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Radiation and Children Section 2: Radiation Level and Health Effects

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Keywords: DNA, iodine 131, health, nuclear, children, radiation, reactive oxygen, thyroid, Toshiya Inaba, genes

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In Section 1, I stressed that radiation and radioactivity are found everywhere, so the issue is not whether they are present in the environment, but rather the level. Radiation is harmful because it adversely affects DNA by creating reactive oxygen. Reactive oxygen, however, is produced in our bodies "naturally"even when we are not exposed to radiation.

What level of radiation has no immediate effect on health?

How then can we determine what level of radiation has no immediate effect on health? And how many microsieverts is that?

These questions can be left up to the specialists.

What is important for us is to be able to understand what this language means. For example, we often hear about "a level of radiation that has no immediate effect on the health," but what does that mean? I have avoided this type of language in TV appearances because I think it only causes more anxiety. I do, however, understand why someone would want to use this language. On TV, there's no time for detailed explanations that are even a fraction of what one wants to say, which means that the speaker tends to use language that is safer (for him or her) such as "a level of radiation that has no immediate effect on the health."

What is "a level of radiation that has no immediate effect on the health"?

First, let me explain what this phrase means, using a somewhat exaggerated example. After the atomic bombs were dropped on Hiroshima and Nagasaki, hundreds of thousands of people were exposed to extremely high levels of radiation and died within a month. Many people will remember the Tokaimura nuclear accident in Tokai, Ibaraki Prefecture over a decade ago that resulted in the immediate death of two plant workers.

Even if we have lived with radiation for a long time and studied how to deal with it, there are limits to what we can do. We can do almost nothing against a massive amount of radiation.

If anyone has been exposed to this level of radiation in the most recent nuclear accident, it is the workers who were inside the plant at the time. Fortunately, at this time, they are fine and seem to have suffered no ill effects. The experts expect no change in the future either. So, for people living several kilometers from the plants, there is no likelihood that they have been and will be exposed to "a level of radiation that has an immediate effect on the health."

Later effects of irradiation?

Even if there are no immediate effects, what about later effects of irradiation? Cancer is one such effect that appears later.

Cancer occurs even without irradiation, so when it comes to the effect of radiation, we say that people who have been exposed to radiation are more likely to get cancer than those who have not. Moreover, the onset of cancer is between several years to several decades after irradiation. In Hiroshima and Nagasaki as well, the incidence of cancer is higher among those who were exposed to nuclear radiation than those who were not. This continues to be the case today, over sixty years after the atomic bombing.

But, wait a bit before concluding that irradiation does, after all, causes cancer. Here, it is necessary to stop and consider an important factor: level. And by this, I mean the level of radiation involved.

What level causes cancer later?

What level of radiation will contribute to the incidence of a particular cancer?

Radiation causes reactive oxygen which is an enemy of your skin, and the trouble starts when this reactive oxygen breaks the DNA strands. But living creatures are smart, so when the DNA is broken, it is quickly repaired. Unfortunately, mistakes sometimes occur in the repair process. This is a real problem because it can lead to cancer in the future.

Far more reactive oxygen is produced in your body than by the small amounts of radiation we are exposed to in daily life. Living creatures always have a way of dealing with matters. In this case, cells are more than capable of repairing the DNA that has been broken by the naturally produced reactive oxygen. Even if a small amount of reactive oxygen produced by radiation is involved, it will not increase the frequency of error right away.

As the level of radiation rises, it becomes increasingly difficult for cells to defend themselves against damage, which results in more mistakes in replication. And when instantaneous value of exposure exceeds 100 millisieverts, the probability of cancer visibly increases. Such figures can be confusing, so in the next section, I will explain where this measurement of 100 millisieverts comes from and what instant exposure means.

The original article was posted on the CRN Japanese site in April 2011.

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Toshiya Inaba
Professor and Vice Director of Hiroshima University Research Institute for Radiation Biology and Medicine, Doctor of Medicine.
Graduated from Tokyo University Medical School. After employment at Saitama Children’s Medical Center, St. Jude Children’s Research Hospital, Jichi Medical University School of Medicine, appointed Professor, Hiroshima University Research Institute for Radiation Biology and Medicine in 2001, and Vice-Director since 2009. Specializes in hematology (mechanism of the onset of leukemia, pediatric hematology), microbiology, and radiation biology.
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