March 2015 – FUKUSHIMA, Japan – There’s a steady, low, background level of radioactivity we encounter in everyday life. Some of it is human-made but very diffused, born out of the atomic and nuclear testing of the mid-20th century. Some of it is created naturally: radon gas seeping from marble floors, for instance, or the increased dose of cosmic rays that airline passengers get during a flight. Few people think about these exposures. But since Japan’s Fukushima Daiichi nuclear power plant disaster in March 2011, there’s been worldwide concern that the plant contaminated Pacific Ocean seafood enough to affect human health. During the disaster, explosions in reactor containment buildings sent clouds of radioactive steam into the atmosphere, which drifted over land and sea. In the months and years since the original explosion, leaks of radioactive water from the site have flowed into the ocean as well.
Now a newly published study suggests that there is nothing—much—to worry about. To comprehensively assess the region’s seafood, Pavel Povinec of Comenius University in Slovakia and Katsumi Hirose of Sophia University in Japan collected and analyzed information from samplings of the region’s seawater, fish, shellfish, and seaweed collected since the Fukushima Daiichi disaster. They found that the average annual consumption of all seafoods combined would result in radiation exposure of anywhere from 0.2 to 1.0 millisieverts (mSv) a year, while exposure from fish alone would account for 0.02 to 0.12 mSv a year. By comparison, a woman is exposed to about 0.4 mSv of radiation when she has a mammogram and around 0.03 mSv during a 10-hour airline flight, according to the American Cancer Society. The average American is exposed to around 3 mSv of background radiation a year, according to the organization.
“What they’re doing is mostly compiling these thousands of data that have been collected to try and interpret what the trends are,” said Ken Buesseler, a senior scientist at the Woods Hole Oceanographic Institution who has studied radiation levels in seawater since the Fukushima Daiichi disaster. “It’s very useful for someone to pull them together to see what’s in the fish over time.” The team found that levels of cesium 134 and cesium 137, substances that can increase a person’s cancer risk if the exposure is high enough, spiked in the weeks immediately after the disaster but began to fall sharply by May 2011 thanks to the region’s strong ocean currents. According to the data, levels of radio-cesium are well below the health risk threshold—even when combined with naturally occurring radioactive elements in seafood—and are slowly continuing to fall.
The researchers also looked at data collected on strontium 90, a radioactive substance that when consumed is absorbed by bone. Those levels turned out to be present at low levels in coastal seafood since the nuclear disaster, but they have not subsided much over time. Strontium 90 levels in the region’s seafood spiked twice more since March 2011, they found. Each incident followed a leak of radioactive water from the power plant site. Buesseler said that strontium 90 levels in the region’s seafood should get more attention because there are holding tanks on the Fukushima Daiichi site containing roughly 150 million gallons of wastewater with “more than 100 times the total strontium 90 released in 2011….There’s potential for additional contamination.”
Buesseler noted that the strontium 90 data Povinec and Hirose worked with came from fewer than two dozen fish. “What they did is correct; it’s all they had to go on,” he said. “But it’s of concern that there are so few data of strontium 90 in seafood because over time it’s becoming more significant and it’s of greater health concern.” –Take Part