Radioactive caesium levels in most kinds of fish caught off the coast of Fukushima have not declined since Japan’s nuclear disaster 18 months ago, according to a marine chemist writing in the journal Science.
Dr Ken Buesseler, of the Woods Hole Oceanographic Institution in Massachusetts, concludes that the sea floor or leakage from the damaged reactors must be continuing to contaminate the waters, possibly threatening fisheries for decades.
Though the vast majority of fish tested off Japan’s north-east coast remain below recently tightened food consumption limits of caesium 134 and caesium 137, Japanese government data shows that 40 per cent of bottom-dwelling fish such as cod, flounder and halibut are above the limit.
In analysing data collected by Japan’s Ministry of Agriculture, Fisheries and Forestry, Dr Buesseler found that the levels of contamination in almost all kinds of fish were not declining a year after the disaster on 11 March 2011. That was when an earthquake and tsunami knocked out the Fukushima Dai-ichi plant’s vital cooling system, causing three reactor cores to melt and spew radiation on to the surrounding countryside and ocean.
“The [radioactivity] numbers aren’t going down,” said Dr Buesseler. “Oceans usually cause the concentrations to decrease if the spigot is turned off.
“There has to be somewhere they’re picking up the caesium. Option one is the sea floor as the source of the continued contamination. The other source could be the reactors themselves.”
The safety of fish and other foods from around Fukushima remains a concern among the Japanese, whose diet heavily draws on seafood.