Background
The Association To Help Chernobyl, Chubu-District, Japan has been helping victims of the Chernobyl accident in the Ukraine since 1990. The fact that the accident occurred before the disintegration of the Soviet Union contributed to the overwhelming lack of supplies immediately after the accident. Our activities included provision of medicine and medical equipment to the disaster area, and medical support to the liquidators and other victims. The Ukraine became independent and, as its economy recovered, the medical situation gradually improved. We have been supporting the Zhytomyr Oblast Children's Hospital for many years. Setting up an intensive care unit has helped to improve treatment for the children, who come from throughout the province, and death rates have fallen.
However, we wrestled with the dilemma that the incidence of disease in the contaminated areas continued to rise with no fundamental solution to the problem in sight. We took the view that the cause of the elevated disease rate was the residents' internal exposure to radiation. Fifteen years after the accident, the quantity of radioactive cesium in the residents' bodies was high, from a few thousand to several tens of thousands of becquerels (see Figure 1). The reason for this was clearly diet.
Zhytomyr Province's Narodychi region lies 70 km southwest of the Chernobyl nuclear power plant. In some areas, radioactive contamination of the soil exceeds the range for the "zone of guaranteed voluntary resettlement" (185~555 kilo becquerels per square meter (kBq/m2)) and falls within the range for the "zone of obligatory resettlement" (exceeding 555 kBq/m2). In the Soviet era about two-thirds of the residents resettled, but after the Ukraine became independent, government-supported resettlement ceased due to the dire economic circumstances. Voluntary resettlement was promoted, but due to the collapse of agriculture and the livestock industry, the main industries in the area, about 10,000 people had to remain in the region. We have been supporting these people. Their problems will not be resolved until their internal radiation doses are reduced. This dilemma led us to embark on a new program.
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| Figure 1: Radioactivity in the bodies of people living in Narodychi district (2001) |
1. Planting rapeseed in contaminated soil
Bioremediation is a method of reducing soil contamination by using living organisms. Research on how to deal with soil contamination has been carried out since the era of atmospheric nuclear weapons tests and there is a large literature on the topic. We studied the issue for one year in search of possibilities. However, most of the literature is related to experimental cultivation by university research organizations. Experience of work with real contaminated land was virtually non-existent.
There was no alternative for us but to approach our project in an experimental fashion. Furthermore, when we visited the region, although the agricultural collectives at the time owned vast tracts of land, tractors could not be operated satisfactorily due to the lack of gasoline and diesel fuel.
Fortunately, our group included people who for many years had been involved in the local energy self-sufficiency movement in Nagano Prefecture's Ina City. They had experience in the production and operation of biodiesel and biogas. If we could make use of these skills we thought we might be able to link bioremediation with bioenergy production in Narodychi. Thus was born the Narodychi Restoration and Nanohana (Rape Blossom) Project.
Twenty years after the accident, in the weakly acidic podzolic soil of Narodychi, cesium 137 (Cs-137) has penetrated about 20 cm, while strontium 90 (Sr-90) has penetrated to a depth of about 40 cm below the surface of the soil. We are using the absorbent power of plants to remove these radionuclides. Cesium is chemically similar to potassium, while strontium is chemically similar to calcium. Plants absorb both elements without distinguishing between them. Hence, generally speaking, plants with a high concentration of potassium will be effective absorbers of cesium. Bearing in mind the way we planned to use the plants, we chose rapeseed.
We extract rapeseed oil and use it to produce biodiesel fuel (BDF) and then ferment the dregs, which contain radioactive material, and other biomass to make methane for biogas. The radioactivity in this process is water-soluble. It ends up in the biogas waste liquid and is absorbed by treatment with zeolite, which is then disposed of as low-level radioactive waste. The plan is to create a cycle by coupling bioremediation with bioenergy production.
2. Implementation structure
All kinds of local support are necessary in order to carry out the program. We were able to obtain the full cooperation of the Zhytomyr National University of Agriculture and Ecology in Zhytomyr City in establishing the conditions for cultivation and for radiological and chemical analysis. The Narodychi district soil contamination control station, under the Ministry of Emergency Situations, is undertaking rapeseed cultivation and daily management. BDF production equipment is also located and operated there. The NPO Chernobyl Hostages Fund, with which we have been working for a long time, is in charge of the overall management of funds. The Narodychi district administration office has also been very accommodating by granting various types of approval.
The rapeseed field, located in Narodychi district's Stare Sharno Village, has been provided rent free. It is in a zone 2 area with radioactive contamination in excess of 555 kBq/m2. Residence is prohibited in this zone and in fact no one lives in the village now. BDF equipment is not yet widely available in the Ukraine and so had to be transported from Japan. Made by MSD Corporation of Tendo City in Yamagata Prefecture, it can produce 200 liters of biodiesel fuel in three and a half hours. Since there was no pre-existing biogas equipment, the people from Ina City designed and manufactured it themselves during an extended stay.
The equipment is experimental. The fermentation tank has a volume of 8 m3, and has a planned production capacity of about 2 m3 per day. The system was completed, but many problems awaited us during actual implementation. I will not go into the details, but suffice it to say that the main problems related to the approvals system remaining from Soviet days and the lack of independence of people who had grown up under a communist system that was in place for many years.
3. Rape blossom project commenced
Left for over twenty years Narodychi was overgrown with weeds. We began preparing the soil in the spring of 2007. In April we planted two hectares of rapeseed (Brassica napus). While we were preparing the soil large numbers of storks came and ate the contaminated worms and insects. The birds could not avoid internal radiation exposure, but we sowed our seeds in the hope that a time will come when they will be able to eat clean food.
Rapeseed had never been grown in this soil. The people believed that growing rapeseed would damage the soil. In the spring of 2006, when we went to carry out a preliminary survey, by chance we found a place where a large quantity of Indian mustard (Brassica juncea) was growing naturally. This convinced us that rapeseed would grow here. In order to find the conditions for maximum absorption of Cs-137 and Sr-90 we tried cultivating the rapeseed under many different fertilizer conditions. We experimented with five different conditions: (1) a reference area with no fertilizer, (2) a complete fertilizer area with nitrogen, phosphorous, potassium and calcium, (3) an area with just nitrogen, (4) an area with nitrogen and phosphorous, and (5) an area with nitrogen and potassium.
From each area we took samples of the soil, the growing and harvested rapeseed and carried out chemical tests on the roots, stems, pods and seeds. Associate Professor Nikolai Didukh of Zhytomyr National University of Agriculture and Ecology supervised all the analyses, which were carried out by researchers and postgraduate students. There are two types of rapeseed in the Ukraine, one planted in spring and one planted in autumn. We took a total of 800 samples in the year in order to analyze both types.
The quantity of rapeseed harvested and the degree to which radioactivity was absorbed was greatly affected by rainfall during the cultivation period. We therefore decided to continue the program of data analysis for five years before making a judgment. We produced reports of the results of our analyses each year and will produce our final report, which will include a policy proposal, by March 2012. The total cost will amount to several tens of millions of yen. Beside donations from members, we have received support from organizations including the international volunteer fund of the former Postal Services Agency, the Japan Fund for Global Environment, Mitsui & Co. Ltd. Environment Fund, and The Takagi Fund for Citizen Science. The project is listed on the following page of Mitsui & Co. Ltd. Environment Fund's website:
(http://www.mitsui.com/jp/en/csr/contribution/fund/results/ActivityGrants/1194565_2851.html)
4. Results of rapeseed cultivation analyses
The average soil contamination to a depth of 40 cm below the surface was 500~1000 Bq/kg for Cs-137 and 100~150 Bq/kg for Sr-90. The concentration of Sr-90 was between one fifth and one tenth that of Cs-137. By comparison, the concentration of Sr-90 in Fukushima is so low that it can be disregarded. This is thought to have occurred due to the temperature of the explosion at Chernobyl being much higher than that of the explosions at Fukushima.
The quantity of rapeseed harvested was 1.5 ton/ha for the spring planting and 3.0 ton/ha for the autumn planting. The weight of biomass other than seeds was 1.7~2 times the weight of the harvested seeds. The increased harvest for the autumn planting reflects its longer growing period; from October to the following July. The quantities harvested were almost the same as in Japan. What about the contamination of the rapeseed? Although there was some variation depending on the fertilizer conditions, the highest concentration of Cs-137 contamination was found in the seeds (200~800 Bq/kg).
Sr-90 contamination also varied between the different parts of the plant, the stem being the most contaminated part (300~400 Bq/kg). Sr-90 was absorbed more effectively than Cs-137. That is related to the fact that strontium is more soluble than cesium in the soil.
The so-called transfer factor for Cs-137 (seeds) was 0.6~2.0, while for Sr-90 (stems) it was 2.5~3.2. (Note on terminology: In the regions of the former USSR, radioactivity in Bq/kg in the rape plant ÷ radioactivity in the soil in Bq/kg is referred to as the accumulation factor, whereas the transfer factor is radioactivity in Bq/kg in the rape plant ÷ radioactivity in the soil in kBq/m2.)
A very interesting phenomenon from a scientific perspective was observed in regard to the absorption of Cs-137. During the growth period up until flowering, Cs-137 is spread evenly throughout the plant's biomass, but when the seed forms and harvest approaches the distribution undergoes a big change, with nearly 60% of the Cs-137 in the plant's total biomass moving to the seeds. This is a new discovery whose biological mechanism needs to be studied. No such trend was observed for Sr-90.
In regard to the effect of fertilizer, potassium tends to suppress the absorption of Cs-137, while nitrogen fertilizer greatly enhances the absorption. However, in terms of the whole biomass, the largest quantity was absorbed in the complete fertilizer area. As predicted, when rapeseed oil was produced, both Cs-137 and Sr-90 were below detection level (less than 6~7 Bq). Most of the radioactive material remained in the dregs. This indicates that even when cultivated in contaminated regions rapeseed oil can be used safely. It is also possible to use it to make food and soap, but we are producing BDF and using it in the tractors and trucks in our own fields.
The big question was, what would happen to the level of contamination of the soil. The conclusion is that it is impossible to dramatically reduce the amount of Cs-137 and Sr-90 in the soil in a short period of time. Rapeseed cannot absorb more than 1~3% of the contamination in the soil each year, meaning it would take decades to decontaminate the soil. That is because 20 years after the accident Cs-137 and Sr-90 are tightly bound to the soil particles and there is little soluble material for plants to absorb. It is believed that this is closely related to the nature of the soil, so it is necessary to check whether or not the same applies to soil in Japan.
5. The possibility of renewed agriculture in contaminated soil
Decontaminating the soil is difficult, but a new discovery has opened up the possibility of resuming agriculture in contaminated soil. There are problems with continuous cropping of rapeseed, so it is not possible to cultivate rapeseed on the same soil every year. It is necessary to plant rapeseed on a 3~4-year rotation. During the intermittent years the soil must either be left fallow or planted with other crops. We planted soba (buckwheat), rye, oats, barley and wheat.
As a result of our analyses, despite our feeling of hopelessness that it would be possible, we obtained a clue for resuming agriculture in the contaminated area. The level of contamination of the secondary crops was in all cases extremely low. Even in fields where the contamination level in rapeseed had been 500~700 Bq/kg, radioactivity in the secondary wheat crop was below detection level. For the other crops also, the level of Cs-137 (10~50 Bq/kg) was within the level permitted under the Ukraine's food standards. For Sr-90 the level of contamination (20~40 Bq/kg) exceeded the standard (20 Bq/kg) in some cases, but such a concentration would not be a problem for livestock feed.
This result is due to the fact that rapeseed planted in the first year absorbed the soluble material. It takes time for Cs-137 and Sr-90 bound to the soil to become soluble again and reappear. This discovery indicates the possibility of renewed agriculture in farmland which had been abandoned for many years and where people had given up hope of agriculture because of contamination. Just because there is contamination does not mean that people have to give up hope of agriculture. By adopting a rotation of rapeseed (or other absorber crop)→ secondary crop 1 (easily contaminated crops can be used)→ secondary crop 2 (crops which are not easily contaminated)→ rapeseed, it is possible to cultivate crops without contamination, while at the same time gradually decontaminating the soil.
When I visited the Ukraine for a meeting this July, the Governor of Zhytomyr Province announced to the press, "We rate highly the results of the joint research between Japan and the Ukraine, and from next fiscal year we will begin cultivation of rapeseed and bioenergy production on 300,000 hectares of this province, including in contaminated areas." That plan is now being prepared. It is our great desire to make use of our Ukraine experience in Fukushima.
Masaharu Kawata (The Association To Help Chernobyl, Chubu-District, Japan)
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