衆議院厚生労働委員会「放射線の健康への影響について」

児玉龍彦教授発言　7月27日 英訳版

At the Committee of Health, Labor and Welfare, the House of Representatives.

An unsworn witness: Dr. Tatsuhiko Kodama

Professor at Research Center for Advanced Science and Technology and Director, Radioisotope Center, The University of Tokyo

I am Kodama, the Director of Radioisotope Center, The University of Tokyo. I was very much surprised on March 15th. The University of Tokyo has 27 isotope facilities and our center is responsible for protection from radiation and decontamination of radioactive materials. I myself am a doctor of internal medicine and has been working on decontamination of radioactive materials at radiation facilities in the hospitals of University of Tokyo for past several decades. First, we detected 5 micro Sv (per hour) and reported it to Monbu-Kagaku-Sho (the Ministry of Education, Culture, Sports, Science & Technology of Japan).

After that, in Tokyo, radiation became over 0.5 micro Sv (per hour). This went down once temporarily and, on March 21st, when we had rain in Tokyo and radiation increased to 0.2 micro Sv (per hour) and, since then, the level has been continuously high. At that time, the Chief Cabinet Secretary Mr. Edano, told the Japanese people that there would be no immediate harm to the health. However I thought this would be a very serious problem because the current Radiation Hazard Prevention Act is established to handle and control a small amount of highly radioactive materials. For this, the total amount would not be the issue (since it is small) but the concentration of each radioactive material would be taken into account.

However in the case of Fukushima, 5 micro Sv (per hour) in the area less than 100 km, and 0.5 micro Sv (per hour) in the area less than 200 km from the nuclear power plant were detected. Furthermore, tea leafs in Ashigara and Shizuoka (more than 300 km away from the plant) were contaminated as you all may know. When we think about Radiation Hazard Prevention in such a case, we need to take the total amount of radioactive materials into account. Then how much radioactive materials have been released from the plant? The government and TEPCO have not reported the total amount of the released radioactivity yet.

Then we estimated it. Based on quantity of heat, it is equivalent to 29.6 pieces of Hiroshima-type atomic bombs, and, based on the amount of uranium, it is equivalent to 20 pieces. What is more frightening is that, based on our current knowledge, the residual amount of radioactivity will decrease to 1/1000 one year later in the case of the atomic bomb, but in the case of the nuclear power plant accident, the residual activity will decrease to only one-tenth one year later.

Namely, the accident in Fukushima, as well as that in Chernobyl, released radioactivity equivalent to dozens of atomic bombs and generated much more contaminants that stay long than that created by the atomic bomb. It is important to argue based on this estimate.

When we think about Radiation Hazard, we analyzed it from the view of Systems Biology. This approach works well when the total amount is small since we only need to consider the amount of radioactivity to which the person was exposed. However when the total amount is huge, we need to consider behaviors of particles. Diffusion of particles is Nonlinear Science. It is most difficult calculation in the field of fluid mechanics. The nuclear fuel is something like “sands embedded in plastics”. When it is melted down, a large amount of fine particles are released in the air. The release of fine particles could cause a problem we recently encountered, namely the contamination of hay. For instance, 57000 Bq in Fujiwara, Iwate, 17000 Bq in Osaki, Miyagi, 106000 Bq in Minami-Soma, Fukushima, 97000 Bq in Shirakawa, Fukushima, and 64000 Bq in Iwate (Iwaki?) were detected per kg hay. Thus, the radioactivity can not be plotted on concentric circles. How much and where those particles fell down were affected by the weather or by absorption of the particles by the materials.

I am going to Minami-Soma in Fukushima every week. Our center has worked on decontamination there seven times. When we first arrived, there was only one NaI radiation counter. The Ministry of Agriculture, Forestry and Fisheries sent a notification describing instruction for the food for cows on March 19th. But that was the time when the Mayer of Minami-Soma made the now well-known appeal on the web asking for gasoline, food and water since the stocks of these items were almost gone. In such a situation, who could see and know the notification? Further, even if they could see it, the risk of contamination of hay was not mentioned on it. After they knew the notification, they bought expensive feed from foreign countries and fed the cows with it and given the spring water to cows, that is drinking water for themselves.

In this circumstance, what we need to do is to make it sure that complete measurements can be performed in the contaminated area. When we visited Minami-Soma in the end of May, only one Geiger counter was available there. Although, in the city hall, 20 personal Geiger counters were given from the US military, no one in the Education Committee of the City Hall could read the English instructions and use them. After we arrived there, we told them how to use them and then measurements with 20 Geiger counters became possible. This is what actually happened at that time.

As for the measurement of radioactivity in food, measuring instruments that use semiconductors are developed these days. They are not like germanium counters but can perform imaging. I do not understand why the government does not support to apply it for the measurements and to set up those in the entire country. Although three months have passed since the accident already, why even such simple things have not been done yet. This is outrageous and I am extremely upset about this situation.

Second, I have been a head of the antibody drug project of the Cabinet, and now am running a 3 billion Japanese yen project to perform advanced research. In the research, we label antibody drug with radioisotope and use it for cancer therapy. Namely, since my job is to inject radioisotopes to the human body, I am studying very hard on the issue of internal exposure to radiation.

Therefore I like to mention how internal exposure will affect. The major problem caused by internal exposure is generation of cancer. Internal exposure cuts DNA. When DNA exists as a double helix in a cell, DNA is rather stable. However, when cell division occurs, double helix is temporarily unfastened and DNA is duplicated, giving rise to four single-stranded DNAs. This structure is very sensitive to radiation. Because of this, radiation has a high risk to embryos in pregnant women, juveniles, and highly-proliferative cells of people of growing ages. Even for adults, highly-proliferative cells, such as hairs, bloods, and intestinal epithelium cells, are sensitive to radiation. These are ABC of Radiation Hazard.

I will mention what we know is caused by internal exposure. Not a single mutation can cause cancer. After a first hit was created by radiation, when a second event happened, a cancer would be generated. We call these changes driver mutations or passenger mutations. Anyway I like you to see the references below including cases for Chernobyl and cesium. The highest risk is alpha radiation.

I was surprised to hear that one professor of University of Tokyo said it is OK to drink plutonium. Alpha radiation is most dangerous. It is well known as thorotrast injury to us hepatologists. Although levels of internal exposure are calculated as units of Sv, I do not think it makes any sense at all. Iodine 131 is concentrated in the thyroid gland. Thorotrast is concentrated in the liver. Cesium is concentrated in the urothelium and bladder. Without examining each accumulation point, it will be useless to perform whole body scanning.

Thorotrast is a contrast medium. Since 1890, it had been used in Germany and, since 1930, it had been used in Japan. 20 to 30 years later, it turned out to cause liver cancer in 25 to 30 % of the patients. It took 20 years to accumulate mutations necessary to cause the first cancer. Thorotrast generates alpha radiation and damages cells around it. The first gene to be hit is p53.

We knew DNA sequence of the human genome. The differences between two persons are about three million bases. Therefore it is meaningless if we treat different individuals in a same way. So-called personalized medicine is important. When we examine the effects of internal exposure, it is important to check which genes are damaged and what changes are generated in person to person.

In the case of thorotrast, it is proved that the p53 gene is disrupted in the first step, and the second and the third mutations are created during next 20 to 30 years, and finally the liver cancer and leukemia will occur.

Next is iodine 131. As you know, iodine is concentrated in the thyroid gland. Its accumulation is most evident in growing ages, especially in infants. The Ukrainian researchers reported that the thyroid cancer occurred frequently after the Chernobyl accident in 1991. But, Japanese and the American researchers argued on a journal Nature that they could not find any causality in their report. Because there are no data before 1986, it is claimed that there is no statistical significance. However, 20 years later it turned out to be statistically significant. Because 20 years later the peak observed in 1986 disappeared, the causality became evident without the past data. Thus, the epidemiological proof is very difficult and generally cannot prove it until all cases are over.

Therefore, a strategy to protect children now has to be totally different.

Dr. Shoji Fukushima in the National Bioassay Research Center is now working to find a chemical substance which is concentrated in the urinary tract system of people around Chernobyl. Dr. Fukushima collected more than 500 cases in cooperation with Ukrainian doctors. In the course of the operation for prostatic hypertrophy, they can get the sample of the bladder. After inspecting the bladder samples from the highly contaminated site, although radioactivity in the urine was not so high, 6Bq per liter, mutations in the p53 gene were frequently found. Besides, proliferative cystitis, a state of proliferative precancerosis, in which p38MAP kinase and NF kappa B were activated, were always associated. Thus, it is reported that cancer in the epithelium has been seen at a considerable high rate.

I also was surprised very much by a report that 2-13 Bq were detected in milk from seven mothers in Fukushima. Our Radioisotope Center are sending four staff members to Minami-Soma every week and working to help decontamination of Minami-Soma.

The problem that is happening in Minami-Soma is as follows. The distance from the nuclear power plant, for instance making a concentric circle whose radius is 20 km or 30 km, does not make any sense. It is necessary to measure the radioactivity in every kindergarten. Right now 1,700 children are going to schools in the 30 km zone from the 20 km zone by bus. However, in Minami-Soma, the radioactivity is high in the sea-side, and 70% of schools show relatively low radioactivity. In spite of this, children are moved forcibly by bus to schools that are located in the 30km zone near the Iidate village. It costs one million Japanese yen per day. Please stop such a thing as soon as possible. What makes this situation is a problem of compensation. The money only goes to forced refuge. In a Committee of the House of Councilors, Ex-President of TEPCO, Mr. Shimizu, and the Minister of Economy Trade and Industry, Mr. Kaieda, gave such a speech. Please do not mix these. Please separate the problem of compensation from the issue of the children’s health immediately. I request you to make every possible effort to save and protect the children.

I ask you another request which I leaned from my experience in Fukushima. I want you to separate urgent decontamination from lasting decontamination clearly. We have extensively done urgent decontamination by ourselves. For example, a bottom of the slide, as you can see on a chart, is the place where a small child always touches. When rainwater drips down from the slide, it is concentrated here every time. When there is a tilt between the right and left sides, the raindrop will be concentrated and radiation will be 10 micro Sv (per hour) on only one side in the place where the environmental radioactivity is around 1 micro Sv (per hour). You must urgently decontaminate such a place immediately and vigorously.

Also, a place under a rain gutter where moss is growing is also a place where a kid often touches. When I wash such a place with a high pressure washing machine and remove the moss, the radioactivity decreases, 2 micro Sv to 0.5 micro Sv (per hour).

However, it is very difficult to make the radioactivity less than 0.5 micro Sv (per hour) in every place. This is because all of the buildings, the trees, and areas have been contaminated. It is very difficult to lower the radioactivity in the whole just by washing small parts.

Therefore, when we seriously consider decontamination, how many problems on earth do we need to solve and how much cost on earth do we need to pay? In the case of the itai-itai disease, the total area polluted with cadmium was about 3,000 hectares. By now, the government has spent 800 billion yen to decontaminate the area of 1,500 hectares. How much cost will be needed if the area is 1,000 times larger?

Therefore I want to urgently present the four (three?) proposals.

First, as a national policy, you should measure the radioactivities of food, the soil, and water. You should use the latest imaging machines which are available in Japan. Imaging with the semiconductor is simple. Improve the situation radically by making an assembly-line system using the latest imaging equipment. This is totally possible with the present Japanese technology.

Second, please urgently establish a new law to decrease the radiation exposure of children. All of what I am doing now are illegal. The current Radiation Hazard Prevention Act restricted the amount of radiation and nuclear species that can be handled in the radioisotope facilities. I currently employ all of 27 radioisotope centers of University of Tokyo and support decontamination at Minami-Soma, but most facilities are not allowed to use cesium. It is also illegal to carry radioactive materials by car. However, since I can not leave them to mothers and teachers, our team puts all contaminated materials in drum cans and takes them to Tokyo with us. Carrying them into University of Tokyo is illegal, everything is illegal. It is the Diet’s responsibility that caused such a situation. The isotope centers of National Universities in Japan have many newest machines including germanium detectors. If they are tied hand and foot by the law, how can they work to protect children with all their might. How can we protect children by using all of our power? This is due to a complete negligence by the Diet.

Third, as a national policy, develop technology to decontaminate the soil by gathering powers from all of the companies. Various chemical companies and radiation decontamination companies, for example, Toray, Kurita, Chiyoda technol, atox and Takenaka, have various know-how for decontamination of radioactive materials. The government should establish a decontamination research center by gathering those companies. Since this will cost tens of trillions of yen from public money, I really worry that it may become an inappropriate public work involving the right and money. There is no such margin if we consider the financial state of this country. How can we perform decontamination? When 70,000 people do evacuate, what is the Diet actually doing?

That is all I want to say.

(A comment from translators)

In the last part, Dr. Kodama told that he would request four things but only mentioned three. We guess the he just skipped one thing that is presumably related to precise (personalized and organ-specific) examinatio