Dr. Tsubokura's Radiation Lecture Vol.59
Author: Masaharu Tsubokura
Editors: Akihiko Ozaki M.D., Yuki Senoo
117. Cultivation leads to reduction of contamination
When radioactive cesium is present in the soil, plants absorb it instead of nutrients, and this process results in contamination. Moreover, the extent of absorption of radioactive cesium could vary depending on the types of plants and the soil. On the other hand, numerous countermeasures and efforts have been made to reduce the level of contamination in agricultural products, including soil decontamination and redesigns of the cultivating method, fertilizer types, and growing plants.
Cultivation and tillage are two of the approaches taken to reduce contamination. It has been discovered that the cesium absorption of plants can be mitigated, without conducting complete decontamination of the field, by replacing the top layer of soil with the lower layer (a technique called reverse tillage) and/or by a deep plowing.
Cesium binds tightly to the soil particle and is generally present in the surface of the ground. Therefore, when the field is cultivated, the concentration of cesium contained in the soil lowers as the field is mixed with less contaminated soil.
Some people are concerned about internal exposure caused by contaminated dust, which may be released in the air from the tillage work. However, the level of cesium contained in the dust is normally very insignificant. Furthermore, even participating in tillage for several hours a day for a whole year, a person will only receive internal exposure below a thousandth of a millisievert.
118. Water is barely contaminated
When radioactive cesium is present in the soil, plants absorb it instead of nutrients, and this results in contamination. On the other hand, numerous countermeasures and efforts have been made to prevent contamination in agricultural products, including soil decontamination and redesigns of the cultivating method, fertilizer types, and growing plants.
Some people are concerned about whether releasing water into the decontaminated paddy fields will result in contaminating them again.
However, cesium is generally tightly bound to the soil particles and is hardly disseminated in the water. When radioactive cesium is detected in the water, it is generally due to mud floating at the surface that had accumulated at the bottom. It has been reported that almost no contamination has been found in the water from the pond or dams.
When water is sprinkled for the first time after a nuclear accident, or when accumulation of mud is observed while sprinkling water, it may become safer to remove the mud around the irrigation canal. However, to this point, a large-scale recontamination of a decontaminated field from sprinkling water has not been reported.
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The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on March 26th and 2nd April 2017 was reproduced for MRIC Global under the author's permission.