Effects of the Chernobyl disaster

The Chernobyl disaster of 26 April 1986 triggered the release of radioactive contamination into the atmosphere in the form of both particulate and gaseous radioisotopes., it remains the world's largest known release of radioactivity into the natural environment.
The work of the Scientific Committee on Problems of the Environment suggests that the Chernobyl disaster cannot be directly compared to atmospheric tests of nuclear weapons by simply saying that it is better or worse. This is partly because the isotopes released at the Chernobyl Nuclear Power Plant tended to be longer-lived than those released by the detonation of atomic bombs.
It is estimated that the Chernobyl disaster caused US$235 billion in economic damages.

Radiation effects on humans

In a 2009 United Nations Scientific Committee on the Effects of Atomic Radiation study, the Chernobyl accident had by 2005 caused 61,200 man-Sv of radiation exposure to recovery workers and evacuees, 125,000 man-Sv to the populace of Ukraine, Belarus, and Russia, and a dose to most other European countries amounting to 115,000 man-Sv. The report estimated a further 25% more exposure would be received from residual radioisotopes after 2005. The global collective dose from Chernobyl was earlier estimated by UNSCEAR in 1988 to be "600,000 man Sv, equivalent on average to 21 additional days of world exposure to natural background radiation."

Dose to the general public within 30 km of the plant

The inhalation dose for the public during the time of the accident and their evacuation from the area in what is now the 30 km evacuation zone around the plant has been estimated, based on ground deposition of caesium-137, to be between 3 and 150 mSv.
Thyroid doses for adults around the Chernobyl area were estimated to be between 20 and 1000 mSv, whilst for one-year-old infants, these estimates were higher, at 20 to 6000 mSv. For those who left the area soon after the accident, the internal dose due to inhalation was 8 to 13 times higher than the external dose due to gamma/beta emitters. For those who remained until later, the inhalation dose was 50-70% higher than the dose due to external exposure. The majority of the dose was due to iodine-131 and tellurium and rubidium isotopes.
The ingestion doses in this same group of people have also been estimated using the cesium activity per unit of area, isotope ratios, an average day of evacuation, intake rate of milk and green vegetables, and what is known about the transfer of radioactivity via plants and animals to humans. For adults, the estimated dose ranges from 3 to 180 mSv, while for one-year-old infants, the estimated dose ranges from 20 to 1300 mSv. Again, the majority of the dose was attributed to iodine-131.

Childhood exposure

Ukraine, Belarus and parts of Russia were exposed to radiation after the Chernobyl disaster in 1986, but prior to the disaster, the number of children affected by thyroid cancer was relatively low globally. Every year, about 0.1–2.2 individuals per million of all ages under 15 years old worldwide are affected by thyroid cancer. Research has shown after the Chernobyl disaster the level of thyroid cancer, particularly in children near the radiation exposure, increased. Although iodine-131 has a short half-life compared to other radioactive isotopes, iodine-131 made its way through the food chain through a milk-to-consumer pathway. 95% of iodine-131 was ingested through milk after the disaster. Communities were unaware of the contamination deposited in soil and the transforming capabilities of radiation into other food sources. Children also absorbed radiation after drinking milk.
The absorption rate discovered in children has also been shown to be inversely proportional to age.
There is a high rate of thyroid cancer among children less than 15 years old who were exposed to the radiation after the disaster and an increasing level of dosage as age decreases. This inverse proportion could be explained by the way in which children absorb iodine-131. Children have smaller thyroid glands compared to adults and exhibit a different dosage response after ingesting iodine-131. A cohort study conducted in 2013 discovered a similar trend between age and dosage response. The cohort consisted of 12,000 participants, all of whom were exposed to radiation in Belarus and reported to be under the age of 18 at the time of exposure.

Future study

Studying the populations that were exposed to radiation after the Chernobyl accident has provided data linking exposure to radiation and the future development of cancer.
Cases of pediatric thyroid cancer, likely caused by absorption of Iodine-131 into the thyroid gland, increased in Ukraine and Belarus 3 to 4 years after the accident. Children were most at risk, and cases did not seem to increase in adults. The greatest increase was seen in children who were the youngest at the time of exposure, and most of the pediatric thyroid cases were reported in Gomel, Belarus, where the population was exposed to the highest levels of contamination. The majority of the cases that appeared in the exposed population were papillary thyroid cancer.
Before the accident, the rate of thyroid cancer in children in Belarus was less than 1 per million. By 1995, nine years after the disaster, the number of cases of pediatric thyroid cancer in Gomel Oblast rose to 100 per million per year. Even as adults, those who were exposed to the radiation as children may still be at risk of developing thyroid cancer decades after the exposure. It is important to study the at-risk population throughout their lives and observe if different patterns arise in tumours that develop with longer latency.
A group of experts affiliated with the Agenda for Research on Chernobyl Health has proposed a series of potential studies to examine the ongoing effects of the Chernobyl accident and provide more information on the full extent of related health consequences. Results from lifelong observation of the exposed population could provide more information on risks as well as future protection against radiation exposure.

Short-term health effects and immediate results

The explosion at the power station and subsequent fires inside the remains of the reactor resulted in the development and dispersal of a radioactive cloud which drifted not only over Russia, Belarus, and Ukraine, but also over most of Europe and as far as Canada.
The initial evidence that a release of radioactive material had occurred came not from Soviet sources, but from Sweden, where on 28 April, two days after the disaster itself, workers at the Forsmark Nuclear Power Plant, approximately 1100 km from the Chernobyl site were found to have radioactive particles on their clothing.
It was Sweden's search for the source of the radioactivity, after they had determined there was no leak at the Swedish plant, that led to the first hint of a critical incident in the Western Soviet Union.
Contamination from the Chernobyl disaster was not evenly spread across the surrounding countryside, but rather scattered irregularly, depending on weather conditions. Reports from Soviet and Western scientists indicate that Belarus received about 60% of the contamination that fell on the former Soviet Union. A large area in Russia south of Bryansk was also contaminated, as were parts of northwestern Ukraine.
203 people were hospitalised, of whom 31 died. 28 of them died from acute radiation exposure. Most of these were fire and rescue workers trying to bring the disaster under control, who were not aware of how dangerous the radiation exposure from the smoke was.. 135,000 people were evacuated from the area, including 50,000 from the nearby town of Pripyat, Ukraine. Health officials have predicted that over the next 70 years, there will be a 28% increase in cancer rates in much of the population, which was exposed to the 5–12 EBq of radioactive contamination released from the reactor.
Soviet scientists reported that the Chernobyl Unit 4 reactor contained about 180–190 metric tons of uranium dioxide fuel and fission products. Estimates of the amount of this material that escaped range from 5 to 30%. Because of the heat of the fire, and with no containment building to stop it, part of the ejected fuel was vaporised or particulate and rose into the atmosphere, where it spread.

Workers and "liquidators"

The workers involved in the recovery and clean-up after the disaster, called "liquidators", received high doses of radiation. In most cases, these workers were not equipped with individual dosimeters to measure the amount of radiation received, so experts could only estimate their doses. Even where dosimeters were used, dosimetric procedures varied — some workers are thought to have been given more accurate estimated doses than others. According to Soviet estimates, between 300,000 and 600,000 people were involved in the cleanup of the 30 km evacuation zone around the reactor, but many of them entered the zone two years after the disaster.
Estimates of the number of "liquidators" vary; the World Health Organization, for example, puts the figure at about 600,000; Russia lists as liquidators some people who did not work in contaminated areas. In the first year after the disaster, the number of cleanup workers in the zone was estimated to be 2,000. These workers received an estimated average dose of 165 millisieverts.
Studies on the increase in DNA mutations in the children of liquidators yield varying conclusions. One study identified a sevenfold increase in DNA mutations in children of liquidators conceived after the accident, when compared to their siblings that were conceived before, but another claimed to find no increase in developmental anomalies or a statistically significant increase in the frequencies of germline mutations in their progeny.

Evacuation

Military authorities started evacuating people from the area around Chernobyl on the second day after the disaster. By May 1986, about a month later, all those living within a radius of the plant had been relocated. This area is often referred to as the zone of alienation. However, radiation affected the environment over a much wider scale than this 30 km radius encloses.
According to reports from Soviet scientists, 28,000 square kilometers were contaminated by caesium-137 to levels greater than 185 kBq per square meter. 830,000 people lived in this area. About 10,500 km² were contaminated by caesium-137 to levels greater than 555 kBq/m². Of this total, roughly 7,000 km² lie in Belarus, 2,000 km² in the Russian Federation and 1,500 km² in Ukraine. About 250,000 people lived in this area. These reported data were corroborated by the International Chernobyl Project.