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Health Impact of the Chernobyl Accident

A comprehensive recent (2002) review of the consequences of the Chernobyl accident is available here. A summary of the main points and a few pertinent references is given below.

Radioactive Material Released

Around six tonnes of fragmented nuclear fuel was released at Chernobyl in the explosion and subsequent fire over a ten day period. Low level releases continued for about 40 days after the accident attributable to spot fires and hot areas of the reactor core. The material released represents approximately 3-4% of the total fuel, though volatile elements were released in much higher proportions: 33Xe (Xenon-33) 100%, 131I (Iodine-131) 50-60% and 134Cs (Caesium-134) and 137Cs (Caesium-137) 20-40% of that present in the reactor. In addition, high proportions of short lived radioactive isotopes of Iodine and 132Te (Tellurium-132) were released. A total of around 10 000 petaBecquerels of radioactive material were released. (A Becquerel (Bq) is a measure of activity and equals one nuclear decay per second. A petaBecquerel = 1015 Becquerels.)

In the first year after the accident external doses from ground deposition of radionuclides of half lives of less than one year were restricted to the immediate area around Chernobyl. However, the more volatile elements, Xenon, Iodine and Caesium, where spread over hundreds of kilometers. In the first few months 131I posed a particular health risk because of its short half-life (8 days) and the tendency of ingested Iodine to be concentrated in the thyroid. The main vector for exposure to 131I is through ingestion via cow's milk or leafy vegetables. Over the years following the accident the longer half life Caesium isotopes, 134Cs, with a half life of 2 years and 137Cs with a half-life of 30 years, were responsible for almost all the doses received by populations in the contaminated area through external exposure due to deposition on the soil and through internal exposure after eating contaminated foodstuffs. The exclusion zone (approx. 30km radius around Chernobyl) will have significantly elevated levels of radiation due to 137Cs for around 10 half-lives or 300 years.

Acute Health Effects

There were two immediate deaths due to the accident, one killed by the explosion and one who suffered a coronary thrombosis. A third died the following morning as a result of serious burns. Around 600 000 workers were involved in the clean up. Among these workers, 237 received hospital treatment for acute radiation sickness and of those 28 died. The majority (140) had received does of less than 2 Greys (Gy) and there were no fatalities in this group. At the other extreme, exposure to the highest levels of radiation (>6 Gy) proved almost invariably fatal (20 deaths out of 21 exposed) despite intensive medical care. Among the acute radiation sickness survivors there were eleven deaths between 1987 and 1998, one of acute myeloid leukaemia. Among the survivors, the major cause of continuing disability is cataracts scarring and ulceration.

Long Term Health Effects

Iodine is concentrated by the body in the thyroid gland and so poses a special risk, particularly to children. Children exposed at the time of the Chernobyl accident first began to show an increased incidence of thyroid cancers in 1990 and levels have continued to climb since then. The only documented cause of thyroid cancer is exposure to high levels of ionizing radiation to the neck area when young [1]. The risk of developing thyroid cancer may also be influenced by genetic factors. Generally most thyroid cancers are slow growing and are treatable by surgery. If only part of the thyroid is removed no further treatment is usually necessary. If all the thyroid is removed during treatment patients will need to take daily hormone pills for the rest of their life to replace the hormones formerly produced by the thyroid.

The link between the Chernobyl accident and the increased incidence of childhood thyroid cancer has been well established by many epidemiological studies (see, for example, this reference list). Comparisons on cancer rates among children born in Belarus before and after the accident indicate clearly that the increased cancers are due to exposure at the time of the accident and not just due to increased surveillance [2]. Most of the thyroid cancers seen have been papillary and particularly aggressive, often with distant metastases. They are most prevalent in children 0-5 years old at the time of the accident and in the areas most heavily contaminated with 131I. The effect has been exacerbated by the pre-existing Iodine deficiency in the population. There has been an apparently shorter latency period than expected. Rates are still increasing among children 0-5 years at the time of the accident. Currently the rate among children in Belarus is 40 times the pre-accident levels, with around 4-5 per 100 000 of population per year diagnosed with new thyroid cancers. Neighbouring Ukraine has seen a 2-3 fold increase to 0.4-0.5 per 100 000 per year in childhood thyroid cancers from 1992. In the total population of Belarus the number of thyroid cancers has gone from 1392 diagnosed in the 12 years leading up to the accident (1974-1985) to 5449 new case diagnosed in the 12 years following (1986-1998) [3]. Survivability rates among thyroid cancer suffers is very good with a mortality rate to 2001 among child thyroid cancer suffers in the effected area of 0.7% [4].

Given the short half-life of 131I the use of iodine tablets immediately after an accident to saturate the thyroid can be effective in reducing the take up of radio-iodine by the thyroid by up to 99% [5]. This measure will not limit the overall exposure of the body to radio-iodine, however, the internal exposure could be substantially controlled by the avoidance of leafy vegetables and cow's milk from the area affected by contamination from a nuclear accident.

Epidemiological studies have failed to obtain any link between exposure from Chernobyl fallout and increases in leukaemia or other abnormalities. There is no evidence of an increase in birth defects. Indeed in 2000, UNSCEAR [6] concluded " increase in birth defects, congenital malformations, stillbirths, or premature births could be linked to radiation exposures caused by the accident".

There is predicted excess of deaths due to cancer among the 600 000 recovery workers of 670 or 3.4% of expected cancer deaths [7], though it is not possible to draw any conclusions from the data at this stage since it is still too soon after the accident and confounding factors such as smoking have not been taken into account. Estimates of increases in cancer rates in Europe of 0.01% [8] and for the Northern hemisphere of 0.004% [9] have been made. The consensus of such estimates are well below detectable thresholds.


[1] Memorial Sloan-Kettering Cancer Center

[2] Y. Shibata, S. Yamashita, V. B. Masyakin, G. D. Panasyuk, and S. Nagataki "15 years after Chernobyl: new evidence of thyroid cancer" The Lancet 2001; 358: 1965-6 (Dec. 8).

[3] E. Demidchik, A. Mrochek, Yu. Demidchik et al., "Thyroid cancer promoted by radiation in young people of Belarus (Clinical and epidemiological features)" in Radiation and thyroid cancers, eds. G. Thomas, A. Karaoglou, E. D. Williams (World Scientific, Singapore 1999) pp. 51-4.

[4] Nuclear Energy Agency Organisation for Economic Co-operation and Development, "Chernobyl: Asseement of radiological and health impacts" (2002) p. 87.

[5] World Health Organization (WHO), "Guidelines for Iodine prophylaxis following nuclear accidents: update 1999.";
Use of Potassium Iodide to prevent update of radioactive iodine

[6] United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2000, "Report to the general Assembly, with scientific annexes" Vol. II:Effects.

[7] V. K. Ivanov et al., "Planning of long-term radiation and epidemiological research on the basis of the Russian National Medical and Dosimetric Registry", Proc. Nagasaki Symp. on Chernobyl: Update and Future, ed. S. Nagataki (Elsevier, 1994) pp. 203-16.

[8] R. Lynn et al., "Global impact of the Chernobyl reactor accident", Science 242 (1998) pp. 1513-9.

[9] N. Parmentier and J-C. Nenot, "Radiation damage aspects of the Chernobyl accident", Atmospheric Environment 23 (1989) pp. 771-5.

-- Main.AdrianFlitney - 31 Aug 2005


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