” Some of the radioactive material that escaped the Fukushima Daiichi nuclear reactor in 2011 took a form no one was looking for, scientists have discovered. Now they have to figure out what it means for Japan and for future disasters.
Radioactive cesium—specifically, cesium-137—is one of the waste products of nuclear power. It’s also one of the most dangerous substances in a nuclear disaster like Chernobyl or Fukushima.
One reason why is that the type of radiation it emits is particularly damaging to our bodies. Another is that cesium-137 dissolves in water. That means it can spread quickly through the environment and get into the plants, animal and water we consume.
Until now, scientists and disaster experts thought cesium-137 fallout from the Fukushima reactor meltdown was in this soluble form. That guided their cleanup efforts, like removing and washing topsoil, and helped them map where radiation might spread.
It turns out that wasn’t entirely true. Satoshi Utsunomiya, a geochemist at Kyushu University in Japan, announced over the weekend that he had found cesium-137 in a new form: trapped inside tiny glass particles that spewed from the damaged reactors. These particles are not water soluble, meaning we know very little about how they behave in the environment—or in our bodies. He found the particles in air filters placed around Tokyo at the time of the disaster.
According to Utsunomiya, high temperatures inside the malfunctioning reactors at the Fukushima plant melted and broke down the concrete and metal in the buildings. Silica, zinc, iron, oxygen and cesium-137 fused into millimeter-wide glass microparticles, each about the size of a pin’s head. Lifted into the atmosphere by the fires raging at the plant, they then blew about 240 kilometers southwest to Tokyo.
“As much as 89% of all of the cesium [in Tokyo] was in fact in these particles. It’s profound,” says Daniel Kaplan, a geochemist at Savannah River National Laboratory in South Carolina. He attended Utsunomiya’s lecture describing the findings at the ongoing Goldschmidt Conference in Yokohama, Japan.
Kaplan says similar particles were observed near the Chernobyl reactors after the explosion there in 1986. But they were only seen within about 30 kilometers; beyond that, cesium-137 was only observed in rain.
Japanese researchers had previously found smaller versions of these cesium-containing glassy particles in Tsukuba, about 170 km from Fukushima, although apparently not at such high concentrations. One earlier paper also suggested that cesium-137 might work its way out of the particles over time.
The discovery could change how we model fallout from nuclear disasters. Kaplan explains that it might add a new variable to the models we use to predict where radioactive particles will go and how long they’ll stay there. It might also change how we treat cesium-137 during cleanup and monitoring.
It is probably still too early to say what this means for people living in Tokyo or elsewhere in Japan. Kaplan thinks the amount of radiation they received probably hasn’t changed. Whether they got it from water-soluble cesium-137 or from these particles, the radiation dose was the same—and for Tokyo residents, that number was within the margin of safe exposure.
The bad thing about water-soluble cesium-137 is that it can easily get into our bodies from soil by way of plants and animals. This new discovery alleviates that concern. But it opens up a new possibility we know little about.
“If the particles are in the air—because that’s how they get to Tokyo—then when you are aspirating this air you should find them in some ways on your lungs,” says Bernd Grambow, who studies nuclear waste chemistry as head of the SUBATECH laboratory in France.
Water-soluble cesium-137 that makes it into our lungs passes into the bloodstream and is peed out within a few weeks. But Grambow says we really don’t know what happens to insoluble cesium-137-containing particles if they get in our lungs. Some of them are likely coughed out or removed by our lungs’ other normal processes. As for the rest, Grambow says we don’t know how long they might remain.
He cautions that any internal radiation from particles containing cesium-137 would be much less than the doses people got from external radiation, which would come from cesium-137 and other radioactive elements in the soil or the environment around them. “We don’t know very much, and my point is only that they should be studied,” Grambow says.