Chernobyl: Chapter V. Health impact

As ionising radiation passes through the body, it interacts with the tissues transferring energy to cells and other constituents by ionisation of their atoms. This phenomenon has been extensively studied in the critical genetic material, DNA, which controls the functions of the cells. If the damage to DNA is slight and the rate of damage production is not rapid, i.e. at low dose rate, the cell may be able to repair most of the damage. If the damage is irreparable and severe enough to interfere with cellular function, the cell may die either immediately or after several divisions.

At low doses, cell death can be accommodated by the normal mechanisms that regulate cellular regeneration. However, at high doses and dose rates, repair and regeneration may be inadequate, so that a large number of cells may be destroyed leading to impaired organ function. This rapid, cell death at high doses leads to early deleterious radiation effects which become evident within days or weeks of exposure, and are known as "deterministic effects". These deterministic effects can be life-threatening in the short term if the dose is high enough, and were responsible for most of the early deaths in the Chernobyl accident.

Lower doses and dose rates do not produce these acute early effects, because the available cellular repair mechanisms are able to compensate for the damage. However, this repair may be incomplete or defective, in which case the cell may be altered so that it may develop into a cancerous cell, perhaps many years into the future, or its transformation may lead to inheritable defects in the long term. These late effects, cancer induction and hereditary defects, are known as "stochastic effects" and are those effects whose frequency, not severity, is dose dependent. Moreover, they are not radiation-specific and, therefore, cannot be directly attributed to a given radiation exposure.

For this reason, low dose health effects in humans cannot be measured and, therefore, risk projections of the future health impact of low-dose ionising radiation exposure have to be extrapolated from measured high-dose effects. The assumption is made that no dose of ionising radiation is without potential harm, and that the frequency of stochastic effects at low doses is proportional to that occurring at high doses. This prudent assumption has been adopted to assist in the planning of radiation protection provisions when considering the introduction of practices involving ionising radiations. The ICRP has estimated the risk of fatal cancer to the general population from whole-body exposure to be 5% per sievert (IC90).

The health impact of the Chernobyl accident can be classified in terms of acute health effects ("deterministic effects") and of late health effects ("stochastic effects"). Moreover, there are also social and psychological effects which can influence health.

Radiation-induced health effects

Acute health effects

All the acute deterministic health effects occurred among the personnel of the plant, or in those persons brought in for fire fighting and immediate clean-up operations.

Two deaths were immediately associated with the accident: one person killed by the explosion and another who suffered a coronary thrombosis. A third person died early the morning of the accident from thermal burns. Twenty-eight other persons died later in the treatment centres, bringing the total to 31 deaths in the first weeks after the accident (UN88).

All symptomatic exposed persons from the site were placed in hospitals. Of the total of 499 people were admitted for observation, 237 of these were initially diagnosed as suffering from acute radiation syndrome. The severity and rapidity of onset of their symptoms depended on their dose. The initial early signs and symptoms of radiation sickness from high doses included diarrhoea, vomiting, fever and erythema. Over 200 patients were placed in regional hospitals and specialised centres in the first 24 hours. Patients were allocated to four categories of radiation sickness severity according to their symptoms, signs and dose estimates. The differential white blood cell count showed reduced circulating lymphocytes (lymphocytopenia) which was the initial indicator of the severity of the exposure and became evident in the first 24-36 hours for those most severely irradiated.

No members of the general public received such high whole-body doses as to induce Acute Radiation Syndrome (IA86). This was confirmed in Belarus, where, between May and June 1986, 11 600 people were investigated without the discovery of any cases of acute radiation sickness.

In the highest exposure group of those who were acutely exposed (6-16 Gy), the first reaction was usually vomiting, occurring within 15-30 minutes of exposure. These patients were desperately ill; fever and intoxication as well as diarrhoea and vomiting, were prominent features. Mucous membranes were severely affected, becoming swollen, dry and ulcerated, making breathing and swallowing extremely painful and difficult. Extensive burns both thermal and due to beta radiation often complicated the illness. Within the first two weeks white blood cells and platelets fell dramatically, indicating a very high dose which had compromised the production of blood cells in the bone marrow, making it virtually impossible for the patients to fight infection or to retain the natural clotting activity of the blood. Almost all the patients with such high doses died (20 of 21), in spite of the intensive specialised medical treatment provided.

At lower exposures, the symptoms, signs and laboratory findings improved. Vomiting began later, platelet and white cell counts did not drop so precipitously and the fever and toxaemia were less pronounced. Beta radiation burns to the skin were a major complicating factor and mucous membrane damage was difficult to treat, but survival improved markedly at lower doses, so that no early deaths were noted in the less than 1-2 Gy exposure group (Table 12).

Table 12. Outcome of radiation exposure among persons hospitalised for acute radiation syndrome

Number of patients
Estimated Dose (Gy)











less than 2


Total: 237



There is a large range of medical treatments that can be attempted to mitigate acute radiation syndrome. All these procedures were applied to the persons hospitalised with varying degrees of success. The hospital treatment following the accident included replacement therapy with blood constituents, fluids and electrolytes, antibiotics, antifungal agents, barrier nursing and bone marrow transplantation.

The treatment of the depression of bone-marrow function encountered after the accident was largely supportive. Special hygienic measures were taken; patients' clothes were changed at least twice a day and aseptic techniques used. Those patients who received doses above 2 Gy were given anti-fungal agents after the second week. Antibiotics and gamma globulin were also administered.

Bone-marrow transplantation was undertaken in 13 patients who were judged to have irreversible bone marrow damage after doses greater than 4 Gy. All but two of these patients died, some before the transfused marrow had had a chance to "take", but others had short-term takes. It was concluded that, even after very high radiation doses, the bone marrow may well not be completely destroyed and may recover at least some function at a later stage. It is this recovery which may lead to later rejection of the transplanted marrow through a "Host versus Graft" reaction. The physicians responsible for treating the victims of the accident concluded that bone marrow transplantation should play a very limited role in treatment.

Burns, both thermal and from beta radiation, were treated with surgical excision of tissue that was not viable, and any fluid and electrolyte loss was compensated for by the parenteral feeding set up to treat the gastro-intestinal syndrome which is a prominent feature of acute radiation sickness. The oro-pharyngeal syndrome of mucosal destruction, oedema and the absence of lubrication caused by radiation damage to the mucosa of the mouth and pharynx was extremely difficult to treat, and severely impaired swallowing and breathing.

The organisational aspects of treating large numbers of very ill patients also presented significant problems. Intensive nursing care and monitoring had to be provided 24 hours a day in small units. Personnel had to be taught new techniques of care and patient handling, and a large number of diagnostic samples had to be examined. The logistic requirements of medical handling needed to be well-established before any therapeutic programme could be run efficiently.

There were eleven deaths between 1987 and 1998 among confirmed acute radiation sickness survivors who received doses of 1.3-5.2 Gy. There were three cases of coronary heart disease, two cases of myelodysplasic syndrome, two cases of liver cirrhosis, and one death each of lung gangrene, lung tuberculosis and fat embolism. One patient, classified with Grade II, died in 1988 from acute myeloid leukaemia.

Radiation skin burns were observed in 56 patients. Cataracts scarring and ulceration are the most important causes of persistent disability in acute radiation sickness survivors.

Sexual function and fertility was investigated until 1996 in acute radiation sickness survivors. Functional sexual disturbances predominated, while fourteen normal children were born to acute radiation sickness survivor families, within the first five years.

Patients with acute radiation sickness, Grades III and IV, were severely immuno-suppressed. These abnormalities, however, are not necessarily associated with clinically manifest immuno-deficiency.

Late health effects

There have been many reports of an increase in the incidence of some diseases as a result of the Chernobyl accident. In fact, the accident has, according to present knowledge, given rise to an increase in the incidence of thyroid cancers. Also, it has had negative social and psychological consequences. As far as other diseases are concerned, as yet the scientific community has not been able to relate those to the effects of ionising radiation. However, large research projects have been conducted and are under way to further study the matter. For example, the WHO (WH95) established the International Programme on the Health Effects of the Chernobyl Accident (IPHECA). This programme initially concentrated on pilot projects involving leukaemia, thyroid diseases, oral health in Belarus, mental health in children irradiated before birth and the development of epidemiological registries. The pilot phase came to an end in 1994 and, as a result of the findings, efforts are underway to develop long-term permanent programmes involving thyroid diseases, the accident recovery workers, dose reconstruction and guidance to the public in the event of an accident. It is expected that these new projects will provide further insight into any future health effects.

An estimate (An88) of the total lifetime cancers which could be expected in Europe as a result of the accident suggested an increase of about 0.01% above their natural incidence. Another assessment placed the increase in cancer incidence at 0.004% in the Northern hemisphere, a lower percentage increase due probably to including the large population of the whole hemisphere (Pa89). These predictions are remarkably similar and support the view that the average doses to the general population of the Northern hemisphere were so low that only fractions of a percent increases in cancer incidence could be expected in this population (Pe88, Re87). Large parts of the Northern hemisphere, such as North America (Hu88, Br88), Asia and Siberia, were not significantly contaminated and doses were inconsequential. Therefore, the following sections focus on the late health effects in the population of the contaminated regions of the former Soviet Union.

In the International Chernobyl Project organised by the IAEA (IA91), field studies were undertaken in the latter half of 1990 on the permanent residents of the rural settlements with a surface caesium contamination of greater than 555 kBq/m2, and on control settlements of 2 000 to 50 000 persons, using an age matched study design. Seven contaminated and six control settlements were chosen by the medical team of the Chernobyl Project. Since all persons could not be examined, representative samples were taken from various age groups. In all, 1 356 people were examined, and the aim was to examine about 250 from each of the larger settlements. Three medical teams each spent two weeks conducting medical examinations to provide the data for these assessments.

The medical examinations were quite comprehensive, and the general conclusions reached were that there were no health abnormalities which could be attributed to radiation exposure, but that there were significant non-radiation related health disorders which were similar in both contaminated and control settlements. The accident had had substantial negative social and psychological consequences which were compounded by the socio-economic and political changes occurring in the former Soviet Union. The official data provided to the medical teams was incomplete and difficult to evaluate, and were not detailed enough to exclude or confirm the possibility of an increase in the incidence of some tumour types. On this subject, it was suggested in 1991 that the incidence of cancer in Ukraine showed no large increase even in the most contaminated areas (Pr91).

The International Chernobyl Project Report (IA91) suggested that the reported high thyroid doses in some children were such that there could be a statistically detectable increase in the incidence of future thyroid tumours. The Chernobyl Project team finally concluded that, on the basis of the doses estimated by the team and the currently accepted radiation risk estimates, future increases over the natural incidence of cancer or hereditary defects would be difficult if not impossible to discern, even with very large and well-designed long-term epidemiological studies. However, it should be remembered that this health survey took place four years after the accident, before any increase in cancer incidence might be expected and reflects the status of the people examined in a few months of 1990. The sample size was also criticised as being too small.

Nevertheless, the dose estimates generally accepted indicate that, with the exception of thyroid disease, it is unlikely that the exposure would lead to discernible radiation effects in the general population. Many predictions of the future impact of the accident on the health of populations have been made, all of which, apart from thyroid disease, indicate that the overall effect will be small when compared with the natural incidence and therefore not expected to be discernible (An88, Be87, Hu87, Mo87, De87, Be87).

Thyroid cancer

Early in the development of the Chernobyl accident, it became obvious that the radioiodines were contributing significant thyroid doses (Il90), especially to children, and the then Soviet authorities made every effort not only to minimise doses, but also to record the thyroid doses as accurately as possible. The results of these measurements and dose reconstruction assessments indicated that some groups in the population received high doses to their thyroids, and that an increase in thyroid abnormalities, including cancer, was a very real possibility in the future. This was particularly true for children in the contaminated regions in Belarus, northern Ukraine and the Bryansk and Kaluga regions of the Russian Federation. These were not inconsequential thyroid doses and, as early as 1986, it was predicted by experts from the Soviet Union that the thyroid would be the target organ most likely to show evidence of radiation effects, especially an increased incidence of benign and malignant tumours.

It was known from previous studies of largely external irradiation of the thyroid that an increase in thyroid tumours tended to appear six to eight years following irradiation, and continue for more than twenty years after exposure, particularly in children. What was not expected was that thyroid abnormalities would already become detectable about four years after the accident. At that time, the conventional wisdom was that internal radioiodine exposure was less carcinogenic than external irradiation of the thyroid. Two recent studies found an elevated risk of thyroid cancer mortality following adult 131I treatment for hyperthyroidim, which is in contrast to prevuious studies (Ro98, Fr99). It was estimated that the incidence of thyroid cancers in children, defined as those diagnosed between the ages of 0 and 14, might increase by about 5%, and in adults by about 0.9% over the next 30 years. As will be seen, a substantial increase has been detected in the more contaminated regions. The large number of cases appearing within five year of the accident was surprising, since it had been believed that thyroid cancer had a latency period of at least 10 years. A determined effort was made to estimate doses, record the data, initiate medical examinations and follow the cohorts already identified as being most at risk.

In Ukraine, more than 150 000 examinations were conducted by special dosimetric teams, and a realistic estimate of the collective thyroid dose of 64 000 person-Sv has been made, leading to a projection of 300 additional thyroid cancers (Li93a). In the contaminated regions of Russia, namely Bryansk, Tula and Orel, it was predicted that an excess thyroid cancer total of 349 would appear in a population of 4.3 million (Zv93). This represents an increase of 3 to 6% above the spontaneous rate.

A programme to monitor the thyroid status of exposed children in Belarus was set up in Minsk in May/June 1986. The highest doses were received by the evacuated inhabitants of the Hoiniki rayon (district) in the Gomel oblast. In the course of this study, it was noted that the numbers of thyroid cancers in children were increasing in some areas. For Belarus as a whole (WH90, Ka92, Wi94), there has been a significantly increasing trend in childhood thyroid cancer incidence since 1990 (Pa94). It was also noted that this increase is confined to regions in the Gomel and Brest oblasts, and no significant increase has been noted in the Mogilev, Minsk or Vitebsk areas where the radioactive iodine contamination is assessed to have been lower. Over 50% of all the cases are from the Gomel oblast.

For the eight years prior to 1986, only five cases of childhood (less than 15 years old on the day of accident) thyroid cancer were seen in Minsk, which is the main Belarussian centre for thyroid cancer diagnosis and treatment for children (De94). From 1986 to 1989, 3 to 6 cases of thyroid cancer in children were seen annually in Belarus. In 1990, the number jumped to 31, to 62 in 1991, then to 87 in 1993. By the end of 1998 the total had reached over 600 in Belarus. Nearly 50% of the early (1992) thyroid cancers appeared in children who were aged between one and four years at the time of the accident. Atthe same time 382 were diagnosed in the Ukraine.

The histology of the cancers has shown that nearly all were papillary carcinomata (Ni94) and that they were particularly aggressive, often with prominent local invasion and distant metastases, usually to the lungs. This has made the treatment of these children less successful than expected, whether undertaken in Minsk or in specialised centres in Europe. In all, about 150 000 children in Belarus had thyroid uptake measurements following the accident. Other data from Ukraine and Russia show a similar, but not as pronounced, increase in the incidence of childhood thyroid cancer since 1987.

The increase in Belarus was confirmed by the final report of an EC Expert Panel (EC93) convened in 1992 to investigate the reported increase. In 1992 the incidence of childhood thyroid cancer in Belarus as a whole was estimated to be 2.77 per 100 000, more recent information (Un00) raises the incidence in 1992 to 3.9 per 100 000, whereas in the Gomel and Brest oblasts it was 11.2 and 3.7 respectively. In Belarus, it was observed that children 0-4 years old at the time of accident still had an increase in absolute numbers of thyroid cancers in 1997, while the number of cancers among those who were 5-9 years old seem to decrease after 1995, in those of 10-14 years of age at exposure, the number of cancers seems to be stable for the period 91-97 (Ko99).

There is some difficulty in comparing the numbers quoted by the health authorities of the former Soviet Union with previous incidence statistics, as previous data collection was not sufficiently rigorous. Moreover, the absolute numbers can differ from one report to another, and the age scale taken into consideration can differ between 0-14, 0-17 or 0-18 years of age. However, in Belarus all cases of childhood thyroid cancer have been confirmed since 1986 by international review of the histology and, because of more rigid criteria for data collection, reliance can be placed on accuracy and completeness. An attempt to review incidence estimates was made in the above-mentioned EC Report (EC93). These experts confirmed that the incidence of childhood thyroid cancer (0-14 y) prior to the accident in Belarus (between 0 and 0.14/100 000/y) was similar to that reported by other cancer registries. This indicates that the data collection in Belarus was adequate. They noted that it jumped to 3.9/100 000/y in 1991, and 5.6/100 000 in 1995 and 1997, about a forty-fold increase.

The most recent published rates of childhood thyroid cancer (St95) show unequivocal increases as seen in Table 13. At the time of this writing, three of the 1036 children cited in Table 13 below have died of their disease.

Table 13. Number of cases of thyroid cancers in children under 15 years old at diagnosis and cancer incidence rates number of cases per 100 000 children











































































































When this increase was first reported, it was very quickly pointed out (Be92) that any medical surveillance programme introduced would apparently increase the incidence by revealing occult disease and rectifying misdiagnoses. While this may account for some of the increase (Ro92), it cannot possibly be the sole cause, as the increase is so large and many of the children presented not with occult disease, but with clinical evidence of thyroid and/or metastatic disease. In fact, only 12% of the childhood thyroid cancers were discovered by ultrasound screening alone in Belarus (WH95). In addition, subsequent examination by serial section of the thyroids of persons coming to autopsy in Belarus have confirmed that the number of occult thyroid cancers is similar to that found in other studies (Fu93) and showed none of the aggressive characteristics found in the childhood cancers presenting in life (Fu92).

It can be concluded that there is a real, and large, increase in the incidence of childhood thyroid cancer in Belarus and Ukraine which is likely to be related to the Chernobyl accident. This is suggested by features of the disease, which differ somewhat from the so-called natural occurrence, as well as by its temporal and geographic distribution.

As far as other thyroid disorders are concerned, no difference in Russia was detected by ultrasound examination, in the percentage incidence of cysts, nodules or autoimmune thyroiditis in the contaminated versus the un-contaminated areas (Ts94). Following the accident, children in the Ukrainian contaminated regions exhibited a transient dose-dependent increase in serum thyroxine level, without overt clinical thyrotoxicosis, which returned to normal within 12 to 18 months (Ni94). This was most marked in the youngest children. This finding cannot be regarded as an adverse health effect, as no abnormality was permanent. However, it may be a pointer to future thyroid disease, especially when it may be associated with mild regional dietary iodine deficiency, and indicates the need for continued monitoring.

This increased incidence was not confined to children, as a larger number of adult cases was registered in Belarus and in Ukraine (WH94). In a more recent report (Iv99) 3 082 thyroid cancer cases in persons less than 60 years of age at diagnosis were recorded in Russian Federation between 1982 and 1996 in the four most contaminated regions. Among those 0-17 years of age at time of the accident, 178 cases were found. In the same report we can observe that before the accident, the incidence of cancer in women in these contaminated areas was lower than the national incidence in the Russian federation for the period 1982-1986, but increased.

For the period of 12 years after the Chernobyl accident, thyroid carcinoma increased by 4 057 cases in Belarus, as compared to the same period of time before. Since 1974 to 1985 thyroid carcinomas developed in 1 392 patients, but from 1986 up to July 1998, 5 449 new cases were diagnosed (De99). The standard index reached 7.9 per 100 000 in population above 18 years old and 3-4 per 100 000 in children. Thyroid carcinomas were mainly diagnosed in children born before the accident. Once all 131I had disintegrated, spontaneous carcinomas were diagnosed only in six children born in 1987 and 1988. Since 1996, the number of child patients has gradually decreased, while the incidence rates in adults continue to increase. We can expect during the second decade after the accident a peek of incidence for young people at age from 15 to 34 at the time of the accident. Among children and teenagers (age 0-18 at the time of the Chernobyl accident) we observe among thyroid cancers a mortality of 0.7% (observed time - 1986-2001) (Ke01).

An analysis of thyroid cancers in children and adolescents of the Ukraine (0-18 years of age at the time of surgery) showed that for period 1986 to 1997, 577 cases were registered (Tr99). Among 358 cases in children (0-14 years of age at time of surgery), the incidence per 100 000 children for the whole of the Ukraine has increased from 0.05 before the accident to 0.11 in 1986-1990, 0.39 in 1991-1995, and 0.44 in 1996-1997. The increase of incidence takes place mainly in children who were 5-years old or less in 1986.

Jacob et al reported a correlation between collective dose and incidence of thyroid cancers in 5 821 settlements in the three republics in 1991-1995. Using the southern half of Ukraine as a reference, the excess thyroid cancers risk was found to be linear in the dose interval 0.07 Gy to 1.2 Gy. For the 0-18 years of age group, Jacob et al obtain an excess absolute risk of 2.1 per 104 person-year Gy (Je98). In this study the authors did not relate any age (at exposure)-dependence for excess absolute risk for the birth cohort 1968-1985 (Je99) in contradiction with the Trosko report (Tr99) and the Japanese observations within the framework of the Sasakawa project in Belarus (Sh98). In another study, Ivanov et al (Iv99) reported excess absolute risk for children and adolescents comparable to those described by Jacob et al, 2.21 per 104 person-year Gy for girls and 1.62 for boys, described also a dose-risk linear relationship, but observed a dependence of risk with age at exposure, 14 times higher than in adults than for 0-4 years, 2.3 for children and adolescents.

The radiogenic nature of these thyroid tumours is supported by their relationship with thyroid exposure dose, clinical and morphological changes, aggressiveness of cancers, geostatistical studies (Bl97). This is in spite of the increase of ultrasound screening, which can explain a part of the increase in observed cases. However certain uncertainties remain, such as iodine deficiency and genetic predisposition, as well as the role of 131I. For example, it has been suggested that the geographical distribution of thyroid cancers cases correlates better to the distribution of short-lived radioisotopes (132I, 133I and 135I) than to that of 131I (Av95).

Table 14. Thyroid cancers and risk for children 0-18 years old at the time of the Chernobyl accident for the years 1991-1995 in three cities and 2 729 settlements in Belarus and the Russian Federation

Thyroid dose



Person years at risk

Observed number of cases

Expected number of casesa

Exsess absolute riskb

(104 PY Gy)-1

0-0.1 (0.05)

0.1-0.5 (0.21)

0.5-1.0 (0.68)

1.0-2.0 (1.4)

>2.0 (3.0)

1 756 000

1 398 000

386 000

158 000

56 000











2.6 (0.5-6.7)

1.9 (0.8-4.1)

2.0 (0.9-4.2)

2.3 (1.1-4.9)

2.4 (1.1-5.1)

a) Calculated by multiplying the age-specific incidence observed in Belarus in 1983-1987 by three.
b) 95% confidence intervals in parentheses.

In the six most contaminated regions of the Russian Federation, the thyroid cancer incidence increased over time in adults. The incidence was 11 per 100 000 for women compared to 4 for the Russian Federation as a whole and 1.7 and 1.1 respectively for men.

In a study of Lithuanian recovery operation workers, three thyroid cancers were detected. There was no significant difference compared with the Lithuanian male population and no association with level of radiation dose or duration of stay in the area of Chernobyl. In Europe, where several studies were carried out, no increase of thyroid cancer among children was observed.

The majority of the estimates indicate that the overall health impact from these thyroid disorders will be extremely small and not detectable when averaged over the population potentially at risk. This viewpoint is widely held by the competent risk assessors who have examined the potential effects of the accident.

Other late health effects

From data in the Russian National Medical Dosimetric Registry (RNMDR), the reported incidence of all types of disease has risen between 1989 and 1992 (Iv94). There has also been a reported increase in malignant disease which might be due to better surveillance and/or radiation exposure. The crude mortality rate of the liquidators from all causes in the Russian Federation has increased from 5 per 1 000 in 1991 to 7 per 1 000 in 1992. The crude death rate from respiratory cancer is reported to have increased significantly between 1990 and 1991, and for all malignant neoplasms between 1991 and 1992. It is not clear what influence smoking has had on these data, and the overall significance of these findings will need to be established by further surveillance, especially when there are distinct regional variations in the crude death rate and the mortality rates from lung, breast and intestinal cancer are rising in the general population of the Russian Federation.

From the dosimetric data in the RNMDR (Iv94), a predicted excess 670 cancer deaths may occur in the exposed groups covered by the Registry, peaking in about 25 years. This is about 3.4% of the expected cancer deaths from other causes. Data from the other national dose registries is not readily available in the published literature.

In view of the difficulties associated with these Registry data, such as the dose estimates, the influence of such confounding factors as smoking, the difficulty in follow-up, the possible increase in some diseases in the general population and also the short time since the accident, it is not possible to draw any firm conclusions from these data at this time. The only inference that can be made is that these groups are the most exposed and that, if any radiation effects are to be seen, they will occur in selected cohorts within these registries, which will require long-term future surveillance.

A predicted increase of genetic effects in the next two generations was 0.015% of the spontaneous rate, and the estimated lifetime excess percentage of all cancers as a result of living in the strict control zones was 0.5%, provided that a lifetime dose limit of 350 mSv was not exceeded (Il90).

Childhood leukemia incidence has not changed in the decade since the accident. There is no significant change in the level of leukemia and related diseases in the contaminated (more than 555 kBq/m2) and noncontaminated territories of the three states (WH95). Other attempts through epidemiological studies have failed to establish a link between radiation exposure from the Chernobyl accident and the incidence of leukemia and other abnormalities. No epidemiological evidence of an increase in childhood leukemia around Chernobyl (Iv93, Iv 97), in Sweden (Hj94, To96), Germany (Mi97) or the rest of Europe (Pa92, Wi94) has been established. However, if the last NEA report recommended to be prudent, to withold final judgement, 6years later, no increased risk of leukemia related to ionising radiation has as yet been found among recovery operation workers. The probability of observing a significant increase of leukemias decreases with time, and the next five years will be conclusive.

Other studies

Various reports (Pa93, Sc93, Se95, St93, Ve93) have been published on the incidence of chromosome aberrations among people exposed both in the contaminated regions and in Europe. Some of these have shown little or no increase, while others have. This may reflect the wide variation in dose. However, there is a trend for the incidence of chromosome aberrations to return to normal with the passage of time. Other studies have not shown evidence of lymphocytic chromosome damage (Br92).

In East Germany one study found no rise in foetal chromosome aberrations between May and December 1986. Chromosome aberrations are to be expected in any exposed population, and should be regarded as biological evidence of that exposure, rather than an adverse health effect.

Another study in Germany suggesting a link between Down's syndrome (Trisomy 21) and the Chernobyl accident has been severely criticised and cannot be accepted at face value because of the absence of control for confounding factors (Sp91), and it was not confirmed by more extensive studies (Li93). Another study in Finland (Ha92) showed no association of the incidence of Trisomy 21 with radiation exposure from Chernobyl.

In a group of Belarussian children born to exposed mothers with in utero doses ranging from 8 to 21 mSv, no relationship between birth defects and residency in contaminated areas was seen (La90). At this time, no clear trends in data for birth anomalies in Belarus or Ukraine be established (Li93, Bo94). Later study of Lazuk et al. has shown increase of birth defects and malformations in contaminated areas (1997), but no changes could be related to exposure to ionising radiation since the same increase was observed in the city of Minsk used as control.

Two epidemiological studies in Norway concluded that no serious gross changes as to pregnancy outcome were observed (Ir91), and that no birth defects known to be associated with radiation exposure were detected (Li92). In Austria, no significant changes in the incidence of birth defects or spontaneous abortion rates which could be attributed to the Chernobyl accident were detected (Ha92a).

A review by the International Agency for Research on Cancer (IARC) showed no consistent evidence of a detrimental physical effect of the Chernobyl accident on congenital abnormalities or pregnancy outcomes (Li93, EG88). No reliable data have shown any significant association between adverse pregnancy outcome or birth anomalies even in the most contaminated regions and the doses indicate that none would be expected.

On the basis of many studies, UNSCEAR in its last report (UN00) conclude that "no increase in birth defects, congenital malformations, stillbirths, or premature births could be linked to radiation exposures caused by the accident".

No association between thyroid abnormalities and 137Cs activity in the body or soil contamination was seen in 115 000 children in the Sasakawa framework health and Medical cooperation project (Ya97).

There have been reports that have suggested that radiation exposure as a result of the accident resulted in altered immune reactions. While immune suppression at high whole-body doses is known to be inevitable and severe, at the low doses experienced by the general population it is expected that any detected alterations will be minor and corrected naturally without any medical consequences. These minor changes may be indicative of radiation exposure, but their mild transitory nature is unlikely to lead to permanent damage to the immune system. All immunological tests of radiation exposure are in their infancy, but tests such as stimulated immunoglobulin production by lymphocytes hold promise for the future as a means of assessing doses below one Gy (De90).

Psychological and social health effects

One of the most significant effects of the Chernobyl accident has been the degridation of the social fabric in the affected territories. This has, it is felt (UN02), contributed to a general decline in well being through an increase in health effects that are related to the accident, but which are not necessarily radiation related. That is, the non-cancer health effects that are currently being studied seem not to result directly from irradiation, but from the stresses (physical and psychological) that have persisted since the accident.

In addition, the severity of the psychological effects of the Chernobyl accident appears also to be related to the public's growing mistrust of officialdom, politicians and government, especially in the field of nuclear power. Public scepticism towards authority is reinforced by its difficulty in understanding radiation and its effects, as well as the inability of the experts to present the issues in a way that is comprehensible. The impression that an unseen, unknowable, polluting hazard has been imposed upon them by the authorities against their will, fosters a feeling of outrage.

Public outrage is magnified by the concept that their existing or future descendants are also at risk from this radiation pollution. This widespread public attitude was not confined to one country, and largely determined the initial public response outside the Soviet Union. The public distrust was increased by the fact that the accident that they had been told could not happen, did happen, and it induced anxiety and stress in people not only in the contaminated areas but, to a lesser extent, all over the world.

While stress and anxiety cannot be regarded as direct physical adverse health effects of irradiation, their influence on the well-being of people who were exposed or thought that they might have been, may well have a significant impact on the exposed population. Several surveys have shown that the intensity of the anxiety and stress are directly related to the presence of contamination. It should also be remembered that the stress induced by the radiological contamination caused by the accident was in addition to that produced in the general population by the upheaval in local social structures due to massive evacuation and relocations, and the severe economic and social hardship caused by the break-up of the Soviet Union.

These non-radiological effects related to the Chernobyl accident have been studied extensively. Symptoms such as headaches, depression, sleep disturbance, inability to concentrate, and emotional imbalance have been reported and seen to be related to the difficult conditions ands stressful events that followed the accident (Le96, Le96a). The psychological development of 138 belarussian children who were exposed in utero was compared with 122 children from non contaminated areas. A correlation was found between anxiety among parents and emotional stress in children; No differences could be related to ionising radiation (Ko99).

It was concluded that the Chernobyl accident has had a significant long-term impact on psychological well-being, health-related quality of life, and illness in the affected populations. However, none of these findings could be directly associated with ionising radiation (Ha97, UN00).

Within the former Soviet Union

Within the Soviet Union additional factors came into play to influence the public reaction. It should be remembered that this accident occurred during the initial period of "glasnost" and "perestroika". After nearly seventy years of repression, the ordinary people in the Soviet Union were beginning openly to express all the dissatisfaction and frustration that they had been harbouring. Distrust and hatred of the central government and the Communist system could be expressed for the first time without too much fear of reprisal. In addition, nationalism was not repressed. The Chernobyl accident appeared to epitomise everything that was wrong with the old system, such as secrecy, witholding information and a heavy-handed authoritarian approach. Opposition to Chernobyl came to symbolise not only anti-nuclear and anti-communist sentiment but also was associated with an upsurge in nationalism.

The distrust of officialdom was so great that even scientists from the central government were not believed, and more reliance was placed on local "experts" who often had very little expertise in radiation and its effects. The then Soviet Government recognised this problem quickly, and tried to counteract the trend by inviting foreign experts to visit the contaminated areas, assess the problems, meet with local specialists and publicise their views in open meetings and on television. These visits appeared to have a positive effect, at least initially, in allaying the fears of the public. In the contaminated Republics, anxiety and stress were much more prevalent and were not just confined to the more heavily contaminated regions (WH90a). Several surveys conducted by Soviet (Al89) and other researchers (Du94) have shown that the anxiety induced by the accident has spread far beyond the more heavily contaminated regions.

During this period there was severe economic hardship which added to the social unrest and reinforced opposition to the official system of government. Anti-nuclear demonstrations were commonplace in the larger cities in Belarus (Gomel and Minsk), and Ukraine (Kiev and Lvov) in the years following the accident (Co92). The dismissive attitude of some Soviet scientists and government officials in describing the public reaction as "radiophobic" tended to alienate the public even further by implying some sort of mental illness or reaction which was irrational and abnormal. It also served as a convenient catch-all diagnosis which suggested that the public was somehow at fault, and the authorities were unable to do anything about its manifestations.

The concern of people for their own health is only overshadowed by their concern for the health of their children and grandchildren. Major and minor health problems are attributed to radiation exposure no matter what their origin, and the impact that the accident has had on their daily lives has added to the stress. Whole communities are facing or have faced evacuation or relocation. There are still widespread restrictions on daily life affecting schooling, work, diet and recreation.

The accident has caused disruption of social networks and traditional ways of life. As most inhabitants of the contaminated settlements are native to the area and often have lived there all their lives, relocation has in many cases, destroyed the existing family and community social networks, transferring groups to new areas where they may well be resented or even ostracised. In spite of these drawbacks, about 70% of the people living in contaminated areas wished to be relocated (IA91). This may well be influenced by the economic incentives and improved living standards that result from relocation by the government.

There are two additional circumstances and events which have tended to increase the psychological impact of the accident, the first of which was an initiative specifically designed to alleviate these effects in Ukraine. This was the introduction of the compensation law in Ukraine in 1991. Some three million Ukrainians were affected in some way by the post-accident management introduced, upon which approximately one sixth of the total national budget was spent (Du94). Different surveys have shown a general feeling of anxiety in all sectors of the population, but it was particularly acute among those who had been relocated. People were fearful of what the future might bring for themselves and their offspring, and were concerned about their lack of control over their own destiny.

The problem is that the system of compensation may well have exaggerated these fears by placing the recipients into the category of victims. This tended to segregate them socially and increased the resentment of the native population into whose social system these "victims" had been injected without consultation. This had the effect on the evacuees of increasing stress, often leading to withdrawal, apathy and despair. Locally, this compensation was often referred as a "coffin subsidy"! It is interesting to note that the 800 or so mostly elderly people who have returned to their contaminated homes in the evacuated zones, and hence receive no compensation, appear to be less stressed and anxious, in spite of worse living conditions, than those who were relocated. It should be pointed out that compensation and assistance are not harmful in themselves, provided that care is taken not to induce an attitude of dependence and resignation in the recipients.

The second factor which served to augment the psychological impact of the accident was the acceptance by physicians and the public of the disease entity known as "vegetative dystonia". This diagnosis is characterised by vague symptoms and no definitive diagnostic tests. At any one time, up to 1 000 children were hospitalised in Kiev, often for weeks, for treatment of this "disease" (St92). The diagnosis of vegetative dystonia appears to be tailor-made for the post-accident situation, assigned by parents and doctors to account for childhood complaints and accepted by adults as an explanation for vague symptoms.

There is great pressure on the physicians to respond to their patients' needs in terms of arriving at an acceptable diagnosis, and "Vegetative Dystonia" is very convenient as it will fit any array of symptoms. Such a diagnosis not only justifies the patients' complaints by placing the blame for this "disease" on radiation exposure, it also exonerates the patient from any responsibility, which is placed squarely on the shoulders of those responsible for the exposure - the Government. When the need for extended hospitalisation is added, the justification to accept this as a real disease is enhanced. It can be understood why there is an epidemic of this diagnosis in the contaminated areas.

Outside the former Soviet Union

Social and psychological effects in other countries were minimal compared with those within the former Soviet Union, and were generally exhibited more as concerned social reactions rather than health symptoms. In the contaminated regions of the former Soviet Union, many people were convinced that they were suffering from radiation induced disease, whereas in the rest of the world, where contamination was much less, news of the accident appeared to reinforce anti-nuclear perceptions in the general population. This was evidenced, for example, by the demonstrations on 7 June 1986 demanding the decommissioning of all nuclear power plants in the Federal Republic of Germany (Ze86). While in France public support for nuclear power expansion dropped since the accident, 63% of the population felt that French nuclear power reactors operated efficiently (Ch90). The minimal impact of the Chernobyl accident on French public opinion was probably due to the fact that about 75% of their electrical power is derived from nuclear stations, and in addition, France was one of the least contaminated European countries.

The Swedish public response has been well-documented (Dr93, Sj87). In the survey, the question was asked: "With the experience that we now have, do you think it was good or bad for the country to invest in Nuclear Energy?" Those that responded "bad" jumped from 25% before, to 47% after Chernobyl. The accident probably doubled the number of people who admitted negative attitudes towards nuclear power (Sj87). This change was most marked among women, who, it was felt, regarded nuclear power as an environmental problem, whereas men regarded it as a technical problem which could be solved. Media criticism of the radiation protection authorities in that country became more common, with the charge that the official pronouncements on the one hand said that the risk in Sweden was negligible, and yet on the other, gave instructions on how it could be reduced. The concept that a dose, however small, should be avoided if it could be done easily and cheaply, was not understood.

This sort of reaction was common outside the former Soviet Union, and while it did not give rise to significant health effects, it tended to enhance public apprehension about the dangers of nuclear power and foster the public's growing mistrust of official bodies.

In addition, public opinion in Europe was very sceptical of the information released by the Soviet Union. This mistrust was reinforced further by the fact that the traditional sources of information to which the public tended to turn in a crisis, the physicians and teachers, were no better informed and often only repeated and reinforced the fears that had been expressed to them. Added to this were the media, who tended to respond to the need to print "newsworthy" items by publishing some of the more outlandish claims of so-called radiation effects.

The general public was confused and cynical and responded in predictable but extreme ways such as seeking induced abortions, postponing travel and not buying food that might conceivably be contaminated. Another global concern that was manifested, was the apprehension over travel to the Soviet Union. Potential travellers sought advice from national authorities on whether to travel, what precautions to take and how they could check on their exposure. Many people, in spite of being reassured that it was safe to travel, cancelled their trip, just to be on the safe side, exhibiting their lack of confidence in the advice they received.

As has been seen, governments themselves were not immune from the influence of these fears and some responded by introducing measures such as unnecessarily stringent intervention levels for the control of radionuclides in imported food. Thus, in the world as a whole, while the effects on individuals, due to anxiety and stress, were probably minimal, the collective perception and response had a significant economic and social impact. It became clear that there was a need to inform the public on radiation effects, to provide clear instructions on the precautions to be taken so that the public regains some level of personal control, and for the authorities to recognise the public's need to be involved in the decisions that affect them.

In summary

It can be stated that:

  • Thirty-one people died in the course of the accident or soon after and another 134 were treated for the acute radiation syndrome. Forty-one of these patients received whole-body doses from external irradiation of less than 2.1 Gy, 2& between 6.5 and 16 Gy.
  • Extensive accident-related health effects are apparent in the affected regions of the former Soviet Union, manifested as anxiety and stress, as well as diverse health effects not directly related to radiation exposure. Severe forms induce a feeling of apathy and despair often leading to withdrawal. In the rest of the world these individual effects were minimal.
  • In the last decade, there has been a real and significant increase in childhood and, to a certain extent, adult carcinoma of the thyroid in contaminated regions of the former Soviet Union (Wi940) which should be attributed to the Chernobyl accident until proven otherwise.
  • In children, the thyroid cancers are:

    - largely papillary and particularly aggressive in nature often self presenting with local invasion and/or distant metastases;

    - more prevalent in children aged 0 to 5 years at the time of the accident, and in areas assessed to be the more heavily contaminated with 131I;

    - apparently characterised by a shorter latent period than expected; and

    - still increasing for children younger than 5 years in 1986.

Iodine deficiency and screening, have almost certainly had an influence on observed risk factors can be said that the increase of thyroid cancers in children is clearly established to be linked to exposure of radioactive iodine isotopes releases. The number of these cancers is still increasing in adults. Conversely, no increase in leukaemia has been observed to date.

No increase of congenital abnormalities, adverse pregnancy outcomes or any other radiation induced disease in the general population, either in the contaminated regions or in Western Europe, could be attributed to this exposure sixteen years after the accident. It is unlikely that surveillance of the general population will reveal any significant increase in the incidence of cancer but continued follow-up is necessary to allow planning of public health actions and to gain a better understanding of influencing factors.

The present knowledge of the effects of protracted exposure to ionising radiations is limited, since the dose-assessments rely heavily on high-dose exposure. An increase in cancer rates was already observed before the Chernobyl accident in the affected areas and, moreover, a general increase in mortality has been reported in recent years in most areas of the former USSR.

Among recovery operation workers, no increase of leukaemia has been identified more than sixteen years after the accident.

Among the health consequences resulting from the Chernobyl accident, are radiological consequences, and other, non-radiological health problems. The radiological aspects have been studied in great detail since the accident, and have been well characterised, within the limits of scientific uncertainty of radiological sciences. However, increasingly, medical specialists are studying other health effects that are not associated with radiation exposure, but more with the effects of significant and prolonged stress, physical and psychological. These effects, which have been classified as "Vegetative Dystonia", are increasingly recognised as real, but are felt to result from the social, cultural and psychological stress caused by the accident and the general social degradation that followed the accident and the end of the Soviet Union. To obtain a more exact understanding of these "accident-related effects", it is important to expand current studies to include specialists from studies of the health and social effects of other natural and technological disasters.

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