Effects of Radiation Exposure of Children
One of the characteristics of the Fukushima Daiichi Accident is the fact that people are very much concerned about the impact of radiation exposure on children.
The protection of children in the accident aftermath has been of particular concern, and parents are extremely worried about the protection of their offspring. They are suspicious that the levels of dose applied for the protection of the population as a whole do not provide sufficient safety for their offspring. The doubt may have been amplified by the natural tendency of human beings to be sensitive about children and infants. I believe that it is the time for UNSCEAR to start efforts to provide a clear summary of the current information on radiation risk of children and infants and for ICRP to start efforts for revision of their recommendation to include a radiation protection scheme for children.
ICRP has developed a radiation protection scheme for three categories of exposed individuals: workers in occupational exposure, members of the public in public exposure, and patients in medical exposure. ICRP seems to consider that the children are included in one of these categories and that a definite ICRP document with recommendations specifically dedicated to the protection of children and infants is not needed at present.
Because of anatomical and physiological differences, radiation exposure has a different impact on children compared with adults. UNSCEAR had started a general review of these differences before the Fukushima-Daiichi accident; its conclusions on this subject are expected to be finalized soon.
Radiation Dose of Children
There are differences in the doses received by children and adults from exposure to the same distribution of radioactive material in the environment, for example, when there are elevated levels of radionuclides on the ground. So far, ICRP has not provided age-dependent dose conversion coefficients for the members of the public .
Very recently ICRP organized a task group on Age-dependent Dose Conversion Coefficients for External Exposures to Environmental Source in Committee 2. The objectives of the group are to provide age-dependent dose conversion coefficients for the members of the public that are applicable to the situation where a large amount of radionuclides are released from nuclear facilities to the environment as in the present accident.
If radionuclides are ingested or inhaled, the presence of radionuclides in one organ in the human body can give higher radiation doses to another organ because the organs of children are in closer proximity to one another than those of adults. In addition, both metabolism and physiology depend on age, which also affects the biokinetics and concentrations of radionuclides in different organs and thus the dose to those organs for a given intake.
For internal exposure, the necessity for internationally accepted dose coefficients for members of the public became particularly evident after the Chernobyl reactor accident. An ICRP report entitled “Age-dependent doses to members of the public from intake of radionuclides: Part 1” was published as ICRP Publication 56 . The report provided age-dependent dose coefficients (Sv/Bq) as organ equivalent dose and effective dose per unit intake of radionuclides. Then, Parts 2 to 5 were published [15–18]. Moreover, dose coefficients for embryo and fetus, as well as dose coefficients for infants through mother's breast milk, have been published as ICRP reports [19, 20]. These dose coefficients were successfully used for the internal dose assessments for the residents in the Fukushima disaster.