Tiny radioactive particles persist indoors years after Fukushima

Radioactive microparticles were still coating buildings near the Fukushima Daiichi nuclear power plant five years after the disaster, according to a study in Chemosphere.

The researchers found caesium-rich microparticles (CsMPs) in the dust of an abandoned primary school 2.8 kilometres southwest of the plant.

CsMPs are usually 5 micrometres in size or smaller (<PM5), and pose a threat to human health if inhaled because they’re highly radioactive.

They also don’t dissolve well in water, meaning they’re likely to persist  in the environment and in bodies of people and animals.

“Given the small size of the particles, they could penetrate into the deepest parts of the lung, where they could be retained,” says senior author Associate Professor Satoshi Utsunomiya, a researcher at Kyushu University, Japan.

The researchers had previously shown that the 2011 Fukushima nuclear disaster, which was triggered by an earthquake and subsequent tsunami, released CsMPs. They found CsMPs in a wide area including as far south as Tokyo, about 300km away.

While they had shown  CsMPs were distributed widely in the Fukushima exclusion zone, but had not yet shown that the particles could get indoors.

“When entering the school building, we were all shocked by what we saw. Five years had passed by the time of sampling in 2016, but everything was left as it was at the moment of the 2011 earthquake. It’s as if time had stood still,” says Utsunomiya.

The researchers examined dust samples from floors near the school entrance, on its second floor, and in the school yard.

They found CsMPs at both indoor locations, with higher concentrations near the door.

“The CsMPs may present a threat; as shown in our work, CsMPs may accumulate locally and form hot spots, even in indoor environments,” says Utsunomiya, although the exact health effects of CsMPs are still unclear.

“The potential occurrence of CsMPs in indoor environments dictates a need for detailed studies of indoor CsMPs in residential areas impacted by Fukushima Daiichi nuclear power plant fallout,” says co-author Professor Gareth Law, from the University of Helsinki, Finland.

“I believe it is our duty to conduct rigorous scientific research on the tragic Fukushima events, to find and publicize new knowledge that will be important to society and the next generation,” says Utsunomiya.

“Maybe one day time can begin again for abandoned buildings like the school, but for that to happen, significant clean-up efforts are needed, and if that is to proceed, we first need to know about the forms and extent of contamination in those buildings, such that workers and potential occupants can be protected.”

Japan will be releasing treated radioactive water – nuclear waste from the plant – into the Pacific Ocean later this year.