15th Anniversary of the Chernobyl Accident

In September 2000 the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) published its Report to the General Assembly, with Scientific Annexes, a document of some 1220 pages, published in two volumes. Annex J (vol. 2, pp. 453-551) deals with exposures and effects of the Chernobyl accident. Recently updated dosimetric findings in the regions of the former Soviet Union most highly contaminated by radioactive fallout, and an updated evaluation of the health effects of the Chernobyl accident, prepared as an outline of a future Report, will be discussed during the 50th session of UNSCEAR, to be held in Vienna between April 23rd and 27th 2001.

The Committee has stated that apart from about 1800 thyroid cancer cases registered in children and in some adults, there is no evidence of any major public health impact attributable to radiation exposure after the accident. There is no increase in overall cancer incidence or mortality or in non-malignant disorders that could be related to radiation exposure. The incidence of leukemia, which due to its short latency time is a good indicator of radiation harm, is not elevated among about 5 million inhabitants of the contaminated regions, nor among the evacuated persons or recovery operation workers. However, there is a widespread psychological reaction to the accident, due to fear of radiation, and not to the actual radiation dose received by individuals. These reactions lead to psychosomatic disorders and epidemic symptoms such as headache, depression, sleep disturbances, inability to concentrate and emotional imbalance, not unlike similar social reactions following major disasters of non-nuclear origin (such as floods, earthquakes or landslides).

The increase in the number of registered thyroid cancers is very likely due to a screening effect. The normal incidence of "occult" thyroid cancers (which, while not causing any visible clinical disturbance, are histologically malignant and aggressive) is very high in most countries (e.g., about 13,000 per 100,000 inhabitants in the United States). This number should be compared with the highest incidence of thyroid cancers recorded in the highly contaminated region of Bryansk (Russia), of 26.6 per 100,000 inhabitants. Document prepared for this year’s session of UNSCEAR provide several similar examples of such screening effects, e.g. an increase in chronic lymphocyte leukemia, a disease known as not being caused by ionizing radiation.

Among the workers of the Chernobyl nuclear power stations and rescue operators, 30 persons died after having received a very high dose of ionizing radiation. No deaths directly attributable to exposure from the Chernobyl radiation have been found in the population of the contaminated regions. Cancer incidence rates over the most contaminated regions of Ukraine are found to be consistently lower than rates over the country as a whole. The incidence of solid cancers among Russian recovery operation workers is observed to be significantly lower than that in the general population.

This is to be expected. The whole-body radiation dose due to the Chernobyl fallout received during the past fifteen years by individuals in the most contaminated parts of the former Soviet Union (about 1 mSv per year), is ten to a hundred times lower than the dose of ionizing radiation from natural sources received by individuals in many regions of the world. Neither radiation-induced diseases nor any genetic disorders have ever been found in these regions. Genetic disorders have not been found even in the offspring of Hiroshima and Nagasaki victims exposed to a very high radiation dose.

The Committee has stated that the population of the contaminated regions of Belarus, Russia and Ukraine need not live in fear of serious health consequences from the Chernobyl accident. Lives have been disrupted by this accident, but from the radiological point of view, a generally positive prospect for the future health of most individuals, is foreseen.