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Chernobyl - Ten years after

by Abel J. González

On 26 April 1986, a catastrophic explosion at Unit 4 of the Chernobyl nuclear power plant in the Ukrainian Republic - close to the point marking the three-way border with the Republics of Belarus and Russia - sent a very large amount of radioactive material into the atmosphere. The event was to become one of the most protracted and controversial themes of the modern technological era. The Chernobyl accident caused widespread concern over its radiological consequences, and also focused attention on nuclear safety generally. The accidents aftermath evolved together with the unfolding of glasnost and perestroika in the former USSR and soon became bound up with many misunderstandings and apprehensions about the radioactive release and its real or perceived effects.

There was initial secrecy and confusion about the accident - candidly reported in Prof. Leonid Ilyins book, Chernobyl: Myths and Reality. The people living in the affected areas learned about the event mainly from hearsay rather than from authoritative reporting. The first evidence of the accident outside the USSR resulted from measurements in nordic countries showing an unexpected increase in environmental radioactivity. This initial lack of transparency had an impact on public confidence, and subsequently so did the confusing and at times contradictory nature of the information released. Perceptions of the catastrophe ranged from those who believed that Chernobyl had been one of the worlds worst ever disasters to those who saw it as a relatively limited health problem despite the tragic circumstances.

A decade later, in April 1996, more than 800 experts from 71 countries and 20 organizations - observed by over 200 - journalists met to review the Chernobyl accidents actual and possible future consequences, and to put these into proper perspective. They came together at the international conference on One Decade after Chernobyl: Summing up the Consequences of the Accident, held at the Austria Center in Vienna. The Chernobyl Conference was a model of international co-operation: six organizations of the UN family, including the IAEA, and two important regional agencies were involved in its organization. (See box).

Between the accident in 1986 and this Chernobyl conference, the IAEA participated in a range of scientific endeavours which sought to quantify the actual consequences. (See boxes).

The aim of the Chernobyl Conference was to consolidate "an international consensus on the accident's consequences, to agree on proven scientific facts, and to clarify information and prognoses in order to dispel confusion". The results of the Conference speak for themselves. (See the following article for Highlights of the Chernobyl Conference: Summary of Results). Some important issues have been summarised here and are separately analysed in reports featured in this edition of the IAEA Bulletin.

Radioactive fallout. Although even today there is no complete consensus on the amount of radioactive material released by the Chernobyl accident, the best estimates - which are of the magnitude of 10¹⁹ international units of activity, called becquerels - are illustrative of the catastrophic nature of the accident. Two chemical elements in the radioactive plume formed by the materials released dominated the radiological consequences: iodine and caesium. There is a family of mainly short-lived radioactive isotopes of iodine: a significant one is iodine-131, whose activity falls by half every eight days. Radioiodines were mainly responsible for irradiation of the thyroid gland of the people living in nearby regions shortly after the accident. Of the radioactive caesiums, the most significant is caesium-137, a long-lived nuclide whose activity falls by half every 30 years. Caesium-137 was transported through the atmosphere for long distances, deposited variably over vast areas, mainly in Europe and - to a minor but measurable extent - elsewhere over the whole northern hemisphere. The deposited caesium became the main cause of whole body radiation exposure in the long term. (See box).

Radiation doses. The release of radioactive material was expected to have severe direct consequences for people and ecosystems in and near the Chernobyl plant site. Radiation damage correlates with the radiation dose incurred by people and biota. Dose is a quantity related to the amount of radiation energy absorbed by the mass of biological matter. The dose incurred by people is expressed in sieverts and, most commonly, in the submultiple millisieverts - one millisievert being a thousandth of a sievert (for comparison purposes, people receive on average an annual dose of 2.4 millisieverts from natural background radiation). Many of the plant workers and many people who helped to deal with the accident's aftermath - who were called 'liquidators' - received high doses, some of thousands of millisieverts, and suffered clinical radiation syndromes. Twenty-eight people died as a consequence of their radiation injuries. Over 100,000 members of the public who were evacuated from the contaminated areas, and also those who remained living in the less affected regions, received, or are committed to receiving, relatively low whole body doses: over their lifetimes, these will be comparable with or lower than doses they would receive in a lifetime from natural sources of radiation. (See box). Doses to the thyroid gland - particularly of children - were a notable exception and are presumed to have been very high. Another exception was doses in local ecosystems.

Environmental damage. Lethal radiation doses were reached in some radiosensitive local ecosystems, within a few kilometres of the accident, notably in coniferous trees and for voles. Doses fell sharply within a few months and the ecosystems eventually recovered. No sustained severe impacts on the environment have been observed so far. (See box). A report by M. Dreicer and R. Alexakhin addresses the environmental consequences of the accident in more detail.

A by-product of the environmental contamination was the contamination of foodstuffs produced in the affected areas. Although for some time after the accident key foodstuffs showed activity levels exceeding the maximum levels permitted by the Codex Alimentarius,* no food now produced by collective farms exceeds these levels. Exceptionally, wild food products - such as mushrooms, berries and game - from forests in the more affected areas as well as fish from some European lakes remain above Codex levels. An important aspect in controlling the contamination of the human habitat was the agricultural countermeasures undertaken in the affected areas; these are examined by J. Richards and R. Hance in a related report.

Health effects. Health effects attributed to the accident have commanded the most concern on the part of the public, decision-makers and political authorities, and the Chernobyl Conference devoted a great deal of time to the topic. Clinically observed (and individually attributable) effects were discussed separately from long-term effects which can only be attributed to radiation after long studies of a statistical epidemiological nature of large populations.** (See box). Among the latter, thyroid effects is a special case that was treated separately from other longer term health effects.

Clinically observed effects. The number of people who suffered clinically observed health effects individually attributable to radiation exposure due to the Chernobyl accident was relatively modest, given the accidents dimensions. A total of 237 persons, all of them workers dealing with the accident, were suspected of suffering clinical syndromes of radiation exposure and were hospitalized, and 134 of them were diagnosed with acute radiation syndrome. Of these, 28 died of the consequences of radiation injuries (three other persons died at the time of the accident: two due to non-radiation blast injuries and one due to a coronary thrombosis). (See graph). Some years after the accident, 14 additional persons in this group died; however, their deaths were found to be not necessarily attributable to radiation exposure. A following report in this edition by Dr. G. Wagemaker et al. describes the clinically observed effects in more detail.

Thyroid effects. The situation in relation to thyroid effects is serious. Up to the end of 1995, there were more than 800 cases of thyroid cancer reported in children, mainly in Belarus. (See graph). Thyroid cancer may be induced by causes other than radiation, but all these cases seem to be likely associated with radiation exposure due to the accident. They represent a dramatic increase in the normal incidence of this rare type of cancer and the increase seems not to persist among children born after 1986. Thyroid cancer is usually non-fatal with early diagnosis, treatment and attention. At the time of the Chernobyl Conference, three of the affected children had already died. The prospects cannot be precisely predicted: the high incidence is expected to continue for some time and the number of reported cases may be in the thousands; the mortality will depend very much on the quality and intensity of the treatment given to the affected children. Prof. E.D. Williams et al. reviewed the thyroid effects in a separate report.

Longer term health effects. There is no evidence to date of any increase in the incidence of any malignancies other than thyroid carcinoma or of any hereditary effects attributable to radiation exposure caused by the Chernobyl accident. This conclusion, surprising for some observers, is in accordance with the relatively small whole body doses incurred by the populations exposed to the radioactive material released. The lifetime doses expected to be incurred by these populations are also small. In fact, the risks of radiation induced malignancies and hereditary effects are extremely small at low radiation doses and, as the normal incidences of these effects in people are relatively high, it is not surprising that no effects could be detected. (See box).

An exception to the lack of evidence of long-term effects might have occurred in the group of liquidators: taking into account the relatively high doses reported in this group, an increase in the incidence of leukaemia might have been detected. For all other malignancies and hereditary effects, the theoretically predicted number of cases due to radiation exposure from the accident are so small in comparison with the background incidence as to be impossible to confirm statistically.

The reason why the theoretically expected increase in the incidence of leukaemia in the liquidators has not become evident requires further investigation. It could be that the dose was lower than reported, or that the epidemiological studies of this group are somehow inadequate. Less plausibly, the risk factors for radiation induced leukaemia could be lower than the currently estimated cases of leukaemia in the 200,000 registered liquidators who worked in 1986-87, which was of the order of 200 over a lifetime as compared to a spontaneous number of around 800. (See graph). Dr. E. Cardis et al. go into greater detail in their report on the long-term health effects.

A retrospective look at the findings of the International Chernobyl Project in 1990 in relation to health effects is provided by Dr. Fred Mettler.

Social and other impacts. The Chernobyl Conference found that social, economic, institutional and political impacts were also important consequences of the Chernobyl accident. A background paper prepared jointly by officials of Belarus, Russia and Ukraine described the catastrophe in terms of economic and social disruption. (See box). Large economic losses attributed to the accident were reported in this official document and also in the national statements delivered at the Chernobyl Conference. For the period 1986-91, the total direct losses and outlays in the former USSR were stated as exceeding 23,000 million roubles. The expenditures were accounted for - inter alia - by: losses of capital assets and in production; population resettlement, including construction of dwellings and other facilities; forest protection, water conservation, and soil decontamination and treatment; and, various compensations and payments of allowances to the population. The President of Belarus, reported that, "According to our most modest estimates, the economic damage incurred following the Chernobyl accident is equal to 32 annual budgets of the Republic, i.e. US $ 235,000 millions. For these purposes we allocate annually 20-25% of the State budget". The Russian Federation Minister for Civil Defence, Emergencies and Elimination of Consequences of Natural Disasters reported that, "Over the past years, trillions of roubles have been made available for the rehabilitation of the parts of Russia affected by the accident". For the Ukraine, its Prime Minister reported that, "The total expenditure in eliminating the consequences of the accident over the period 1992 to 1996 alone, paid out of the Ukrainian national budget, exceeds US $ 3,000 millions".

Certainly, a major social problem lies in the significant psychological symptoms detected among the population, such as anxiety, depression and various psychosomatic disorders attributable to mental distress. It has been found that it is extremely difficult to discern whether these effects are attributable solely to the Chernobyl accident or to economic hardships and other social problems in the region: the levels of these disorders in the areas concerned seem to be surprisingly high whether people were directly affected by the accident or not. (See graph). In a separate report, Dr. Britt-Marie Drottz-Sjoeberg et al. look at social and psychological effects in more detail.

Nuclear safety issues. For the public as well as for the responsible authorities, the Chernobyl accident prompts the question: Are Chernobyl-type reactors now safe? Experts say that the possibility of a repeat of the accident has virtually been ruled out because of safety improvements that have been made at plants of this type. Other safety improvement issues at the remaining Chernobyl units and reactors of the same RBMK type require attention. In addition, there is the separate issue of the safety of the remaining debris at Chernobyl, most of which is contained within the structure known as the sarcophagus. All these issues were discussed thoroughly at an international forum, One Decade After Chernobyl: Nuclear Safety Aspects, which preceded the Chernobyl Conference and was reported on at the Conference. (See box). More details about the forum and its conclusions are presented by Mr. L. Lederman in a following report.

Outlook. The scientific assessments of the consequences of the Chernobyl accident have now been discussed and corroborated ten years later by a wide and representative international gathering of experts. The results provide the public at large, decision-makers and political leaders with authoritative information about these consequences. This ought to put an end to much of the misinformation that has arisen over the consequences of the accident.

The radiation levels that can still be detected in most affected areas are sufficiently low as to permit normal economic and social activity to be resumed. The health effects have not turned out to be as catastrophic as some feared and others reported. But a number of radiation effects did occur and more are expected to occur and should be dealt with. Moreover, the socio-economic impacts are very serious.

All efforts should now be concentrated on using our better understanding of the consequences to help those who have truly been affected and are still in need of help.