Two new international studies examining the impact of the 2011 Fukushima nuclear accident on the north Pacific Ocean have concluded that radioactive contamination levels in the waters and most marine life inhabiting them are now within acceptable safe levels.
An international team of researchers, headed by Daniel Madigan of Harvard University, tested large predators, including tuna, swordfish, and sharks in the waters off Japan, Hawaii, and California, and found no detectable levels of “Fukushima-derived” radioactive cesium 134 and 137.
“The cesium (134 and 137) isotopes are of particular concern because they were discharged in large quantities following the disaster, exhibit relatively long half-lives (2.1 and 30 years respectively), and tend to accumulate in the muscle tissues that people like to eat,” stated a blog post from the Virginia Institute of Marine Sciences, whose Kevin Weng, an assistant professor from the department of fisheries Science, was a co-author of the study.
“Our work shows that radioactivity from the Fukushima disaster is very low in open-ocean vertebrates,” Weng commented in the blog.
Lead author Madigan, of Harvard University, concurred, saying that calculations of how much radioactive cesium a person would ingest by eating seafood from the north pacific “shows that impacts to human health are likely to be negligible.”
“For marketed fish to be restricted from trade, the cesium levels would have to be more than 1600 times higher than in any samples we measured,” he added.
Meanwhile, another study, headed by chemical oceanographer Jay Cullen of the University of Victoria in Canada, found radioactive contamination following the Fukushima disaster never actually reached unsafe levels in the north Pacific, either for marine life or human health.
The Fukushima nuclear plant experienced multiple reactor meltdowns and explosions after becoming inundated by megatsunami, which were triggered by a magnitude 9 earthquake that led to a huge release of radioactive materials both into the air and sea resulting in the evacuation of 160,000 residents.
While Madigan and his team had found that contamination levels in the north Pacific had now returned to pre-Fukushima accident levels, Cullen claims that the levels are now lower than they have been for over 50 years.
Indeed, those contamination levels were about one-tenth of those found in the north Pacific in the late 1950s and ‘60s before the ban of nuclear weapons testing, his study claims.
"We're confident in saying that the levels that we see now in our part of the Pacific from Fukushima are below those levels that represent a significant health risk either to the Pacific Ocean or to human beings in Canada or the west coast of North America," said Cullen.
Surveys undertaken in Japan would tend to support these findings, though it is interesting that while those studies claim no detectable levels in marine life tested in the waters off Fukushima the Madigan-led international study found high levels of cesium in an olive ridley sea turtle.
Indeed there are others who have their doubts about whether the Pacific could justifiably be labelled as free of Fukushima-derived radiation. Just over a year ago, Ken Bessemer, a marine radiochemist with the Woods Hole Oceanographic Institution (WHOI) and director of the WHOI Center for Marine and Environmental Radioactivity, stated in an article for PBI that levels radiation levels in the Pacific, while not dangerously high, indicated that radioactive materials continued to leak into the Pacific.
unprecedented in its total release of radioactive contamination into the ocean. "[T]he fact remains that this event is unprecedented in its total release of radioactive contamination into the ocean," Bessemer wrote. "... it is incorrect to say that Fukushima is under control when levels of radioactivity in the ocean indicate ongoing leaks, caused by groundwater flowing through the site and, we think, enhanced after storms."