Chernobyl: Assessment of Radiological and Health Impact
2002 Update of Chernobyl: Ten Years On
The scale and severity of the Chernobyl accident with its widespread radioactive contamination had not been foreseen and took by surprise most national authorities responsible for emergency preparedness. No provisions had been made for an accident of such scale and, though some radiation protection authorities had made criteria available for intervention in an accident, these were often incomplete and provided little practical help in the circumstances, so that very few workable national guidelines or principles were actually in place. Those responsible for making national decisions were suddenly faced with an accident for which there were no precedents upon which to base their decisions. In addition, early in the course of the accident there was little information available, and considerable political pressure, partially based on the public perception of the radiation danger, was being exerted on the decision makers. In these circumstances, cautious immediate action was felt necessary, and measures were introduced that tended to err, sometimes excessively so, on the side of prudence rather than being driven by informed scientific and expert judgement.
The town of Pripyat was not severely contaminated by the initial release of radionuclides, but, once the graphite fire started, it soon became obvious that contamination would make the town uninhabitable. Late on 26 April it was decided to evacuate the town, and arrangements for transport and accommodation of the evacuees were made. The announcement of evacuation was made at 11:00 hr the following day. Evacuation began at 14:00 hr, and Pripyat was evacuated in about two and one half hours. As measurements disclosed the extensive pattern of deposition of radionuclides, and it was possible to make dose assessments, the remainder of the people in a 30-km zone around the reactor complex were gradually evacuated, bringing the total evacuees to about 135 000.
Other countermeasures to reduce dose were widely adopted (Ko90). Decontamination procedures performed by military personnel included the washing of buildings, cleaning residential areas, removing contaminated soil, cleaning roads and decontaminating water supplies. Special attention was paid to schools, hospitals and other buildings used by large numbers of people. Streets were watered in towns to suppress dust. However, the effectiveness of these countermeasures outside the 30-km zone was small. An attempt to reduce thyroid doses by the administration of stable iodine to block radioactive uptake by the thyroid was made (Me92), but its success was doubtful.
The Soviet National Committee on Radiation Protection (NCRP) proposed a 350-mSv lifetime dose intervention level for the relocation of population groups (Il87). This value was lower by a factor of 2 to 3 than that recommended by the International Commission on Radiological Protection (ICRP) for the same countermeasure. Nevertheless, this value proposed by the NCRP was strongly criticised as being a very high level. The situation was further complicated by the political and social tension in the Soviet Union at that time. As a result, the NCRP proposal was not adopted by the Supreme Soviet. Later, a special Commission was established which developed new recommendations for intervention levels. These recommendations were based on the levels of ground contamination by the radionuclides 137Cs, 90Sr and 239Pu. As has been mentioned above, large areas were contaminated mainly by 137Cs and a ground contamination level by this radionuclide of 1 480 kBq/m2 was used as the intervention criterion for permanent resettlement of population, and of 555 to 1 480 kBq/m2 for temporary relocation.
People who continued to live in the heavily contaminated areas were given compensation and offered annual medical examinations by the government. Residents of less contaminated areas are provided with medical monitoring. Current decisions on medical actions are based on annual doses. Compensation is provided for residents whose annual dose is greater than 1mSv. The use of locally produced milk and mushrooms is restricted in some of these areas. Relocation is considered in Russia for annual doses above 5 mSv.
As is mentioned in the section on health impacts effects, in Chapter V, the Soviet authorities did not foresee that their attempts to compensate those affected by the accident would be misinterpreted by the recipients and increase their stress, and that the label of “radiophobia” attributed to these phenomena was not only incorrect, but was one that alienated the public even more. Some of these initial approaches have been recognised as being inappropriate and the authorities are endeavouring to rectify their attitude to the exposed population.
The progressive spread of contamination at large distances from the accident site has caused considerable concern in Member countries, and the reactions of national authorities to this situation have been extremely varied, ranging from a simple intensification of the normal environmental monitoring programmes, without adoption of any specific countermeasures, to compulsory restrictions concerning the marketing and consumption of foodstuffs. This variety of responses has been accompanied by significant differences in the timing and duration of the countermeasures.
In general, the most widespread countermeasures were those which were not expected to impose, in the short time for which they were in effect, a significant burden on lifestyles or the economy. These included advice to wash fresh vegetables and fruit before consumption, advice not to use rainwater for drinking or cooking, and programmes of monitoring citizens returning from potentially contaminated areas. In reality, experience has shown that even these types of measures had, in some cases, a negative impact which was not insignificant.
Protective actions having a more significant impact on dietary habits and imposing a relatively important economic and regulatory burden included restrictions or prohibitions on the marketing and consumption of milk, dairy products, fresh leafy vegetables and some types of meat, as well as the control of the outdoor grazing of dairy cattle. In some areas, prohibitions were placed on travel to areas affected by the accident and on the import of foodstuffs from the Soviet Union and Eastern European countries. In most Member countries, restrictions were imposed on the import of foodstuffs from Member as well as non-member countries.
The range of these reactions can be explained primarily by the diversity of local situations both in terms of uneven levels of contamination and in terms of national differences in administrative, regulatory and public health systems. However, one of the principal reasons for the variety of situations observed in Member countries stems from the criteria adopted for the choice and application of intervention levels for the implementation of protective actions. In this respect, while the general radiation protection principles underlying the actions taken in most Member countries following the accident have been very similar, discrepancies arose in the assessment of the situation and the adoption and application of operational protection criteria. These discrepancies were further enhanced by the overwhelming role played in many cases by non-radiological factors, such as socio-economic, political and psychological, in determining the countermeasures.
This situation caused concern and confusion among the public, perplexities among the experts and difficulties to national authorities, especially in maintaining their public credibility. This was, therefore, identified as an area where several lessons should be learned from the accident and efforts directed towards better international harmonisation of the scientific bases and coordination of concepts and measures for the protection of the public in case of emergency.
Nowhere was this problem better illustrated than by the way that contaminated food was handled. In some countries outside the Soviet Union the main source of exposure to the general population was the consumption of contaminated food. Mechanisms to handle locally produced as well as imported contaminated food had to be put in place within a few weeks of the accident. National authorities were in an unenviable position. They had to act quickly and cautiously to introduce measures to protect the “purity” of the public food supply and, what is more, they had to be seen to be effective in so doing. This inevitably led to some decisions which even at the time appeared to be overreactions and not scientifically justified. In addition, dissenting opinions among experts added to the difficulties of the decision makers.
Some countries without nuclear power programmes and whose own food was not contaminated, argued that they did not need to import any “tainted” food and refused any food containing any radionuclides whatsoever. This extreme and impracticable measure might well have been regarded as an example of how well the authorities of those countries were protecting the health of their population. Sometimes this attitude appeared to promote a neighbourly rivalry between countries to see which could set the more stringent standards for food contamination, as though, by so doing, their own citizens were more protected. The result was that often slightly contaminated food was destroyed or refused importation to avoid only trivial doses.
In 1986, the EC imposed a ban on the importation of food containing more than 370 Bq/kg of radiocaesium for milk products and 600 Bq/kg for any other food, regardless of the quantity consumed in the average European diet. Thus, food items with a trivial consumption (and dose), such as spices, were treated the same as items of high consumption such as vegetables. However, these values were later relaxed for some food items in order to remove inconsistent treatment of food groups.
In some special circumstances, decisions had to be made based on the local situation. For example, in some Northern European communities, reindeer meat is a major component of the diet; due to the ecological circumstances, these animals tend to concentrate radiocaesium, which will then expose the populations which depend on them. Special countermeasures, such as pasturing reindeer in areas of lower contamination, were introduced in some countries to avoid this exposure.
The variety of solutions led to confusion and made any international consensus on Derived Intervention Levels for food extremely difficult to achieve, and it was only with the WHO/FAO Codex Alimentarius Meeting in Geneva in 1989 that any agreement was reached on guideline values for the radioactivity of food moving in international trade (Table 4).
Table 4. Codex Alimentarius Guideline values for food moving in international trade (FA91)
|Foods for general consumption|
131I, 134Cs, 137Cs
|Infant foods and milk|
It should be remembered that these guideline values were developed to facilitate international trade in food, and should be regarded as levels “below which no restrictions to trade need be implemented for radiological reasons”. Levels above these do not necessarily constitute a health hazard, and if found, the competent national authority should review what action should be taken.
Often the national authorities were not able accurately to predict the public response to some of their advice and pronouncements. For example, in some European countries, soon after the accident the public were advised to wash leafy vegetables. The national authority felt that this was innocuous advice as most people washed their vegetables anyway, and they were unprepared for the public response which was to stop buying these vegetables. This resulted in significant economic loss to local producers which far outweighed any potential benefit in terms of radiological health.
In some countries, the public was told that the risks were very small but, at the same time, were given advice on how to reduce these low risks. It was very difficult to explain this apparently contradictory advice, and the national authority came under criticism from the media (Sj87). Outside the Soviet Union, the initial confusion led to inconsistent and precipitate actions which, although understandable, were sometimes ill-advised and unjustified.
However, it should be emphasised that great progress has been made since this early confusion. As a result of the actions of the international organisations to harmonise intervention criteria and the willingness of countries to cooperate in this endeavour, a firm groundwork for uniform criteria based on accepted radiation protection principles has been established, so that relative consistency can hopefully be expected in their implementation in the event of a possible future nuclear accident.
Today, territories where populations receive a dose lower than 1 mSv per year are declared as zones permitting normal life. For areas higher than 1 mSv/year authorities continue to give social compensations, depending on the dose. Areas where annual dose is higher than 20 mSv per year are exclusion zones. With the new estimation of doses, some settlements in Russia have lost their status as contaminated area by a decree (N° 5924, 18 December 1997) which came into operation the 1 February 1998. This decision was badly received by local populations and local authorities.
The opposite is also true, as of the 1st of January 1999, 8 397 people were still living in areas where evacuation is an obligation (contamination higher than 30 Ci.km-2).
The relocation of evacuees has not been completely resolved, as of 2000, more than 11 000 evacuees are still living in temporary provisory settlements.
Limits on trade exchange of agricultural productions were the same for the three republics up to 1997. They were lowered a first time in 1987, a second time in 1991 in the three republics, but in Ukraine these limits were lowered a fourth time on 25 June 1997 and now apply to four main products: 100 Bq per litre for milk (instead of 370 Bq/l in 1991); 200 Bq/kg for meat (instead 740 in 1991); 20 Bq/kg for bread and potatoes (instead of, respectively, 370 and 600 since 1991). In Russia, with the exception of Briansk, and Kalouga areas (jizdra, Khvastovitchi and Oulianovskii), a new regulation was adopted the first of March 1998 (SanPiN 184.108.40.2060-96) for agricultural products and for milk the limit is now 50 Bq.kg-1 of 137Cs (Bo99) (Table 5).
Table 5. Evolution of limits for trade exchange since 1986 in Russia, Bielorussia and Ukraine, the italics values for 1997 are only for Ukraine
|06 May 86||30 may 86||87||88||91||93||97 (Ukraine)||98 (Russia)|
|Meat||3 700||1 850||1 850||740||740||200|
In Russia, more than ten years after the accident, several programmes have been agreed upon to compensate for the delays in the implemantation of previous plans. A national centre of ecological medicine has been created in St.-Petersburg for health assistance to the liquidators. It can provide up to 1 500 sick people per year with high quality medical treatment. This centres was expanded to other national hospitals in the Russian federation. Ten expert councils have been created to establish a potential links between diseases and the Chernobyl accident. Four socio-psychological readaptation centres have been created in the Bryansk, Orel and Toula areas in Russia. These centers have been charged with delivering justice, social and psychological assistance to all those affected by the accident. Lastly a dosimetry register has been created, in 1999, in which more than 500 000 people have been registered (including 170 000 liquidators).
Several significant programmes were launched during 1998-2000, to take in account the huge delay of all national programmes, Including a National programme for the protection of the public, a Programme for Chernobyl children, and a Programme for settlements for liquidators (Bo99).
Lastly the Russian authorities are aware that some aspects of current federal law must be changed to eliminate significant obstacles to ending certain programmes that no longer contribute to the elimination of the consequences of the accident.
The Chernobyl accident took authorities by surprise as regards to its extent, duration and far reaching contamination. As there were no guidelines for such an accident, little information was available and great political and public pressure to do something were experienced, overprecautious decisions were often taken in and outside the Soviet Union. The social and psychological impact of some official decisions on the public were not expacted, and variable interpretations or even misinterpretations of ICRP recommendations, especially for intervention levels for food, led to inconsistent decisions and advice. These added to public confusion and provoked mistrust and unnecessary economic losses. However, there were exceptions, and very soon international efforts began to harmonise criteria and approaches to emergency management.
More than 16 years later the confusion still exist in spite of significant international efforts of harmonization. For example, in 1997 the Ukrain unilaterally lowered its radiological restrictions on trade, below the levels previously harmonised for Russia, Belarus and the Ukraine, reinforces this confusion. Lastly, the Russian federation has realised the need to change some apects of its former law, which has become an obstacle to appropriately addressing accident consequences.