RADIOACTIVE contamination from the Fukushima power plant has been carried around the world and far out to sea, adding to fear and confusion over the danger posed by the leaked material. Japanese officials have taken steps to evacuate residents from five villages outside the exclusion zone around the beleaguered plant, where the severity of the crisis was upgraded to the worst rating possible on an international nuclear disaster scale.

The move puts the incident at the crippled power station on a par with Chernobyl in 1986, the only previous nuclear disaster to be given the highest ranking.

Michael Mariotte, head of the Nuclear Information Research Service, an advocacy organisation, said those living in the villages were leaving for good. “The people are not being evacuated because of the threat of a large fast release, or releases that could cause acute symptoms. It is because radiation in these areas is too high to stay over the long term. It is not an evacuation per se. It is a permanent relocation. That is why they are not rushing it.”

The upgrading resulted in differing opinions from Japanese officials, with the Nuclear Safety Commission estimating the total amount of leaked radiation to be only one-tenth of that released at Chernobyl. Meanwhile an official for Tepco, the utility company that runs the plant, admitted the radiation leak could eventually top that of the Ukrainian disaster.

Monitoring stations around the globe have picked up small amounts of radioactive iodine and caesium that have carried on the wind from the power station and landed on the ground and in water courses, but the levels are considered far too low to be dangerous to human health.

“The releases into the atmosphere will travel around the world, but we have incredibly sensitive detection systems. If there had been a major release we would know about it,” said Gerry Thomas, a molecular pathologist and director of the Chernobyl tissue bank at Imperial College London.

But measurements of radiation levels in Europe have led at least one group to raise concerns over safety. A French NGO, the Commission for Independent Research and Information on Radioactivity, said levels of radiation were no longer negligible, a claim Thomas dismissed as “absolutely ridiculous”.

Japan’s location has helped lessen the effect of radiation from the damaged plant reaching other countries. The prevailing winds are westerlies, so the radioactive plume has typically blown out over the sea and had to cover thousands of miles before it reaches landfall in the US.

Trace amounts of iodine-131 were discovered in drinking water in Idaho and Washington in the US last week, but were so low that the Environmental Protection Agency said an infant would have to drink around 7,000 litres to receive a radiation dose equivalent to one day’s worth of natural background radiation. — The Guardian, London