctr17/202.204.

Citation

Kaeriyama, H.  2021.  Radioactive cesium in the North Pacific after the Fukushima Dai-ichi nuclear power plant accident.  N. Pac. Anadr. Fish Comm. Tech. Rep. 17: 202–204.  https://doi.org/10.23849/npafctr17/202.204.