Health effects of the Chornobyl accident
The 1986 accident at the Chornobyl nuclear plant in Ukraine was the largest uncontrolled radioactive release in history.
Introduction
The initial steam explosion at the Chornobyl nuclear plant resulted in the deaths of 2 workers, and 134 plant staff and emergency workers suffered acute radiation syndrome due to high doses of radiation. Of these 134 people, 28 later died.
The total number of cases of thyroid cancer registered in the 1991–2015 period, for those under 18 years of age in 1986, approached 20,000. This figure includes those for:
- the whole of Belarus and Ukraine
- the 4 most contaminated regions of the Russian Federation
About 5,000 thyroid cancer cases were due to radioactive iodine (iodine-131) exposure to children or adolescents at the time of the accident.
The remaining 15,000 cases are due to a variety of factors, such as:
- increased spontaneous incidence rate with aging of the population
- awareness of thyroid cancer risk after the accident
- improved diagnostic methods to detect thyroid cancer
There were no other demonstrated increases in the rates of solid cancers, leukemia and non-cancerous diseases from the radiation exposure.
In the 3 most affected countries (Belarus, the Russian Federation and Ukraine) radiation doses to the general public were relatively low.
The Chornobyl accident
On April 26, 1986, steam and hydrogen explosions at the Chornobyl plant’s Unit 4 led to a rupture in the reactor vessel. The resulting fire lasted 10 days.
The explosions and fire caused the release of large amounts of radioactive iodine and cesium into the air, mostly near the plant. The wind carried some material over Belarus, the Russian Federation, Ukraine and other parts of Europe.
The following information summarizes the health assessments published in:
- the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2008 Report titled Health effects due to radiation from the Chernobyl accident
- the UNSCEAR 2017 white paper titled Evaluation of data on thyroid cancer in regions affected by the Chernobyl accident
The findings in these reports are based on approximately 30 years of studies of the health consequences of radiation exposure from the Chornobyl accident. UNSCEAR acknowledges that thyroid cancer after the Chornobyl accident is a major issue. It also acknowledges that further investigation is needed to determine the long-term consequences.
Radiation released during the Chornobyl accident
Workers and the public were exposed to 3 main types of radionuclides:
- iodine-131
- cesium-134
- cesium-137
When iodine-131 (I-131) is released into the environment, it is quickly transferred to humans and taken up by the thyroid gland. I-131 has a short half-life (8 days). A half-life is the time required for the activity of a radionuclide to decrease, by a radioactive decay process, by half. Children exposed to radioactive iodine usually receive higher doses than adults because their thyroid gland is smaller and they have a higher metabolism.
Cesium isotopes have longer half-lives (approximately 2 years for cesium-134 and 30 years for cesium-137). This translates to a higher chance of long-term exposure through:
- ingestion of contaminated food and water
- inhalation of contaminated air from radionuclides deposited in soil
Worker health impacts
There were 600 workers onsite on the day of the accident. Of these workers, 134 suffered acute radiation sickness and 28 died in the first 3 months. Recovery took several years for those who survived radiation sickness.
Increased incidences of leukemia and cataracts were recorded for those exposed to higher doses of radiation among the 600 workers onsite. There has been no observed increase in the incidence of solid cancers or leukemia to those workers exposed to lesser doses of radiation. There is also no evidence of increases in other non-cancerous diseases from ionizing radiation.
Between 1986 and 1990, 530,000 registered recovery-operation workers worked at the accident site. They were exposed to doses ranging from 20 millisieverts (mSv) to 500 mSv (averaging 120 mSv). This group’s health is still being closely followed.
Public health impacts
One hundred and fifteen thousand (115,000) members of the public were evacuated from the area around the plant. They received an average effective radiation dose of 30 mSv.
Radiation doses to the public in the 3 contaminated countries (Belarus, the Russian Federation and Ukraine) were relatively low. There was an average effective dose of 9 mSv, which is about the same dose received from a medical computed tomography (CT) scan (10 mSv). The worldwide average effective dose from natural background radiation is around 2.4 mSv per year. In Canada it is 1.8 mSv per year.
Almost 20,000 cases of thyroid cancer were reported in children and adolescents who were exposed at the time of the accident as of 2015. They lived in Belarus, the Russian Federation and Ukraine.
Approximately 5,000 of these thyroid cancer cases are probably linked to children drinking fresh milk containing radioactive iodine from cows. The cows ate contaminated grass in the first few weeks following the accident.
The remaining 15,000 cases are due to a variety of factors, such as:
- an increased spontaneous incidence rate with aging of the population
- awareness of thyroid cancer risk after the accident
- improved diagnostic methods to detect thyroid cancer
The radiation dose due to the Chornobyl accident in other European countries was less than 1 mSv. In more distant countries, radiation from the accident had no impact on annual background doses and was considered to be non-significant to public health.
Psychological or mental health problems
According to several international studies, people exposed to radiation from Chornobyl:
- have high anxiety levels
- are more likely to report unexplained physical symptoms and poor health
Concerns about fertility and birth defects
There is no evidence of decreased fertility in men or women in the affected regions. Doses to the general population were low. It is therefore unlikely that there would be:
- an increase in stillbirths
- adverse pregnancy outcomes
- delivery complications
- negative impacts on children’s overall health
Monitoring remains important and is ongoing, however.
Summary of health effects
The UNSCEAR 2008 report on Chornobyl confirmed that:
- new research data has become available
- the major conclusions about the 1986 Chornobyl accident’s health consequences are basically consistent with previous assessments
The UNSCEAR 2017 white paper acknowledges that thyroid cancer is the major health issue in individuals who were children or adolescents at the time of the accident. It also states that further investigation is needed to determine the long-term consequences of radiation exposure.
The past fear of an increase in leukemia rates has not materialized, nor have any fertility problems arisen. Psychological effects like high anxiety and general poor health were observed, as past assessments indicated.
Previous studies showed that there were no global consequences of the accident in Asia and North America, and this is still true today.
How the health effects of the Chornobyl accident apply to the CNSC
The health effects of the Chornobyl nuclear accident had a profound impact on the nuclear industry globally, including Canada. The Canadian Nuclear Safety Commission (CNSC) uses the lessons learned from this disaster, as well as many other sources of information, to improve its regulatory framework.
The CNSC collaborates and communicates with international organizations and stakeholders to:
- prepare and respond to emergencies
- monitor and assess health and environmental effects
- build trust and transparency
These activities ensure that the nuclear industry in Canada operates in a way that prioritizes safety, and the protection of health and the environment.
The CNSC is an independent regulatory body. It regulates the use of nuclear energy and materials to:
- protect health, safety, security and the environment
- implement Canada’s international commitments on the peaceful use of nuclear energy
- disseminate objective scientific, technical and regulatory information to the public
The following are examples of how the Chornobyl nuclear accident applies to the CNSC’s work.
Regulatory framework
CNSC staff review and update regulations to improve the CNSC regulatory framework. Reviews are done regularly and are informed by licensing and compliance activities as well as international events and experience.
Collaboration
The CNSC collaborates with international organizations and other nuclear regulatory bodies. The Chornobyl nuclear power plant accident highlighted the need for international communication and collaboration, sharing of knowledge and best practices.
Emergency preparedness
The CNSC ensures that nuclear facilities have comprehensive emergency preparedness and response plans. It conducts regular emergency exercises and requires ongoing radiation monitoring. The organization also has public communication strategies in place in the unlikely event of an accident.
CNSC staff understand the potential health effects of a nuclear accident, based on the Chornobyl accident and other world events. The potential health effects include:
- thyroid cancer and other disease risks
- mental health effects and psychosocial consequences
Emergency dose reference levels and generic criteria, rather than the annual public dose limit of 1 mSv per year, help guide public safety decisions in an emergency to prevent and reduce these outcomes. These plans must address protective actions to prevent or limit health effects, including:
- distribution and instructions to take potassium iodide (KI) pills
- sheltering in place
- evacuation
- food restrictions
Human health and the environment
The CNSC protects human health and the environment, through establishing environmental regulations and standards. It also ensures that nuclear facilities have comprehensive environmental monitoring programs and measures in place to minimize or prevent impacts to the environment.
CNSC staff carry out these activities by:
- verifying compliance with these regulations and standards
- reviewing environmental monitoring reports
- conducting independent environmental monitoring to verify that health and the environment remain protected
CNSC staff work with health authorities and other stakeholders to assess the health of people living near nuclear facilities. They also conduct radiation research to advance our understanding of radiation exposure and health. This includes the consequences of a hypothetical severe nuclear accident.
At the time of the Chornobyl nuclear power plant accident, there was a lack of transparency about:
- the radiation releases to the environment
- communication of the health impacts
Trust and transparency
The CNSC strives to build trust and transparency with the public, Indigenous Nations and communities, and stakeholders. It holds public Commission proceedings and has terms of reference for long-term engagement with Indigenous Nations and communities.
The CNSC also:
- posts reports on environmental sampling and monitoring
- shares research findings
- provides updates about key developments in nuclear safety, including updates on incidents like Chornobyl
The CNSC continues to improve nuclear safety in Canada by learning from the past, including the Chornobyl accident. Safety, health, and the well-being of all people in Canada and the environment are always a priority.
Related links
- Health effects of the Chernobyl accident and special health care programmes (WHO, 2006)
- Environmental Consequences of the Chernobyl Accident (IAEA, 2006)
- Canada’s Response to Fukushima provides information on CNSC’s response to the Fukushima nuclear accident
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