134Cs and 137CS activities in coastal seawater along Northern Sanriku and Tsugaru Strait, northeastern Japan, after Fukushima Dai-ichi Nuclear Power Plant accident

A total of 37 seawater samples were collected at 10 sites along the coastline of the Northern Sanriku and Tsugaru Strait, 250-450 km north of the Fukushima Dai-ichi Nuclear Power Plant in April-December 2009 and May June 2011, and analyzed for Cs-134 and Cs-137 activities using low-background gamma-spectrometry. The Cs-134 and Cs-137 activities measured in these samples in May 2011 were found to be 2-3 mBq/L and 2.5-4 mBq/L, respectively. By June, these values had decreased by 25-45%/month and 5-30%/month, respectively. These results can be plausibly explained by surface infusion of these isotopes into the sea by atmospheric transport from Fukushima and their subsequent reduction by water migration to off-shore and deeper regions. (C) 2011 Elsevier Ltd. All rights reserved.