For the last two decades, attention has been focused on investigating the association between exposure caused by radionuclides released in the Chernobyl accident and late effects, in particular thyroid cancer in children. Doses to the thyroid received in the first few months after the accident were particularly high in those who were children and adolescents at the time in Belarus, Ukraine and the most affected Russian regions and drank milk with high levels of radioactive iodine. By 2005, more than 6,000 thyroid cancer cases had been diagnosed in this group, and it is most likely that a large fraction of these thyroid cancers is attributable to radioiodine intake. It is expected that the increase in thyroid cancer incidence due to the Chernobyl accident will continue for many more years, although the long-term increase is difficult to quantify precisely.
Among Russian recovery operation workers with higher doses there is emerging evidence of some increase in the incidence of leukaemia. However, based on other studies, the annual incidence of radiation-induced leukaemia would be expected to fall within a few decades after exposure. In addition, recent studies of the recovery operation workers indicate that opacities of the eye lens might be caused by relatively low radiation doses.
Among the 106 patients surviving radiation sickness, complete normalization of health took several years. Many of those patients developed clinically significant radiation-induced cataracts in the first few years after the accident. Over the period 1987-2006, 19 survivors died for various reasons; however, some of these deaths were due to causes not associated with radiation exposure.
Apart from the dramatic increase in thyroid cancer incidence among those exposed at a young age, and some indication of an increased leukaemia and cataract incidence among the workers, there is no clearly demonstrated increase in the incidence of solid cancers or leukaemia due to radiation in the exposed populations. Neither is there any proof of other non-malignant disorders that are related to ionizing radiation. However, there were widespread psychological reactions to the accident, which were due to fear of the radiation, not to the actual radiation doses.
There is a tendency to attribute increases in the rates of all cancers over time to the Chernobyl accident, but it should be noted that increases were also observed before the accident in the affected areas. Moreover, a general increase in mortality has been reported in recent decades in most areas of the former Soviet Union, and this must be taken into account when interpreting the results of the accident-related studies.
The present understanding of the late effects of protracted exposure to ionizing radiation is limited, since the dose-response assessments rely heavily on studies of exposure to high doses and animal experiments. Studies of the Chernobyl accident exposure might shed light on the late effects of protracted exposure, but given the low doses received by the majority of exposed individuals, any increase in cancer incidence or mortality will be difficult to detect in epidemiological studies.
The accident at the Chernobyl nuclear power plant in 1986 was a tragic event for its victims, and those most affected suffered major hardship. Some of the people who dealt with the emergency lost their lives. Although those exposed as children and the emergency and recovery workers are at increased risk of radiation-induced effects, the vast majority of the population need not live in fear of serious health consequences due to the radiation from the Chernobyl accident. For the most part, they were exposed to radiation levels comparable to or a few times higher than annual levels of natural background, and future exposures continue to slowly diminish as the radionuclides decay. Lives have been seriously disrupted by the Chernobyl accident, but from the radiological point of view, generally positive prospects for the future health of most individuals should prevail.
