Three and a half years after the earthquake and tsunami that damaged the Fukushima nuclear power planet in Japan, radiation from that disaster has been detected just off the coast of Northern California.

Researchers from the Woods Hole Oceanographic Institution who have been monitoring both natural and man-made sources of radioactivity say they've detected tiny amounts of the telltale radioactive compounds 100 miles due west of the coastal city of Eureka.

When the Dai-ichi nuclear power plant was damaged in 2011, the resultant meltdown released cesium-134 and some other radioactive elements into the nearby ocean, elements that have slowly been transported eastward by ocean currents that are also diluting them.

As a result, the radioactivity detected off California is at trace levels and harmless, the researchers say.

"The levels are only detectable by sophisticated equipment able to discern minute quantities of radioactivity," says WHOI marine chemist Ken Buesseler, leader of the monitoring project.

The cesium-134 off California, identified as coming from Fukushima, is at a level far below any amount that might represent a risk to marine life or to human health, the researchers say.

It is also 1,000 times lower than what the U.S. Environmental Protection Agency has set as safe levels for drinking water, they say.

When and where the radioactivity will be detected next is hard to estimate, they explain.

"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," Buesseler says.

No federal agency is presently funding any monitoring of the ocean's radioactivity in U.S. coastal waters, prompting Buesseler and his colleagues to turn to crowdfunding to create a citizen-science effort in which members of the public collected water samples along the U.S. West Coast and in Hawaii.

Results of the analyses have been posted to a website where the public can view them.

That's important to counter irrational fears and rumors that have sprung up about the Fukushima radiation, Buesseler says.

"People were making irrational decisions about spending time at the coast, or attributing starfish deaths to Fukushima," he says. "Dental x-rays and airplanes have greater exposures than what we are measuring."

Other experts agreed that public fears over the radiation have been unfounded.

"There are people here in California who are worried they could get fried by going to a beach, and this research confirms that those fears are wrong and inappropriate," says Daniel Hirsch, a nuclear policy researcher at the University of California, Santa Cruz, who was not involved in the study.

Buesseler says he will present his findings later this week at the annual meeting of the Society of Environmental Toxicology and Chemistry North America.

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