Californians Will Soon Be Swimming in Fukushima-Irradiated Water

Radiation took two-and-a-half years to make it across the ocean—but don’t worry, the levels of radiation are harmless

California beach
Sandy Huffaker/Corbis

As predicted, currents have finally washed radioactive contamination from the Fukushima nuclear meltdown across the Pacific Ocean to within 100 miles of California’s coast. Here’s why this is no cause for panic.

Researchers from the Woods Hole Oceanographic Institution report that they’ve found cesium-134, a radioactive remnant with short half-life of about two years. This point is important for the researchers. The entire Pacific Ocean basin still has radioactivity from nuclear weapons testing decades ago, but the cesium-134 from that period has long since disappeared. The cesium-134 is therefore a signature of the Fukushima disaster only. And there isn’t much of it:

The amount of cesium-134 reported in these new offshore data is less than 2 Becquerels per cubic meter (the number of decay events per second per 260 gallons of water). This Fukushima-derived cesium is far below where one might expect any measurable risk to human health or marine life, according to international health agencies.  And it is more than 1000 times lower than acceptable limits in drinking water set by US EPA.

The work was intended to allay fears about radiation reaching North America. “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,” Daniel Hirsch, a nuclear policy researcher at the University of California, Santa Cruz, not involved in the study, told Science. The group’s crowd-funded data can be explored at

The researchers will continue to monitor radioactivity on the Pacific to ensure that swimming and eating fish from off the California coast remains safe. Levels of radiation near the Fukushima disaster site, however, are still too high for the approximately 80,000 people who still can’t return to their homes.

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