Monitoring efforts along the Pacific Coast of the U.S. and Canada have detected the presence of small amounts of radioactivity from the 2011 Fukushima Dai-ichi Nuclear Power Plant accident 100 miles (150 km) due west of Eureka, California. Scientists at the Woods Hole Oceanographic Institution…
Monitoring efforts along the Pacific Coast of the U.S. and Canada have detected the presence of small amounts of radioactivity from the 2011 Fukushima Dai-ichi Nuclear Power Plant accident 100 miles (150 km) due west of Eureka, California. Scientists at the Woods Hole Oceanographic Institution (WHOI) found the trace amounts of telltale radioactive compounds as part of their ongoing monitoring of natural and human sources of radioactivity in the ocean.
In the aftermath of the 2011 tsunami off Japan, the Fukushima Dai-ichi Nuclear Power Plant released cesium-134 and other radioactive elements into the ocean at unprecedented levels. Since then, the radioactive plume has traveled west across the Pacific, propelled largely by ocean currents and being diluted along the way. At their highest near the damaged nuclear power plant in 2011, radioactivity levels peaked at more than 10 million times the levels recently detected near North America.
“We detected cesium-134, a contaminant from Fukushima, off the northern California coast. The levels are only detectable by sophisticated equipment able to discern minute quantities of radioactivity,” said Ken Buesseler, a WHOI marine chemist, who is leading the monitoring effort. “Most people don’t realize that there was already cesium in Pacific waters prior to Fukushima, but only the cesium-137 isotope. Cesium-137 undergoes radioactive decay with a 30-year half-life and was introduced to the environment during atmospheric weapons testing in the 1950s and ’60s. Along with cesium-137, we detected cesium-134 which also does not occur naturally in the environment and has a half-life of just two years. Therefore the only source of this cesium-134 in the Pacific today is from Fukushima.”
The amount of cesium-134 reported in these new offshore data is less than 2 Becquerels per cubic meter (the number of decay events per second per 260 gallons of water). This Fukushima-derived cesium is far below where one might expect any measurable risk to human health or marine life, according to international health agencies. And it is more than 1000 times lower than acceptable limits in drinking water set by US EPA.
Scientists have used models to predict when and how much cesium-134 from Fukushima would appear off shore of Alaska and the coast of Canada. They forecast that detectable amounts will move south along the coast of North America and eventually back towards Hawaii, but models differ greatly on when and how much would be found.
“We don’t know exactly when the Fukushima isotopes will be detectable closer to shore because the mixing of offshore surface waters and coastal waters is hard to predict. Mixing is hindered by coastal currents and near-shore upwelling of colder deep water,” said Buesseler. “We stand to learn more from samples taken this winter when there is generally less upwelling, and exchange between coastal and offshore waters maybe enhanced.”
The offshore radioactivity reported this week came from water samples collected and sent to Buesseler’s lab for analysis in August by a group of volunteers on the research vessel Point Sur sailing between Dutch Harbor, Alaska, and Eureka, California. These results confirm prior data described at a scientific meeting in Honolulu in Feb. 2014 by John Smith, a scientist at Fisheries and Oceans Canada in Dartmouth, Nova Scotia, who found similar levels on earlier research cruises off shore of Canada. Buesseler and Smith are now working together on a new project, led by Jay Cullen at the University of Victoria, Canada, that involves Canadian academic, government and NGO partners to determine and communicate the environmental risks posed by Fukushima for Canada’s Pacific and Arctic coasts and their inhabitants.
Buesseler believes the spread of radioactivity across the Pacific is an evolving situation that demands careful, consistent monitoring of the sort conducted from the Point Sur.
Ocean scientists need to do more work offshore to understand how ocean currents will be transporting cesium on shore. The models predict cesium levels to increase over the next two to three years, but do a poor job describing how much more dilution will take place and where those waters will reach the shore line first.
Ken Buesseler is a senior scientist at the Woods Hole Oceanographic Institution (WHOI) who specializes in the study of natural and man-made radionuclides in the ocean. His work includes studies of fallout from atmospheric nuclear weapons testing, assessments of Chernobyl impacts on the Black Sea, and examination of radionuclide contaminants in the Pacific resulting from the Fukushima nuclear power plants. Dr. Buesseler has served as Chair of the Marine Chemistry and Geochemistry Department at WHOI, as Executive Scientist of the U.S. Joint Global Ocean Fluxes Planning and Data Management Office, and two years as an Associate Program Director at the U.S. National Science Foundation, Chemical Oceanography Program. In 2009, he was elected Fellow of the American Geophysical Union and in 2011 he was noted as the top-cited ocean scientist by the Times Higher Education for the decade 2000-2010. He is currently Director of the Center for Marine and Environmental Radioactivity at WHOI.