Health Effects of the Chernobyl Accident

February 2015

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.
  • From 1986 to 2005, more than 6,000 cases of thyroid cancer were reported in children who were exposed at the time of the accident; 15 of these cases were fatal.
  • 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 effects published in the 2008 United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) report entitled Health effects due to radiation from the Chernobyl accident. The findings in this report are based on more than 20 years of studies of the health consequences of radiation exposure from the Chernobyl accident.

Chernobyl Explosion

A photograph taken hours after the Chernobyl explosion, showing extensive damage to Unit 4.

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.

Warning Signs

Signs warn against entering areas around Chernobyl affected by high levels of radiation.

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 2005 there have been over 6,000 cases of thyroid cancer reported in children and adolescents who were exposed at the time of the accident. 15 of these cases were fatal. Long-term increases in thyroid cancer incidence are difficult to predict, but more cases are expected over the next few decades. A large number of these thyroid cancers is likely attributable to children drinking milk containing radioactive iodine from cows who had eaten contaminated grass.

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.

Chernobyl Firefighters

Firefighters who first responded to the Chernobyl disaster are memorialized in a nearby statue.

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.


Chernobyl today

Today the Chernobyl site is maintained and monitored extensively by a team of dedicated caretakers.

The 2008 UNSCEAR 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. Thyroid cancer in individuals who were children at the time of the accident remains the major health consequence. 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: