NHK World 
May 29, 2011
Japan’s science ministry has detected extraordinarily high levels of radioactive cesium in seafloor samples collected off Miyagi and Ibaraki Prefectures.
Experts say monitoring should be stepped up over a larger area to determine how fish and shell fish are being affected.
The ministry collected samples from 12 locations along a 300-kilometer stretch off Fukushima prefecture’s Pacific coast between May 9th and 14th. It hoped to get an idea about the spread of nuclear contamination caused by the accident at the Fukushima Daiichi nuclear power plant.
Radioactive substances were found in all locations, including those off Miyagi and Ibaraki Prefectures, which had not been previously investigated.
Radioactive cesium 137, measuring 110 becquerels per kilogram or about 100 times the normal level, was found in samples collected from the seabed 30 kilometers off Sendai City and 45 meters beneath the surface.
- A d v e r t i s e m e n t
Samples collected from the seabed 10 kilometers off Mito City and 49 meters beneath the surface measured 50 becquerels or about 50 times the normal level.
Professor Takashi Ishimaru of the Tokyo University of Marine Science and Technology says plankton most probably absorbed the radioactive substances carried by the current near the sea surface, and then sank to the seabed.
He said monitoring must be stepped up over a larger area, as radioactive materials in the seabed do not dissolve quickly, and can accumulate in the bodies of larger fish that eat shrimp and crabs that live on the seafloor.