Radiation in the Air is Not Transferred to Crops! Harmful Rumors Come from Misunderstandings

Soil physics, one of my research fields, may not be familiar to the public. Research on soil physics is applied to a wide range of fields and some of them will completely change your “common sense.” For example, one of the themes of our laboratory, the Laboratory of Land Resource Science, is that investigating greenhouse gases emitted from farmland. We often think that carbon dioxide (CO2), a greenhouse gas, is emitted by the avtivities of factories and urban life; however, methane (CH4) generated in paddy fields has about a 30 times more potent greenhouse effect than CO2 and the nitrous oxide (N2O) produced there is about 300 times more potent than CO2. When water is supplied to a paddy field, soil in the field is changed to an anaerobic condition that generates CH4; when the soil dries, the paddy field is changed to an aerobic condition that produces N2O. Therefore, we make efforts to investigate water management practices to maintain rice yields while reducing the emission of CH4 and N2O. In addition, we have started to research on CH4 transfer between the ocean and the atmosphere using a ship carrying a gas flux measuring device specifically developed for this research. In fact, some experts have said that the ocean is the sink of CO2 and the source of CH4. Note that this statement is based only on theoretical calculations and there are very few reports based on actual measurements. Our experimental verification is one of the world’s first attempts.

In soil physics research, repeat observation, investigation, and verification are the common approach to conclusive evidence. This is the basic attitude not only to soil physics but also to all scientific fields. Of course, it takes time to obtain conclusive evidence and I sometimes get frusctated with this. As a scientist, however, I cannot easily make a statement based on speculation.

It is important for urban consumers to understand that crops harvested in rural areas in Fukushima are safe by knowing what kind of efforts are made in the areas. In these terms, the inspection of all rice (screening) and sample inspections of fruits and vegetables (monitoring), which are carried out in Fukushima, are effective. We’ve held symposiums on radioactive contamination several times after the accident at the nuclear power plant. Before the inspections were carried out, farm producers in Fukushima Prefecture came to our symposiums to claim eagerly that they’d put everything into growing these crops and so we should please eat them safely. Although the crops that were produced were safe, few people bought them due to the harmful rumors. The producers might want to change the situation; however, just making claims will not persuade or bring relief to consumers. The consumers’ anxiety only first started to be fade by beginning the inspections and presenting numerical evidence showing that the crops were safe.

Last March, I went to a university in Malaysia. The radiation dose around the university was over 0.3 μSv/h. By the way, South Korea prohibits the import of Japanese seafood due to radiation contamination. The radiation dose at Gimpo International Airport was 0.14 μSv/h, which was higher than that of Haneda Airport, 0.06 μSv/h. To investigate the source of the radiation dose, I broght a measurement device that can determine the sources of gamma ray. This investigation revealed that the radiation dose at the airport came from potassium and thorium. Granite contains potassium, and Korean Peninsula is mostly made of granite. Thus, the radiation dose in a building built of concrete using granite gravels is naturally high. In Malaysia, there is rock known as dolomite that contains thorium. That is, people have lived in areas with a radiation dose similar to that of current Iitate Village for a long time.

In addition, a high air dose does not cause an increase in the radiation dose of crops harvested in a given area. Many people may misunderstand this point. I was previously surprised to hear a college professor saying that she did not eat Ampo persimmon, a special variety from Fukushima. Even if a persimmon is dried in a place having a high air dose, radiation will not be transferred to the persimmon as radiocesium. When the root of a crop absorbs soil water which is contaminated with radiocesium, the radiocesium accumulates in the crop. This is how the radiation dose of the crop becomes high. Even if a crop is exposed to external radiation, the radiation does not remain in the crop. The current air dose of Iitate Village is about 0.3 μSv/h; however, as mentioned above, the level of radiocesium in crops harvested using the new technology is below the detection limit.