Ken Buesseler checking a CTD sampler to collect data at Fukushima coast. (Photo: Ken Kostel, WHOI)

Fish caught off Fukushima still show high levels of radiation

JAPAN
Friday, October 26, 2012, 23:30 (GMT + 9)

Many fish caught off the coast of Fukushima are still showing high levels of radioactive cesium. This indicates that, since the catastrophic earthquake and tsunami that caused the nuclear disaster on 11 March 2011, the seafloor or leakage from the damaged reactors must still be contaminating the area – something that could affect fisheries for decades, a researcher warned.

According to data collected by Japan's Ministry of Agriculture, Fisheries and Forestry (MAFF), 40 per cent of bottom-dwelling fish such as cod, flounder and halibut are above the limit of cesium-134 and cesium-137, Ken Buesseler, a marine chemist at the Woods Hole Oceanographic Institution (WHOI) in Massachusetts informed in an article published this week in the journal Science.

Buesseler looked at a year’s worth of the government’s data and found that the levels of contamination in almost all kinds of fish are still not falling, BBC reports.

"The (radioactivity) numbers aren't going down. Oceans usually cause the concentrations to decrease if the spigot is turned off," Buesseler clarified, The Associated Press reports. "There has to be somewhere they're picking up the cesium."

Fish monitoring data from the Japanese Ministry of Agriculture, Forestry and Fisheries (MAFF) showed the change in total cesium (137Cs + 134Cs in Bequerels per kilogram) in bottom-dwelling (demersal) fish from the five prefectures in East Japan closest to the Fukushima Dai-ichi nuclear power plant (left plot). It also revealed differences in total cesium for five different fish types. (Image: Jack Cook, Woods Hole Oceanographic Institution)

"Option one is the seafloor is the source of the continued contamination. The other source could be the reactors themselves," he said.

Most fish and seafood from along the Fukushima coast are banned from the domestic market and export. Although in June, authorities lifted bans on octopus and sea snails that showed very low levels of radiation, the most contaminated fish were caught in August 2012 -- the two greenlings, which are bottom-feeders, had cesium levels of more than 25,000 Bq per kg, 250 times the level the Japanese Government considers safe.

A government fisheries official, Chikara Takase, at that point said that the high numbers were detected only in certain kinds of fish sampled in the restricted waters closest to the nuclear plant.

Plant operator Tokyo Electric Power Co admitted that some radioactive water used to cool the Fukushima reactors leaked into the ocean, most recently last 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.

Hideo Yamazaki, a marine biologist at Kinki University, also thinks that the cesium is leaking from the plant and that it will contaminate seafood for more than 10 years. He believes the plant will continue to leak until cracks and other damage are repaired, and it remains unclear how and when that work will be completed, as radiation levels in the reactors are too high for humans and robots.

Buesseler said predicting patterns of contamination requires careful study of the ocean waters and sediments to determine how quickly the ecosystem will recover.

Related article:

- Fish caught off Fukushima exceeds cesium legal limit

By Natalia Real
editorial@fis.com
www.fis.com

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