There is no evidence yet of radiation from Japan's 2011 nuclear disaster in kelp samples from Baja California to Alaska, a team of scientists announced Wednesday.
Kelp Watch 2014, one of two studies measuring the eastward migration of radioactive isotopes from the Fukushima Daiichi meltdown, issued its first batch of results, finding no indication of the material in the kelp forests that hug the West Coast.
Leading researchers predict that when the radioisotopes do arrive this year, the concentrations will be very low, far beneath levels that would pose a danger to human health.
"I would say enjoy the ocean," said Steven L. Manley, a Cal State Long Beach biological sciences professor and co-director of Kelp Watch 2014.
A team of about 45 scientists and educators collected kelp samples in February and March from 36 locations along the Pacific coast, Manley said. Twenty-six of those samples have been analyzed, including 17 from California.
The key finding so far is the lack of cesium 134 -- one of the primary radioactive substances released due to the accident -- in any of the analyzed samples. Cesium 134, with a half-life of about two years, disappears relatively quickly from the environment. So if elevated levels of the isotope were detected, Fukushima Daiichi would be the source, researchers say.
A related, more persistent isotope, cesium 137, was found in low levels in all West Coast samples. The concentrations were consistent with background radiation lingering from nuclear weapons testing in the Pacific Ocean in the 1950s and 1960s. Cesium 137 has a half-life of about 30 years, meaning its presence is halved in that period of time.
Manley and fellow co-director Kai Vetter, a nuclear engineering professor at UC Berkeley, chose to analyze kelp because it is an easy, reliable way to measure radioactivity. Kelp is abundant, and it concentrates isotopes in surrounding seawater.
Vetter and Manley's team collected 14 pounds of kelp blades from each sampling location, then dried and ground them into powder. The samples were analyzed at Lawrence Berkeley National Laboratory, where Vetter is director of applied nuclear physics.
The levels of cesium 137 in the samples ranged from 0.08 to 0.44 becquerels per kilogram. Those levels were roughly 10,000 times lower than those of naturally occurring potassium 40 also found in the kelp samples.
The levels of cesium 137 detected by Kelp Watch 2014 are similar to previous results obtained by Ken Buesseler, a marine chemist at Woods Hole Oceanographic Institution in Massachusetts. Buesseler is leading a second project to measure radiation from Fukushima Daiichi in ocean water up and down the West Coast.
Buesseler found cesium 137 concentrations of between 1.5 and 2 becquerels per cubic liter in samples taken this winter in California and Washington. Those background levels are several thousand times below the U.S. Environmental Protection Agency's limit for cesium 137 in drinking water.
Kelp Watch 2014 will take additional samples in the summer and fall.