Cesium-134, the so-called fingerprint of Fukushima, was measured in seawater samples from the west coast of the United States and a salmon sampled from Canada, researchers said.
Releases from the Fukushima reactors have included dozens of radioactive elements, but with regard to materials released into the ocean, most of the attention has been on three radioactive isotopes released in large amounts: iodine-131, cesium-137, and cesium-134, according to the Woods Hole Oceanographic Institution (WHOI).
Iodine-131 from Fukushima decaying quickly is no longer detectable in the environment. Cesium-137 has a relatively long half-life (30 years), but it is also present in the ocean as a result of nuclear weapons testing in the 1950s and the 1960s. Because of its short half-life, cesium-134 can only have come from Fukushima.
Cesium-134 was measured, for the first time, in seawater samples from Tillamook Bay and Gold Beach in the U.S. northwest state of Oregon, the Statesman Journal newspaper reported, citing the WHOI.
Cesium-134 has also been detected in a Canadian salmon for the first time, the Fukushima InFORM project, led by University of Victoria chemical oceanographer Jay Cullen, reported in November.
Samples, in both cases, indicate that radiation from the nuclear disaster at extremely low levels is not harmful to humans or the environment.
Each of the seawater samples taken in January and February of 2016 and later analyzed measured 0.3 becquerels per cubic meter of cesium-134. And the level in a single sockeye salmon, sampled from the Okanagan Lake in the summer of 2015, was more than 1,000 times lower than the action level set by Health Canada.
Radiation contamination at Fukushima was "unprecedented" for the oceans, Ken Buesseler, a senior scientist at the WHOI told Xinhua earlier this year.
"While in total Chernobyl was a bigger source of human-made radioactivity, most of the Fukushima releases entered the ocean, more than 80 percent, so for the oceans this was a bigger source," Buesseler said.
Buesseler, who called for more efforts to make environmental and health assessments of the Fukushima accident, said even when radiation levels become lower than any safety standards, people can still learn something about the fate and transport of radioactive compounds in this way.
On March 11, 2011, a magnitude-9.0 earthquake -- one of the largest ever recorded -- struck the eastern coast of Japan. The tsunamis caused by the quake badly damaged the Fukushima Dai-ichi nuclear power plant, eventually causing four of the six reactors there to release radiation into the atmosphere and ocean.
Emergency crews used seawater to cool the damaged reactors at the power plant. Because of the plant's location along the coast, much of the water was washed into the Pacific, resulting in the largest accidental release of radiation to the ocean in history.
