The Chernobyl nuclear disaster, particularly in the first ten days after the accident, resulted in large amounts of radioactive material being released and distributed over large areas of Ukraine, the Russian Federation and Belarus, and to a much lesser extent across regions in Scandinavia and Central Europe. Around five to 7.2 million people were living in the areas with the highest radiation exposure at the time of the accident.
There are very different figures on the number of deaths caused by the Chernobyl accident and the additional deaths to be expected as a result of cancer, and there is still a bitter debate to this day. Around 50 dead are directly linked to the accident in Chernobyl. The UN Chernobyl Forum estimated that the number of deaths due to illness was 4,000 in 2006.
Is Cesium causing cancer?
After evaluating around 50 reports and studies, Greenpeace found 93,000 deaths from cancer. According to a study published by the nuclear-critical medical organization IPPNW in 2011, over 112,000 liquidators had died as a result of their work. For the whole of Europe, IPPNW forecasts almost 240,000 additional cancer cases due to the accident in Chernobyl by 2056.
Acute health effects have so far been observed in the employees and emergency services involved in the clean-up work. Furthermore, the number of thyroid cancer cases among children who were exposed to iodine-131 as children in the affected regions of the three above-mentioned republics has increased significantly. So far, no reliable or conclusive data are available on other cancers in these regions. In addition, increased numbers of cases for certain cancers are expected.
Estimates of additional cancer to be expected in the future are generally subject to great uncertainty, particularly in regions away from the scene of the accident. Outside the states of the former Soviet Union, possible health effects are estimated to be so small that they will be very difficult, if not impossible, to detect in epidemiological studies.
In Germany, no measurable health effects have been and will probably not be observed in the future either. The average radiation exposure of the population due to the radioactivity shipped from Chernobyl to Germany is currently less than 0.01 mSv (Milli-Sievert) per year.
For comparison: The average radiation exposure of the population in Germany is about four milli-sieverts per year, which results approximately equally from the natural radiation exposure and from the use of ionizing radiation and radioactive substances in medical examinations. The natural radiation exposure varies considerably depending on the geological nature of the subsoil and the lifestyle and eating habits.
Radiation exposure and radiation damage
Large amounts of radionuclides were released into the environment in the reactor accident in Chernobyl. In particular, the radioactive isotopes of cesium and iodine were distributed across large parts of Europe. These released in humans
an external radiation exposure from the passing radioactive cloud as well as from the deposited radionuclides and
an internal radiation exposure from the inhalation of radioactive particles in the air as well as through the absorption of contaminated food and drinking water.
With radiation damage, a basic distinction is made between deterministic and stochastic damage.
Deterministic radiation damage is caused by high doses of ionizing radiation. They are often acute and only occur if the dose exceeds a certain threshold within a short period of time. For most acute radiation damage, this threshold is around 500 milli-sieverts and higher.
There is no threshold for stochastic radiation damage. They can therefore be caused both above and below the threshold values for deterministic damage mentioned above. The stochastic damage includes radiation-related cancer and leukemia. They often only appear years to decades after exposure to radiation. The following applies to stochastic radiation damage: The higher the radiation dose, the more likely the damage is to occur.
The stochastic diseases caused by radiation cannot be differentiated in the clinical picture from similar diseases caused by other influences or occurring spontaneously. Evidence that radiation is responsible for these late or long-term consequences can only be provided by epidemiological studies, that is, statistically. It is examined whether certain diseases are observed more frequently in the irradiated group of people than in an otherwise similar group of the population. Evidence in individual cases is not (thus far) possible.
More than five million people lived in areas classified as contaminated (more than 37,000 becquerels (Bq) per square meter). Before that, about 400,000 of them lived in areas with higher pollution (more than 555,000 becquerels per square meter) and were evacuated from the immediate vicinity of the accident reactor. In spring and summer 1986, the number of evacuees was around 116,000, and an additional 220,000 in the following years. According to the current state of knowledge, no acute radiation damage was observed in this population, especially among the evacuated people from the area around Chernobyl.
Across Belarus, Ukraine, and the four most affected areas of Russia, a significant increase in thyroid cancer has been observed, especially in children and adolescents who were 0 to 18 years old in the first days (to two months) after the accident exposed to radioactive iodine unprotected. Between 1991 and 2005, around 6,900 thyroid cancers were identified in the population of the above areas. The thyroid cancer rate increased more than six-fold, especially in people who were younger than ten years at the time of the accident. This was obviously a direct result of radiation exposure, since thyroid cancer would hardly occur in children and adolescents without radiation exposure.
As of 2004, at least nine children have been shown to have died of thyroid cancer. Another six patients died from other causes of death. However, most patients were successfully treated for the first time by surgical removal of the thyroid gland and subsequent radioiodine therapy.
Other solid tumors
While the increase in diseases of thyroid tumors in children and adolescents is clearly related to radiation exposure from Chernobyl, which was also shown by analytical epidemiological studies, the other solid tumor diseases such as breast cancer in women have so far been less informative. Some of these studies indicate increased disease rates. In the case of liquidators, for example, an increase in solid new cancer cases of 18 percent was observed between 1992 and 2009. However, the results of all these studies are still subject to great uncertainties and confirmation by further analytical studies is still pending. It should also be borne in mind that solid tumors can sometimes occur with a long delay of 20 years or more.
Ionizing radiation can trigger leukemia. These can appear after about two years. After the accident in Chernobyl, studies on the liquidators used there should provide information about the increased incidence of leukemia. Although the latest studies in Belarus, Russia and Ukraine indicate an increased incidence of leukemia among liquidators, the methodological shortcomings of these studies (such as uncertainties in dose estimation and other factors not taken into account) do not allow any clear conclusions to be drawn. So far there are no indications for increased leukemia rates in persons who were exposed before birth or as children.
The liquidators showed a connection between the level of exposure and the risk of developing cataracts (cataracts). These studies also provided new insight that cataracts may occur at a dose ten times lower than previously thought (0.7 gray (Gy) versus five gray). However, a critical analysis with newer data is necessary in order to validate the results and to better estimate the risk even at low exposures.
Estimation of expected additional cancer cases
Due to the great uncertainties in estimating the level and distribution of exposure, no exact estimates can be given for the risk, but only a range that reflects the magnitude and the range of fluctuation of the risk. Accordingly, the International Agency for Research on Cancer (IARC) has estimated the number of additional radiation-related cancer cases in Europe to be 25,000, with an uncertainty range of 11,000 to 59,000.
The IARC estimates that 16,000 of these cancer cases will be fatal. Based on the exposure estimates and the established risk coefficients for radiation-induced cancer, the Chernobyl Forum (2005) assumes that the approximately 600,000 particularly affected people (200,000 liquidators from 1986 to 1987, 120,000 evacuated people from particularly contaminated regions, 280,000 residents) of the most radioactively contaminated areas), up to 4,000 additional deaths from cancer can be expected.