Radiocesium in Japan Sea associated with sinking particles from Fukushima Dai-ichi Nuclear Power Plant accident

Hideki Kaeriyama; Ken Fujimoto; Mutsuo Inoue; Masayuki Minakawa

doi:10.1016/j.jenvrad.2020.106348

Radiocesium in Japan Sea associated with sinking particles from Fukushima Dai-ichi Nuclear Power Plant accident

J Environ Radioact. 2020 Oct:222:106348. doi: 10.1016/j.jenvrad.2020.106348. Epub 2020 Jul 10.

Authors

Hideki Kaeriyama¹, Ken Fujimoto², Mutsuo Inoue³, Masayuki Minakawa²

Affiliations

¹ National Research Institute of Fisheries Science, Fisheries Research and Education Agency, 2-12-4, Fukuura, Kanazawa, Yokohama, Kanagawa, 236-8648, Japan. Electronic address: kaeriyama@affrc.go.jp.
² National Research Institute of Fisheries Science, Fisheries Research and Education Agency, 2-12-4, Fukuura, Kanazawa, Yokohama, Kanagawa, 236-8648, Japan.
³ Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa, 923-1224, Japan.

PMID: 32892904
DOI: 10.1016/j.jenvrad.2020.106348

Abstract

This study examined the temporal variations in radiocesium concentration associated with sinking particles in the northeastern Japan Sea between September 2010 and July 2012. We analyzed sediment trap samples from this period after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011. Cesium-134 was detected in samples collected between May and July 2011 at a depth of 1100 m (4.2-11 mBq g-dry^-1) but not in other periods at 1100 m or deeper (3100 and 3500 m). These results confirmed the deposition of FDNPP-derived radiocesium on the surface water in the late April 2011, which rapidly sank with sinking particles to a depth of at least 1100 m, in the northeastern Japan Sea, about 40 days after the deposition in the North Pacific. If FDNPP-derived ¹³⁷Cs was excluded, no seasonal changes were detected in the ¹³⁷Cs activity concentration of the sinking particles, and the ¹³⁷Cs activity concentration of the particles increased with increasing depth. Judging from the concentration of ¹³⁷Cs of sinking particle and seasonal variation of total mass flux and organic matter content, the lithogenic particle seems to be important for radiocesium associated with sinking particles. These data also strongly suggest a difference in sinking features of particles between 2010-2011 and 2011-2012 deployments. Due to the existence of benthic front, shallow water (1100 m) and deep water (3500 m) are separated during 2010-2011 deployment, but in the winter of 2011-2012, this front disappeared and the particles in surface water seem to have sunk to the depth of 3100 m. The sinking velocity of the particles at 1100 m was estimated to be 33-62 m day^-1, with a mean sinking velocity of 43 m day^-1. These values were comparable to those estimated at depths shallower than 1000 m in the North Pacific after the FDNPP accident, or in the Mediterranean, North, and Black Seas after the Chernobyl accident.

Keywords: (134)Cs; (137)Cs; Fukushima Dai-ichi Nuclear Power Plant accident; Japan Sea; Sinking particle.

MeSH terms

Black Sea
Cesium Radioisotopes* / analysis
Fukushima Nuclear Accident*
Japan
Nuclear Power Plants
Radiation Monitoring*
Water Pollutants, Radioactive*

Substances

Cesium Radioisotopes
Water Pollutants, Radioactive