Recent sampling of West Coast kelp shows no evidence of radiation from Japan's crippled Fukushima nuclear power plant.
The plume of radiation is expected to arrive on U.S. shores this spring, scientists say, although at very low levels that won't harm humans or the environment.
The new results are from samples primarily collected from Feb. 24 through March 14 as part of Kelp Watch 2014.
The project uses coastal kelp beds as radiation detectors.
It's a collaborative effort led by Steven Manley, marine biology professor at California State University, Long Beach, Kai Vetter, head of applied nuclear physics at the Lawrence Berkeley National Laboratory and a nuclear engineering professor at the University of California, Berkeley.
"Our data does not show the presence of Fukushima radioisotopes in West Coast Giant Kelp or Bull Kelp," Manley said. "These results should reassure the public that our coastline is safe, and that we are monitoring it for these materials. At the same time, these results provide us with a baseline from which we can compare samples gathered later in the year."
The samples analyzed to date were gathered from as far north as Kodiak Island, Alaska, to as far south as Baja California. Two sites in the tropics--Hawaii and Guam, where non-kelp brown algae were sampled--also were negative for Fukushima radiation. Kelps are not found in the tropics.
The project also has Giant Kelp from Chile in South America that will serve as a "Fukushima-free" reference site, far removed from any potential influence from the nuclear power plant.
"The samples of greatest concern were those from the north, Alaska to Washington State, where it is thought the radioactive water will first make contact with North America," Manley said. "The tell-tale isotopic signature of Fukushima, Cs-134, was not seen, even at the incredibly low detection limits provided by Dr. Vetter's group at the Berkeley Lab and UC Berkeley."
The second of the three 2014 sampling periods is scheduled to begin in early July.
More information about Kelp Watch 2014 is available at http://kelpwatch.berkeley.edu/