RADIATION, FOOD AND HEALTH
Mr. J. W. LUCAS, B.Sc., F.R.I.C.

I would like to insist at the very start that it is very important to be able to distinguish between what is known to be scientific fact, and what is very largely speculation. There remain considerable gaps in our knowledge of the effects of radiation. This is especially so in cases of very small doses of radiation delivered at a slow rate to the human body.

The position has been very ably reviewed in a recent technical report of the World Health Organisation, Radiation Hazards in Perspective, where it is stated that in Germany there are each year 3,000-4,000 new cases of silicosis in miners. Members of the Congress need hardly be reminded of the association of lung cancer with habits of smoking, of the shocking fatalities on the roads, and the appalling destruction of wildlife in the U.S, through the indiscriminate use of chemicl pesticides. Dr.LeRoy, Professor of Medicine at Chicago University and a participant in the Japanese investigations after the explosions of the two atomic bombs, is puzzled about the "vast" apprehension that we find about radiation . . . about the hazards which are magnified out of all proportion to the facts which are available."

I would remind you that Madame Curie, one of the great pioneers in radioactivity, and the discoverer of radium and polonium, spent a very long working life-time with these hazardous materials, and still managed to attain a goodly age of 67, although there is some evidence that she may eventually have succumbed from radiation injuries.

Radioactivity and radiations have been present in man's environment throughout the whole of his existence on the earth. It is probable that they may even have played some part in his evolution. It is, however, only within the last sixty years that their existence has been discovered, as none of the bodily senses have any direct and immediate response to them. It is probable that some of the unnatural apprehension derives from this very fact, although it is of interest that some recent investigations in Russia and Germany seem to suggest that there may well be some subtle effects on the nervous system of animals, but Man himself is not immediately conscious of undergoing exposure to radiatton.

It is possible that some form of radiation is the basis of phenomena such as medical radiesthesia and of dowsing, but if this is correct it is a much more subtle type of radiation than we are concerned with in this lecture. Radioactivity may, indeed, be far more widespread than is generally accepted, but at the present moment it has only been identified in a relatively small number of natural elements, and principally among the heaviest elements known to Man, such as uranium, thorium, and radium. The solar universe may be taken as a model of the atom but on a vastly larger scale. The chemical transformations of matter are associated with the outlying shells of electrons, but radioactive phenomena involve the nuclei of atoms which are in an excited and energetic state. This surplus energy of nuclei is emitted in the form of penetrating radiation in a purely random manner when a large number of atoms are involved. Radiation is therefore basically a form of energy released by matter on an atomic scale. The quantity of energy emitted in spontaneous radioactivity is on a relatively modest scale; one gram of radium distributed throughout the body would only be capable of raising the body temperature by about one five-thousandth of a degree Centigrade. The quantity of energy deposited by radia-tion is not a good indication of its capability for damage, as the energy is deposited in matter in a highly specific manner involving the outer electrons of atoms. These interactions lead to chemical changes and if the substances are the biochemicals of living tissue these changes may trigger off biological effects after a "latent period ".

In the passage of radiation through matter the deposition of energy and the specific interactions may occur for some distance along the track of the radiation. All radiations have the ability to penetrate through matter and the effects may be produced at some distance from the source of the radiation. Different radiations vary in their ability to penetrate, but all types are capable of travelling some distance in air, and of passing through at least several layers of tissue cells. I would therefore like you to appreciate at the outset that the radiations emitted by radioactive substances can have an effect when the substances are outside the body (external exposure) or inside the body (internal exposure). Generally the latter mode of exposure is the more serious and requires the more careful attention. it arises when foodstuffs become contaminated by radioactive substances; the radiations will not have any harmful effect on the quality of the food, but the food will serve as a source of the substances in human diet. The radiations emitted within the body may then lead to some injurious effects.

An important source of a range of radioactive substances is the process of nuclear fission, which occurs in a controlled manner in an atomic reactor or in an uncontrolled manner in an atomic weapon.

Most of the fission products are radioactive forms of elements which occur naturally in the earth's crust. A radioactive species shares the same chemical properties as its natural form, but is otherwise distinguished by the quality of radiation which it emits and the rate at which it undergoes disintegration. The latter is usually expressed by the half-life, which is the time in which the initial amount and activity of the radioactive substance has decayed to exactly one half. The half-life of iodine-131 is about 8 days so that a quantity of this substance in the soil or in a plant will decrease to one-half in 8 days, to one-quarter in 16 days, one-eighth in 24 days, etc. The half-lives of the fission products vary considerably, the majority being very short with a few extending to about 30 years, e.g., strontium-90 and caesium 137. Carbon 14 has a half-life of about 5,000 years and is therefore very persistent in the biosphere. Iodine-131 and caesium-137 emit very penetrating radiation and may give rise to both external and internal radiation hazards, whereas carbon-14 and strontium-90 emit less penetrating radiations and are primarily an internal risk.

Nuclear fission occurs naturally on an extremely small scale especially in mineral sources of the element uranium, but can be disregarded as a source of natural radiation exposure of Man. It has however been shown that Man is exposed continuously to other sources of radiation, a typical exposure being about 100 units every year at the earth's surface. This is the annual dose of radiation received by internal organs of the body such as the bone-marrow and the gonads. Three principal sources contribute to this dose- (1) a heavenly contribution in the form of cosmic rays, (2) an earthly contribution from natural radio-elements in all rocks and soils, and (3) a personal contribution from radio-elements in the body. The first two are external sources and are responsible for about 75% of the total annual dose. Cosmic radiation originates outer space and is distinguished by its very high energy and great penetration through all forms of matter, the dose increasing with the height above the earth's surface-three-fold at about 30 kilometres. Intense levels of solar radiation also occur in space during periods of solar activity. Cosmic rays in view of their very high energy also have the ability to transmute atoms in the earth's atmosphere, an important example being the continuous formation of carbon-14 in small amounts. This radioactive form of carbon is therefore present to a small extent in atmospheric carbon dioxide, and is incorporated into plants during photosynthesis. The environmental dose is due to the presence of natural radio-elements in the rocks and in all soils, and hence in most materials employed in building. The radiations are moderately penetrating, so that Man is continually exposed to them both in and out of doors.

The third source of natural exposure, representing the remaining 25%, is entirely internal and is due to the entry of radio-carbon, and the other radio-elements of the soil into foodstuffs and hence into the human body. The carbon enters into the composition of all the bodily tissues, the radio-potassium, which is responsible for most of the dose, enters the body fluids and tissue cells and radium is retained in the mineral structure of the bone.

The total dose of 100 units a year represents an average value which is typical of extensive parts of the U.K. There are some regional variations in the value, a notable increase occurring in regions where there is a great deal of granite in the underlying rocks and where it is also employed for building purposes. Granite has a rather higher radium content. I would also like you to consider that there are a number of regions of the earth, where the average annual dose is more than ten times the figure I have quoted as typical. These comparatively small regions appear to be perfectly capable of sustaining life without any obvious harmful effects, although they are under close observation by the W.H.O. in order to ascertain if there are any detectable effects at all. Examples are to be found in the Kerala peninsula of Travanecre, India; and parts of the coast-line of Brazil, where small communities are living on beds of moderately radioactive sands. Other areas include a small island in Lake Chilwa, Nyasalaland and an island of a few thousand Polynesians about 1,500 miles from Auckland, New Zealand. At La Paz in Bolivia there are 300,000 people living at a height of about 30 km. and receiving about 3 times the average cosmic ray dose. In view of the perfectly natural and unavoidable exposure of man to radiation it is perhaps not at all unreasonable to suggest, "that traces, as it were, of ionising radiation subserve some useful or even necessary function, just as traces of some chemical elements are necessary as micro~nutrients" (Ritchie Calder, "Living with the Atom.")

The whole population of the world is subject to this background radiation; more and more people are now receiving extra doses from artificial man-made sources. Most of the additional exposure comes from the medical applications of X-rays and of radiation from radio~element5 used in diagnosis and in treatment. The results of 2 million exposures carried out in 1957 in the U.K. have been analysed, and it is concluded that the average annual population exposure to the gonads had been increased by 19.3% of the annual background dose. 14.3% is due to diagnostic procedures and the remainder to treatment.

A small additional exposure comes from the development of the nuclear power industry, supplemented to a very minor extent by other activities in the industrial field; the maximum allowable occupational exposure for the whole body, which includes the critical organs such as the bone marrow and the gonads~ has been set at 5,000 units a year, which is 50 times the typical background exposure. Further very small additions to background radiation arise from television tubes, luminous watches, and shoe fitting fluoroscopes in shops, and of course from weapons tests.

All nuclear weapons which are exploded on or above the ground release their debris of mixed fission products into the atmosphere. in the case of the earlier nominal type of weapon. the explosive energy is derived entirely from nuclear fission, and is only sufficient to raise the radioactive mushroom cloud into the lower atmosphere, or troposphere. There will be a rapid "close-in" fall-out near the site of the explosion, and a fairly rapid fall-out in a belt as the cloud circulates around the earth. In the case of the more modern H-bomb, a fission core is included to provide the very high tempera-tures necessary to initiate the hydrogen fusion reaction. The energy release is now at least 1,000 times as great, and much of the debris is now lofted into the upper atmospheres the stratosphere; the rate of fall-out is slower, but may still be fairly rapid for tests which have been carried out in more northerly latitudes. Some of the debris returns to the ground by dry deposition, but most of it is washed out by rainwater, so that the extent of fall-out in any country is dependent on the amount of rainfall. The higher the rainfall in any region the greater the fall-out and the greater the contamination of soils and of vegetation. The amount of fall-out tends to increase in the Spring months of any one year and is greatest in northern temperate zones. The subsequent contamination of plants may occur directly by the exposure of upper parts to rainwater, or indirectly via the roots and contaminated soil. For a few years after a series of tests direct contamination is likely to be the more serious; some years after the cessation of tests long-lived fission products in the soil will be the only source of contamination. The extent of the contamination in any particular case will depend on the type of plant, and on the fission product.

In the case of iodine-131 only "close-in" and tropospheric fall-out are important as the content of the stratosphere will have decayed by the time it returns to earth. In th.e early weeks after testing, plants will be contaminated directly from rainwater and to a lesser extent from the soil. The iodine activity may well decay by the time the plant is harvested and used as food. Grass may, however, become extensively contaminated for a time, and as cattle crop a large area of herbage, the milk will collect an appreciable amount of the activity, and will be the principal source of iodine in the human diet for some weeks during and after a series of tests. The iodine subsequently collects in the thyroid gland and may be hazardous for young children. It should be possible to convert milk which is Contaminated by iodine into cheese or into powdered milk; the product will then be perfectly safe in a matter of about 40 days after the collection of the milk. The iodine is concentrated in all animal thyroids and quite substantial amounts have been reported in the case of sheep and cattle. As the radiation is highly penetrating, abattoir employees may be subject to some additional exposure.

The greatest long-term risk to the individual among the fission products is undoubtedly strontium-90, a fact which was recognised by Dr. Comar as early as 1948. The strontium may enter plants either by the direct or indirect processes. Stable elementary strontium does occur in nature, and is usually associated with calcium, to the extent of about one part in a thousand. The calcium is a principal and essential element in the composition of bone, the "standard man" containing about 1 kilogram of the element, of which all but one gram is in the skeleton. The strontium is similar in behaviour to calcium but as far as is known it is not an essential element. The bone is of course forming rapidly in the case of children, but even in the case of adults it is in a dynamic state, the calcium content undergoing constant replacement at a slow rate. In western countrj~ about ~rds of the calcium requirements are obtained from milk and milk products, which are therefore principal sources of radio-strontium in human diet. Fortunately both animals and Man display a marked discrimination in favour of calcium if there are adequate supplies available; the amount of strontium-90 retention in bone is therefore dependent on the calcium intake as well as on the strontium ingestion. It is usual to express strontium content in terms of the "strontium unit" (S.U.) which is the amount of strontium-90 per gram of calcium. For every 4 S.U.s in diet, about 1 unit will enter the newly forming bone. It follows that anything which is done to boost the calcium in the diet, e.g. by the use of mineral calcium either as carbonate or phosphate, reduces the entry of strontium into the bone. This is being done in the case of white flour and plant milk substitutes.

The situation with respect to caesium-137 is different from strontium in a number of respects. Uptake of fission product from the soil is negligible, so that plant contamination is entirely from the direct action of rainwater. There should be very little caesium contamination of plants a few years after the cessation of tests. Caesium as a chemical has certain affinities with natural potassium, which is also an essential constituent of all living organisms. Both the potassium and the caesium are found in the plasmas and cells of the body and have a fairly rapid cycle of uptake and elimination. It the caesium-137 is no longer present in diet it will soon disappear from the body. The main source of caesium in human diet is animal produce such as milk and meat. The caesium which is accumulating in the soil can also irradiate the body through the penetrating radiations which it is emitting. The radio-carbon produced in weapons testing will behave in an identical manner with the natural substance formed by the action of cosmic radiation, resulting in some small increase in the amounts in foods and in man. It will be present in all tissues.

The dose commitment by the year 2,000 has been estimated for the gonads and the bone marrow, which are generally recognised to be the most critical organs of the body from the point of view of sensitivity to radiation damage. The estimates are as follows: -
- a) the genetic dose-from caesium 137 and carbon-14 in the body, and from caesium 137 on the ground; about 1% of the background dose.
- b) the bone-marrow dose-from strontium-90 in bone, and strontium-90, carbon-14 in bone-marrow, from caesium 137 in the body, and from caesium 137 on the ground; about 2% of the background.

It is evident that the dose commitment from fall-out is only a small fraction of the additional dose from medical practice, and is very much less than regional variations in the background dose. The values would, of course, be under-estimated if the frequency of testing were maintained in future years, and would be increased many times in a nuclear war, it is very pertinent to enquire whether these additions to the background are likely to have any harmful consequences for man. I must make it clear that there is absolutely no scientific evidence available which would enable a categorical answer to be given to this question. Any harmful effects which have resulted from radiation have all been due to doses which are very much higher than the background. Any estimates of damage at low doses are based on extrapolations of what is known at the much higher dose, and these estimates are coloured by one's attitude to the whole problem.

The average population dose from fall-out is so small at present that harmful effects are unlikely to be detected and any special precautions would hardly be justified. Some suggestions for coping with the problem are, however, discussed, and would certainly prove of some value if testing were resumed some time into the future, or alternatively, if there should be some accident to a fluclear power station. Of particular interest in this connection, especially to vegetarians, are the steps which can be taken to minimise the contamination of foods.

An elementary precaution which can be taken to protect growing plants is to grow them under glass especially during the Spring months when the fall-out tends to be somewhat higher. Strontium contamination from the soil may be reduced by liming, and by the use of green manure and dung; the surface use of compost appears to be of some value as the roots of plants tend to go deeper where the strontium only penetrates very slowly. Suitably reinforced humus to combat the radio-iodine risk has also been suggested. Care has to be exercised in the use of lime as an excess of calcium in the soil can lead to other serious deficiencies and loss of productivity in plants. In the event of exposed parts of plants becoming contaminated, discarding of the outer parts, and thorough washing of the edible parts can reduce direct contamination by as much as 50%. Experiments which have been carried out in the U.S.A. suggest that it would even be possible to reduce indirect contamination via the roots by thorough washing. Another approach to lowering the contamination level in plants is suggested by other work which is also being carried out in the U.S.A. It is known that plants differ in the amounts of strontium that they can accumulate from soil and a recent investigation of varieties of barley and wheat shows large differences in radio-strontium concentration. The authors conclude that the hazard associated with radio-strontium can be reduced by "growing varieties that absorb low quantities of strontium or by growing varieties that accumulate low concentrations of strontium in plant parts used for food."

If widespread contamination by fission products should occur, milk would become a serious source of these substances in human diet. The potential seriousness of the problem is shown by the fact that the Agricultural Research Council in the U.K. maintains a nation-wide sampling and analysis programme representing the country's production of milk. The Medical Research Council have recommended contamination levels to deal with any emergency situation that might arise. It is of interest that the Ministry of Science has recently announced the allocation of a modest sum of money to study a milk processing plant, in which the fission products would be removed by ion-exchange, similar to a process widely used in water softening. On the other hand the vegetarian would be strongly advised to consider the use of plant milk substitutes, which are now being extensively studied. Plant milks have the advantage of being reinforced by mineral calcium, and may be prepared from plants grown in regions much less subject to the radioactive fall-out. Both of these factors would be expected to reduce the strontium risk in particular. A sample of Wanderlac, which Professor Hawthorn of Glasgow kindly analysed for me in 1960, had about one-half the number of strontium units compared with the then country-wide mean value for milk in the U.K. and only about one-tenth of the value in certain special regions of high annual rainfall. A recent publication in the journal Nature by members of the Medical Research Council in which they have reported experiments on themselves is also of interest in considering the milk problem. It has been known for some time that calcium, and hence strontium, are readily available to the body when supplied as milk. They are not so readily available when supplied in the form of cereals as the calcium, and presumably the strontium, are bound up in an insoluble form. In the experiment carried out by the authors using contaminated sources of food, and involving a mixed diet of milk and cereals, the calcium and the strontium were found to be equally available. On the other hand it would be of interest to ascertain whether the situation would still be the same on a diet which excluded milk, and relied on cereals and plant-milks solely as principal sources of calcium.

It is possible to reduce the level of strontium-90 in the body by using certain chemicals which have a high affinity for the element, but their practice is dangerous and is not recommended except in case of a serious emergency. A great deal of work is also being carried out on the subject of protection against radiation by the administration of certain chemicals, and although there do appear to be several promising lines of research, there is very little prospect of their success at the moment.

In conclusion I would like to repeat that I have endeavoured to be strictly factual and objective in my survey of the subject, and I hope that this will enable you to view the problems carefully and dispassionately. I have every confidence, and am optimistic that we can avoid the horrors of nuclear warfare, and that with continuing care and restraint Man can exploit the tremendous forces which are now available to him in a peaceful and constructive manner to the betterment of the human condition and without prejudice to the health of the present and future generations.