Most of the radioactive material that rained down on Tokyo following the meltdown at the Fukushima Daiichi Nuclear Power Plant was encapsulated in glassy microparticles, researchers have found.

The findings, which will be presented on Monday at the Goldschmidt conference in Japan, show that the radioactive fallout from the 2011 earthquake and subsequent nuclear disaster has been poorly understood. Previously, it was assumed that most of the radiation that fell dissolved in rain. This would mean that it would wash out of the soil and through the environment with the hydrologic cycle.

However, what actually happened is that, in the midst of the meltdown, molecules of radioactive caesium and nanoparticles of iron-zinc oxides became embedded in silicon oxide glass. This occurred because of the interaction between the molten core and the concrete containment units.

These tiny glass particles entered the air and fell as soot on the surrounding region. Because the radioactive molecules are contained in an insoluble medium, they will not wash out of the soil with rainwater to the same extent.

A lone house sits on the scarred landscape, inside the exclusion zone, close to the devastated Fukushima Daiichi Nuclear Power Plant on February 26, 2016 in Namie, Fukushima Japan. The area is now closed to residents due radiation contamination from the Fukishima nuclear disaster.
A lone house sits on the scarred landscape, inside the exclusion zone, close to the devastated Fukushima Daiichi Nuclear Power Plant on February 26, 2016 in Namie, Fukushima Japan. The area is now closed to residents due radiation contamination from the Fukishima nuclear disaster. 
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“It looks like the clean-up procedure, which consisted of washing and removal of top soils, was the correct thing to do,” says Dr. Satoshi Utsunomiya, who will present the findings on Monday. “However, the concentration of radioactive caesium in microparticles means that, at an extremely localised and focused level, the radioactive fallout may have been more (or less) concentrated than anticipated.”

Beyond the consequences for the environment, there are significant consequences for human health. Breathing caesium encased in glass particles may have a very different impact from exposure to it as radioactive rain, and it may be dangerous at a much higher or lower concentration. The half-life of the material may also depend heavily on the medium.

This information will be valuable in assessing the ongoing impacts the Fukushima disaster. Hopefully, no nuclear meltdown on that scale occurs again, but if one does, this new science will help governments better respond to the crisis.

Photos via Getty Images / Christopher Furlong, Getty Images / Matt Cardy

Jacqueline Ronson is a science writer based on Vancouver Island, Canada. Before that she lived way up in Whitehorse, where she reported for the Yukon News. These days she likes to talk to smart people about the future of the planet, ride her bicycle, play her banjo, and frolic.