What dose did you receive? KeystoneUSA-ZUMA/REX/Shutterstock

“We don’t need to worry,” says Nikolaos Evangeliou at the Norwegian Institute for Air Research, whose team has conducted the first global survey of radiation exposure caused by the meltdown of three nuclear reactors at the Fukushima-Daiichi nuclear plant in Japan after a tsunami struck in 2011.

Evangeliou’s team has calculated the approximate exposure of everyone on Earth to two radioactive isotopes of caesium, using all the data available so far. Most of this came from the Comprehensive Test Ban Treaty Organization, which monitors radiation in the environment using a global network of measuring stations.

“More than 80 per cent of the radiation was deposited in the ocean and poles, so I think the global population got the least exposure,” Evangeliou told the annual meeting of the European Geosciences Union in Vienna, Austria, last month. He has estimated the dose that most individuals received to be 0.02 millisieverts. “What I found was that we got one extra X-ray each,” says Evangeliou.


Impact on wildlife

Even in Japan, the average person’s radiation dose was low: 0.5 millisieverts, which is close to the annual recommended limit for breathing in naturally occurring radon gas. In comparison, the average annual exposure from background levels of radiation in the UK is around 2.7 millisieverts a year.

Doses were unsurprisingly higher for residents of Fukushima and neighbouring areas during the first three months of the accident, ranging from 1 to 5 millisieverts. But such doses are still relatively low – a typical CT scan delivers 15 millisieverts, for example, while it takes 1000 millisieverts to cause radiation sickness.

But Evangeliou says that the effects on wildlife around the plant might be more severe. Already, he says, increased levels of radiation around Fukushima have been linked to declines in bird populations there between 2011 and 2014. “There have also been reports of declines in other species such as insects and some mammals,” he says.

However overall, Evangeliou says the hazards posed by fallout from the Chernobyl nuclear accident in Ukraine in 1986 are still much greater than those from Fukushima, because the fallout was larger, and it fell upon more densely populated areas.

Read more: A nuclear ghost town in Japan welcomes back residents this week

We have corrected the estimated dose most individuals received.