A protester shouts slogans during an anti nuclear rally in downtown Tokyo.
Researchers found “modestly elevated levels” of two radioactive isotopes in 15 Bluefin tuna caught off the coast of San Diego, California in August 2011, according to the study published online on Monday by the Proceedings of the National Academy of Sciences (PNAS).
The researchers said the elevated radioactivity posed no risk to public health as the observed levels were more than an order of magnitude lower than the Japanese safety limit and were lower than other naturally present isotopes.
The study was authored by Daniel Madigan of California’s Stanford University and Zofia Baumann and Nicholas Fisher, both from Stony Brook University in New York.
The study found slightly higher levels of radioactive cesium-134 and cesium-137 in the 15 tuna, compared to Bluefin tuna caught in the same area before the Fukushima nuclear disaster and to Yellowfin tuna – which keep to the eastern Pacific – caught before or after the accident.
The study said the results provide “unequivocal evidence” that the fish had carried Fukushima-derived radioactive material across the ocean over the course of their easterly migration.
“These findings indicate that Pacific Bluefin tuna can rapidly transport radionuclides from a point source in Japan to distant eco regions and demonstrate the importance of migratory animals as transport vectors,” it said.
The researchers emphasized that the cesium isotopes do not endanger public health, especially as they gives off far less radiation than potassium-40, a naturally-present isotope found in all the fish.
The massive 9.0-magnitude earthquake and tsunami on March 11 2011 killed thousands of people and crippled the cooling systems at the Fukushima plant, causing meltdowns in some of its reactors.
Radiation leaked into the air, soil and sea around the plant, forcing tens of thousands of people to evacuate their homes. – Sapa-AFP