Update on the effects of atomic radiation

SCIENCE & TECHNOLOGY Friday, October 3, 2008, Chandigarh, India

Update on the effects of atomic radiation
K.S. Parthasarathy
The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in its much awaited latest review published on August 5, 2008, concluded that radiation is not riskier than what was stated in earlier reports.
Regulatory agencies can breathe easy as they need not alter the dose limits they prescribed to radiation workers and public
The report (Volume I) consists of the main text and two of the five annexes: “Epidemiological studies of radiation and cancer” and “Epidemiological evaluation of cardiovascular disease and other non-cancer diseases following radiation exposure”. UNSCEAR may publish the remaining annexes before the end of 2008.
UNSCEAR’s assessment of the risk of radiation depended heavily on the study of A-bomb survivors. The new analysis using the radiation doses recently re-estimated by the Radiation Effects Research Foundation, showed that the cancer risk factors may be lower.
The committee considered cancer incidence and mortality due to cancers in 20 organs and tissues among A-bomb survivors; these were eight more than those in the earlier study. Nearly half of the survivors are still alive. Those exposed in childhood are now reaching the age at which larger numbers of cancers would be expected to arise spontaneously. There is compelling need to continue the study of A-bomb survivors for their entire life span.
The UNSCEAR observed that the cancer risks obtained in new findings from the study of nuclear workers in 15 countries, studies of persons living near Techa river in the Russian Federation who were exposed due to radioactive discharges from Mayak plant and a study of persons exposed to fallout from the nuclear test site in Kazakhstan are generally more than those obtained from the study of A-bomb survivors. However, there are concerns about bias in these studies.
The committee found significant associations between radiation exposure and cardiovascular diseases and other non-cancer diseases. Such associations can occur at doses below those hitherto considered as thresholds for other effects.
Specialists consider that the harmful effects of irradiation originate in the irradiated cells. But there is evidence that non-irradiated cells may show effects such as “genomic instability” (cells surviving irradiation may produce daughter cells that over generations show changes though daughter cells themselves were not irradiated), “bystander effects” (the ability of exposed cells to convey damage to neighbouring cells not directly irradiated) and other effects.
The committee concluded that the available data provide some disease associations but not for causation. It recommended future research designing studies that emphasize reproducibility, low dose responses and causal associations with health effects.
High doses of radiation may suppress immunity mainly due to cell destruction. Low dose irradiation may suppress the immune system or stimulate it. The immune system may remove aberrant cells which have potential to form tumours. A-bomb survivors show perturbations to stable immune systems. In the final document, the Committee proposed methods to estimate risk from radon, a well established carcinogen, present in dwellings.
To determine radiation risk at typical doses to workers, we need low dose studies. But most low dose studies have inadequate statistical power.
The UNSCEAR completed the report in 2005. The Committee acknowledged that resource crunch was the cause for the delay in publishing the report which is now called UNSCEAR 2006. According to a UN specialist, financial restrictions and-sometimes benign neglect- has slowed down the Committee’s work.
UNSCEAR reports provide the scientific basis to arrive at dose limits (safe levels of radiation to radiation workers and members of the public).
Set up in 1956, the UNSCEAR published 17 documents. The first two reports UNSCEAR 1958 and 1962 paved the way for prohibition of atmospheric weapon testing in 1963.
India has been a member of the UNSCEAR from its very inception. Traditionally, the Chairman of UNSCEAR is from a non-nuclear weapons’ state.
V.R. Khanolkar, a pioneer in pathology from India was Vice-Chairman in years 1958-1959; A.Gopal Ayengar a geneticist and the first research scientist Homi Bhabha recruited into the Department of Atomic Energy was Vice-Chairman in 1964-1965 and Chairman in 1966-1967.
Let us hope that UNSCEAR will continue to function effectively in spite of various limitations.
The writer is former Secretary, Atomic Energy Regulatory Board