There is a gap between accepted facts and popular perceptions about the risks of radiation. Here David Sowby and Frank Turvey try to put things in perspective.
Over the past 70 years, a great deal of international effort has gone into the study and understanding of the health effects of radiation. Indeed, it is probable that more is known about the effects of radiation than of other environmental hazards.
The results of current knowledge were summarised most recently in 2000 and 2001 by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). UNSCEAR's latest estimates of the main sources of our exposure to ionising radiation are shown below as annual doses counted in microsieverts, a measure of exposure to radiation:
Natural background ............ 2,400
Diagnostic examinations ....... 400
Nuclear weapons testing ............ 5
Chernobyl accident .................... 2
Nuclear power ......................... 0.2
These figures are for comparison only. They do not indicate whether this radiation could make you ill as the health effects if any caused by low exposures are difficult if not impossible to measure.
It will be seen that by far the largest average doses come from natural background and diagnostic medical procedures. Natural background radiation comes from cosmic rays, radiation from the Earth's crust, natural radioactivity in our bodies and inhalation of radon gas.
We are inescapably surrounded by low level radiation from our natural background, and it is impossible to know whether our health would be better, worse or no different without it. Humans have evolved to live with this radiation.
Much is known about the harmful effects of high doses of radiation, but assumptions have to be made about the effects at low doses. This leads to the presumption that effects increase in proportion to increasing dose, and that there is no safe level of radiation.
This, while hotly debated by the scientific community, is the basis for radiation protection. Accordingly, cancer, in the long term, is the principle effect at low doses. Hereditary illnesses are also theoretically possible, but have never been observed in a human population.
Many studies have been made of the health effects of the Chernobyl accident. After assembling all the available information, UNSCEAR in its 2000 report confirmed the deaths from radiation exposure of 30 rescue workers who received very high doses.
Other workers who had received significant exposures are still being followed up to determine any radiation-related deterioration in health, with none being found to date.
In addition, the incidence of some 2,000 treatable thyroid cancers in individuals exposed to radioactive fallout during childhood in severely contaminated areas is attributed mostly to the accident. This is greater than might be expected, based on previous knowledge of exposure and incidence.
This unexpected result may be aggravated by a deficiency of stable iodine in the normal diet of those affected. Additional thyroid cancers are now expected to occur. Apart from this increase in thyroid cancer, which has unfortunately resulted in some deaths, no increases in the incidence of other types of cancer have been observed that could be attributed to radiation exposure.
There were psychological reactions due to fear of radiation, trauma caused by mass evacuations, and the general social and economic disruptions which ensued, but none was caused directly by the actual radiation exposure. So far, there is no evidence that radiation exposure produced congenital non-malignant disorders in "Chernobyl children", of the type seen so often on television and elsewhere.
There is a tendency to attribute increases in the rate of all cancers and other disorders in the Chernobyl region to the reactor accident in 1986. However, it should be pointed out that increases were observed before the accident; furthermore, increases in cancer mortality have been reported recently in most parts of the former Soviet Union.
Improved diagnostic facilities may have led to more effective early detection. At any rate, it is extremely unhelpful and even misleading to hint or to suggest that gross disorders of the type shown on many television programmes are directly attributable to radiation exposures received as a consequence of the Chernobyl accident. To do so can only delay the detection of the real causes and hinder the use of preventative measures.
For many years it has been claimed - and seems to be widely accepted - that radioactive contamination from the Windscale nuclear reactor fire in October 1957 affected Ireland, and was the cause of a cluster of Down's syndrome babies born to former students of a Dundalk secondary school for girls. There is no scientific basis for this claim whatsoever.
The radioactive plume from Windscale moved southward from the stricken reactor over the middle of England and its footprint may be seen there to this very day. No similar evidence can be found on this side of the Irish Sea.
APART from this evidence of the plume going in the opposite direction, there has been no evidence of a connection between exposure to radiation and Down's syndrome among the children and grandchildren of the survivors of the Hiroshima and Nagasaki bombing.
A recent study by G. Dean et al ( research done for the Health Research Board published in Occupational Environmental Medicine 2000) concluded that previously proposed possible explanations - namely an influenza epidemic or contamination from the Windscale nuclear reactor fire, both of which occurred in October 1957 - can be effectively eliminated because they cannot account for the cluster of Down's syndrome. In any case, their action would not be so localised.
Yet another claim often made is that the cancer incidence in Co Louth is 14 per cent above the average, and that this is because of the county's proximity to Sellafield. This figure may be correct, but what is not explained is that the cause of the cancers involved (lung, oesophagus and bladder) is believed to be smoking, and not radiation.
The chronic leakage of radioactive substances into the Irish Sea is certainly undesirable, but we should remember that daily consumption of fish from the Irish Sea still only results in an annual dose of less than two units, which is a fraction of the extra dose we receive on a one-hour flight to, say, London. This has been explained frequently by the RPII but seems not to sink in.
The real worry about Sellafield is the possibility of an accident or a terrorist attack. In this event, it is most unlikely that there would be immediate fatalities, but there could be delayed effects, such as induced cancers, and there is little doubt that our economy would suffer because of the hurt to the tourist, agriculture and fishing industries.
In our view, it is very important that radiation should not be blamed for our woes and diseases when no other cause is obvious. To do so delays the identification of the real cause and its elimination. It also causes needless distress to many patients undergoing medical diagnosis or therapy involving radiation.
David Sowby is former scientific secretary of the International Commission on Radiological Protection. Frank Turvey is former assistant chief executive and current board member of the Radiological Protection Institute of Ireland. The views expressed are his own.