The results were from a research cruise in June 2011 to study the amount spread, and impacts of radiation released March 11, 2011, when a magnitude-9 earthquake caused a tsunami that devastated the northeast coast of Japan and severely damaged the Fukushima Daiichi Nuclear Power Plant, the Woods Hole Oceanographic Institution in Massachusetts reported Tuesday.
"Our goal was to provide an independent assessment of what the Japanese were reporting and also to get further off shore to sample in places where we thought the currents would be carrying most of the radionuclides," researcher leader Ken Buessler, a Woods Hole marine chemist, said.
The research cruise, which began 350 miles off the Japanese coast and came as close as 18 miles to the damaged power plant, conducted extensive water sampling from the surface to as deep as 3,200 feet and made net tows to collect samples of phytoplankton, zooplankton and small fish.
Although levels of radioactivity in marine life sampled during the cruise were well below levels of concern for humans and the organisms themselves, the researchers said, radioactive materials accumulating on the seafloor might pose a long-term threat to the marine ecosystem.
"There are still likely to be hot spots in sediments close to shore and closer to the power plant that may have resulted in very contaminated species in those areas," marine biologist Nicholas Fisher from the State University of New York, Stony Brook, said. "Further study and appropriate monitoring will help clarify this issue."