Growing Solutions to Radioactive Waste

In their efforts to clean up radioactive contamination from the world’s second-worst nuclear disaster, scientists and public servants are enlisting help from a surprising source: living organisms like sunflowers and mushrooms. More than a year after the post-tsunami meltdowns of three nuclear reactors at the Fukushima Daiichi Nuclear Power Station, efforts to decontaminate the area are well underway.

Unlike the Soviets after the Chernobyl disaster who evacuated hundreds of thousands of residents and abandoned a huge swath of Belarus, the Japanese government is hoping to reclaim the area around Fukushima and make it livable again. The many individual radioactive elements unleashed after the tsunami in Japan each pose unique cleanup challenges. Some materials, like forms of radioactive iodine, have half-lives that are counted in days, and have already largely decayed. Some plutonium, on the other hand, has a half-life that lasts tens of thousands of years, but plutonium particles are quite heavy and what was not swept out to sea remains largely within the Daiichi plant grounds.

Two elements, cesium and strontium, are drawing particular attention because they spread widely across the region and may persist in the environment for decades because of their long half-lives. In urbanized areas, efforts to get rid of these materials are underway. Public officials have organized efforts to scrub down buildings and bulldoze the top layers of soil from playgrounds and parks where radioactive particles rained down. But these projects require the disposal of huge volumes of tainted soil and dirt. Between 15 and 30 million cubic meters of this waste may need to be disposed, according to government estimates.

Cleaning forested areas also presents challenges because removing the soil dramatically disrupts the local ecology. The contaminated region is also home to many farms and rice paddies, and farmers are hoping to restore the ground from which they make their living.

So scientists are also working on methods to draw the radioactive materials out of the topsoil, ponds and lakes, leaving smaller volumes of more concentrated waste to be disposed. A mix of cutting edge science and traditional agricultural knowledge form the basis of a technique called phytoremediation. Phytoremediation uses plants and living organisms to clean up contaminated areas. Plants naturally draw materials from soil through their roots. Some plants tend to draw in particular materials, including heavy metals. These metals accumulate in the plants themselves, which can then be harvested, dehydrated and carefully incinerated to reduce the total volume of waste that must be disposed.

After Chernobyl, researchers found that sunflowers grown in floating planters removed 90% of radioactive strontium from ponds. In Japan, efforts to use sunflowers to decontaminate soil ran aground. Although over eight million sunflowers were planted in the fields around Fukushima, they proved ineffective, according to government researchers. Sunflower roots stretch roughly a meter below ground, but most of the contamination remains in the top few inches of the soil. The type of soil can affect the uptake of metals, and the clay-like dirt in many contaminated areas is especially difficult for plants to draw metals from.

But researchers have reported far greater success using fungi and algae to draw in radioactive materials like cesium and strontium from dirt and water. Hiroshima International University professor Ken Sasaki reduced radioactivity in sludge from Fukushima swimming pools by roughly 90% in three days using a mix of algae and bacteria. Another team from Northwestern University and Argonne National Laboratory reported similar success removing strontium from water using freshwater algae. In October 2011, a species of single-celled green algae that had been discovered five years ago was painted onto roads and walls in Fukushima Prefecture, as it was found to remove 80% of radioactive strontium and 40% of cesium in just 10 minutes. And reports that mushrooms from Japan have been found to carry extraordinary levels of radioactivity also sparked interest in using these fungi to draw up radioactive material.

“Nuclear waste cleanup is a problem we have to solve,” said Derk Joester, a senior author with the study of freshwater algae, who was a teenager living in southern Germany during the Chernobyl disaster. “Even if all the nuclear reactors were to shut down tomorrow, the existing volume of waste is great, and it is costly to store. We need to isolate highly radioactive ‘high-level’ waste from ‘low-level’ waste. The algae offer a mechanism for doing this, which we would like to understand and optimize.”