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Chernobyl Nuclear Accident

2. How has human health been affected by the Chernobyl accident?

  • 2.1 How much radiation were people exposed to?
  • 2.2 What is the death toll of the Chernobyl accident?
  • 2.3 What diseases are linked to the accident?
    • 2.3.1 Thyroid Cancer in Children
    • 2.3.2 Leukaemia, Solid Cancers and Circulatory Diseases
    • 2.3.3 Cataracts
  • 2.4 Have there been or will there be any effects on reproduction?
  • 2.5 What was the psychological impact on exposed populations?

The source document for this Digest states:

The report of the Expert Group provides a summary on health consequences of the accident on Belarus, the Russian Federation and Ukraine and responds to five of the most important health-related questions concerning the impact of the Chernobyl accident.

Source & ©: UN Chernobyl Forum,
 Chernobyl’s Legacy: Health, Environmental and Socio-economic Impacts (2006)
Forum Expert Group Report: Health Consequences, p11

"Interaction of ionizing radiation (alpha, beta, gamma and other kinds of radiation) with living matter may damage human cells, causing death to some and modifying others. Exposure to ionizing radiation is measured in terms of absorbed energy per unit mass, i.e., absorbed dose. The unit of absorbed dose is the gray (Gy), which is a joule per kilogram (J/kg). The absorbed dose in a human body of a few grays may cause acute radiation syndrome (ARS) as happened with some of the Chernobyl emergency workers.

Because many organs and tissues were exposed as a result of the Chernobyl accident, it has been very common to use an additional concept, that of effective dose, which characterizes the overall health risk due to any combination of radiation. The effective dose accounts both for absorbed energy and type of radiation and for susceptibility of various organs and tissues to development of a severe radiation-induced cancer or genetic effect. Moreover, it applies equally to external and internal exposure and to uniform or non-uniform irradiation. The unit of effective dose is the sievert. One sievert is a rather large dose and so the millisievert or mSv (one thousandth of a Sv) is commonly used to describe normal exposures.

Living organisms are continually exposed to ionizing radiation from natural sources, which include cosmic rays, cosmogenic and terrestrial radionuclides (such as 40K, 238U, 232Th and their progeny including 222Rn (radon)). UNSCEAR has estimated annual natural background doses of humans worldwide to average 2.4 mSv, with a typical range of 1–10 mSv. Lifetime doses due to natural radiation would thus be about 100–700 mSv. Radiation doses to humans may be characterized as low-level if they are comparable to natural background radiation levels of a few mSv per year.]

Source & ©: UN Chernobyl Forum
 Chernobyl’s Legacy: Health, Environmental and Socio-economic Impacts (2006)
Doses of Ionizing Radiation, p. 12

2.1 How much radiation were people exposed to?

The source document for this Digest states:

Emergency and recovery operation workers
Emergency and recovery operation workers

Three population categories were exposed from the Chernobyl accident:

  • Emergency and recovery operation workers who worked at the Chernobyl power plant and in the exclusion zone after the accident;
  • Inhabitants evacuated from contaminated areas; and
  • Inhabitants of contaminated areas who were not evacuated.

With the exception of the on-site reactor personnel and the emergency workers who were present near the destroyed reactor during the time of the accident and shortly afterwards, most of recovery operation workers and people living in the contaminated territories received relatively low whole-body radiation doses, comparable to background radiation levels accumulated over the 20 year period since the accident.

The highest doses were received by emergency workers and on-site personnel, in total about 1000 people, during the first days of the accident, ranging from 2 to 20 Gy, which was fatal for some of the workers. The doses received by recovery operation workers, who worked for short periods during four years following the accident ranged up to more than 500 mSv, with an average of about 100 mSv according to the State Registries of Belarus, Russia, and Ukraine.

Effective doses to the persons evacuated from the Chernobyl accident area in the spring and summer of 1986 were estimated to be of the order of 33 mSv on average, with the highest dose of the order of several hundred mSv.

Ingestion of food contaminated with radioactive iodine did result in significant doses to the thyroid of inhabitants of the contaminated areas of Belarus, Russia, and Ukraine. The thyroid doses varied in a wide range, according to age, level of ground contamination with 131I, and milk consumption rate. Reported individual thyroid doses ranged up to about 50 Gy, with average doses in contaminated areas being about 0.03 to few Gy, depending on the region where people lived and on their age. The thyroid doses to residents of Pripyat city located in the vicinity of the Chernobyl power plant, were substantially reduced by timely distribution of stable iodine tablets. Drinking milk from cows that ate contaminated grass immediately after the accident was one of the main reasons for the high doses to the thyroid of children, and why so many children subsequently developed thyroid cancer. The general public has been exposed during the past twenty years after the accident both from external sources (137Cs on soil, etc.) and via intake of radionuclides (mainly, 137Cs) with foods, water and air, see Fig.2. The average effective doses for the general population of ‘contaminated’ areas accumulated in 1986– were estimated to be between 10 and 30 mSv in various administrative regions of Belarus, Russia and Ukraine. In the areas of strict radiological control, the average dose was around 50 mSv and more. Some residents received up to several hundred mSv. It should be noted that the average doses received by residents of the territories ‘ contaminated’ by Chernobyl fallout are generally lower than those received by people who live in some areas of high natural background radiation in India, Iran, Brazil and China (100–200 mSv in 20 years).

FIG. 2. Pathways of exposure to man from environmental releases of radioactive materials.

The vast majority of about five million people residing in contaminated areas of Belarus, Russia and Ukraine currently receive annual effective doses from the Chernobyl fallout of less than 1 mSv in addition to the natural background doses. However, about 100  000 residents of the more contaminated areas still receive more than 1 mSv annually from the Chernobyl fallout. Although future reduction of exposure levels is expected to be rather slow, i.e. of about 3 to 5% per year, the great majority of dose from the accident has already been accumulated.

The Chernobyl Forum assessment agrees with that of the UNSCEAR 2000 Report in terms of the individual and collective doses received by the populations of the three most affected countries: Belarus, Russia and Ukraine.

Table: Summary of average accumulated doses to affected populations from Chernobyl fallout

Source & ©: UN Chernobyl Forum
 Chernobyl’s Legacy: Health, Environmental and Socio-economic Impacts (2006)
How much radiation were people exposed to as a result of the accident?, p.11-14

2.2 What is the death toll of the Chernobyl accident?

The source document for this Digest states:

ARS was diagnosed in 134 emergency workers

The number of deaths attributable to the Chernobyl accident has been of paramount interest to the general public, scientists, the mass media, and politicians. Claims have been made that tens or even hundreds of thousands of persons have died as a result of the accident. These claims are highly exaggerated. Confusion about the impact of Chernobyl on mortality has arisen owing to the fact that, in the years since 1986, thousands of emergency and recovery operation workers as well as people who lived in ‘contaminated’ territories have died of diverse natural causes that are not attributable to radiation. However, widespread expectations of ill health and a tendency to attribute all health problems to exposure to radiation have led local residents to assume that Chernobyl-related fatalities were much higher.

Acute Radiation Syndrome mortality

The number of deaths due to acute radiation syndrome (ARS) during the first year following the accident is well documented. According to UNSCEAR (2000), ARS was diagnosed in 134 emergency workers. In many cases the ARS was complicated by extensive beta radiation skin burns and sepsis. Among these workers, 28 persons died in 1986 due to ARS. Two more persons had died at Unit 4 from injuries unrelated to radiation, and one additional death was thought to have been due to a coronary thrombosis. Nineteen more have died in 1987–2004 of various causes; however their deaths are not necessarily — and in some cases are certainly not — directly attributable to radiation exposure. Among the general population exposed to the Chernobyl radioactive fallout, however, the radiation doses were relatively low, and ARS and associated fatalities did not occur.

Cancer mortality

ARS was diagnosed in 134 emergency workers
Radiation doses were relatively low

It is impossible to assess reliably, with any precision, numbers of fatal cancers caused by radiation exposure due to Chernobyl accident. Further, radiation-induced cancers are at present indistinguishable from those due to other causes.

An international expert group has made projections to provide a rough estimate of the possible health impacts of the accident and to help plan the future allocation of public health resources. These predictions were based on the experience of other populations exposed to radiation that have been studied for many decades, such as the survivors of the atomic bombing in Hiroshima and Nagasaki. However, the applicability of risk estimates derived from other populations with different genetic, life-style and environmental backgrounds, as well as having been exposed to much higher radiation dose rates, is unclear. Moreover small differences in the assumptions about the risks from exposure to low level radiation doses can lead to large differences in the predictions of the increased cancer burden, and predictions should therefore be treated with great caution, especially when the additional doses above natural background radiation are small.

The international expert group predicts that among the 600 000 persons receiving more significant exposures (liquidators working in 1986–1987, evacuees, and residents of the most ‘contaminated’ areas), the possible increase in cancer mortality due to this radiation exposure might be up to a few per cent. This might eventually represent up to four thousand fatal cancers in addition to the approximately 100 000 fatal cancers to be expected due to all other causes in this population. Among the 5 million persons residing in other ‘contaminated’ areas, the doses are much lower and any projected increases are more speculative, but are expected to make a difference of much less than one per cent in cancer mortality.

Such increases would be very difficult to detect with available epidemiological tools, given the normal variation in cancer mortality rates. So far, epidemiological studies of residents of contaminated areas in Belarus, Russia and Ukraine have not provided clear and convincing evidence for a radiation-induced increase in general population mortality, and in particular, for fatalities caused by leukaemia, solid cancers (other than thyroid cancer), and non-cancer diseases.

However, among the more than 4000 thyroid cancer cases diagnosed in 1992–2002 in persons who were children or adolescents at the time of the accident, fifteen deaths related to the progression of the disease had been documented by 2002.

Some radiation-induced increases in fatal leukaemia, solid cancers and circulatory system diseases have been reported in Russian emergency and recovery operation workers. According to data from the Russian Registry, in 1991–1998, in the cohort of 61 000 Russian workers exposed to an average dose of 107 mSv about 5% of all fatalities that occurred may have been due to radiation exposure. These findings, however, should be considered as preliminary and need confirmation in better-designed studies with careful individual dose reconstruction.

Source & ©: UN Chernobyl Forum
 Chernobyl’s Legacy: Health, Environmental and Socio-economic Impacts (2006)
How many people died from the accident and how many more are likely to die in the future?,
p.14-16

2.3 What diseases are linked to the accident?

    • 2.3.1 Thyroid Cancer in Children
    • 2.3.2 Leukaemia, Solid Cancers and Circulatory Diseases
    • 2.3.3 Cataracts

2.3.1 Thyroid Cancer in Children

The source document for this Digest states:

One of the principal radionuclides released by the Chernobyl accident was iodine-131, which was significant for the first few months. The thyroid gland accumulates iodine from the blood stream as part of its normal metabolism. Therefore, fallout of radioactive iodines led to considerable thyroid exposure of local residents through inhalation and ingestion of foodstuffs, especially milk, containing high levels of radioiodine. The thyroid gland is one of the organs most susceptible to cancer induction by radiation. Children were found to be the most vulnerable population, and a substantial increase in thyroid cancer among those exposed as children was recorded subsequent to the accident.

From 1992 to 2002 in Belarus, Russia and Ukraine more than 40003 cases of thyroidcancer were diagnosed among those who were children and adolescents (0–1 8 years) at the time of the accident, the age group 0–14 years being most affected; see Fig. 3.

3 [More recent statistics from the national registries of Belarus and Ukraine indicate that the total number of thyroid cancers among those exposed under the age of 18, is currently close to 5000. The numbers differ slightly depending on the reporting methods, but the overall number observed in the three countries is certainly well above 4000.]

FIG. 3. Incidence rate of thyroid cancer in children and adolescents exposed to 131I as a result of the Chernobyl accident (Jacob et al., ).

The majority of these cases were treated, with favourable prognosis for their lives. Given the rarity of thyroid cancer in young people, the large population with high doses to the thyroid and the magnitude of the radiation-related risk estimates derived from epidemiological studies, it is most likely that a large fraction of thyroid cancers observed to date among those exposed in childhood are attributable to radiation exposure from the accident. It is expected that the increase in thyroid cancer incidence from Chernobyl will continue for many more years, although the long term magnitude of risk is difficult to quantify.

It should be noted that early mitigation measures taken by the national authorities helped substantially to minimize the health consequences of the accident. Intake of stable iodine tablets during the first 6–30 hours after the accident reduced the thyroid dose of the residents of Pripyat by a factor of 6 on average. Pripyat was the largest city nearest to the Chernobyl nuclear plant and approximately 50 000 residents were evacuated within 48 hours after the accident. More than 100 000 people were evacuated within few weeks after the accident from the most contaminated areas of Ukraine and Belarus. These actions reduced radiation exposures and reduced the radiation related health impacts of the accident.

Source & ©: UN Chernobyl Forum
 Chernobyl’s Legacy: Health, Environmental and Socio-economic Impacts (2006)
What diseases have already resulted or might occur in the future
from the Chernobyl radiation exposure?, Thyroid Cancer in Children, p.16-18

2.3.2 Leukaemia, Solid Cancers and Circulatory Diseases

The source document for this Digest states:

A number of epidemiological studies, including atomic bomb survivors, patients treated with radiotherapy and occupationally exposed populations in medicine and the nuclear industry, have shown that ionizing radiation can cause solid cancers and leukaemia (except CLL4 [CLL is Chronic Lymphoid Leukaemia that is not thought to be caused by radiation exposure]). More recent findings also indicate an increased risk of cardiovascular diseases in populations exposed at higher doses (e.g. atomic bombing survivors, radiotherapy patients).

There is therefore no convincing evidence at present that the incidence of leukaemia or cancer has increased in children
Mortality is likely to become less significant as time progresses

An increased risk of leukaemia associated with radiation exposure from Chernobyl was, therefore, expected among the populations exposed. Given the level of doses received, however, it is likely that studies of the general population will lack statistical power to identify such an increase, although for higher exposed emergency and recovery operation workers an increase may be detectable. The most recent studies suggest a two-fold increase in the incidence of non-CLL leukaemia between 1986 and 1996 in Russian emergency and recovery operation workers exposed to more than 150 mGy (external dose). On going studies of the workers may provide additional information on the possible increased risk of leukaemia.

However, since the risk of radiation-induced leukaemia decreases several decades after exposure, its contribution to morbidity and mortality is likely to become less significant as time progresses.

There have been many post-Chernobyl studies of leukaemia and cancer morbidity in the populations of ‘contaminated’ areas in the three countries. Most studies, however, had methodological limitations and lacked statistical power. There is therefore no convincing evidence at present that the incidence of leukaemia or cancer (other than thyroid) has increased in children, those exposed in-utero, or adult residents of the ‘contaminated’ areas. It is thought, however, that for most solid cancers, the minimum latent period is likely to be much longer than that for leukaemia or thyroid cancer — of the order of 10 to 15 years or more and it may be too early to evaluate the full radiological impact of the accident. Therefore, medical care and annual examinations of highly exposed Chernobyl workers should continue.

The absence of a demonstrated increase in cancer risk — apart from thyroid cancer — is not proof that no increase has in fact occurred. Such an increase, however, is expected to be very difficult to identify in the absence of careful large scale epidemiological studies with individual dose estimates. It should be noted that, given the large number of individuals exposed, small differences in the models used to assess risks at low doses can have marked effects on the estimates of additional cancer cases.

There appears to be some recent increase in morbidity and mortality of Russian emergency and recovery operation workers caused by circulatory system diseases. Incidence of circulatory system diseases should be interpreted with special care because of the possible indirect influence of confounding factors, such as stress and lifestyle. These findings also need confirmation in well-designed studies.

Source & ©: UN Chernobyl Forum
 Chernobyl’s Legacy: Health, Environmental and Socio-economic Impacts (2006)
Leukaemia, Solid Cancers and Circulatory Diseases, p.18-19

2.3.3 Cataracts

The source document for this Digest states:

Examinations of eyes of children and emergency and recovery operation workers clearly show that cataracts may develop in association with exposure to radiation from the Chernobyl accident. The data from studies of emergency and recovery workers suggest that exposures to doses somewhat lower than previously experienced, down to about 250 mGy may be cataractogenic.

Continued eye follow-up studies of the Chernobyl populations will allow confirmation and greater predictive capability of the risk of radiation cataract onset and, more importantly, provide the data necessary to be able to assess the likelihood of any resulting visual dysfunction.

Source & ©: UN Chernobyl Forum
 Chernobyl’s Legacy: Health, Environmental and Socio-economic Impacts (2006)
What diseases have already resulted or might occur in the future from the Chernobyl radiation exposure?, Cataracts, p.19

2.4 Have there been or will there be any effects on reproduction?

The source document for this Digest states:

Because of the relatively low dose levels to which the population of the Chernobyl-affected regions was exposed, there is no evidence nor any likelihood of observing decreased fertility among males or females in the general population as a direct result of radiation exposure. These doses are also unlikely to have any effect on the number of stillbirths, adverse pregnancy outcomes, delivery complications or the overall health of children.

Birth rates may be lower in contaminated areas because of concern about having children (this issue is obscured by the very high rate of medical abortions) and the fact that many younger people have moved away. No discernable increase in hereditary effects caused by radiation is expected based on the low risk coefficients estimated by UNSCEAR (2001) or in previous reports on Chernobyl health effects. Since 2000, there has been no new evidence provided to change this conclusion.

There has been a modest but steady increase in reported congenital malformations in both contaminated and uncontaminated areas of Belarus since 1986, see Fig. 4. This does not appear to be radiation-related and may be the result of increased registration."

FIG. 4. Prevalence at birth of congenital malformations in 4 oblasts of Belarus with high and low levels of radio nuclide contamination (Lazjuk et al., 1999).

Source & ©: UN Chernobyl Forum
 Chernobyl’s Legacy: Health, Environmental and Socio-economic Impacts (2006)
Have there been or will there be any inherited or reproductive effects?, p.19-20

2.5 What was the psychological impact on exposed populations?

The source document for this Digest states:

The Chernobyl accident resulted in many people being traumatized by the rapid relocation, the breakdown in social contacts, fear and anxiety about what health effects might result. Are there persistent psychological or mental health problems?

Any traumatic accident or event can cause the incidence of stress symptoms, depression, anxiety (including post-traumatic stress symptoms), and medically unexplained physical symptoms. Such effects have also been reported in Chernobyl-exposed populations. Three studies found that exposed populations had anxiety levels that were twice as high as controls, and they were 3–4 times more likely to report multiple unexplained physical symptoms and subjective poor health than were unaffected control groups.

Exposed populations had anxiety levels that were twice as high as controls
Exposed populations had anxiety levels that were twice as high as controls

In general, although the psychological consequences found in Chernobyl exposed populations are similar to those in atomic bombing survivors, residents near the Three Mile Island nuclear power plant accident, and those who experienced toxic exposures at work or in the environment, the context in which the Chernobyl accident occurred makes the findings difficult to interpret because of the complicated series of events unleashed by the accident, the multiple extreme stresses and culture-specific ways of expressing distress.

In addition, individuals in the affected populations were officially categorized as “sufferers”, and came to be known colloquially as “Chernobyl victims,” a term that was soon adopted by the mass media. This label, along with the extensive government benefits earmarked for evacuees and residents of the contaminated territories, had the effect of encouraging individuals to think of themselves fatalistically as invalids. It is known that people’s perceptions — even if false — can affect the way they feel and act. Thus, rather than perceiving themselves as “ survivors,” many of those people have come to think of themselves as helpless, weak and lacking control over their future.

Renewed efforts at risk communication, providing the public and key professionals with accurate information about the health and mental health consequences of the disaster, should be undertaken.

Source & ©: UN Chernobyl Forum
 Chernobyl’s Legacy: Health, Environmental and Socio-economic Impacts (2006)
Are there persistent psychological or mental health problems?, p.20


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