The number of deaths attributable to the Chernobyl accident has been of paramount interest to the general public, scientists, the mass media, and politicians. Claims have been made that tens or even hundreds of thousands of persons have died as a result of the accident. These claims are highly exaggerated. Confusion about the impact of Chernobyl on mortality has arisen owing to the fact that, in the years since 1986, thousands of emergency and recovery operation workers as well as people who lived in ‘contaminated’ territories have died of diverse natural causes that are not attributable to radiation. However, widespread expectations of ill health and a tendency to attribute all health problems to exposure to radiation have led local residents to assume that Chernobyl-related fatalities were much higher.
Acute Radiation Syndrome mortality
The number of deaths due to acute radiation syndrome (ARS) during the first year following the accident is well documented. According to UNSCEAR (2000), ARS was diagnosed in 134 emergency workers. In many cases the ARS was complicated by extensive beta radiation skin burns and sepsis. Among these workers, 28 persons died in 1986 due to ARS. Two more persons had died at Unit 4 from injuries unrelated to radiation, and one additional death was thought to have been due to a coronary thrombosis. Nineteen more have died in 1987–2004 of various causes; however their deaths are not necessarily — and in some cases are certainly not — directly attributable to radiation exposure. Among the general population exposed to the Chernobyl radioactive fallout, however, the radiation doses were relatively low, and ARS and associated fatalities did not occur.
It is impossible to assess reliably, with any precision, numbers of fatal cancers caused by radiation exposure due to Chernobyl accident. Further, radiation-induced cancers are at present indistinguishable from those due to other causes.
An international expert group has made projections to provide a rough estimate of the possible health impacts of the accident and to help plan the future allocation of public health resources. These predictions were based on the experience of other populations exposed to radiation that have been studied for many decades, such as the survivors of the atomic bombing in Hiroshima and Nagasaki. However, the applicability of risk estimates derived from other populations with different genetic, life-style and environmental backgrounds, as well as having been exposed to much higher radiation dose rates, is unclear. Moreover small differences in the assumptions about the risks from exposure to low level radiation doses can lead to large differences in the predictions of the increased cancer burden, and predictions should therefore be treated with great caution, especially when the additional doses above natural background radiation are small.
The international expert group predicts that among the 600 000 persons receiving more significant exposures (liquidators working in 1986–1987, evacuees, and residents of the most ‘contaminated’ areas), the possible increase in cancer mortality due to this radiation exposure might be up to a few per cent. This might eventually represent up to four thousand fatal cancers in addition to the approximately 100 000 fatal cancers to be expected due to all other causes in this population. Among the 5 million persons residing in other ‘contaminated’ areas, the doses are much lower and any projected increases are more speculative, but are expected to make a difference of much less than one per cent in cancer mortality.
Such increases would be very difficult to detect with available epidemiological tools, given the normal variation in cancer mortality rates. So far, epidemiological studies of residents of contaminated areas in Belarus, Russia and Ukraine have not provided clear and convincing evidence for a radiation-induced increase in general population mortality, and in particular, for fatalities caused by leukaemia, solid cancers (other than thyroid cancer), and non-cancer diseases.
However, among the more than 4000 thyroid cancer cases diagnosed in 1992–2002 in persons who were children or adolescents at the time of the accident, fifteen deaths related to the progression of the disease had been documented by 2002.
Some radiation-induced increases in fatal leukaemia, solid cancers and circulatory system diseases have been reported in Russian emergency and recovery operation workers. According to data from the Russian Registry, in 1991–1998, in the cohort of 61 000 Russian workers exposed to an average dose of 107 mSv about 5% of all fatalities that occurred may have been due to radiation exposure. These findings, however, should be considered as preliminary and need confirmation in better-designed studies with careful individual dose reconstruction.