10. Developing and Trialing a System to Monitor Radionuclides in Individual Plots of Farmland to Help Reconstruction Farming in Contaminated Areas

Some of the earliest research conducted in areas contaminated by the Fukushima nuclear disaster entailed monitoring the distribution of ambient radiation doses and the extent to which the soil had been contaminated. Initially, there were a large number of researchers gathering a variety of measurements, but gradually such measurements came to be released by the administrative authorities, and the independent research was discontinued. The public bodies representing the administrative authorities reported radioactive contamination in each area as shown in Figs. 10.1 and 10.2. Thanks to the release of such data, residents in the disaster zones and the Japanese public in general were able to understand the actual risk presented to them by radiation and take appropriate defensive measures themselves.

The results of these surveys indicated that areas around the Fukushima Daiichi Nuclear Power Station and to the northwest of it were severely contaminated by radiation. At the same time, damage was also found in many other areas including the Aizu Basin; the southern part of Miyagi Prefecture near the border with Fukushima Prefecture; along the border between Iwate and Miyagi Prefectures; northern Tochigi Prefecture; areas around the borders of Ibaraki, Chiba, and Saitama Prefectures; and northern Gunma Prefecture.

There are three important issues in response to radioactive contamination: the first is compensation for damage incurred, the second is decontamination of the living environment, and the third is decontamination of the agricultural and forestry production bases. This chapter focuses on the last two issues, relating to decontamination.

Decontamination of the living environment is currently under way to lower ambient radiation doses, so that accumulated doses do not exceed an annual level of 1 mSv and people can live safely in the areas affected. However, decontamination that focuses mainly on the areas where people live and work cannot lower the overall ambient radiation dose in regions where radionuclides are scattered over a wide area.

The agricultural and forestry industry production bases that require decontamination include paddy fields, non-paddy arable fields, pastures, and forests. It is important to note that agriculture and forestry are the main industries in the areas contaminated by radiation. If the recovery of these industries is delayed by the contamination incurred, not only will this cause the industries themselves to decline locally, but it will also exert a major impact on people’s lives and the conservation of the natural environment in the areas affected.

Although rehabilitation of agriculture and forestry in the contaminated areas is an urgent issue, the national government has been slow to respond, faced as it is with the need to allocate huge budgets for decontamination and compensation. Meanwhile, the agricultural and forestry industries in these areas are on the verge of a crisis because of a whole array of factors including the contamination itself, the damage caused by negative reputation, the evacuation of farmers to other locations, and the outflow of young people from the remaining habitable areas.

At Tokyo University of Agriculture, we believe that if Fukushima Prefecture’s agriculture is to be saved, it is essential to create and effectively utilize a system for monitoring the radioactive contamination in each individual parcel of farmland. We are therefore currently developing such a system, as well as a mechanism for putting it to practical use, in the heavily contaminated Tamano district of Soma, adjacent to the village of Iitate.

In this chapter, we describe the research outcomes verified to date relating to the characteristics and applications of the monitoring system we are developing.

Three factors explain why radioactive contamination is severely inhibiting recovery in agriculture and forestry.

Having understood the full implications of these problems, we have been assisting in the recovery effort, guided by the following approaches.

Our fundamental approaches to recovering agriculture and forestry in irradiated areas can be summarized thus. To put these principles into practice to bring about tangible recovery, we need to establish a system for each district to monitor radionuclides in individual parcels of cultivated land, matching decontamination measures to specific circumstances. We also need to select and produce safe crops and support the development of new agricultural businesses.

As already described, it is clear that radioactive contamination is significantly inhibiting the recovery of the agriculture and forestry industries of Tamano. Thus, we are attempting to develop a practical monitoring system to ensure that safe agricultural commodities are produced and shipped.

In specific terms, this aim involved collecting and analyzing basic data to develop a monitoring system that could help us to decide decontamination measures, implement them, and evaluate their effects, for each parcel of farmland. Such basic data included the ambient radiation dose (1 m above ground), the soil surface dose (1 cm from the ground), the concentration of radionuclide in the soil (at 0–5 cm and at 5–10 cm depths), the depth of the topsoil, and the soil characteristics (cation-exchange capacity, exchangeable calcium, exchangeable potassium, available phosphoric acid, total nitrogen, soil acidity, etc.). We started the survey in June 2012, and by September we had collected basic data on 646 parcels (142 ha) of farmland including paddy fields, non-paddy arable fields, pastures, and greenhouses across Tamano. Table 10.3 and Figs.10.5 and 10.6 present the aim of surveying each item, the method used, and state of research; Table 10.4 presents the number of farmland parcels surveyed and their areas. In terms of area, paddy fields, non-paddy arable fields, and pastures accounted for 34 ha, 46 ha, and 62 ha, respectively, amounting to a total of 142 ha. In terms of numbers of parcels, paddy fields, non-paddy arable fields, and pastures accounted for 263 parcels, 278 parcels, and 105 parcels, respectively, making a total of 646 parcels. In the Higashi Tamano and Nishi Tamano areas, the parcels comprised mainly paddy fields and non-paddy arable fields, whereas in the Fukuryozen and Ryozen areas, the parcels comprised mainly pastures and non-paddy arable fields (Table 10.4). Table 10.5 shows part of the database created.

The monitoring system we developed has been actively used in decontaminating farmlands. Decontamination of paddy fields has already been completed, and the decontamination of meadows and grazing lands is currently in progress. In addition to its use in publicly funded decontamination of farmlands, the monitoring system has also been actively used by individual farmers, who familiarized themselves with the concentrations of radionuclide in their own farmlands to adopt their own countermeasures. We therefore provided the data for each parcel of farmland in the form of feedback to all the owners and cultivators. In addition, the map of radioactive substance concentrations in farmlands across the entire area was provided to the chiefs of the Higashi Tamano, Nishi Tamano, Ryozen, and Fukuryozen areas, and was also made available to all residents by displaying it at assembly halls and other public buildings in each area. Ideally, the monitoring system should be used by the farmers themselves to monitor radionuclide in each area as a whole. We therefore need to structure the system so that the farmers can measure such substances simply, rapidly, and accurately. Therefore, we estimated the cost of the monitoring system development (Lurhathaiopath et al. 2014) and proposed the direction of agricultural policy in the radioactive contamination area.