A closer look // By Eugene K. ChowFukushima decontamination efforts proves to be daunting task

For the past several months Japan has been steadily recovering from the catastrophic earthquake and tsunami that ravaged the country on 11 March, but now cleanup crews have begun to tackle one of their most difficult jobs yet – decontaminating areas hit by radioactive fallout.

This month, in an effort to make Fukushima safe to inhabit once more, engineers are attemptingto decontaminate at least 1,000 square kilometers, or roughly 621 square miles, of land. Workers will power-spray buildings, scrape soil off fields, and remove fallen leaves and undergrowth from woods near houses.

As decontamination efforts move forward, government officials, farmers, and local residents will have to strike a delicate balance between removing all contaminated soil, leaves, bark, and other elements and preserving the natural environment.

“You remove leaf litter from the forest floor and radiation levels fall,” explained Shinichi Nakayama, a nuclear engineer with the Japan Atomic Energy Agency (JAEA) who is overseeing nineteen decontamination pilot projects. “You take away the deeper layers and they fall more. But you take it all away and the ecosystem is destroyed. Water retention goes down and flooding can occur.”

“Decontamination can be really effective, [but] what you have is a tradeoff between dose reduction and environmental impact,” added Kathryn Higley, a radioecologist at Oregon State University.

According to Higley, the radioactive particles that Japanese cleanup crews are trying to remove tend to mix with the soil, making it nearly impossible to decontaminate areas without removing large amounts of soil, leaves, and living plants.

John Till, a nuclear risk assessment expert and the president of Risk Assessment Corporation, said within a few years, radioactive particles will disappear from the surface of plants, but will likely remain in the soil and attach strongly via ion exchange. In particular the clay soils commonly found throughout Fukushima have a strong tendency to attract fallout, which will eventually make its way into plants.

To decontaminate the area, the Japanese Ministry of Environment estimates that Fukushima will have to remove as much as 31 million cubic meters of contaminated soil and debris at a cost of more than 1 trillion yen.

So little is known about the risk of long-term exposure to low doses of radiation that Japanese cleanup efforts are largely experimental. In the past, studies have found that cancer rates increase when individuals are exposed to 100 millisieverts of radiation, but levels in Fukushima have been found to be much lower. Measurements taken in December