Japan's fish still radioactive from Fukushima nuclear disaster

As the sun comes up over Tokyo's Tsukiji fish market, it is business as usual. Cranes are lifting the carcasses of rime-covered tuna from the holds of battered fishing boats.

Traders are using their own sign language to purchase crates of skipjack, shellfish and seaweed. And there is a steady flow of trucks leaving the market, carrying maritime produce to wholesalers, restaurants and supermarkets across Tokyo and the surrounding Kanto region.

The pace is frenetic, and the trading at times frantic.

Only no one is uttering the thoughts that must be on the minds of everyone connected with Japan's fisheries: how much of the catch coming through the world's largest fish market is contaminated with radioactivity from the disaster that befell the Fukushima Dai-ichi nuclear plant on March 11 last year?

Those thoughts will have been brought to the fore - but remained unspoken - after a marine chemist at the Woods Hole Oceanographic Institute in Massachusetts published an article in the journal Science, which showed levels of caesium in fish caught off northeast Japan are not falling more than one year after the disaster.

In the article, Ken Buesseler used Japanese government samplings of caesium-134 and caesium-137 and concluded that 40 per cent of bottom-dwelling fish are still above official safety levels for consumption.