Chernobyl nuclear power plant accident

On 26 April 1986, a nuclear power plant accident occurred in Chernobyl, present Ukraine. The accident contaminated large areas in Ukraine, Belarus, and Russia with various radioactive substances. People and some domestic animals were evacuated, but the wild animals and plants in the area were exposed to high levels of radiation. The harmful effects of radiation have since been detected in several species. The accident caused direct health effects for a couple of hundred people. Millions of people are affected by the late effects of the accident.

Some of the employees working at the Chernobyl plant on the night of the accident suffered severe radiation injuries. Three people were killed in the plant area on the night of the accident. One of them died of burns, one was buried under falling structures and one suffered a heart attack. In the morning following the accident, 203 people were taken to hospital, suspected of having radiation sickness. Later on, 134 radiation sickness diagnoses were confirmed.

In the following weeks, 28 of them died. Of the 106 surviving people, 19 died by 2006. Four of them died of a malignant bone marrow disease, probably caused by exposure to radiation. No one in the population exposed to the fallout is known to have suffered from radiation sickness or radiation burns.

More than 100,000 people were evacuated from nearby areas

Pripyat, the city located closest to the Chernobyl nuclear power plant with a population of 49,000, was evacuated within two days of the accident. An exclusion area was formed around the power plant and it was evacuated of people in the first week of May. Altogether 50,000 people were evacuated from this area reaching 30 kilometres from the site of the accident.

In the following months, another 17,000 people were evacuated from the most contaminated villages outside the exclusion area. Altogether, 116,000 people were evacuated in 1986. In later years, tens of thousands of people were moved from villages in Belarus, Ukraine and Russia.

Thyroid cancer increased in the 1990s

People who were near the accident site got significant thyroid doses due to releases of radioactive iodine. Part of the thyroid dose was caused by iodine in the breathing air on the first days and part by iodine obtained later on via foodstuffs, especially milk. The iodine accumulates in the thyroid gland. Therefore, radiation dose to the thyroid gland of the people exposed to radioactive iodine is several times higher than the doses to  other organs.

Since 1990, there has been a strong increase in thyroid cancer in children and adolescents in the contaminated areas of Belarus, Ukraine and Russia. Of those exposed in childhood, more than 5,000 have developed thyroid cancer between 1991 and 2005. A significant number of these cases is undoubtedly due to radioactive iodine exposure.

More than a thousand children have developed thyroid cancer while under 15 years of age. It is certain that almost all of these cancers were induced by radiation. They could have been avoided if the children had promptly received iodine tablets and the use of contaminated milk had been prohibited at the very beginning.

Children under five years of age at the time of exposure are at the highest risk of developing cancer. In older children and adolescents the risk is lower. Exposure in adult age has not been demonstrated to be clearly associated with thyroid cancer. The mortality rate for thyroid cancer has been very low (about 1%), but the patients will need hormonal medication for the rest of their life.

No other impacts of radiation were detected

Many reports have been published on the increase of various diseases as a result of the Chernobyl accident. In addition to thyroid cancer, no certain connection has been demonstrated between other health effects and radiation. For example, there were no changes in the number of children’s leukaemia cases in the ten years following the accident. No connection has been demonstrated between exposure to radiation and problems in pregnancy. No radiation exposure-related increase has been detected in malformations or other development disorders, chromosomal anomalies, such as Down syndrome, or the number of stillborn babies.

The accident caused many social, financial and psychological problems, both to the evacuated people and to those who continued living in the contaminated areas. Evacuations led to new problems, with people losing their familiar environment and social structures. The situation was further complicated by the financial and social changes experienced when the Soviet Union fell apart. The distress of parents certainly also affected children. All these factors have an effect on the population’s general health. These problems are discussed in more detail in the UN report published in 2002.

However, what has affected morbidity rates the most is the fact that the health of people living in and evacuated from the contaminated areas has been checked on a regular basis, and all abnormal findings have been included in statistics. Figures obtained in this way are not comparable with figures obtained from population that seek treatment on their own initiative.

Possible cancer cases are difficult to detect statistically

The population groups with the highest exposure are people who participated in the decontamination work in 1986–1987, those evacuated from nearby areas and those staying on in the contaminated areas; 600,000 people altogether. An international group of experts has estimated that cancer mortality may increase among them by a few per cent due to the exposure, which would mean approximately four thousand extra cancer deaths in the decades to come. The number of expected cancer deaths due to all other causes totals more than 100,000. In other population groups the radiation doses are low and it is very difficult to predict the number of cancer cases.

A minor increase in cancer morbidity rates is difficult to detect statistically. So far, in addition to thyroid cancer, no clear correlation has been demonstrated between the population’s radiation exposure and cancer morbidity.

The effects of the accident on animals and the ecosystem

The Chernobyl accident has offered an opportunity to study the effects of ionising radiation on ecosystems. We are able to study the effects of radiation on wild animals because of the remaining high dose rate caused by external radiation in the isolated precautionary action zone covering a distance of 30 kilometres from the ruptured reactor. Several studies have been conducted on insects (such as butterflies, bumblebees, grasshoppers and dragonflies), spiders, birds and mammals (including elk, deer, wolves, lynx, wild boar, bats).

Even today, over 30 years after the Chernobyl nuclear power plant accident, the scientific community is unable to reach a consensus on how long-term exposure to radiation has affected wild animals. The data on the effects of radiation is conflicting. Observations made in nature and the reference values recommended by the International Commission on Radiological Protection’s (ICRP), for example, do not unambiguously set a limit value for effects on animals.

It is also unclear which radiation level causes a considerable impact on the ecosystem. The uncertainty of research results is increased by the uneven distribution of the concentrations of radioactive substances in the area, fluctuations in the transmission of the substances and, as a result, the challenges of evaluating the actual radiation dose in living organisms. However, studies have indicated that ecosystems can recover even from vast disruption and recover their diversity. The seed production of the pines in the Chernobyl area, for example, regained its usual levels in only a few years after the accident.

The accident and the resulting radioactive pollution killed most of the pines in the forest near the nuclear power plant, impaired the production of pine seeds, reduced the number of invertebrates in the soil and increased the mortality of small mammals. The effects were clear and consistent with the established views of the harmful effects of radiation.

The forest of dead pines is called the Red Forest. The direct impact of radiation killed the trees, while the consequent, indirect effects transformed the lighting and nutrients in the area. Over time, a deciduous forest took over the previous pine forest. As the forest type changed, the fauna in the area was replaced by species better suited to the new biome, increasing biodiversity in the area.

The disruptions and changes caused by the Chernobyl disaster in the species and biodiversity have influenced the subsequent transformation of the area over time. Before the accident, people also played a role in the ecosystem. As the area was evacuated and the influence of people was lost, new opportunities opened up for various species. Long-term studies on large mammals have shown that species previously vacant in Chernobyl, such as the bison and Przewalski's horse, now thrive in the area.