Impact on human health caused by exposure to radiation (Vol. 4)

Hello, everyone. My name is Daichi, an expert providing the information on the radiation issues in an easy-to-understand manner.

Today as a continuous work from the previous articles, I would like to respond to the following questions:

– How serious impacts would be caused by dose of 1mSv or 100mSv?
– What is the relationship between exposure to radiation and risk for cancer in our daily life?
– What is the relationship between exposure to radiation and hereditary effects?

Table of contents of this article

I have been involved with the radiation-relevant issues, like the policy on the decontamination activities and the management of the Interim Storage Facility, after the accident of the Fukushima Daiichi Nuclear Power Plant in 2011.

I received a doctorate in the field of radiation, while working in Fukushima.

Impact on human health caused by exposure to radiation (Vol. 4)

In the previous articles: (Impact on human health caused by exposure to radiation (Vol. 1))(Impact on human health caused by exposure to radiation (Vol. 2))(Impact on human health caused by exposure to radiation (Vol. 3)), the following points were mainly covered.

– Outline, generating mechanism and difference of threshold values of each organ and tissue for the deterministic effects
– Outline, generating mechanism and relationship between dose and risk for cancer for the stochastic effects

As a continuous work from the previous articles, this article covers a lot of kinds of exposure to radiation in our daily life, to understand better the relationship between dose and risk for cancer, as well as the hereditary effects.

Various kinds of exposure to radiation in our daily life

Let’s look at the table of dose scale, the table of dose scale, published by the National Institutes for Quantum and Radiological Science and Technology, in order to understand better magnitude of dose of 1mSv or 100mSv, which have been so far covered.

The left side represents the artificial radiation, and the right side represents the natural background radiation.

Dose from Dental X-ray is up to 0.01mSv, and Chest X-ray is around 0.06mSv.

When taking an airplane, people are more affected by cosmic ray, compared with the case they are on the ground, and they will be exposed with dose of around 0.2mSv for a round trip between Tokyo and New York.

Dose limit for the public under the planned exposure situation, which ICRP has recommended, is 1mSv/y (except for medical exposure) of effective dose.

By the way, regarding the categories of exposure (planned, emergency, existing), please visit this article, and regarding the kinds of exposure (occupational, medical, public), please visit this article.

Average dose of Japanese people derived from natural radiation, like cosmic ray and foods, is around 2.1mSv/y.

Regarding annual dose of Japanese people and people in the world, please visit this article.

Dose from X-ray examination for stomach is larger than X-ray examination for chest and it could amount up to around 3mSv per examination.

Dose from Computed Tomography using X-ray could be around 5-30mSv per examination.

There are regions, where dose to people is higher than other regions, due to natural radioactive materials in the ground, such as radium and uranium.

For example, the Kerala region in southwest India is one of the representative places with high level of natural background and dose to people in this region could be around from a couple of mSv to a couple of tens of mSv.

Even so, no increase of relative risk for cancer has been observed in this region.

In addition, the ICRP recommends that, for example, dose limit for occupational exposure under the planned exposure situation needs to be less than 100mSv of effective dose for every five years, as well as 50mSv effective dose in every single year.

For the detail please also visit this article.

Further to that, people are exposed to radiation with dose of a couple of Gy on their skin, when taking a treatment by cardiac catheter, by using X-ray for perspective diagnosis.

Lastly, during cancer treatment using radiation, sometimes people could be exposed to radiation with dose of more than 10Gy, aiming at killing cancer cells, although radiation is concentrated in the specific part of the body.

These exposures with high dose are examples under the planned exposure situation, and exposure under the appropriate management.

However, unintentional exposure without proper management, with dose more than 1Sv, in a short period to time could possibly cause the deterministic effects, which is covered in this article.

These data implies that it is highly unlikely for us to be exposed with dose of 100mSv in our daily life, other than very exceptional and emergency situations, like accident of nuclear power plants, or planned medical exposure.

Relationship between exposure to radiation and risk for cancer in our daily life

Then, would it possible, for the dose which we are exposed to in our daily life, to contribute to increase of risk for cancer?

If so, how much risk would be increased?

The following figure is data of American people, but it represents proportion of habits, which could contribute to development of cancer.

Smoking, diet and obesity in adulthood and lack of exercise occupy around 30%, 30% and 5%, respectively, but on the other hand, impact caused by radiation and ultraviolet ray is estimated as only around 2%.

It means, according to this analysis, that in our daily life, in terms of prevention of development of cancer, quitting smoking, diet management and more exercise are more effective rather than measures against exposure to radiation.

Even if difference of races and dietary habit are taking into account, this could be true to Japanese people.

Relationship between exposure to radiation and hereditary effects

At last, of the stochastic effects, which are covered in this article, the rest of the effects, that is, relationship between exposure to radiation and the hereditary effects, will be explained.

As mechanisms to cause the hereditary effects due to the exposure to radiation, for example, genetic information could be changed, which DNA possesses, or morphological defect of chromosome could also appear, which could lead to negative impact, on offspring of exposed people.

The ICRP estimates, that risk for the hereditary effects could increase by 0.2% per absorbed dose of 1Gy.

As shown in the above figure, absorbed dose of 1Gy is quite high radiation level, except for medical exposure.

Even in the case of medical exposure, it will be well-planned before its implementation and limited in very local and small targeted spots of body, therefore, it is highly unlikely, that people are exposed to absorbed dose of 1Gy, as long as they are not under the unusual and unexpected situation.

As covered in the previous article, risk for death from cancer will increase by 0.5%, with dose of 100mSv, so under the assumption of exposure with gamma ray to whole body, the risk could increase by around 5%, with absorbed dose of 1Gy.

So impact on the hereditary effect (increase by 0.2% per 1Gy) will be much lower than that of death from cancer.

Actually, epidemiological surveys have been implemented, for children of atomic bomb survivors in Hiroshima and Nagasaki, with regard to congenial disorders, genetic mutation, chromosome aberration, cancer, mortality rates and other kinds of disorders.

However, even if compared with children of non-atomic bomb survivors, no significant difference has been so far observed, between two groups of people.

These surveys has gradually revealed that the hereditary effects caused by exposure to radiation is not so high as assumed in the past.

Key points when considering the effects on human health caused by exposure to radiation

Up here regarding impact on human health caused by exposure to radiation, the deterministic effects as well as the stochastic effects have been covered.

With regard to the deterministic effects, there are different threshold values for each organ and tissue, taking account of its sensitivity to radiation.

Therefore, it is important to view details for impact on each organ and tissue.

On the other hand, with regard to the stochastic effects, they are usually discussed in the context of risk for cancer, especially for whole body.

Therefore, it is important, first to get to know rough magnitude/scale of dose, using the above dose table as one of the references, and take necessary measures for radiation protection, which are neither too much nor too less, for optimized radiation protection.

Summary

First this article showed kinds and scale of dose in our daily life, to understand　the　magnitude of dose of 1mSv and 100mSv.

In addition, a various kinds of proportion of factors in our daily life are shown, which could attribute to development of cancer and that explains that in normal situation, it is difficult to distinguish the effect of exposure to radiation with other factors like, because it is buried in other factors like smoking.

And also it is explained that risk of the hereditary effects are smaller than that of development of cancer, and that the hereditary effects have not been observed from the result of epidemiological surveys for atomic bomb survivors of Hiroshima and Nagasaki.

At last it is underlined that when considering impacts on health caused by exposure to radiation, it is important first to get to know the scale of the impacts, based on the information on kinds of effects (e.g. the deterministic effects, the stochastic effects), dose and other relevant information, followed by optimized measures which are neither too much nor too less.

By the way, above-mentioned contents are summarized in the following videos.

It would be appreciated to visit them at your convenience.

– Japanese version

– English version

You can read the same article in Japanese here.

Thank you very much for reading this article.

See you next time!