Over The Horizon

Chernobyl: One Decade After

What effects has the 1986 Chernobyl nuclear accident had? The news media have specialised in wild and unsubstantiated reports of "thousands of cancer deaths", malformed animals, photographs of children suffering from leukemia, with the distinctive baldness of chemotherapy; and also of elderly people still living in the exclusion zone and apparently suffering from terminal illnesses. Another favourite image is of the "children of Chernobyl" enjoying holidays in other countries to relieve the symptoms of illness which, it is implied, afflicts them.

An international conference has reviewed the scientific, medical, environmental, social and political issues involved in assessing Chernobyl's impact. It is clear the effects of the accident have given rise to social and economic impacts which are of greater significance than radiation exposure.

The explosion and damage to the reactor resulted in 30 deaths that could be directly attributed to the accident. These occurred in plant operators and fire services and other rescue workers. Of the total personnel in attendance at the accident a total of 134 were diagnosed as having received high radiation doses and suffering from acute radiation sickness. Many also were suffering from skin burns from beta radiation. Of the 134, 28 died as a consequence of the high doses received in spite of undergoing intensive treatment and bone marrow transplantation; two died at the site from injuries caused by the explosion.

Of the heavily exposed survivors of the accident an additional 14 persons have died over the following decade but the deaths are not correlated with the doses received and only some may have been attributable to radiation exposure.

There has been a substantial increase in reported cases of childhood thyroid cancer in Belarus, Ukraine, and some parts of Russia, generally attributed to exposure to radioiodine during the early phases of the accident in 1986. Up to the end of 1995, a total of about 800 cases (including 400 in Belarus alone) have been reported in children who were under age 15 at the time of diagnosis. To date, three children have died from thyroid cancer. Over the next decades, there will most probably be an increase in the incidence of thyroid cancer among those who were children in 1986; the estimated number of cases is in the range of a few thousand but there is considerable uncertainty about this. The group at risk should be closely monitored throughout their lives, since treatment should be successful in most cases that are diagnosed early.

Apart from increases in thyroid cancer, there has been no statistically significant deviation in the incidence rates of other cancers that can be attributed to radiation exposure due to the accident. Based on predictive models, the total lifetime numbers of excess cancers will be greatest among the "liquidators" (emergency and recovery workers) and among the residents of "contaminated" territories of the order of 2,000-2,500 among each group (the size of the exposed groups is 200,000 liquidators who received mean doses of about 100mSv) and 3.7 million residents of "contaminated" areas (mean doses about 7 mSv). These increases would be difficult to detect epidemiologically against expected background cancers of 41,500 and 433,000 respectively, for the two groups. Smaller numbers of cancers could arise from evacuees from the 30 km zone and from residents of "strict control zones".

The number of deaths from leukemia predicted is of the order of 200 among the liquidators who worked at Chernobyl in 1986-87, and about 200 also for residents in the contaminated territories. Leukemia is an early indicator of radiation health impact, and the fact that it has not been observed to date provides reassurance that predictions are not greatly in error.

Many changes in health have been seen in the exposed population that are not the result of radiation exposure. There are significant health disorders and symptoms, such as anxiety, depression, and various psychosomatic disorders attributable to mental stress among the population in the region that appear to be out of all proportion to likelihood of radiation induced health effects. The psychological impact cannot be completely dissociated from that of the break-up of the Soviet Union.

The International Chernobyl Project study in 1990 found significant differences between "contaminated" and "clean" areas for symptoms attributable to stress, 45% (30% in "clean" areas) believed that they had an illness due to radiation exposure. The level of general health was low and almost all ailments were attributed by the population to radiation. These effects (confirmed by other studies) were compounded by poor public understanding of radiation; initial secrecy; subsequent lack of effective communication; and the collapse of the centralised political and economic systems. Distrust of "authorities" is widespread.

No obvious long-term impacts on populations or ecosystems have been seen. Effective countermeasures can be taken at specific sites to achieve significant reduction in the uptake of radiocaesium into food. In general, no food produced by the collective farm system exceeds established international radiation levels, although some foods produced by private farmers do.

After the accident there were media reports on severe birth defects in agricultural animals outside the 30 km zone in 1988/89. When this was studied further by a Ukrainian expert group, the frequency of these reported defects were similar in the highly contaminated and non-contaminated regions of Ukraine, which indicates that the occurrence of the birth defects was not likely to have been related to radiation. Confounding factors include the possible excess use of fertilisers.

Andrew McEwan, National Radiation Laboratory

A fuller report can be found in Radiation Protection News & Notes No. 35.