Health effects of ionizing radiation on children

We all live with radiation, from both natural and artificial sources, in our everyday lives. The impacts of radiation exposure are different for children and adults, as their bodies are structurally and functionally different. This material is for anyone who wants to understand how radiation can affect children’s health.

Understanding radiation doses
Measures to keep people safe
- International radiation protection efforts and the CNSC’s regulatory framework
  - Protective measures for nuclear energy workers who are pregnant or breastfeeding
How radiation can affect children and adults differently
Child health effects
Summary Table
References

Understanding radiation doses

Generally speaking, a “dose” is the quantity of radiation that someone is exposed to. The dose of radiation determines the potential health effects. When referring to a radiation dose:

A sievert (Sv) is the unit used to measure a dose of radiation. It allows for comparisons across different types of radiation and how the radiation affects living things.
1 Sv = 1,000 millisieverts (mSv)

Radiation doses can be classified into 4 categories called “dose bands,” based on the level of radiation:

Very low dose: Less than 10 mSv
Low dose: 10 mSv to 100 mSv
Moderate dose: 100 mSv to 1,000 mSv
High dose: More than 1,000 mSv

The summary table outlines dose limits, potential sources of exposure, and health effects for these different dose bands, for different populations, including children.

We all live with radiation, from both natural and artificial sources, in our everyday lives. Canadians receive 1 to 4 mSv (average 1.8 mSv) of natural background radiation each year^{Footnote 1}. The amount of radiation we receive from artificial sources has been increasing worldwide due to greater use of radiation for medical diagnosis and treatment, especially in western countries^{Footnote 2}. At the same time, decades of scientific research has resulted in measures to protect people from potentially harmful radiation doses, and to strike a balance between the risks and benefits of radiation.

Measures to keep people safe

There are many measures in place to protect people from potentially harmful radiation exposure.

International radiation protection efforts and the CNSC’s regulatory framework

Several international organizations are involved in the fields of radiation science and radiation protection:

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) assesses and consolidates scientific information on the sources, effects and risks of radiation exposure.
The International Commission on Radiological Protection advances the science of radiological protection (from UNSCEAR and other scientific sources) for public benefit; in particular, by providing recommendations and guidance on all aspects of protection against ionizing radiation.
The International Atomic Energy Agency establishes radiation safety standards for the protection of health.

Together, these efforts and all available scientific information inform the CNSC’s regulatory framework, which is used to safely regulate the Canadian nuclear industry. This framework includes:

acts and regulations
licences and certificates
regulatory documents

Within the CNSC’s regulatory framework, important regulations include:

the Radiation Protection Regulations, which establish dose limits that ensure that people, including children, do not receive potentially harmful radiation doses from the nuclear industry:
- The dose limit for members of the public is 1 mSv per calendar year^{Footnote 3}.
- The dose limit for a nuclear energy worker (NEW) is 50 mSv in a 1-year dosimetry period, and 100 mSv in a 5-year dosimetry period.

The Radiation Protection Regulations also require every CNSC licensee to keep exposure to ionizing radiation as low as reasonably achievable, taking into account social and economic factors (this is known as the ALARA principle). As such, actual doses from nuclear activities and facilities are expected to be much lower than the regulatory dose limits.

These regulations also include specific measures that licensees must take to protect nuclear energy workers who are pregnant or breastfeeding (explained in more detail in the next section).

the General Nuclear Safety and Control Regulations, which require every licensee to take all reasonable precautions to control the release of nuclear or hazardous substances into the environment^{Footnote 4}. The CNSC’s environmental protection framework establishes limits for concentrations of nuclear substances in our environment (e.g., water, soil, air, wildlife, plants) so that the health of people living near nuclear facilities is protected.

Protective measures for nuclear energy workers who are pregnant or breastfeeding

Under the Radiation Protection Regulations, CNSC licensees are required to inform all nuclear energy workers (NEWs), in writing, of:

the fact that they are NEWs
the risks associated with radiation to which they may be exposed in the course of their work
dose limits that apply to NEWs
the radiation dose levels they have received, on an annual basis
their responsibilities during an emergency and the risks associated with radiation to which they may be exposed during the control of an emergency^{Footnote 3}.

Further, CNSC licensees must inform NEWs, (namely female NEWs), in writing, of:

the risks associated with the exposure of embryos and fetuses to radiation
the risks to breastfed infants from intakes of nuclear substances
the importance of informing the employer that they are pregnant or breastfeeding, as soon as feasible
their rights if they are pregnant or breastfeeding
dose limits for pregnant NEWs^{Footnote 3} (4 mSv for the balance of the pregnancy, once the NEW has informed the licensee, in writing, of the pregnancy).

These requirements are in place to protect unborn children and infants, and to enable pregnant and breastfeeding NEWs to continue working safely in the nuclear industry.

Having a CNSC licensee provide this information to NEWs helps them decide if and when to inform the licensee (their employer) that they are pregnant or breastfeeding, so that they are granted the appropriate protective measures.

Once informed by a NEW, in writing, of a pregnancy, the Radiation Protection Regulations require the licensee to assess working conditions and to make accommodations or adaptations for the pregnant NEW to keep radiation exposure below the dose limit and ALARA.
Similarly, once informed by a NEW, in writing, that the NEW is breastfeeding, the licensee is required to assess working conditions and to make accommodations or adaptations for the breastfeeding NEW to limit intake of nuclear substances^{Footnote 3}.

These accommodations/adaptations will end when the NEW informs the licensee that they are no longer pregnant or breastfeeding^{Footnote 5}.

The summary table outlines dose limits, potential sources of exposure, and health effects associated with the different dose bands for various populations, including NEWs.

How radiation can affect children and adults differently

The impacts of radiation exposure (risks and outcomes) can be different for children and adults since their bodies are structurally and functionally different.

Physical differences

Children have smaller bodies than adults. Their organs are also smaller and closer together, so radiation in one organ may affect a neighbouring organ^{Footnote 2} ^{Footnote 6}. Moreover, the overlying tissues of a child’s body provide less shielding – so a given exposure may result in a higher dose to a child’s organs^{Footnote 2} ^{Footnote 6}.

Behavioural differences

Children tend to be more physically active than adults. Higher breathing rates associated with physical activity could mean more radiation exposure to the lungs^{Footnote 6}.

Infants and young children tend to drink more milk than adults^{Footnote 6}. If the milk is contaminated, children would be more exposed than adults. For example, after the 1986 Chornobyl accident, children who drank milk contaminated with radioactive iodine had an increased risk of developing thyroid cancer.

However, a child’s potential increased exposure and overall dose resulting from both these behaviours may be offset by the decreased volume of air and food intake, compared to an adult^{Footnote 7}.

General differences in health effects

Cancer effects

To fully understand the differences in cancer risks between children and adults, it is important to consider the child’s age, sex, cancer type, and specific body part affected^{Footnote 2} ^{Footnote 6}:

For about 25% of tumour types, children are more radiosensitive (sensitive to radiation) than adults^{Footnote 6}. Organs particularly sensitive to radiation in children are the brain, thyroid gland, skin, breast, and bone marrow (radiation doses to bone marrow known to cause leukemia)^{Footnote 2} ^{Footnote 6}.
Conversely, for about 10% of tumour types (lungs and ovaries), children are less radiosensitive than adults^{Footnote 2} ^{Footnote 6}.
For about 15% of tumour types (liver and bladder), children have the same radiosensitivity and cancer risk as adults^{Footnote 6}.
For about 50% of tumour types, the data are too weak to draw conclusions, or there is only a weak or non-existent relationship between radiation exposure and risk at any age of exposure^{Footnote 6}.

Non-cancer effects

Non-cancer effects of exposure to radiation include cognitive defects, cataracts and thyroid nodules. Differences in non-cancer effects, in children vs. adults, are evident at moderate doses above 500 mSv, and usually at doses that are substantially higher, such as those associated with radiation therapy^{Footnote 6}. Given these risks, medical professionals consider both the benefits and risks of radiation therapy when determining best treatment options.

The summary table outlines dose limits, potential sources of exposure, and health effects for the different dose bands, for children and other populations.

Child health effects

The doses discussed in this section that could cause negative health effects are higher than the dose limits for nuclear energy workers and members of the public living near nuclear facilities, and much higher than what most people are normally exposed to.

Lessons learned about radiation’s health effects on children

Accidents at nuclear facilities have advanced our understanding of the health effects that can result when people are exposed to doses that are much higher than background and operational doses:

Following the 1986 Chornobyl accident, when evacuees received doses of approximately 30 mSv:
- There has been no observable increase in childhood leukemia or solid cancer, except for thyroid cancer^{Footnote 9}.
- An increase in thyroid cancer has been observed among children who drank milk contaminated with radioactive iodine (with high doses to the thyroid, upwards of 1000 mSv)^{Footnote 8} ^{Footnote 9}. Most of what is known about thyroid cancer risk in children comes from health studies related to the Chornobyl accident.
Following the 2011 Fukushima accident, when a child living in the area could have received a total dose of up to approximately 10 mSv in the first year after the accident:
- There has been no observable increase in childhood leukemia or solid cancer^{Footnote 10}.
- Absorbed doses to the thyroid were substantially lower than after the Chornobyl accident. Although an increased risk of thyroid cancer is possible among children most exposed to radiation, the occurrence of a large number of radiation-induced thyroid cancers can be discounted^{Footnote 11}.
- Overall, there is no expected increase in lifetime cancer risk that would be discernible over the baseline level for that population^{Footnote 8} ^{Footnote 10}.

Protection during an emergency

Canada has protective actions, based on lessons learned from Chornobyl and Fukushima, that can be implemented during a nuclear emergency. These actions are in place to reduce potentially harmful exposures to radiation and can include:

ingestion of potassium iodide (KI) to protect the thyroid
sheltering and/or evacuation
restrictions on locally sourced food, milk, and drinking water to protect members of the public and Indigenous Nations and communities

For persons participating in the control of a nuclear emergency, the aim is to keep all individual doses below 50 mSv^{Footnote 3}. In some exceptional cases, the dose received should not exceed 500 mSv^{Footnote 3} if a person is involved in emergency actions to:

prevent health effects in the surrounding population that are fatal, life-threatening, or could result in permanent injury
to prevent the development of conditions that could significantly affect people and the environment

Further, a licensee should not request that a pregnant woman participate in the control of a nuclear emergency^{Footnote 3}.

Future children

No hereditary effects from radiation exposure have been observed in humans. Specifically, in the offspring of people exposed to radiation (either as adults or as children), there has been:

no observable evidence of changes to cells that carry hereditary information
no observable changes in sex ratio (i.e., proportion of boys vs. girls born)
no observable increase in congenital anomalies
no observable increase in cancer risk^{Footnote 6}.

This includes the children of people exposed to the atomic bombs in Japan, and the children of survivors of childhood/adolescent cancers treated with high doses of radiotherapy to the reproductive organs^{Footnote 6}.

Unborn children

It has been observed that radiation exposure can affect the embryo and fetus, as they are particularly sensitive to radiation. X-rays and gamma rays can penetrate the body, so the embryo/fetus could be exposed when the pregnant mother is exposed. They could also be exposed if the pregnant mother:

ingests contaminated food or drink
undergoes a nuclear medicine procedure for diagnosis or treatment of disease^{Footnote 2}

Risks to the embryo/fetus are related to the stage of pregnancy and the dose of radiation absorbed. Higher doses of radiation could lead to malformation of developing organs, and perhaps cause death at around the time of birth. Organs particularly susceptible are the eyes, brain, and skeleton^{Footnote 2}. These risks of malformed organs are:

most significant when the organs are developing during the first trimester (weeks 2 to 8 of gestation)
somewhat lower in the second trimester
lowest in the third trimester^{Footnote 5}

After week 8 of gestation, the organ most susceptible is the brain^{Footnote 2}. An acute dose above 100 mSv between weeks 8 and 15 of gestation, or an acute dose above 200 mSv between weeks 16 and 25 gestation, could cause brain damage^{Footnote 5}.

Doses to the uterus of 10 mSv may result in 2 out of 1,000 (0.2%) live-born children affected with:

death (around the time of birth)
malformation
intellectual disability
cancer (leukemia in particular)^{Footnote 2}

Note: These effects are less common than the number of live births affected by these conditions naturally (60 out of 1000, or 6%)^{Footnote 2}.

Evidence from Japanese survivors of the atomic bombings:

showed that a radiation dose of 1,000 mSv before birth increased the risk of extreme intellectual disability by about 40%^{Footnote 2} ^{Footnote 12}
suggests that the lifetime cancer risk from in-utero exposure may be similar to exposures in early childhood^{Footnote 5} ^{Footnote 12}
shows that the risk of solid thyroid nodules (non-cancer) is also elevated among those exposed in-utero (similar to the Chornobyl accident); however, this risk is similar to the risk from exposure in early childhood^{Footnote 13} ^{Footnote 14}

Children between 5 and 20 years old

Compared to adults, children can be less susceptible, similarly susceptible, or more susceptible to radiation-induced cancer, depending on the type of cancer:

A given dose is twice as likely to cause a child to develop brain cancer^{Footnote 2}, compared to an adult.
The increased risk of leukemia following a dose of 10 mSv to the red bone marrow would not be discernible from natural childhood leukaemia rates, but there is evidence that a dose of about 25 mSv to the bone marrow may cause a very slight increase in leukemia risk (about 2 additional cases per 10,000)^{Footnote 8}.
Females exposed as children, compared to those exposed as adults to the same dose to the breast, above 10 mSv, have a 3 to 5 times higher risk of developing breast cancer in adulthood^{Footnote 8}.
- Doses less than 10 mSv to the breast would not likely result in a noticeable difference in breast cancer incidence compared to background radiation rates^{Footnote 8}.
Children older than 5 years who receive 200 mSv to the thyroid are twice as likely as adults to develop thyroid cancer later in life^{Footnote 8}. Further, the risk of radiation-induced thyroid nodules (non-cancerous) increases the younger the child is at exposure^{Footnote 6}.

Infants and young children, specifically (birth to 5 years old)

In infants and young children, the thyroid gland is particularly sensitive to radiation. The thyroid can be exposed to radioactive iodine through ingestion of contaminated breast or animal milk^{Footnote 2} ^{Footnote 8}.
For a given intake of radioactive iodine, the dose to the thyroid could be up to 8 or 9 times that of an adult^{Footnote 2}.

Medical uses of radiation

Radiation in medicine (e.g., X-rays, CT scans, radiation therapy) represents the greatest artificial source of radiation exposure.
The radiation dose from 1 CT scan can vary from less than 0.1 mSv to over 50 mSv to a specific organ (with an average of 6.4 mSv^{Footnote 15}), and depends on the type of scan, the age of the child and the scanner settings^{Footnote 16} ^{Footnote 17}. There is preliminary evidence that the increase in childhood leukemia resulting from CT scans is 1 excess cancer per 10,000 CT scans^{Footnote 18}.
Radiation therapy is one of the few means by which a child could be exposed to moderate or high doses of radiation^{Footnote 6} (from 100 mSv to over 1,000 mSv).

Summary table

This table summarizes dose limits, potential sources of exposure, and health effects for different dose bands and populations.

Dose band à	Very low dose: < 10 mSv	Low dose: 10 mSv to 100 mSv	Moderate dose: 100 mSv to 1,000 mSv	High dose: > 1,000 mSv
CNSC dose limit	1 mSv: Annual public dose limit 1 mSv: Annual dose limit for a non-nuclear energy worker (non-NEW) 4 mSv: Dose limit for a pregnant NEW for duration of pregnancy	50 mSv: Annual dose limit for a nuclear energy worker (NEW) 100 mSv: 5-year dose limit for a NEW	Not applicable (above dose limit)	Not applicable (above dose limit)
Examples of radiation sources and exposures	0.001 mSv^{Footnote 19}: Typical annual dose from living near a Canadian nuclear power plant 0.005 mSv^{Footnote 19}: Dental X-ray 0.1 mSv^{Footnote 19}: Typical chest X-ray 1 mSv^{Footnote 19}: Typical annual dose to a NEW ≤~10 mSv: Dose observed in the most exposed children in Fukushima, first year after the accident	Multiple CT scans Evacuees near the Chornobyl accident site ≤~30 mSv^{Footnote 10}: Thyroid dose observed in the most exposed children in Fukushima, from infancy to age 5, first year after the accident ≤~25 mSv^{Footnote 10}: Thyroid dose observed in the most exposed children in Fukushima, above age 5, first year after the accident	Radiation therapy Thyroid dose observed in the most exposed children, from the Chornobyl accident	Radiation therapy Thyroid dose observed in the most exposed children, from the Chornobyl accident
Hereditary effects (effects on future children)	Not observed	Not observed	Not observed	Not observed
Health effects on an unborn child (In-utero)	Not discernible from naturally occurring conditions (i.e., death, malformation, intellectual disability, or cancer (leukemia in particular))	10 mSv: 2 in 1,000 (0.2%) live-born children affected with one of the following: death, malformation, intellectual disability, or cancer (leukemia in particular)	>100 mSv: Brain damage from acute dose at 8–15 weeks gestation >200 mSv: Brain damage from acute dose at 16–25 weeks gestation	1,000 mSv: 40% higher risk of extreme intellectual disability
Health effects on children	Not discernible from naturally occurring childhood leukemia rates (10 mSv to red bone marrow) Not discernible from naturally occurring breast cancer later in life (<10 mSv)	~25 mSv to bone marrow: Very slight increase in leukemia risk (increase of ~2 in 10,000 children) >10 mSv to breast: females exposed as children vs. adults have 3-5 times higher risk of breast cancer in adulthood	Radioactive iodine dose to thyroid of 200 mSv: Child twice as likely as adults to develop thyroid cancer later in life >500 mSv: Start to see higher rates of cognitive defects, cataracts, thyroid nodules in children (vs. adults)	Evidence of one additional case of childhood leukemia from 10,000 CT scans

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Date modified:: 2024-05-16

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