UNSCEAR 2008: ANNEX D

UNSCEAR 2008
ANNEX D: HEALTH EFFECTS DUE TO RADIATION FROM THE CHERNOBYL ACCIDENT

VI. LATE HEALTH EFFECTS

B. Theoretical projections

"In order to guide decision-making on public health resource management, and given that there is a latent period between exposure and the appearance of any increased incidence in stochastic effects, various groups have attempted to predict the health impact on populations exposed to radiation by applying radiation risk models to the estimates of population dose."

"These models are based partially on epidemiological data and partially on an understanding of biological processes."

"The major source of data for modelling increased incidence of stochastic effects due to radiation exposure remains the detailed study of long-term health effects among the survivors of the atomic bombings in Japan."

"However, applying those data to the populations exposed as a result of the Chernobyl accident requires various assumptions to be made. These include how to transfer the risk profile between populations with different demography, ethnic origins and background disease rates, and how to transfer the results from a population acutely exposed to high doses and dose rates to one that essentially received increased protracted radiation doses at levels comparable to natural background over several years and for which no increased incidence has actually been observed."

1. Review of published projections

"Subsequently, a large number of radiation risk projections have been made by various groups regarding the health consequences of the Chernobyl accident."

"They predicted a potential increase in cancer mortality due to radiation-induced cancer in the range from 3% for the most affected parts of the former Soviet Union to 0.01% for the rest of Europe."

"All the projections were based on estimates of population doses made at the time; they usually assumed thelinear non- threshold (LNT) model for the dependence of increased cancer incidence or mortality following an increase in dose, and used nominal parameters derived from reports of UNSCEAR and of the ICRP and/or from some national publications, e.g."

2. Scientific limitations

"It is important to understand the considerable statistical uncertainty associated with any projection based on modelling, which lends itself rather to estimations that are within an order of magnitude or even more."

"The currently available epidemiological data do not provide any basis for assuming radiogenic morbidity and mortality with reasonable certainty in cohorts of the residents of the areas of the three republics and other countries in Europe who received total average doses of below 30 mSv over 20 years. Any increases would be below the limit of detection. At the same time, it cannot be ruled out that adequate data on the effects of low-dose human exposure will be obtained as further progress is made in understanding the radiobiology of man and other mammals, and using this knowledge to analyse the epide- miological data."

3. UNSCEAR statement

"The Committee has decided not to use models to project absolute numbers of effects in populations exposed to low radiation doses from the Chernobyl accident, because of unacceptable uncertainties in the predictions."