Dr. Tsubokura's Radiation Lecture Vol.58

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

115. Soil bound cesium is not absorbed by plants

When radioactive cesium is present in the ground, plants absorb it instead of nutrients, and this results in contamination.

However, plants do not actively absorb cesium present in the soil. Most cesium is bound to soil particles or fully captured within soil particles, so plants cannot absorb it.

For plants to absorb cesium, it must be dissolved in water; however, it has been found that cesium scarcely dissolves in water.

Therefore, when cesium is detected in water, it is generally because the device is measuring the soil-bound cesium present in the water. Since plants are not able to absorb soil-bound cesium, cesium will be detected in water but not in the plants.

It has been revealed that mud particles bound more strongly to cesium than sand particles, which is why the degree of radiation contamination in plants is affected by the type of soil they grow in.

116. There is no contaminated milk with radioactive substances exceeding the reference

After the Chernobyl disaster, milk was heavily contaminated due to the grass being contaminated with radioactive iodine. This accidental contamination of milk led to children’s thyroid glands being exposed to radioactive iodine. On the other hand, milk distribution was restricted in the early phase of the post-disaster period after the Fukushima Daiichi nuclear disaster. As a result, radiation damage to thyroid glands was much suppressed compared to the case after the Chernobyl accident.

Some people may consider milk a source of radiation exposure, which was a rumor disseminated just after the nuclear accident. However, since radioactive iodine has a short half-life, it no longer exists in our environment. Furthermore, various countermeasures have been implemented to prevent contamination of milk with radioactive cesium, including the management of feed for cattle and decontamination of grass by the reverse tillage method.

The reference level for radiation dose limits in milk is 50 becquerels, which is half of the reference level of other food (100 becquerels per kilogram). Milk has been evaluated thousands of times since 2012, and even when contamination has been detected, the levels have never approached the reference level.

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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.

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