Temporal variations in 134Cs and 137Cs concentrations in seawater along the Shimokita Peninsula and the northern Sanriku coast in northeastern Japan, one year after the Fukushima Dai-ichi Nuclear Power Plant accident

• Published in: Journal of environmental radioactivity 2013-10, Vol.124, p.239-245
• Main Authors: Kofuji, Hisaki, Inoue, Mutsuo
• Format: Article
• Language: English
• Subjects: 134Cs; 137Cs; Applied sciences; Atmospherics; Coastal environments; Coastal seawater; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Fukushima Dai-ichi Nuclear Power; Marine; Natural water pollution; Northern Sanriku; nuclear power; Nuclear power generation; Nuclear power plants; Peninsulas; Plant accident; Pollution; Pollution, environment geology; Radioactivity; radionuclides; Sea water; seawater; Seawaters, estuaries; Surface water; temporal variation; Water treatment and pollution
• ISSN: 0265-931X; 1879-1700
• DOI: 10.1016/j.jenvrad.2013.06.003

Ninety-six seawater samples were collected between May 2011 and March 2012 at 6 sites along the Shimokita Peninsula and the northern Sanriku coast, 250–450 km north of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP). Cesium-134 and 137Cs concentrations were determined by low-background γ-spectrometry. During May–June 2011, 134Cs and 137Cs concentrations in surface waters decreased from 1.0–2.8 to 0.7–1.5 mBq/L and from 2.1–3.9 to 1.9–3.0 mBq/L, respectively. These decreases were due to diffusion and advection in the ocean after atmospheric input of the FDNPP-derived radionuclides. However, in July–August 2011, the concentrations of both radionuclides in the water samples collected on the Pacific side of the Shimokita Peninsula and the northern Sanriku coast exhibited 30–50-fold increases (∼40 mBq/L for 134Cs and ∼50 mBq/L for 137Cs) over concentrations observed at these sampling sites in June 2011 in contrast to the gradual decreases in the concentrations on the Tsugaru Strait side of the Shimokita Peninsula. These results suggest that radiocesium-contaminated waters offshore in the Pacific Ocean were transported to coastal regions along the Pacific side of the Shimokita Peninsula and the northern Sanriku coast by ocean currents. •Seawater samples were collected along the coastline 250–450 km north of Fukushima.•134Cs and 137Cs concentrations in May–June 2011 were 1–3 mBq/L and 2–4 mBq/L.•134Cs and 137Cs in July–August 2011 sharply increased to ∼40 mBq/L and ∼50 mBq/L.•The increase in Cs concentrations was due to influx of offshore contaminated water.