Health Impacts

Chernobyl Accident, Appendix

(Updated December 2014)

The health effects of the Chernobyl accident have been the subject of unprecedented study by health professionals and unprecedented speculation and exaggeration by parts of the media. This Appendix summarises two authoritative and expert assessments of the situation, and provides links to two others:

Exposures and Effects of the Chernobyl Accident

The conclusions of the Annex J report by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) are reproduced here. The full report is available from UNSCEAR2.

Conclusions

402. The accident of 26 April 1986 at the Chernobyl nuclear power plant, located in Ukraine about 20 km south of the border with Belarus, was the most serious ever to have occurred in the nuclear industry. It caused the deaths, within a few days or weeks, of 30 power plant employees and firemen (including 28 with acute radiation syndrome) and brought about the evacuation, in 1986, of about 116,000 people from areas surrounding the reactor and the relocation, after 1986, of about 220,000 people from Belarus, the Russian Federation and Ukraine. Vast territories of those three countries (at that time republics of the Soviet Union) were contaminated, and trace deposition of released radionuclides was measurable in all countries of the northern hemisphere. In this Annex, the radiation exposures of the population groups most closely involved in the accident have been reviewed in detail and the health consequences that are or could be associated with these radiation exposures have been considered.

403. The populations considered in this Annex are (a) the workers involved in the mitigation of the accident, either during the accident itself (emergency workers) or after the accident (recovery operation workers) and (b) members of the general public who either were evacuated to avert excessive radiation exposures or who still reside in contaminated areas. The contaminated areas, which are defined in this Annex as being those where the average 137Cs ground deposition density exceeded 37 kBq m-2 (1 Ci km-2), are found mainly in Belarus, in the Russian Federation and in Ukraine. A large number of radiation measurements (film badges, TLDs, whole-body counts, thyroid counts, etc.) were made to evaluate the exposures of the population groups that are considered.

404. The approximately 600 emergency workers who were on the site of the Chernobyl power plant during the night of the accident received the highest doses. The most important exposures were due to external irradiation (relatively uniform whole-body gamma irradiation and beta irradiation of extensive body surfaces), as the intake of radionuclides through inhalation was relatively small (except in two cases). Acute radiation sickness was confirmed in 134 of those emergency workers. Forty-one of these patients received whole-body doses from external irradiation of less than 2.1 Gy. Ninety-three patients received higher doses and had more severe acute radiation sickness: 50 persons with doses between 2.2 and 4.1 Gy, 22 between 4.2 and 6.4 Gy, and 21 between 6.5 and 16 Gy. The skin doses from beta exposures, evaluated for eight patients with acute radiation sickness, were in the range of 400-500 Gy.

405. About 600,000 persons (civilian and military) have received special certificates confirming their status as liquidators (recovery operation workers), according to laws promulgated in Belarus, the Russian Federation and Ukraine. Of those, about 240,000 were military servicemen. The principal tasks carried out by the recovery operation workers included decontamination of the reactor block, reactor site and roads, as well as construction of the sarcophagus and of a town for reactor personnel. These tasks were completed by 1990.

406. A registry of recovery operation workers was established in 1986. This registry includes estimates of effective doses from external irradiation, which was the predominant pathway of exposure for the recovery operation workers. The registry data show that the average recorded doses decreased from year to year, being about 170 mSv in 1986, 130 mSv in 1987, 30 mSv in 1988, and 15 mSv in 1989. It is, however, difficult to assess the validity of the results that have been reported because (a) different dosimeters were used by different organizations without any intercalibration; (b) a large number of recorded doses were very close to the dose limit; and (c) there were a large number of rounded values such as 0.1, 0.2, or 0.5 Sv. Nevertheless, it seems reasonable to assume that the average effective dose from external gamma irradiation to recovery operation workers in the years 1986-1987 was about 100 mSv.

407. Doses received by the general public came from the radionuclide releases from the damaged reactor, which led to the ground contamination of large areas. The radionuclide releases occurred mainly over a 10-day period, with varying release rates. From the radiological point of view, the releases of 1311 and 137Cs, estimated to have been 1,760 and 85 PBq, respectively, are the most important. lodine-131 was the main contributor to the thyroid doses, received mainly via internal irradiation within a few weeks after the accident, while 137Cs was, and is, the main contributor to the doses to organs and tissues other than the thyroid, from either internal or external irradiation, which will continue to be received, at low dose rates, during several decades.

408. The three main contaminated areas, defined as those with 137Cs deposition density greater than 37 kBq m-2 (1 Ci km-2), are in Belarus, the Russian Federation and Ukraine; they have been designated the Central, Gomel-Mogilev-Bryansk and Kaluga-Tula-Orel areas. The Central area is within about 100 km of the reactor, predominantly to the west and northwest. The Gomel-Mogilev-Bryansk contaminated area is centred 200 km north-northeast of the reactor at the boundary of the Gomel and Mogilev regions of Belarus and of the Bryansk region of the Russian Federation. The Kaluga-Tula-Orel area is in the Russian Federation, about 500 km to the northeast of the reactor. All together, territories from the former Soviet Union with an area of about 150,000 km2 were contaminated with 137Cs deposition density greater than 37 kBq m-2. About five million people reside in those territories.

409. Within a few weeks after the accident, more than 100,000 persons were evacuated from the most contaminated areas of Ukraine and of Belarus. The thyroid doses received by the evacuees varied according to their age, place of residence, dietary habits and date of evacuation. For example, for the residents of Pripyat, who were evacuated essentially within 48 hours after the accident, the population-weighted average thyroid dose is estimated to be 0.17 Gy and to range from 0.07 Gy for adults to 2 Gy for infants. For the entire population of evacuees, the population-weighted average thyroid dose is estimated to be 0.47 Gy. Doses to organs and tissues other than the thyroid were, on average, much smaller.

410. Thyroid doses also have been estimated for the residents of the contaminated areas who were not evacuated. In each of the three republics, thyroid doses are estimated to have exceeded 1 Gy for the most exposed infants. For residents of a given locality, thyroid doses to adults were smaller than those to infants by a factor of about 10. The average thyroid dose was approximately 0.2 Gy; the variability of the thyroid dose was two orders of magnitude, both above and below the average.

411. Following the first few weeks after the accident, when 131I was the main contributor to the radiation exposures, doses were delivered at much lower dose rates by radionuclides with much longer half-lives. Since 1987, the doses received by the populations of the contaminated areas came essentially from external exposure from 134Cs and 137Cs deposited on the ground and internal exposure due to the contamination of foodstuffs by 134Cs and 137Cs. Other, usually minor, contributions to the long-term radiation exposures include the consumption of foodstuffs contaminated with 9OSr and the inhalation of aerosols containing plutonium isotopes. Both external irradiation and internal irradiation due to 134Cs and 137Cs result in relatively uniform doses in all organs and tissues of the body. The average effective doses from 134Cs and 137Cs that were received during the first 10 years after the accident by the residents of contaminated areas are estimated to be about 10 mSv.

412. The papers available for review by the Committee to date regarding the evaluation of health effects of the Chernobyl accident have in many instances suffered from methodological weaknesses that make them difficult to interpret. The weaknesses include inadequate diagnoses and classification of diseases, selection of inadequate control or reference groups (in particular, control groups with a different level of disease ascertainment than the exposed groups), inadequate estimation of radiation doses or lack of individual data and failure to take screening and increased medical surveillance into consideration. The interpretation of the studies is complicated, and particular attention must be paid to the design and performance of epidemiological studies. These issues are discussed in more detail in Annex I, " Epidemiological evaluation of radiation-induced cancer".

413. Apart from the substantial increase in thyroid cancer after childhood exposure observed in Belarus, in the Russian Federation and in Ukraine, there is no evidence of a major public health impact related to ionizing radiation 14 years after the Chernobyl accident. No increases in overall cancer incidence or mortality that could be associated with radiation exposure have been observed. For some cancers no increase would have been anticipated as yet, given the latency period of around 10 years for solid tumours. The risk of leukaemia, one of the most sensitive indicators of radiation exposure, has not been found to be elevated even in the accident recovery operation workers or in children. There is no scientific proof of an increase in other non-malignant disorders related to ionizing radiation.

414. The large number of thyroid cancers in individuals exposed in childhood, particularly in the severely contaminated areas of the three affected countries, and the short induction period are considerably different from previous experience in other accidents or exposure situations. Other factors, e.g. iodine deficiency and screening, are almost certainly influencing the risk. Few studies have addressed these problems, but those that have still find a significant influence of radiation after taking confounding influences into consideration. The most recent findings indicate that the thyroid cancer risk for those older than 10 years at the time of the accident is leveling off, the risk seems to decrease since 1995 for those 5-9 years old at the time of the accident, while the increase continues for those younger than 5 years in 1986.

415. There is a tendency to attribute increases in cancer rates (other than thyroid) over time to the Chernobyl accident, but it should be noted that increases were also observed before the accident in the affected areas. More- over, a general increase in mortality has been reported in recent years in most areas of the former USSR, and this must also be taken into account in interpreting the results of the Chernobyl-related studies. Because of these and other uncertainties, there is a need for well designed, sound analytical studies, especially of recovery operation workers from Belarus, the Russian Federation, Ukraine and the Baltic countries, in which particular attention is given to individual dose reconstruction and the effect of screening and other possible confounding factors.

416. Increases of a number of non-specific detrimental health effects other than cancer in accident recovery workers have been reported, e.g. increased suicide rates and deaths due to violent causes. It is difficult to interpret these findings without reference to a known baseline or background incidence. The exposed populations undergo much more intensive and active health follow-up than the general population. As a result, using the general population as a comparison group, as has been done so far in most studies, is inadequate.

417. Adding iodine to the diet of populations living in iodine-deficient areas and screening the high-risk groups could limit the radiological consequences. Most data suggest that the youngest age group, i.e. those who were less than five years old at the time of the accident, continues to have an increased risk of developing thyroid cancer and should be closely monitored. In spite of the fact that many thyroid cancers in childhood are presented at a more advanced stage in terms of local aggressiveness and distant metastases than in adulthood, they have a good prognosis. Continued follow-up is necessary to allow planning of public health actions, to gain a better understanding of influencing factors, to predict the outcomes of any future accidents, and to ensure adequate radiation protection measures.

418. Present knowledge of the late effects of protracted exposure to ionizing radiation is limited, since the dose- response assessments rely heavily on high-dose exposure studies and animal experiments. The Chernobyl accident could, however, shed light on the late effects of protracted exposure, but given the low doses received by the majority of exposed individuals, albeit with uncertainties in the dose estimates, any increase in cancer incidence or mortality will most certainly be difficult to detect in epidemiological studies. The main goal is to differentiate the effects of the ionizing radiation and effects that arise from many other causes in exposed populations.

419. Apart from the radiation-associated thyroid cancers among those exposed in childhood, the only group that received doses high enough to possibly incur statistically detectable increased risks is the recovery operation workers. Studies of these populations have the potential to contribute to the scientific knowledge of the late effects of ionizing radiation. Many of these individuals receive annual medical examinations, providing a sound basis for future studies of the cohort. It is, however, notable that no increased risk of leukaemia, an entity known to appear within 2- 3 years after exposure, has been identified more than 10 years after the accident.

420. The future challenge is to provide reliable individual dose estimates for the subjects enrolled in epidemiological studies and to evaluate the effects of doses accumulated over protracted time (days to weeks for thyroid exposures of children, minutes to months for bone-marrow exposures of emergency and recovery operation workers, and months to years for whole-body exposures of those living in contaminated areas). In doing this, many difficulties must be taken into consideration, such as (a) the role played by different radionuclides, especially the short-lived radioiodines; (b) the accuracy of direct thyroid measurements; (c) the relationship between ground contamination and thyroid doses; and (d) the reliability of the recorded or reconstructed doses for the emergency and recovery operation workers.

421. Finally, it should be emphasized that although those exposed as children and the emergency and recovery operation workers are at increased risk of radiation- induced effects, the vast majority of the population need not live in fear of serious health consequences from the Chernobyl accident. For the most part, they were exposed to radiation levels comparable to or a few times higher than the natural background levels, and future exposures are diminishing as the deposited radionuclides decay. Lives have been disrupted by the Chernobyl accident, but from the radiological point of view and based on the assessments of this Annex, generally positive prospects for the future health of most individuals should prevail.

Exposures and effects of the Chernobyl accident, Annex J to Volume II of the 2000 United Nations Scientific Committee on the Effects of Atomic Radiation Report to the General Assembly, is available at the UNSCEAR 2000 Report Vol. II webpage (www.unscear.org/unscear/en/publications/2000_2.html). It is also available (along with other reports) on the webpage for UNSCEAR's assessments of the radiation effects of The Chernobyl accident (www.unscear.org/unscear/en/chernobyl.html).

Lessons of Chernobyl - with particular reference to thyroid cancer

The Chernobyl catastrophe was a dramatic personal experience for me - a difficult exam, which I am not sure that I passed. For many people engaged in radiological protection, though not all, it was a watershed that changed their view on the paradigm on which the present safety regulations are based, the holy mantra of LNT - the linear no-threshold assumption, according to which even the lowest, near-zero doses of radiation may cause cancer and genetic harm. For everybody it might serve as a yardstick for comparison of radiation risks from natural and man-made sources. It also sheds light on how easily the global community may leave the realm of rationality when facing an imaginary emergency.

The LNT assumption is in direct contradiction to a vast sea of data on the beneficial effects of low doses of radiation. When in 1980, as a chairman of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), I tried to convince its members that we should not ignore but rather peruse and assess these data, published in the scientific literature since the end of 19th century, everybody in the Committee was against it. In each of the next seven years I repeated the proposal, to no avail. Finally, the accident at Chernobyl appeared to be an eye opener: two years after the accident, in 1988, the Committee saw the light and decided to study radiation hormesis, i.e. the adaptive and beneficial effects of low levels of radiation. Six years of the Committee's work and hot discussions later, Annex B "Adaptive responses to radiation in cells and organisms" appeared in the UNSCEAR 1994 Report, fourteen years after my original proposal. The Annex started a virtual revolution in research related to radiation protection but, because of many vested interests and conservatism to change the international and national regulations, there is still a long way to go.

The LNT/hormesis controversy is not limited to radiation. It poses questions for practically all noxious physical, chemical and biological agents which we meet in life [1]. Ionizing radiation was discovered rather lately - at the end of the 19th century - but, like these other agents, it has been with us since time immemorial.

The Chernobyl accident was a radiation event unique in human history, but not in the history of the biosphere. There is evidence of a number of episodes of greater radiation levels during the evolution of life on earth, e.g. due to supernovae. In terms of human losses it was a minor event as compared with many other man-made catastrophes but, in political, economic, social and psychological terms, its impact was enormous. Let's have a look at what happened.

About 9 a.m. on Monday 28 April 1986 at the entrance of CLOR in Warsaw I was greeted by my assistant with a statement: "Look, at 7:00 we received a telex from Mikolajki monitoring station saying that the radioactivity of air is there 550 000 times higher than a day before. A similar increase I found in the air filter from our station in the backyard, and the pavement in front of the institute is highly radioactive". Soon, to our relief, we found that the isotopic composition of radioactive dust was not from a nuclear explosion, but rather from a nuclear reactor. Reports inflowing successively from our 140 monitoring stations suggested that a radioactive cloud over Poland traveled westwards and that it arrived from the Soviet Union, but it was only about 6 p.m. that we learned from BBC radio that its source was in Chernobyl.

This was a terrible psychological shock. The air over the whole country was filled with the radioactive material, at levels hundreds of thousands times higher than anything we experienced in the past, even in 1963 - a record year for fallout from nuclear test explosions. It is curious that all my attention was concentrated on this enormous increase in air radioactivity, although I knew that on this first day of "Chernobyl in Poland", the dose rate of external radiation penetrating our bodies reached 30 µR per hour, or 2.6 mSv per year, i.e. only by a factor of 3 higher than a day before. This dose rate was four times lower than I would experience visiting places in Norway, where the natural external radiation (up to 11.3 mSv/year) from the rocks is higher than over the Central European plane. It was also some 100 times lower than in an Iranian resort Ramsar, where the annual dose reaches about 250 mSv per year, or more than 300 times lower than at the Brazilian beaches (790 mSv per year) or in South-West France (up to 870 mSv per year). No adverse health effects have ever been reported among the people living in these areas with high natural background radiation.

But, in 1986, the impact of a dramatic increase in atmospheric radioactivity dominated the thinking of myself and of everybody. This state of mind led to immediate serious consequences in Poland, in the Soviet Union, throughout the Europe, and later all over the globe. First, there were different hectic actions, such as ad hoc coining of different principles and emergency countermeasures, the sense and quality of which lagged far behind the excellent measuring techniques and monitoring systems. An example of this was the radionuclide concentration limits (derived intervention levels) implemented a few days after the accident by various countries and international organizations, which varied by a factor of up to 50,000. The base of some of these limits was not scientific, but reflected the emotional state of the decision makers, and also political and mercantile factors. For example, Sweden allowed for 30 times more activity in imported vegetables than in the domestic ones, and Israel imposed lower limits for radioactivity in food imported from Eastern than from Western Europe. The limit of cesium-137 concentration in meat of 6 Bq/kg was accepted in the Philippines and 6000 Bq/kg in Norway.

The monetary costs of such restrictions were estimated in Norway. At first, the cesium-137 limit for meat was accepted there as 600 Bq/kg, which from a health physics point of view is meaningless, as consumption of 1 kg of such a meat would correspond to a dose of 0.0078 mSv. If somebody would eat 0.25 kg of this meat each day for 1 year the internal radiation dose would reach 0.7 mSv. This limit was often surpassed in mutton, and the farmers received compensation for destroying the meat, and for special fodder they were forced to feed the sheep for months before slaughtering. Such a low limit could have destroyed the living of Lapps whose economy depends on reindeer, an animal having a special food chain based on lichens. Due to this chain the reindeer meat contained in 1986 high concentrations of cesium-137, reaching up to 40,000 Bq/kg. In November 1986, Norwegian authorities introduced a limit of 6000 Bq/kg of reindeer meat and game. Ordinary Norwegian diet includes only about 0.6 kg of reindeer meat per year, thus this limit was aimed to protect Norwegians against a radiation dose of 0.047 mSv/year. In 1994, the costs of this "protection" were evaluated: they reached over $51 million.

Sweden was not better. When the farmers near Stockholm discovered that the Chernobyl accident contaminated the milk of their cows with cesium-137 above the limit of 300 Bq per liter imposed by Swedish authorities, they wrote to them and asked if their milk could not be diluted with uncontaminated milk from other regions, until the limit were attained, for instance by mixing 1 liter of contaminated milk with 10 liters of clean milk. To the farmers' surprise the answer was "no", and the milk was to be discarded. This was strange, as it always was possible to do so for other pollutants in foodstuffs, and we also dilute the fumes from fireplaces or ovens with the atmospheric air. Authorities explained that even though one could reduce the individual risk by diluting the milk, at the same time, one would increase the number of consumers, and thus the risk would remain the same, although now spread over a larger population [3]. This was a dogmatic application of the LNT assumption, and of its offspring, the concept of "collective dose" (i.e. reaching terrifyingly great numbers of "man-sieverts", by multiplying tiny innocuous individual radiation doses by large number of exposed people). I believe that, in an earlier paper, I demonstrated clearly the lack of sense and negative consequences both of the LNT assumption and of the population dose concept [4]. Their dogmatic application may quite probably have caused the costs of the Chernobyl accident to exceed $100 billion in Western Europe [5].

The most nonsensical action, however, was the evacuation of 336 000 people from the regions of the former Soviet Union, where during the years 1986 - 1995 the Chernobyl fallout increased the average natural radiation dose (about 2.5 mSv per year) by 0.8 to 1.4 mSv per year, i.e. by about 30% to 50% [6]. The evacuation was based on radiation limits recommended by the International Commission for Radiological Protection (ICRP) for "the event of major radiation accidents" and on recommendations for protection of the general population, which were tens to hundreds of times lower than natural doses in many countries. In the asphalt paved streets of the "ghost town" of Pripyat, from which about 50 000 people were relocated, and where nobody can enter without special permission, the total external gamma dose rate measured by a Polish team in May 2001 was 0.9 mSv per year, i.e. the same as in Warsaw, and five times lower than at the Grand Central Station in New York. The evacuation led to development of mass psychosomatic disturbances, great economical losses, and traumatic social consequences. Obviously, ICRP will never accept responsibility for the disastrous effects of this dogmatic application of its armchair lucubrations which has caused the present system of "radiation protection [to] become a health hazard"[3].

In Poland, to save the population from effects of exposure to iodine-131, the government, upon my instigation, administered during three days a single dose of stable iodine to about 18.5 million people, the greatest prophylactic action in the history of medicine performed in so short a time. My medical colleagues and the Ministry of Health were rightly proud of the ingenious and innovative way they implemented this countermeasure. Recently several countries, including the USA, planned to follow in our flight. However, now I see this action as nonsensical. We endeavored to save Polish children from developing thyroid cancers by protecting them from a radiation dose of 50 mSv to the thyroid gland [7]. At this dose ICRP recommended implementation of stable iodine prophylaxis. But in studies of more than 34 000 Swedish patients whose thyroid glands received radiation doses reaching up to 40 000 mSv from iodine-131, there was no statistically significant increase in thyroid cancers in adults or children, who had not already been thought to have cancer before treatment with iodine-131. In fact, an opposite effect was observed: there was a 38% decrease in thyroid cancer incidence as compared with the non-irradiated population [8, 9]. In a much smaller British study of 7417 adult hyperthyroid patients whose thyroids received average radiation doses from iodine-131 reaching 300 000 mSv, a 17% deficit in incidence of all studied cancers was found [10]. Without the stable iodine prophylaxis and milk restrictions, the maximum thyroid dose would have reached about 1000 mSv in about 5% of Polish children [7]. All that I would now expect from this dose is a zero effect.

Fourteen years after the Chernobyl accident in the officially termed "highly contaminated" areas of the former Soviet Union, except for thyroid cancers, no increase in incidence in solid cancers and leukemia was reported. In its 2000 Report, UNSCEAR stated that the "population need not live in fear of serious health consequences", and "generally positive prospects for the future health of most individuals should prevail" [6]. No epidemics of cancers in the Northern Hemisphere, direly predicted from the LNT assumption to reach tens and hundreds of thousands, or even millions of cases, has ever occurred.

The number of 1800 new thyroid cancers registered among the children from Belarus, Russia and Ukraine should be viewed in respect to extremely high occurrence of the "occult" thyroid cancers in normal populations [11-14]. These cancers, not presenting adverse clinical effects, are detected at post mortem, or by ultrasonography examinations. Their incidence ranges from 5% in Colombia, to 9% in Poland, 13% in the USA, and 35% in Finland [12]. In Finland occult thyroid cancers appear in 2.4% of children 0 to 15 year old [11]. In Minsk, Belarus the normal incidence of occult thyroid cancers is 9.3% [15]. The greatest incidence of "Chernobyl" thyroid cancers in children under 15 years old, of 0.027%, was registered in 1994 in the Bryansk region of Russia, which was less by a factor of about 90 than the normal incidence of occult thyroid cancers among the Finnish children. The "Chernobyl" thyroid cancers are of the same type and similarly invasive as the occult cancers [13]. The first increase of these cancers was registered in 1987 in the Bryansk region, Russia, one year after the accident. Since 1995, the number of registered cancers tends to decline. This is not in agreement with what we know about radiation induced thyroid cancers, the latency time for which is about 5 years after irradiation, and the risk of which increases until 15 - 29 years after exposure [6]. In the United States the incidence rate of thyroid tumors detected between 1974 and 1979 during a screening program was 21 times higher than before the screening [16], an increase similar to that observed in three former Soviet countries. I believe that the increased registration of thyroid cancers in contaminated parts of these countries is a classical screening effect.

There were 28 fatalities caused by very high doses of radiation to rescue workers and employees of the power station, and 3 deaths in this group due to other reasons. Among 237 members of the reactor staff and emergency workers, initially examined for signs of acute radiation sickness, this diagnosis was confirmed in 134 patients. From among these patients, 11 died up to 1998. The causes of death were as follows: 3 cases of coronary heart disease, 2 cases of myelodysplastic syndrome, two cases of liver cirrhosis, and one death each of lung gangrene, lung tuberculosis and fat embolism. One patient, who was classified with Grade II acute radiation sickness (acute radiation dose of 2.2 - 4.1 Gy) died from acute myeloid leukemia. A substantial increase in the incidence of leukaemia amongst recovery operation workers was predicted, but the evidence for a measurable radiation effect on this incidence is somewhat mixed. The average standardized incidence ratio (SIR) for leukemia ranged among these workers for Belarus, Russia and Ukraine from 0.94 to 7.76, but the problem is that similar increase was found for chronic lymphatic leukemia, a subtype deemed not to be induced by radiation exposure. Contribution of a screening or diagnostic bias to these excesses cannot be excluded. The SIR for all cancers combined in the recovery operation workers ranged from 0.70 to 1.02 in Belarus, from 0.91 to 1.01 in Russia, and from 1.05 to 1.11 in Ukraine.

In the general population of the contaminated regions of Belarus, the SIR for leukemia was 0.46 to 0.62 (i.e. 46% to 62% of the normal incidence in Belarus), 0.93 to 0.99 in Russia and 1.05 to 1.43 in Ukraine. The SIR for all cancers combined ranged from 0.30 to 0.69 in Belarus, from 0.89 to 0.98 in Russia, and from 0.80 to 0.82 in Ukraine. Hence, the incidence of all cancers appears to have been lower than it would have been in a similar but unirradiated group. The only real adverse health consequence of the Chernobyl catastrophe among about five million people living in the contaminated regions is the epidemics of psychosomatic diseases [6]. These diseases were not due to irradiation with Chernobyl fallout, but were caused by radiophobia, induced by years of propaganda before and after the accident, and aggravated by improper administrative decisions. As a result of these decisions, several million people in three countries have "been labeled as, and perceive themselves as, actual or potential victims of Chernobyl"[17]. This was the main factor behind the economic losses caused by the Chernobyl catastrophe, estimated for Ukraine to reach $148 billion until 2000, and $235 billion until 2016 for Belarus [17].

In 1986 most of my professional colleagues and I, the authorities, and the public in Poland and elsewhere, were pre-conditioned for irrational reactions. Victims of the LNT dogma, we all wished to protect people even against the lowest, near zero doses of ionizing radiation. The dogma influenced behavior of everybody, leading to a mass psychosis, in fact to the greatest psychological catastrophe in history [2], into which the accident in Chernobyl, with the efficient help of media and national and international authorities, quickly evolved. It seems that professionals, international and national institutions, and the system of radiological protection did not meet the challenge of the Chernobyl catastrophe.

The following main lessons can be deduced from this accident:

(1) Ionizing radiation killed only a few occupationally exposed people. Due to rapid decay of short-lived radionuclides, the Chernobyl fallout did not expose the general population to harmful radiation doses. Near the burning reactor, the area covered by the dangerous radioactive fallout where, on April 26 1986, the radiation dose rate reached 1 Gy per hour (after one year it had decreased by a factor of about 3000), was limited to two patches totaling together about 0.5 km2 in an uninhabited location, and reaching a distance of 1.8 km from the burning nuclear reactor. Several hundred meters outside the 1 Gy isoline the dose rate dropped by two orders of magnitude, to a level of 0.01 to 0.001 Gy per hour. This is a completely different situation than after a surface explosion of a 10 Mt nuclear bomb, when the 1 Gy per hour isoline can reach a distance of 440 km, and the lethal fallout can cover tens of thousands km2, and endanger the life of millions of people.

(2) The reported excess of thyroid cancers in children and in adults exposed to Chernobyl fallout is not consistent with the knowledge on effects of medical use of iodine-131. The report of an "excess" appears to be an effect of screening, and is only a small fraction of the normal occult thyroid cancers incidence occurring in populations unexposed to iodine-131.

(3) Radionuclides were injected high into the stratosphere, at least up to 15 km altitude, which made possible its long distance migration in the whole Northern Hemisphere, and a penetration over the Equator down to the South Pole [18]. With unique, extremely sophisticated radiation monitoring systems, implemented in all developed countries, even the most tiny debris from the Chernobyl reactor was easily detected all over the world. No such system exists for any other potentially harmful environmental agent. Ironically, this excellence of radiological protection ignited the mass anxiety, with its disastrous consequences in the former Soviet Union, and strangulation of nuclear energy development elsewhere.

(4) Psychosomatic disorders and the screening effects were the only detectable health consequences among the general population. Fighting the panic and mass hysteria could be regarded as the most important countermeasure to protect the public against the effects of a similar accident should it occur again.

(5) This was the worst possible catastrophe of a badly constructed nuclear reactor, with a complete meltdown of the reactor core, followed by the ten-days long completely free emission of radionuclides into the atmosphere. Nothing worse could happen. It resulted in a comparatively small occupational death toll, amounting to about half of that of each weekend's traffic in Poland, and tens or hundreds of times lower than that of many other industrial catastrophes, and it is unlikely that any fatalities were caused by radiation among the public. In the centuries to come, the Chernobyl catastrophe will be seen as a proof that nuclear power is a safe means of energy production.

UNDP and UNICEF, The Human Consequences of the Chernobyl Nuclear Accident: A strategy for Recovery. 2002, United Nations Development Programme (UNDP) and the UN Children's Fund (UNICEF) with the support of the UN Office for Co-ordination of Humanitarian Affairs (OCHA) and WHO. p. 1-75.

Kownacka, L. and Z. Jaworowski, Nuclear weapon and Chernobyl debris in the troposphere and lower stratosphere. The Science of the Total Environment, 1994. 144: p. 201-215.