Dissolved radiocaesium in seawater off the coast of Fukushima during 2013-2015

During 2013-2015, the dissolved Cs-137 activity concentrations in seawater off the coast of Fukushima were one or two orders as high as those before the Fukushima accident. The activity concentrations in the surface-layer seawater at NPE2, NP0, NP2, NPE1, AN7, I01, E and A stations, which are located within about 10 km from the coast, relatively higher than those outside the 10 km zone. These relatively high concentrations (> 10 mBq L-1) seem to be affected by several factors, including increased river input or contaminated water input from the Fukushima Dai-ichi Nuclear Power Station due to heavy rain events.