Fukushima's Radioactive Plume Reaches Waters Off California Coast

Cesium-134 from the Fukushima nuclear disaster was detected 100 miles offshore from Eureka, California. Kimimasa Mayama/Pool/Reuters

Traces of radioactive cesium-134 from the Fukushima nuclear disaster in Japan have made their way to waters 100 miles off the coast of Northern California and will continue to drift, a monitoring institute reported Monday.

The levels are very low—the element has been dispersed and diluted in the Pacific over three years and several thousands of miles since the time and place of the 2011 nuclear meltdown. The amount of cesium-134 detected—two becquerels per cubic meter—is more than 1,000 times lower than the limits set by the U.S. Environmental Protection Agency for drinking water, and is far below the amount that would be of concern for human health or marine life, according to the Woods Hole Oceanographic Institution.

"The levels are only detectable by sophisticated equipment able to discern minute quantities of radioactivity," Ken Buesseler, a Woods Hole marine chemist who is leading the monitoring effort, said in a statement.

No U.S. federal agency conducts or pays for monitoring of ocean radioactivity off the country's coast, so Buesseler's data is the result of a crowdfunded program he began last January to gather samples and track the cesium's drift. Results of the sampling off of the West Coast of the U.S., Alaska and a smattering of sites in Central America are posted to a dedicated website.

Woods Hole projects that the radioactive plume will continue to move toward the Americas and may travel down the U.S. coast before redirecting toward Hawaii. But models can "differ greatly" depending on the specifics of the plume's future path, Woods Hole notes.

"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," Buesseler said. "We stand to learn more from samples taken this winter when there is generally less upwelling, and exchange between coastal and offshore waters may be enhanced."