Radioactive cesium was detected in the ocean as far as 600 kilometers to the east of the crippled Fukushima No. 1 nuclear power plant, scientists said, in amounts that reached 100 times pre-accident levels.
Radioactive cesium was detected in the ocean as far as 600 kilometers to the east of the crippled Fukushima No. 1 nuclear power plant, scientists said, in amounts that reached 100 times pre-accident levels.
A team of Japanese and U.S. researchers, including Jun Nishikawa, an assistant professor of marine ecosystems at the University of Tokyo, sampled seawater and plankton off the shore of Fukushima in June 2011. That was three months after the Great East Japan Earthquake and tsunami triggered a major nuclear accident at the plant and contaminated the waters offshore.
"The concentrations of radioactive substances in seawater is sufficiently low in the outer ocean, but cesium continues to be detected in high concentrations in fish," Nishikawa said. "Continued surveys are necessary."
About 100 times the levels of cesium in plankton before the accident at the plant was detected in many places.
Samples were collected at 50 locations between 30 km to 600 km to the east of the Fukushima plant, located on the coast. A maximum combined concentration of 7.8 becquerels of cesium-134 and cesium-137 per liter of seawater occurred 130 km offshore, where ocean currents formed an eddy.
A maximum 102 becquerels of cesium was detected per kilogram of dry plankton 300 km offshore.
The research results were published online on April 2 in the Proceedings of the National Academy of Sciences of the United States. The paper was written jointly by scientists at the Woods Hole Oceanographic Institution, Stony Book University in Stony Brook, New York, and the University of Tokyo.