Radioactivity from the Fukushima nuclear disaster in Japan has been detected in Pacific bluefin tuna caught off the California coast. Bluefin tuna, one of the biggest, fastest fish in the ocean, brought Fukushima radioactivity to U.S. shores months before ocean currents washed contaminated debris onto beaches. Levels of radioactivity in the tuna were within safe levels, but as fish spend longer periods in Japanese waters, that could change.
The mighty Pacific bluefin tuna
After the March 2011 earthquake and tsunami wrecked the Fukushima nuclear plant, elevated radiation levels were found in small fish and plankton in Japanese waters. But Pacific bluefin tuna can grow up to 10 feet long and weigh more than 1,000 pounds. They spawn off the coast of Japan and swim east at up to 30 miles per hour to waters off California and Mexico. Scientists were surprised to find that nuclear fallout lingered in the huge fish because they are known to metabolize and shed radioactivity fairly efficiently.
On May 28 researchers reported that the radioactive isotopes cesium-137 and cesium-134 were detected in 15 tuna caught near San Diego last August, four months after the Fukushima reactors exploded and months before ocean currents washed radioactive debris on beaches in Alaska and the Pacific Northwest. The levels of radioactive cesium detected in the fish were 10 times higher than amounts previously measured in tuna off the California coast.
In the report, published online in the Proceedings of the National Academy of Sciences, researchers said that because cesium 134 is generated only by nuclear power plants and weapons—and that there was none in the Pacific for several years before the Fukushima disaster—any cesium 134 in tuna off California had to come from Fukushima.
Swimming through cesium 134
To rule out the possibility that the radiation was carried to the west coast by ocean currents or the atmosphere, researchers analyzed bluefin tuna that migrated to Southern California before the Fukushima disaster and no trace of cesium 134 was found. Off the coast of Japan, the tuna likely swam right through plumes of cesium 134, ingesting it through their gills and eating other fish contaminated with the isotope.
Find another protein source?
The levels of cesium 134 in the fish are considered acceptable by government guidelines, but if you believe that any amount of radioactivity in food is bad, you may want to consider replace tuna with some other source of protein. Especially since bluefin migrating from Japanese waters that arrive this summer will have been swimming in radioactive waters much longer than those analyzed in the study.