Possible Health Effects of Low Level Exposures to Ionising Radiation

The United Nations Scientific Committee on the Effects of Ionising Radiations (UNSCEAR), in its 1993 report to the General Assembly states that ‘ The Committee’s interest in the biological effects of radiation is mainly concentrated on the effects of low doses’(1). This highlights the fact that today probably no other topic in radiation sciences has been drawing so much attention as the likely health effects of exposure to ionising radiation at low levels. This is so for several valid reasons. In occupations dealing with radioactivity and ionising radiations, while one can bring down the radiation fields and exposures to very low levels by proper practices and control, they can not be totally eliminated. This will be over and above the background radiation which is ubiquitous with wide spatial variation depending on the geochemical and other features of the area. Further, the health effects associated with these low level exposures are, if at all, likely to be a small fraction of natural incidence of such maladies. An obvious question would be, why not extrapolate backwards from the high exposure risk data which is more or less well established. This is not always possible since such extrapolations are wrought with severe uncertainties due to dose-rate effect, repair mechanism, adaptive response etc. Thus the exact determination of the health risk at low exposures continues to be a challenging task. Various aspects of this problem are presented in the paper.