Health Effects of the Chernobyl Accident

March 2022

Quick facts

• The 1986 accident at the Chernobyl nuclear plant in Ukraine was the largest uncontrolled radioactive release in history.
• The initial steam explosion resulted in the deaths of two workers. 134 plant staff and emergency workers suffered acute radiation syndrome (ARS) due to high doses of radiation; of those, 28 of them later died from ARS.
• The total number of cases of thyroid cancer registered in the 1991–2015 period among those under 18 years of age in 1986 (for the whole of Belarus and Ukraine, and for the four most-contaminated oblasts of the Russian Federation), approached 20,000.
  • About 5,000 thyroid cancer cases were attributable to radioactive iodine (iodine-131) exposure to those who were 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, and 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 three most-affected countries – Belarus, the Russian Federation and Ukraine – radiation doses to the general public were relatively low.

The 1986 accident at the Chernobyl nuclear plant in Ukraine was the largest uncontrolled radioactive release in history.

On April 26, 1986, steam and hydrogen explosions at the Chernobyl plant's Unit 4 led to a rupture in the reactor vessel and a fire that 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 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 and the UNSCEAR 2018 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 Chernobyl accident. UNSCEAR acknowledges that thyroid cancer after the Chernobyl accident is a major issue and that further investigation is needed to determine the long-term consequences.

Radiation released during the Chernobyl accident

Workers and the public were exposed to three main types of radionuclides: iodine-131, cesium-134 and cesium-137.

When iodine-131 is released into the environment, it is quickly transferred to humans and taken up by the thyroid gland. However, I-131 has a short half-life (8 days). 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), increasing the chance of long-term exposure through ingestion of contaminated food and water, inhalation of contaminated air, or from radionuclides deposited in soil.

Worker health impacts

On the day of the accident, there were 600 workers onsite. 134 suffered acute radiation sickness, 28 of whom died in the first three months. For those who survived radiation sickness, recovery took several years.

Among the 600 workers onsite, increased incidences of leukemia and cataracts were recorded for those exposed to higher doses of radiation; otherwise, there has been no increase in the incidence of solid cancers or leukemia among the rest of the exposed workers. There is no evidence of increases in other non-cancerous diseases from ionizing radiation.

The 530,000 registered recovery operation workers who worked at the accident site between 1986 and 1990 were exposed to doses ranging from 20 to 500 mSv (averaging 120 mSv). This cohort's health is still being closely followed.

Public health impacts

The 115,000 members of the public who had to be evacuated from the area around the plant received an average effective radiation dose of 30 mSv. Radiation doses to the general public in the three contaminated countries (Belarus, the Russian Federation and Ukraine) were relatively low, with an average effective dose of 9 mSv, about the dose of a medical CT scan (i.e., 10 mSv). The total worldwide average effective dose from natural background radiation is around 2.4 mSv per year. In Canada, it is 1.8 mSv per year.

Among the residents of Belarus, the Russian Federation and Ukraine, as of 2015 there had been almost 20,000 cases of thyroid cancer reported in children and adolescents who were exposed at the time of the accident. Approximately 5,000 of these thyroid cancers are likely attributable to children drinking fresh milk containing radioactive iodine from cows who had eaten contaminated grass in the first few weeks following 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, and improved diagnostic methods to detect thyroid cancer.

The radiation dose due to Chernobyl in other European countries was less than 1 mSv. In more distant countries, radiation from the accident had no impact on the 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 Chernobyl have high anxiety levels and 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. Because doses to the general population were low, it is unlikely that there would be any increase in stillbirths, adverse pregnancy outcomes, delivery complications, or negative impacts on children's overall health. Regardless, monitoring remains important and is ongoing.

Summary

The UNSCEAR 2008 report on Chernobyl confirmed that, while new research data has become available, the major conclusions about the 1986 Chernobyl accident's health consequences are essentially consistent with previous assessments. The UNSCEAR 2018 White Paper acknowledges that thyroid cancer is the major health issue (in individuals who were children or adolescents at the time of the accident) and that further investigation is needed to determine the long-term consequences of radiation exposure. The previous fear of an increase in leukemia rates has not materialized, nor have any fertility problems arisen. As previous assessments indicate, psychological effects – such as high anxiety – and general poor health were observed. Previous studies have shown that there were no global consequences of the accident in Asia and North America, which remains true today.

For more information on Chernobyl:

• 2008 United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) report entitled Health effects due to radiation from the Chernobyl accident (Annex D)
• Health Effects of the Chernobyl Accident and Special Health Care Programmes (WHO, 2006)
• Environmental Consequences of the Chernobyl Accident (IAEA , 2006)
• United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2018 White Paper titled Evaluation of data on thyroid cancer in regions affected by the Chernobyl accident