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Study shows muddy seabed off Fukushima coast has higher levels of contamination via The Asahi Shimbun

Concentrations of radioactive cesium on the seafloor after the 2011 Fukushima nuclear disaster were discovered to be higher in muddy depressions than on the rocky seabed, maritime researchers said.

“We are learning that the nuclear accident didn’t contaminate the entire ocean, but created spots that tend to have higher radioactive levels than others,” said Blair Thornton, a researcher from the University of Tokyo’s Institute of Industrial Science. “We want to continue investigating.”

At the request of the Nuclear Regulation Authority, a team of researchers from the University of Tokyo, the National Maritime Research Institute and Kanazawa University charted a distance of more than 1,000 kilometers. Sites measured ran 50 km north to south and 25 km west to east off the coast of Fukushima Prefecture, where the stricken Fukushima No. 1 nuclear power plant is located.

They used a ship equipped with an instrument specially developed to measure seafloor gamma ray levels while simultaneously surveying the underwater landscape using sonar.

Per every kilogram of seabed soil, the average concentration of cesium-137 was 90 becquerels. But of the locations charted 4 km offshore, 20 sites measured higher than 1,000 becquerels and some locations 6 km offshore registered levels as high as 2,000 becquerels.

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