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Ussr Nuclear Tests (Statement)

Volume 649: debated on Thursday 23 November 1961

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asked the Parliamentary Secretary for Science whether he will now issue a statement explaining in simple terms the nature and extent of the hazards expected as a result of fallout caused by recent Russian tests of nuclear devices.

The nature of a nuclear bomb explosion

When a nuclear bomb explodes in the atmosphere it creates an intense fireball which behaves rather like a vast hot air balloon and rises at high speed taking with it much of the debris of the bomb and possibly some earth from under the bomb, depending on the height and size of the burst. When the debris comes down, possibly adhering to particles of atmospheric dust, it is called fallout. Fallout contains many radioactive materials, and the two which have given rise to the greatest concern for the health -If the individual are Strontium 90 and Iodine 131. Both these materials are liable to become concentrated in certain parts of the human body, Strontium 90 in bone and Iodine 131 in the thyroid gland. Iodine 131 gives off radiation, but after a few weeks this becomes negligible. Strontium 90 continues to give off radiation for many years. In addition, the possible genetic effects of the radioactive materials in fallout, particularly Caesium 137 and Carbon 14, need to be considered.

The deposition of fallout

The amount of fallout from a particular bomb and where and when the fallout is deposited are governed by a number of factors. These include the kind of bomb, the height and location of the explosion, and the wind and weather conditions both at the time and for some time afterwards. A 50-megaton bomb does not necessarily produce fifty times more fall-out than a 1-megaton bomb. The height reached by the debris is important. Debris left in the lower atmosphere will be swept along by prevailing wind and weather and will fall to earth near the explosion in a few hours, and at greater distances in a matter of weeks. Debris which reaches very great heights, however, may take years to come down. Most of the debris from very large bombs is likely to reach great heights so that when it comes down most of the Iodine 131 will have disappeared. It is difficult to predict how much Iodine 131 will reach us from any bomb. This depends very much on the weather pattern, especially the direction of the wind during the few weeks when Iodine 131 is important. Because of its long life most of the Strontium 90 will, however, eventually come down, though over a period of years; the most rapid deposition from the present series of tests is not expected before the spring of next year.

Health and genetic risks

On reaching this country fallout shows first in samples of the air. It is, however, so much diluted that it is relatively harmless to breathe.

Fallout is deposited on crops, grass, soil and open water, and the rate of deposition is increased by rainfall. For practical purposes, it is the radioactivity which finds its way into fresh milk which is of the greatest importance. This is because for much of the year cows obtain their food by grazing large areas and, therefore, consume relatively large quantities of radioactive material. The risk is much reduced in late autumn and winter; even in those parts of the country where cattle remain on pastures, grass is a less important part of their diet, and other foods are much less contaminated by any fallout which has recently arrived.

Iodine 131

The possible risk from Iodine 131 in cows' milk is likely to be limited to children under one year old. This is because the thyroid uptake is greatest at the age of six months and because Iodine 131 is concentrated in their very small thyroid glands. As they grow older the size of the thyroid increases so that Iodine 131 is less highly concentrated. For this reason the risk to older children, even the one to five year olds, is very much less.

Strontium 90

Strontium 90 also gets into the body largely in milk. Once in the body it finds its way into the bones where it remains many years. This is why particular attention is paid to levels of Strontium 90 in milk and in the bones of young children who are growing rapidly.

Genetic effects

Radiation exposure may produce genetic effects, that is effects which may show up in succeeding generations. So far as these genetic effects are concerned, the most important components of fallout are Caesium 137 and Carbon 14. These may give rise to general irradiation of the body, including the reproductive cells, both from outside and from within after ingestion in food.

The effect of the Russian tests

During the current series of tests the Russians have so far exploded over 30 bombs in varying sizes up to about 50 megatons. From this series the total energy released is greater, but not much greater, than that of all tests in the years 1957 and 1958. Thus the yield of radioactive materials which produce fallout may well be comparable with the total yield from all tests in those years. The actual fallout may be less for many reasons such as the debris from very large weapons rising to such great heights.

Monitoring programme

The situation is being carefully watched. Fallout is analysed thoroughly and frequently. Samples of air and rainwater are analysed at an Atomic Energy Authority laboratory at Harwell and public drinking water supplies by the Government Chemist. Some of the air samples are collected by aircraft of the Royal Air Force.

Milk samples are collected at more than two hundred centres throughout the British Isles which handle over 40 per cent. of the country's total milk supply. This milk is analysed for radioactivity at the Agricultural Research Council's Laboratory near Wantage, which also monitors samples of other foodstuffs.

The forms of analysis described above together enable timely warning to be given of any likely risk to health. Reports are made frequently to the Government and the advice of the Medical and Agricultural Research Councils is always available.

Levels of risk

Leading scientific authorities advise the Government on the levels of Iodine 131 and Strontium 90 which the human body can carry without undue risk. These authorities do not believe that the recent bomb tests, including the 50-megaton bomb, will cause Strontium 90 in human bones to reach the level of risk. There is, therefore, no need to avoid milk because of Strontium 90. An equal assurance could not at first be given regarding Iodine 131 because the amount which reaches the earth's surface depends so much on the nature of the explosions and on the weather in the ensuing few weeks. The Government therefore prepared plans to make dried and evaporated milk available for all young children under one year of age should the need arise, and the monitoring of Iodine 131 in milk was intensified.

No special measure would be called for unless, in any large area of the country, the average concentration of Iodine 131 in milk were to reach 130 micro-microcuries per litre over a period of any year, of 260 micro-microcuries per litre over six months and so on. This means that if the level on any one day reached 130 micro-microcuries per litre it would have to stay at this level for a whole year before the milk created a risk to health, even to a child of one year or under. This level has been set so as to give a margin of safety both in the most vulnerable age group in the population (children under one year) and for people in places where the Iodine 131 is above average.

Throughout the country the quantity of Iodine 131 which has so far entered milk is less than one-sixth of that which would give rise to the level specified by the Medical Research Council, and it has not reached one-quarter in any major region. More Iodine 131 must be expected to arrive during the next few weeks; changes in the weather may even cause the levels for a short time to exceed the average for the past weeks. However there is now no likelihood that the bomb tests which have so far occurred will cause the quantity of Iodine 131 in milk produced in any part of the country to reach that which could make it unsafe even for very young children.

It is not yet possible to predict the total additional dose of genetically significant radiation to which the population will be subjected by the current series of Russian tests, but from what we know of those which have already taken place this dose might be comparable to that incurred from the test explosions which had taken place up to the end of 1958. In 1960 the M.R.C. assessed this dose for the current generation of thirty years as being just over one per cent. of that received from natural background radiation, and concluded that the genetic effects of such a dose would be likely to be very few by comparison with those spontaneously arising in the population from other causes. The genetic effects of natural background radiation are themselves believed to be very few.

The present situation

The Government are satisfied that no special measures are necessary to protect the health of any section of the population from the fallout from nuclear weapons which have so far been exploded. Milk throughout the country is safe for children of all ages. The Government will, however, maintain in readiness their plans to give the public ample warning if danger threatens in the future and to provide safe milk for babies should the need ever arise.