Image credit: Bedford Institute of Oceanography
According to a study published on December 29, 2014 by the Proceedings of the National Academy of Sciences, a radiation plume from the March, 2011 accident in Fukushima, Japan took about 2.1 years to cross the waters of the Pacific Ocean and reach the shores of North America.
Following the March 11, 2011 magnitude 9.0 earthquake and resulting tsunami, the Fukushima Daiichi nuclear power plant released cesium 134 and cesium 137 into the ocean. Researchers knew that a small percentage of this radioactive material would be carried by currents across the Pacific, eventually reaching the west coast of North America.
Computer models could predict when this might happen, but by taking actual samples of the ocean water and testing them for cesium 134 and cesium 137 the scientists could see for certain when it happened.
John Smith, a research scientist at the Bedford Institute of Oceanography in Dartmouth, Nova Scotia, is the lead author of the paper. Smith said:
We had a situation where the radioactive tracer was deposited at a very specific location off the coast of Japan at a very specific time. It was kind of like a dye experiment. And it is unambiguous – you either see the signal or you don’t, and when you see it you know exactly what you are measuring.
Just three months after the tsunami, Smith and his team began sampling ocean water from as far as 1,500 kilometers (930 miles) off the coast of British Columbia. They took measurements from the same sites every June from 2011 to 2013, collecting 60 liters of water and then analyzing it for traces of cesium 134 and cesium 137.
In June of 2011 they detected no signature from the Fukushima disaster at any of the test sites. In June of 2012 they found small amounts of the Fukushima radiation at the westernmost station, but it had not moved any closer to shore. By June of 2013, however, it had spread all the way to the continental shelf of Canada.
The amount of radiation that finally made it to Canada’s west coast by June 2013 was very small – less than 1 Becquerels per cubic meter. (Becquerels are the number of decay events per second per 260 gallons of water.) That is more than 1,000 times lower than acceptable limits in drinking water, according to the Environmental Protection Agency.
Computer models that match fairly closely with the hard data that Smith collected suggest that the amount of radiation will peak in 2015 and 2016 in British Columbia, but it will never exceed about 5 Becquerels per cubic meter. Smith said:
Those levels of cesium 137 are still well below natural levels of radioactivity in the ocean.
Because of the structure of the currents, the radiation levels in Southern California are expected to peak a few years later, but by that time they will be even smaller than the highest levels of radiation expected in Canada.
“Even when levels are small like this, it is important to collect systematic data so we can better predict how another event might move through the ocean,” said
Ken Buesseler is a marine chemist at Woods Hole Oceanographic Institute, who was not involved in the study. Buesseler leads a citizen scientist group called Our Radioactive Oceans, to track the arrival of the Fukushima radioactivity plume in the U.S. He noted that his group’s results matched Smith’s. He said:
What we really need for understanding what happens after events like Fukushima is data like this on a regular basis.
Bottom line: A radiation plume from the March, 2011 accident in Fukushima, Japan took about 2.1 years to cross the waters of the Pacific Ocean and reach the shores of North America, according to a study published on December 29,2014 by the Proceedings of the National Academy of Sciences.
–From Earth Sky
From Grist:
Nuclear energy gives plenty of people the heebie-jeebies: Like horror-movie ghosts and ancestral curses, you can’t see or feel or smell it, but it can still kill you. So when Japan’s Fukushima Daiichi plant was damaged in March 2011, releasing a flood of radioactive cesium-tinged water into the Pacific, nervous nancies the world over took note. And that note, typically, was: PANIC!!!!!1!!11!
First of all: No. Don’t. While some wafting fallout hit the U.S. in the first months after the disaster (results: TBD), ocean-borne radiation took the long way around to get to us. Specifically, 2.1 years, according to an analysis published last month in PNAS.
The study, conducted by scientists from the Bedford Institute of Oceanography, in Nova Scotia, monitored water at test sites off the coast of British Columbia. They were looking for atoms of cesium 134 and 137, the two molecules released at Fukushima — and, sure enough, eventually they found them. In June 2012, they found the smallest signs of the radiation only at their westernmost testing site; a year later, the signal made it to the Canadian continental shelf, but still far offshore. Then, in November 2014, a group from the Woods Hole Oceanographic Institution found traces of Fukushima radiation 100 miles off California.
To reiterate: Don’t panic. By the time it made it to this side of the Pacific, that radiation was 10 million times weaker than it was when it left Japan, and 1,000 times below the safe threshold for drinking water (for nerds: We’re talking under 2 Becquerels per cubic meter [260 gallons]). In fact, that’s even lower than the background radiation levels in the ocean, where residual cesium 137 still lurks from atmospheric nuclear testing in the past 50 years. According to WHOI scientist Thomas Buesseler as cited by Quartz, you could swim in that water for six hours a day, every day, and still absorb less radiation than you would from a single dental x-ray.
None of which is to say that a nuclear power plant still hemorrhaging toxic waste into the ocean is NBD. There are real concerns about the fishing industry in Japan, where ecosystems continue to be dosed with the irradiated water, and some concerns about Pacific tuna, which may be vulnerable thanks to their epic migratory patterns.
Did I mention not to panic? Even though you are not likely to turn into a three-eyed mutant thanks to minute amounts of ambient radiation, the Fukushima disaster raises interesting questions about what we know about our interconnected world — and I’m not just talking about Twitter. How, exactly, does an event in one part of the world ripple outward? Scientists have models of Pacific currents, but, given the vastness of the ocean and the confounding number of variables, nothing beats old-fashioned observation. The Fukushima radiation serves as a kind of dye test, showing exactly how water from a single release point traverses the ocean.
And, in fact, the computer models turn out to be pretty accurate. Since irradiated water has continued to leak from the damaged reactors in the past three years, radiation levels will continue to rise, peaking in Canada in 2015 and 2016 and a few years later in Southern California. But — once and for all, drop the adrenaline and iodine tablets, you’re fine — the levels are never expected to exceed the very-safe limit of 5 Becquerels per cubic meter. Now you can go back to panicking about the very real threat of global warming instead.
Categories: Condition of Oceans, Oceanography, Radioactive Plume
Neptune 911! 
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