The isotopes cesium-134 and cesium-137 were found in the tiny plantlike creatures from the coast of Japan’s Hokkaido Island to Guam.
The samples were taken early last year, less than a year after the tsunami that overwhelmed the plant, but the findings were just announced at a meeting of the Japan Geoscience Union.
Cesium-134 has a half-life of two years while it takes 30 years for cesium-137 to decay by half.
Scientists say the isotopes were being dispersed across the Pacific in plankton, and were accumulating up the food chain as the tiny creatures were eaten by larger marine life.
Further studies are being conducted to see how much cesium was building up in fish and possibly marine mammals.
Radiation was flushed into the Pacific after three meltdowns occurred at the Fukushima nuclear plant.
More than two years after the March 2011 disaster, plant operators are struggling to contain the 400 tons of radioactive water poured over the melted cores of reactors 1, 2 and 3 to prevent the fuel from melting and burning again.
Photo: Tokyo Electric Power Company