ON the weekend beginning May 3rd, 1986 the unthinkable happened. Radioactive fall out from an accident at a nuclear power plant was deposited on Ireland. Reactor Number 4 at Chernobyl, near Kiev, had exploded on April 26th, releasing a large amount of radioactivity to the atmosphere.
The accident caused, and is still causing, serious problems (health, social and economic) in areas near the reactor.
Outside the former USSR, the problems were much less severe, although some radioactive fallout was recorded over most parts of the northern hemisphere. The fall out caused widespread public alarm throughout Europe, but happily the health effects there will be slight. Food exporting countries were faced with serious disruptions in the flow of exports to non European countries. No government in Europe was properly prepared to deal with the situation that presented itself, and important lessons have been learned.
A large fraction of the radioactivity in the reactor core was released to the atmosphere. Such released activity (cloud) is moved about by the prevailing winds and gradually falls back to earth (fall out). The radioactivity is washed down in abundance when the radioactive cloud encounters precipitation - rain or snow. Despite predictions that the fall out would never reach Ireland, it did, and for a few days beginning on May 3rd the radioactive cloud was over Ireland. Fortunately, the cloud was somewhat dispersed, and much of the activity had decayed by the time it reached our shores. Unfortunately it rained for much of the time the loud was overhead.
The main radioactive elements in the fall out were Iodine-131 (I-131) and Caesium 137 and -134 (Cs-137, Cs-134). The immediate concern was I-131 (half-life eight days). The long-term risk is Cs-137 (half-life 30 years). The half-life of a radioactive element is the time it takes for half of the activity to disappear. In eight days, half of the I-131 that arrived on the weekend of May 3rd disappeared. Eight days later half again vanished (one quarter of original remained), etc. By 10 half-lives (80 days), only 0.1 per cent of the original is left. On the other hand, 30 years must elapse before the original activity of Cs137 is halved.
Fall-out initially contaminates foliage surfaces and is then washed into the soil. Radioactivity from grass quickly enters the milk of grazing cows, and I-131 in milk was the first concern, particularly with reference to nursing babies. A reference level of 500 Becquerels (Bq) per litre (1) for I-131 in milk was set by the EU (radioactivity is measured in units called Bq). In other words, if levels reached this threshold it was recommended that governments would introduce controls to restrict public consumption. The highest level I recall being recorded in Ireland was 440 Bq/l, and the highest level we measured in Cork was 250 Bq/l of I-131 in milk.
Cs-137 is a much longer-term risk. Prior to the Chernobyl experience it was generally thought that when Cs entered the soil, it would become immobilised and would not re-enter growing plants to any great extent.
We now know that the behaviour of Cs depends on soil type. Poor, peaty soils allow the radioactivity back into plants. This was, and is, a problem for sheep grazing poor pasture on high hills in areas that received higher than average fall-out. The situation is controlled in Ireland by taking sheep off the hills and "finishing" them for several weeks by grazing lowland pasture, where little or no Cs-137 re-enters the grass.
During these weeks the sheep excrete the Cs ingested on the hills, and measurements assure us that our mutton is essentially free (-1 0Bq/kg) of artificial radioactivity. The situation is carefully monitored by the Radiological Protection Institute of Ireland, and by the Department of Agriculture.
Radiation dose is measured in terms of a unit called the Sievert (Sv). One thousandth of a Sv is a millisievert (mSv). In Ireland we each receive an annual dose of about 4.1mSv from natural radiation (including cosmic radiation, radiation from rocks and radon). Radiation from Chernobyl contributed an extra -0.1-0.2 mSv to each of us in Ireland during the first year after its arrival. Annual doses in subsequent years have been and will be very much lower.
The possible effects from lower doses of radiation, accumulated over a protracted time period, are delayed cancer or genetic defects. With cancer there is a latent period of between several years and 40 years before it is clinically manifested. By definition, genetic effects will not be seen until the next, or succeeding generations.
The extra radiation received in Ireland from Chernobyl may result in 10-20 extra deaths from cancer over the next 70 years. These will be undetectable in the general background of 450,000 cancer deaths over that period attributable to all causes.
However, a dramatic report in 1988 claimed that Chernobyl radiation was responsible for 600 extra deaths in Ireland during the year that followed the arrival of the fall out. The mechanism proposed was that the low level radiation caused further damage to the immune systems of people (mainly elderly) whose immune systems were already weakened.
This claim attracted great media publicity. In collaboration with a statistician, Michael Crowley of UCC, I looked into this report. We showed that no extra deaths were detected in Ireland. The original claim was based (inadvertently) on a statistical error.
We published our findings in The Irish Journal of Medical Science, Vol. 158, pages 114-116, 1989. We contacted the media with the good news, but we failed to excite any significant interest.
I have seen estimates that over the next 70 years there will be an extra 1,000 cancer deaths in Europe (outside the former USSR), and an extra 5,000 deaths in the former USSR, resulting from Chernobyl radiation.
The effects are extremely small in Ireland, but not in the former USSR. Thirty one people died in the course of the accident and 137 people were treated for acute radiation syndrome (ACR). ACR follows a large dose of whole body radiation (1Sv) received over a short period (hours/days). It is characterised by early effects - radiation sickness (vomiting, diarrhoea and other symptoms) and possibly death. Depending on the dose, death may follow within weeks or days. For example if you receive 10Sv in a few hours you will almost certainly die from intestinal damage within 12 weeks.
The thyroid gland is particularly at risk from 1-131. Iodine concentrates in the thyroid. There has been a significant increase in thyroid cancer, particularly in children, in heavily contaminated regions near Chernobyl. The thyroid cancers in the children are particularly aggressive, have a shorter latent period than expected and are still increasing.
Apart from the thyroid cancers, no increase in leukaemia, congenital abnormalities, adverse pregnancy outcomes or any other radiation induced disease has been noted in the former Soviet Union or elsewhere in Europe.
Unfortunately, extensive psychological effects are apparent in the affected regions of the former USSR, manifested as anxiety, distress, stress, apathy and despair. These effects are not apparent elsewhere in Europe.
The public never had much confidence in the nuclear industry, and confidence collapsed entirely after the Chernobyl accident. It remains to be seen if the industry will ever recover.
The transboundary behaviour of the released radiation was demonstrated in the clearest possible manner. All countries in Europe were caught unawares and deficiencies in emergency plans were cruelly exposed. Possibly the only good thing to emerge from Chernobyl is that the experience has spurred all European countries to establish better plans to deal with radiation emergencies. Ireland now has a comprehensive emergency plan. It should be kept in a healthy state of preparedness, but let us hope we never have to use it for real.