Health Studies of Radiological Impact

Health Studies of Radiological Impact

Studies of the health effects of the Chernobyl accident have been ongoing since the event. These studies confirm the scientific basis for our regulation and use of radiation and radioactive materials. These studies also suggest that very low radiation exposures do not appear to be harmful.

UNSCEAR 2011 Report

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) issued in 2011 the most recent and most authoritative comprehensive review of radiation-related health effects of the Chernobyl accident. Decades of research on Chernobyl health effects are also summarized by the UNSCEAR secretariat. The General Conclusions of the report:

“The observed health effects currently attributable to radiation exposure [from the Chernobyl accident] are as follows:

The UNSCEAR report goes on to explain: “From this annex based on 20 years of studies and from the previous UNSCEAR reports, it can be concluded that although those exposed to radioiodine as children or adolescents and the emergency and recovery operation workers who received high doses are at increased risk of radiation-induced effects, the vast majority of the population [of the regions most affected by the Chernobyl accident] need not live in fear of serious health consequences from the Chernobyl accident. Most of the workers and members of the public were exposed to low level radiation comparable to or, at most, a few times higher than the annual natural background levels, and exposures will continue to decrease as the deposited radionuclides decay or are further dispersed in the environment [the radiation dose a patient typically receives from one whole body computer tomography (CT) scan is approximately equivalent to the total dose accumulated in 20 years by residents outside the "strictly controlled zones" of the Chernobyl affected regions following the Chernobyl accident]. Although it is now one decade after the minimum latent period for solid cancers, no increases in cancer incidence (other than of thyroid cancer) have been observed to date that can be attributed to irradiation from the accident.”

The UNSCEAR secretariat summarizes as follows: “Apart from this increase [in thyroid cancers detected and treated among the affected populations of the region], there is no evidence of a major public health impact attributable to radiation exposure two decades after the accident. There is no scientific evidence of increases in overall cancer incidence or mortality rates or in rates of non-malignant disorders that could be related to radiation exposure.”

The UNSCEAR report also notes: “There is no likelihood of a radiation-related decrease in male or female fertility in the general population, given the relatively low dose levels, which are also unlikely to have any effect on the number of stillbirths, adverse pregnancy outcomes, delivery complications, or the overall health of children. No discernable increase in hereditary effects is expected.”

Theoretical Projections

The final report from the Chernobyl Forum in 2005, a United Nations multi-agency effort to arrive at consensus on scientific findings regarding the Chernobyl accident, addressed theoretical predictions of cancer mortality from the Chernobyl accident as follows:

“It is impossible to assess reliably, with any precision, numbers of fatal cancers caused by radiation exposure due to the Chernobyl accident. Small differences in the assumptions concerning radiation risks can lead to large differences in the predicted health consequences, which are therefore highly uncertain. An international expert group has made projections to provide a rough estimate of the possible health impacts of the accident. The projections indicate that, among the most exposed populations (liquidators, evacuees and residents of the so-called “strict control zones”), total cancer mortality might increase by up to a few per cent owing to Chernobyl related radiation exposure. Such an increase could mean eventually up to several thousand fatal cancers. An increase of this magnitude would be very difficult to detect.” Also see World Health Organization fact sheet for an overview of some similar estimates.

Estimates such as these are based largely on a “Linear No-Threshold Hypothesis” – the assumption that radiation risk is proportional to radiation dose at all levels, including very low levels. This hypothesis serves as the cornerstone for radiation exposure protection limits worldwide, since it predicts higher risks than most other models, and thus leads to relatively cautious and conservative radiation exposure guidelines.

However, it is the position of the American Nuclear Society, and many other professional scientific societies and organizations, that there is insufficient scientific evidence to support the use of the Linear No-Threshold Hypothesis in the projection of health effects of chronic low-level radiation. The intervening scientific evidence concerning Chernobyl radiation exposure to date appears to support this position. Many other scientific studies also lend support to rejecting the Linear No-Threshold Hypothesis. This evidence includes studies of populations living in areas with naturally much higher background radiation rates that show no adverse health effects when compared to lower-dose populations, and animal studies which suggest harmful effects when natural background radiation is suppressed. See ANS Technical Brief for more details.

UNSCEAR in its authoritative 2011 report notes: “Any radiation risk projections in the low dose area should be considered as extremely uncertain, especially when the projection of numbers of cancer deaths is based on trivial individual exposures to large populations experienced over many years.” Further scientific progress may someday provide a scientific basis for evaluating the radiation health consequences of the Chernobyl accident among residents of areas with low radiation levels.

The most recent international conference attempting to reach international scientific consensus concerning health effects from the Chernobyl accident was held in Kiev in April 2011. The conference was not successful in reaching consensus, and no formal conclusions were issued, due to differences in scientific judgment.


The Chernobyl accident was a human tragedy with significant public health effects. However, these health effects were largely non-radiological. Overall, the most tragic and important health effect has been psychological – a sense of fatalism caused by bad information. As stated by the Chernobyl Forum final report: “misconceptions and myths about the threat of radiation persist, promoting a paralyzing fatalism among residents.”

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