Traces of radiation from Fukushima detected off California



less Japan's nuclear watchdog members, including Nuclear Regulation Authority members in radiation protection suits, inspect contaminated water tanks at the Tokyo Electric Power Co (TEPCO) Fukushima Dai-ichi nuclear power plant in the town of Okuma, Fukushima prefecture on August 23, 2013. Japan's nuclear watchdog dispatched an inspection team to the crippled Fukushima plant after workers found a huge toxic water leak and unexplained radiation hotspots. Earlier this week around 300 tonnes of radioactive liquid is believed to have escaped from one of the hundreds of tanks that hold polluted water, some of which was used to cool the broken reactors, in an episode dubbed the most serious in nearly two years. Japan's nuclear watchdog members, including Nuclear Regulation Authority members in radiation protection suits, inspect contaminated water tanks at the Tokyo Electric Power Co (TEPCO) Fukushima Dai-ichi nuclear ... more Photo: Japan Pool, AFP/Getty Images Photo: Japan Pool, AFP/Getty Images Image 1 of / 1 Caption Close Traces of radiation from Fukushima detected off California 1 / 1 Back to Gallery

The first faint traces of radioactivity in the ocean from the Fukushima nuclear disaster have been detected 100 miles off Eureka, a scientist who has been monitoring radiation levels across the Pacific reported Monday.

The levels of the radioactive element Cesium-134 were far lower than any radiation that would pose a threat to human or marine life, said Ken Buesseler, a nuclear chemist at the Woods Hole Oceanographic Institution on Cape Cod.

The radioactivity was detected in samples of ocean water volunteers aboard a research vessel from the Moss Landing Marine Laboratory in Monterey County collected last August. The samples were sent for analysis to Buesseler’s lab at Woods Hole.

Buesserler’s findings confirmed a report last February by Canadian scientists who found similar faint traces of radioactivity in the ocean off British Columbia.

Scientists count levels of radioactivity in units called becquerels, and when Buesseler and his colleagues first reported radioactivity in the water off Fukushima, they counted tens of millions of becquerels in a single cubic meter of water, he said.

The radioactivity in water off Eureka measured only 2 becquerels per cubic meter, Buesseler said. It is more than 1,000 times lower than levels the U.S. Environmental Protection Agency considers safe in drinking water, he said.

Two specific radioactive isotopes of the element cesium are formed in nuclear accidents, Buesseler said.

One is cesium-137, whose radioactivity decays very slowly — its half-life is 30 years. The other is cesium-134, which decays rapidly with a two-year half-life. While cesium-137 is still detectable in the world's oceans from Cold War nuclear-weapons tests, any traces of cesium-134 that can be detected could only have come from the Fukushima nuclear accident, he said.

Buessler first monitored radiation levels in the ocean off the coast of Japan three years ago, soon after a tsunami destroyed three nuclear power plants in Fukushima.

No federal government agency finances efforts to track radioactivity in ocean water, so Buesseler has created a volunteer organization of coastal residents to collect water samples periodically and send them to his lab at Woods Hole. He has volunteers collecting water samples along the coast from San Diego to Canada and around Hawaii.

His web site is www.ourradioactiveocean.org.

David Perlman is the San Francisco Chronicle’s Science Editor. E-mail: dperlman@sfchronicle.com