Three and a half years after the Fukushima nuclear meltdown, its radioactive plume has finally traversed the Pacific. That’s according to Woods Hole Oceanographic Institution, which announced yesterday that its scientists had detected traces of cesium-134 some 100 miles (150 km) off the coast of Eureka, California.
That’s not anywhere near as scary as it sounds, according to Ken Buesseler, an oceanographer at WHOI. Consider that cesium levels off Japan’s coast in March 2011, after the earthquake/tsunami that hit Fukushima’s nuclear power plant, were more than 10 million Becquerels per cubic meter.
“What we are reporting off California are total cesium-134 and 137 that are less than 10 Bq/m3,” Buesseler said in a Reddit AMA yesterday. For someone swimming in the water for six hours a day, every day, the levels would equate to a dose that is less than what you’d get from a single dental X-ray—more than 1,000 times less, he said. It’s also more than 1,000 times lower than the acceptable limits in drinking water, as set by the US Environmental Protection Agency.
Since cesium-134 doesn’t occur in the ocean naturally, the traces picked up in the sample, which was collected in August off the California coast, had to have come from Fukushima, swept toward North America by the Kuroshio current. In February 2014, a Canadian scientist reported similar levels near Canada.
The reactor meltdown released another isotope of the element—cesium-137, which has a much longer half-life than the 134 isotope—but that’s long been present in the environment thanks to atmospheric nuclear testing in the 1950s and 1960s by the US, Great Britain, and France.
Ongoing leaks from the reactor mean that cesium levels, though diluted, are inevitably higher near Fukushima. However, it’s safe to swim as close as 1 km from the reactors, said Buesseler—and definitely safe to swim off the west coast of North America.
As for those worried about seafood contamination, cesium doesn’t build up in the food chain the way, say, mercury does, Buesseler noted, adding that “a fish swimming from contaminated waters near Japan loses cesium quickly.” Still, for the last three years, Japan has shuttered commercial fisheries due to concerns about radioactivity levels.
While Americans and Canadians can breathe easy for the moment, many Japanese people are still reeling from the impact of the earthquake/tsunami, which killed more than 16,000. Some 80,000 people who lived near the reactor remain displaced as authorities clean up the radiation.