An international team of scientists has found radioactive substances released into the ocean from the tsunami-crippled nuclear reactors in Fukushima, Japan, have turned up in marine life in the Pacific Ocean, but at concentrations well below levels believed to pose a risk to humans or the animals themselves.
The research team, helmed by scientists with the Woods Hole Oceanographic Institution, said it’s unclear whether radioactive materials are accumulating on the seafloor sediments of if they might pose a long-term threat.
The findings, reported in the online edition of the journal Proceedings of the National Academy of Sciences, are the first reports from a research project scientists organized to measure the concentration, spread and biological impacts of radiation from the damaged Japanese nuclear power plant.
The group of 17 researchers from eight institutions spent 15 days at sea in June 2011 studying ocean currents, and sampling water and marine life up to the edge of the exclusion zone around the reactors. The team found that the concentration of several key radioactive substances – radionuclides -- were elevated but varied widely across the study area, reflecting the complex nature of the marine environment.
"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," said Ken Buesseler, a senior Woods Hole scientist. "We also wanted to provide as wide ranging a look as possible at potential impacts on the marine system to give a better idea of what was going on in the region, but also to provide a stronger baseline from which to measure future changes."
Among the materials released by the Japanese nuclear plants were cesium-134 and -137, two radioactive isotopes that do not occur naturally in the ocean. Cesium-134 has a half-life of a little over two years, and so could come only from the reactors at Fukushima.
The group conducted extensive water sampling from the surface to as deep as 3,200 feet and used nets to sample phytoplankton, zooplankton, and small fish. They also released two dozen “drifters,” instruments that move with ocean currents and report their position via satellite back to shore.
"The radioactivity of the fish we caught and analyzed would not pose problems for human consumption," researchers said. "It does not mean all marine organisms caught in the region are perfectly safe to eat. That's still an open question. 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. Further study and appropriate monitoring will help clarify this issue."
"What this means for the marine environment of the Northwest Pacific over the long term is something that we need to keep our eyes on," said Buesseler.
In a separate report in the the Proceedings of the National Academy of Sciences, Dartmouth University researchers said they had radioactive iodine from Fukushima in the local New Hampshire environment.
Joshua Landis, with Dartmouth’s Department of Earth Science, said the iodine is “a direct consequence of a nuclear reactor's explosion and meltdown half a world away... We live on a really small planet and this demonstrates that what happens in Japan has the potential to affect us."