No Fallout Legacy for Japan's Farms Despite Prior Contamination of Food
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By David Cyranoski of Nature magazine
After the Fukushima nuclear disaster spewed radiation across northern Japan in March, some feared that farming there would be shut down for years. But early studies of how the radiation has accumulated in plants and the soil now suggest that farmers in much of the region can go back to work.
Soon after the meltdown at Fukushima Daiichi, the government evacuated people living within 30 kilometers of the plant, and later imposed restrictions on agricultural products. Those measures are still in place, and the government has not yet announced a clear strategy for dealing with the contaminated areas. "People are panicking because there are no data," says plant radiophysiology expert Tomoko Nakanishi at the University of Tokyo.
Nakanishi is coordinating seven teams to study the impact of the disaster on soil, plants, animals, fisheries and forests for the next decade, measuring contamination levels and assessing the long-term threat. Their first results, to appear in the Japanese journal Radioisotopes in August, paint a surprisingly optimistic picture.
The scientists studied crops at a Tokyo research field, including cabbages and potatoes that were planted a few weeks after rains showered the field with radioisotopes from Fukushima. The crops were harvested on 16 May, and contained low levels of radiation--around 9 becquerels per kilogram (Bq kg-1; wet weight), much lower than the 500 Bq kg-1 safety limit for human consumption. Furthermore, most of the radiation had accumulated on the leaves and could be washed off, suggesting that the plants were not absorbing dangerous levels of radioisotopes directly from the soil.
The more highly exposed fields around Fukushima showed similar results, with most of the radiation in plants accumulated on their surfaces. Wheat leaves that were open at the time of the greatest fallout were heavily contaminated, with combined levels of caesium-134 and caesium-137 ranging from thousands to about 1 million Bq kg-1. But leaves that unfolded afterwards were largely free of contamination. Wheat ears from these plants contained 300-500 Bq kg-1--within the prescribed radiation limit. "It's harvest time now and farmers are wondering what to do," says Nakanishi. "They can throw the current harvest away. But it is OK to plant again."
Despite this good news, the team's data also show that the radioisotopes seem to be stuck firmly to the soil, mainly in the top five centimeters (see 'Skin deep'), and are not being washed away by rain. This might prevent the radioisotopes from entering groundwater, but suggests that cleaning up the more radioactive public spaces in Fukushima prefecture will not be easy.
A separate group from Kobe University, led by radiation expert Tomoya Yamauchi, has found that soil radiation levels at four sites in Fukushima city, some 60 kilometers from the reactors, measured up to 47,000 Bq kg-1--surpassing the 10,000 Bq kg-1 human exposure safety level set by the government. Yamauchi says that these areas, which are outside the current 30-kilometre evacuation zone, should be evacuated immediately.
In May, the agriculture ministry unveiled a ¥490-million (US$6-million) initiative to develop clean-up techniques, including removing contaminated soil. But results from the tests won't come for months, and Nakanishi says that, in the meantime, the information gap is dangerous. Without data on the true depth of soil contamination, local schools are using large machines to scoop up the top 50 centimeters of soil--probably much more than is necessary--and leaving it as radioactive mounds in the corners of school playgrounds.
The agriculture ministry is also testing how well plants can clean the soil in highly contaminated areas, and several non-governmental organizations have followed suit with a campaign of sunflower planting. Nakanishi says that the effort is "nonsense", arguing that such phytoremediation would absorb only small amounts of radioisotopes. Chihiro Inoue, an expert in soil and groundwater remediation at Tohoku University, says that phytoremediation is worth testing, but warns that even if it works, "you're still left with the problem of how to dispose of the [radioactive] plants".
Burying the soil is expensive, however. Inoue says that the cost of cleaning up a school playground could be ¥50 million, and there are more than 100 schools in the affected areas, not to mention parks and other public places. Given that caesium-137, with its 30-year half-life, will be around for a while, soil burial sites would have to be monitored to make sure contaminated soil was not exposed by weather, he says.
Whatever happens, it needs to happen soon, Inoue says. People cannot rebuild their lives until the radiation risks are understood and a plan for reducing them is in place. "We can't wait much longer," he says.
This article is reproduced with permission from the magazine Nature. The article was first published on July 12, 2011.
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8 Comments
Add CommentHow can you title this article , in big type ,
Reply | Report Abuse | Link to this"No Fallout Legacy ..."
when the (much smaller) subtitle says contaminated soil needs urgent clean up, & in more detail in the article it states soil outside the current evacuation zone is contaminated to nearly 5x the safe exposure level, with that survey author urging immediate evacuation???????????
Should we trust official Japanese figures and proclamations? After all, they admitted lying about the situation at the beginning, when they were saying there was only minimal radiation when actually 3 reactors had fully melted down and fallout plus hot particles were spewed around the world. Japanese produce has been banned in several countries such as China and the Koreas because of high readings. They're allowing children in the Fukushima Prefecture to continue going to schools that test far above the REM readings that caused Chernobyl cities and villages to undergo mandatory evacuation, even though children are vastly more sensitive to radiation than adults.
Reply | Report Abuse | Link to thisJapanese universities are not necessarily independent of govt influence, in fact I think normally not, and the govt there has absolutely no credibility with me anymore.
Some people hate good news where nuclear is concerned. Millions of Japanese people live in the two cities bombed with nuclear weapons. The number of deaths associated with the Chernobyl accident is only a tiny fraction of what the alarmists claim. Save yourselves some embarrassment. Go watch a horror movie.
Reply | Report Abuse | Link to thisGood, now just as soon as you take a leisurely swim out in front of the melted down Fukushima reactors, I'll believe that people are being alarmist about fallout and radiation.
Reply | Report Abuse | Link to thisNo problem there Sault, the sea has currents and tides and the level of radiation will now be what known as Buggerall.
Reply | Report Abuse | Link to thisI will go away and worry (maybe) about Global Warming.
Sault,if you want some genuine information about radiation you can go to http://www.iaea.org/newscenter/focus/fukushima/japan-report/
Reply | Report Abuse | Link to thisA report by the International Atomic Energy Association.
Try reading it , you may find that although the Tsunami caused a serious problem, the sky has not fallen.
Sault,if you want some genuine information about radiation you can go to http://www.iaea.org/newscenter/focus/fukushima/japan-report/
Reply | Report Abuse | Link to thisA report by the International Atomic Energy Agency.
Try reading it , you may find that although the Tsunami caused a serious problem, the sky has not fallen.
Note my correction from Association to Agency.
Reply | Report Abuse | Link to thisMy apologies about that error.
Bye for now.