Slight uptick in cesium-137 heralds arrival of Fukushima plume in Northern Bering Sea

After the March 2011 earthquake and subsequent tsunami that caused the destruction of a nuclear powerplant at Fukushima, Japan, Bering Sea coastal residents knew that eventually some of the radiation that escaped the powerplant would show up in the region.
Now it did, but at levels that are well below concern.
The EPA considers water still safe to drink at 7,400 becquerels per cubic meter.
Tests of seawater collected off St. Lawrence Island’s coast in 2014, 2015 and 2017 measured 2 Bq/m3.
A 2018 sample, also collected off St. Lawrence Island, measured 2.4 Bq/m3, a 0.4 increase, according to a paper by Gay Sheffield, UAF Alaska Sea Grant.
“Scientists at Woods Hole attribute this slight increase to Fukushima-related contamination, which has been detected at various locations along the West Coast of the U.S. and Canada,” the paper says. “Despite the 0.4 Bq/m3 increase of cesium-137 in seawater samples from 2018, it is important to note that the levels are still thousands of times lower than the level considered of concern in drinking water by the EPA. The other isotope that was screened for (cesium-134) was not detected in any seawater samples collected near Gambell.”
For the lack of federal or state testing of cesium-137 or cesium-134 in the ocean, the Woods Hole Oceanographic Institution began a crowd-funded experiment that tracked these two radioactive substances. Explained Dr. Ken Buessler, radiochemist with the Woods Hole Oceanographic Institute: “We followed the crowdsourcing model due to public concern on the West Coast and the lack of any US Federal agency taking responsibility.  Some monitoring was done by state agencies but not with methods that would detect what low levels of the radioactive forms of cesium were already in the ocean, and what might be coming from Japan.  So we started OurRadioactiveOcean.org as a way to partner with citizen scientists to make these sensitive measurements.”
Based on their knowledge of ocean currents, St. Lawrence Island residents were concerned that eventually signs of cesium-137 or 134 would show up in the Bering Sea. “Saint Lawrence Island residents anticipated an increase in cesium-137 after the Fukushima disaster, based on their understanding of ocean currents,” wrote Sheffield in the paper.
When they learned about Buessler’s Our Radioactive Ocean program, Sheffield said, it seemed doable to have Bering Sea water tested.
It costs $600 to test one water sample. Over the years, the Alaska Native Tribal Health Consortium, Alaska Sea Grant, Norton Sound Economic Development Corporation, and a private donor have pitched in to drum up the money for testing in 2014, 2015, 2016 and 2018. There was no testing done in 2017. Once enough money is collected, Woods Hole sends out a kit that consists of a plastic tote, a thermometer, a five-gallon container and a data sheet. Sheffield paid for the transfer from Nome to St. Lawrence Island and back. Once the kits arrived in Gambell, Eddie Ungott rode out to sea and filled the bucket with Bering Sea water. The kits were then sent back via Nome to Woods Hole in Massachussetts for analysis.
Dr. Buessler said that agencies are not monitoring with methods that are sensitive enough to measure what is already in the ocean from the atmospheric nuclear testing that peaked in the 1960s. “It is essential to have such sensitive methods as the levels from Japan are similarly low. Without data, the public concerns were not being addressed,” he said in an email to the Nome Nugget.
When asked if the slight increase of cesium-137 can be traced to Fukushima, he said that “given the baseline data at the site, we can be pretty confident that this cesium-137 increase is most likely from Japan releases in 2011. There are no other new sources.” He said that with the passage of time, it is becoming increasingly difficult to detect cesium-134, which was the tell tale indicator of Fukushima derived cesium.  “It is more difficult to measure today, since it has a half-life of only two years, so eight years later only 6 percent remains due to radioactive decay.”
He stressed that the increase is not harmful. “We’ve estimated that even if the levels of cesium were 10 Bq/m3, so four times higher, you could swim in the ocean eight hours/day, 365 days/year, and the additional dose would be more than a thousand times less than a single dental X-ray.  It is not zero, but low indeed, and the dose was higher in fact in the 1960s off the West Coast due to the nuclear weapons testing fallout.”
Asked if there is something to be learned on how ocean currents run, Seth Danielson with the Institute of Marine Science with the College of Fisheries and Ocean Science at the University of Alaska Fairbanks said that “given the number of years it took for this signal to show up in the northern Bering Sea, the radioactivity nearly certainly followed the expected pathway to get here: across the North Pacific, around the rim of the Gulf of Alaska and then around the rim of the Bering Sea basin. “If the time to get here had been a whole lot shorter then we would have had to re-examine assumptions about the probable ocean currents. I know that this cesium-137 signal has been detected at a number of points along its path over the last few years. One may learn something about the mixing of ambient waters by examining changes in concentration over time and distance.”
He added that it is important to know the background levels of radiation so that when accidents like Fukushima occur one can differentiate between the background and new impacts.