Recently the Mainichi News reported the following:
On the 14th, the Ministry of Agriculture, Forestry, and Fisheries released the actual proof of the experimental result on the removal of the radioactive material from the farmland, it was being performed since May in Iitate-mura of Fukushima and other locations.
When 3 to 4 cm of the surface of the farmland was removed, it was confirmed that the cesium could be reduced by 70-90 percent. On the other hand, the experiment on planting the sunflower which supposedly could easily taking in radioactive material and absorbing cesium, it had little effect, and the ministry supposedly said that "at this time it is difficult to have practical use."
According to the said ministry, the amount of cesium which the sunflower planted in Iitate-mura in May was absorbing was about 52 Bq per kilo. Supposed 10 kilo of sunflower were grown per square meter, it was said that the calculation showed that it could absorb only about 1/2000 of cesium existing inside the soil. On the other hand, in the farmland with 4 cm of surface removed, it decreases from 10,370 Bq per kilo to 2599 Bq. While stripping off the surface (3 cm) after hardening the ground with medicine, at the same time did the preparation work of removing the whole root that stretched in the shape of net meshes as seen in farmland that had pasture or grass, cesium decreased by no less than 82 to 97%.
However, by this method, for each 10 ares 30-40 tons of wasted earth would come out. If to estimate that in Fukushima there was about 8300 ha. of farmland with over 5000 Bq per km, then by simple calculation, the earth would go up to about 3,500,000 tons (two TOKYO DOME), and the method to dispose it would become a big subject.
It seems that to remove the top soil is the only way out.