Crops may one day be grown again in the contaminated soil surrounding the Chernobyl nuclear plant, if the ideas of Spanish, Ukrainian and American researchers pay off. The teams say that, over many years, simply mulching crops could drastically reduce radioactive contamination.
Around the Chernobyl plant, an area about one and a half times the size of Luxembourg has been declared off-limits for habitation or cultivation. In much of the exclusion zone, radioactivity is still measurable. It now poses little danger so long as it remains in the ground, but food grown in the area is unfit to eat.
Caesium-137, which has a half-life of 30 years, is the most important radio-nuclide left from Chernobyl’s catastrophic explosion in 1986. Researchers have been looking for ways to prevent it getting into crops planted in contaminated soil. Using lots of potassium fertiliser is one proven method, as plants take up the potassium ion from soil in preference to caesium, preventing further caesium uptake.
Now, Teresa Sauras Yera, a biologist at the University of Barcelona, has found that mulching, the method used by farmers and gardeners to conserve moisture and prevent weeds growing, does the job more cheaply and easily. With colleagues in Spain and at the Institute of Agricultural Radiology in Kiev, Sauras Yera added mulch to soil in the exclusion zone after planting oat seeds over three successive years. One year, they covered the soil with black polyethylene sheets. In the other two years, they used straw. Each year, they saw a reduction of 30 to 40 per cent in the levels of radio-caesium in the oats (Environmental Science & Technology, vol 33, p 882).
The researchers believe the mulch protects the plants’ leaves and roots from radioactive particles carried by rain and wind. Since mulching is cheap, it could be used to limit radioactive contamination, she says. However, radioactivity levels near Chernobyl are still far too high to make the oats safe for consumption.
But mulching still leaves the radioactive elements in the soil — so attempts are being made to remove it. Slavik Dushenkov of the US biotech firm Phytotech says the fast-growing cannabis plant, the source of hemp fibre, could be an answer. Phytotech and the Ukrainian Academy of Agricultural Sciences in Glukhov have been growing hemp around Chernobyl. After processing the plants, they obtained clean hemp fibre and plant remains rich in caesium. The contaminated remains were burnt in a sealed incinerator that caught all the radioactive ash.
But so far, this method looks as if it could remove only about 1 per cent of the caesium, as much of it is tightly bound to soil particles. “Maybe any one of the three processes will not be economic, but all put together may provide significant benefits,” Dushenkov says.
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