Cesium still high in Fukushima fish
Radioactive cesium levels in most kinds of fish caught off the coast of Fukushima haven't declined in the year since the nuclear disaster started, a signal that the seafloor or leakage from the damaged reactors is continuing to contaminate the waters — possibly threatening fisheries for decades, a researcher says.
Although the vast majority of fish tested off the Tohoku region remain below recently tightened food safety limits for cesium-134 and cesium-137, government data show that 40 percent of bottom fish, including cod, flounder and halibut, are still above the limit, Ken Buesseler, a marine chemist at the Woods Hole Oceanographic Institution in Massachusetts, wrote in an article published Thursday in the journal Science.
In analyzing extensive data collected by the Agriculture, Fisheries and Forestry Ministry, he found that the levels of contamination in almost all kinds of fish haven't declined more than a year since the Fukushima No. 1 plant suffered three reactor meltdowns.
"The (radioactivity) numbers aren't going down. Oceans usually cause the concentrations to decrease if the spigot is turned off," Buesseler said in an interview. "There has to be somewhere they're picking up the cesium.
"Option one is the seafloor is the source of the continued contamination. The other source could be the reactors themselves," he said.
The safety of fish and other food from around Fukushima remains a concern among ordinary Japanese, among the world's highest per capita consumers of seafood.
Most seafood from Fukushima's coast is barred from the domestic market and export. In June, authorities lifted bans on octopus and sea snails caught off Fukushima after testing showed very low levels of radiation.
But the most contaminated fish found yet off Fukushima were caught in August, some 17 months into the disaster. The two greenlings, which are bottom-feeders, had cesium levels of more than 25,000 becquerels per kilogram, 250 times the level the government considers safe.
A government fisheries official, Chikara Takase, acknowledged that the figure for the greenlings was "extremely high," but added that high numbers were detected only in limited kinds of fish sampled in the restricted waters closest to the plant. He acknowledged that "we have yet to arrive at a situation that allows an overall lifting of the ban."
To bolster public confidence in food safety, the government in April tightened restrictions for cesium-134 and cesium-137 on seafood to 100 becquerels per kilogram from 500. But the step confused consumers as people noticed that more products were barred.
Tokyo Electric Power Co. said radioactive water used to cool the Fukushima reactors has leaked into the ocean several times — most recently in April.
"Given the 30-year half-life of cesium-137, this means that even if these sources (of contamination) were to be shut off completely, the sediments would remain contaminated for decades to come," Buesseler wrote in Science.
Experts suspect that radioactive water from the plant is seeping into the groundwater at the same time, and is continuing to make its way into the ocean.
Hideo Yamazaki, a marine biologist at Kinki University, agrees with Buesseler's theory that the cesium is leaking from the Fukushima plant and that it will contaminate seafood for more than a decade.
The Japan Times: Saturday, Oct. 27, 2012. (C) All rights reserved