Effects of radiation

Radiation doses in everyday life

mSv: millisieverts

First and foremost, it is important to understand we are constantly exposed to a small amount of radiation no matter where we live or what we do. This is because radioactive substances exist around the world naturally. The effects of radiation therefore depend not on its “presence” but the “amount” of exposure. When our body is exposed to radiation, its energy may damage some DNA (genes) in our cells. However, because our body has enzymes that repair such damage, and can also replace unrepaired cells with healthy cells through the process of metabolism, small amounts of radiation exposure do not have any significant impact on our health.

On the other hand, exposure to a high dose of radiation at once may result in our body’s DNA repair mechanisms being unable to keep up with radiation damage, therefore causing health hazards. According to the ICRP (International Commission on Radiological Protection) these begin to occur after acute exposure exceeds a threshold value of around 0.1 to 0.5 Sv (or 100,000 μSv to 500,000 μSv). Furthermore, according to an epidemiological survey on survivors from the Hiroshima and Nagasaki atomic bombings, it has been agreed that after cumulative exposure doses exceeds around 100 to 200 mSv, the risks of cancer mortality increases as the exposure doses increases.

At the same time, current scientific evidence suggests that the impact of exposure to radiation of less than 100 mSv is too small for us to detect any significance. This is so because cancer-causing factors other than radiation found in various aspects of our life including stress, drinking and smoking, have larger probability of causing cancer mortality than radition exposure of less than 100mSv.

Furthermore, it is important to know that in regards to inheritable characteristics, according to all past research including the atomic bomb cases, there have been no proven cases of radiation exposure resulting in certain characteristics being inherited down generations. Furthermore, there have been no rises in rates of birth defects among children who were fetuses at the time of the Fukushima Daiichi Nuclear Accident.

Risks of Cancer (Radiation)

Source: Website of the National Cancer Center Japan

With regard to the Chernobyl Nuclear Accident (April,1986), there was a much larger release of radioactive materials compared to Fukushima including Iodine, Strontium, and Plutonium. Furthermore, food and drinks consumed by those living in affected areas were mainly self-grown, and internal exposure from the intake of contaminated food, especially the intake of milk contaminated with radioactive iodine, increased radiation doses in their thyroid glands. According to the UN, due to prompt measures not taken in Chernobyl, thyroid cancer was observed in more than 6,000 children and youths who had consumed radioactive iodine-131, of which 15 have lost their lives as of 2005.

On the other hand, in Fukushima’s case, there were very small releases of strontium and plutonium, and iodine that was released disappeared in the early stages. For this reason, as of January 2016, government surveying has mainly focused on the influence of radioactive cesium. Japan also was quick to implement evacuation orders, and placed shipping restrictions on agricultural products, resulting in very minimal amounts of radioactive materials being consumed by residents. It also set strict benchmark values for radioactivity, and systems to conduct vigilant and watchful inspections to make sure foods exceeding the benchmark values will not be sold in markets. As a result, any internal exposure dose has been maintained at levels much lower than 1 mSv.

A preliminary report from the World Health Organization (WHO) in 2013 estimated the radiation doses that residents of Japan outside the evacuated areas received in the year following the accident, and concluded that most people in Fukushima prefecture would have received a radiation dose of between 1 and 10 mSv during the first year after the accident. This is in addition to levels of about 2.4 mSv they would have received from unavoidable natural sources. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) also carried out a realistic dose assessment in 2016 and drew upon the following conclusions:

Both reports agree the most serious health effects of the nuclear accident in Fukushima in the short term appear to be on mental and social well-being. This is further proven by the fact that in-direct casualties in Fukushima are now larger than the numbers of those who lost their lives due to direct damages. Furthermore, the evacuation following the accident caused immediate aggravation of the condition of already vulnerable groups.

Comparison of Estimated Amounts of Released Radionuclides
between Chernobyl and Fukushima Daiichi NPS Accidents

of radionuclides accumulated in the reactor core at the time of the
accidents that were released into the environment