We are exposed to all kinds of radiation, ranging from infrared (heat) to cosmic rays. Radiation is a part of our environment, and nature has evolved a good deal of protection for all animals exposed to it. Our skin, and all of the glands associated with it, protects us against excessive heat, light, and so on. Some types of radiation can go clear through us without doing any harm.
The type of radiation that we are concerned with is "ionizing radiation," which is the kind that is capable of breaking molecules. These rays range from ultraviolet through a wide variety of atomic radiations.
Ultraviolet light can produce skin cancer in man and experimental animals. Human skin can tolerate a good deal of ultraviolet light, and there is a considerable variation in this tolerance from race to race; but, there are limits. The incidence of skin cancer is higher in fair-skinned people who are continually exposed to sunlight. This is especially true of farmers, and others whose occupations keep them in the sun for long periods of time. It occurs with twice the frequency in men as in women. There was a time when the standard of beauty in Europe and in this country was related to a white skin that was free of freckles and blemishes. During that era, physicians rarely saw cancer of the skin in a "beautiful woman." Our standards have changed, and the tan face and freckled nose are considered by many (including me) to be singularly attractive. The price of this attractiveness and the desire for a brown skin is an increased amount of skin cancer. People who receive a good deal of sun should be meticulous about having new skin lesions (sore that do not heal or tumors) removed before they grow to any appreciable size. Since the cure rate in skin cancer, if caught early, is high (over 95 percent) and the surgery is safe, there is little point in taking chances. A cancer of the pigment cells, melanoma, is also caused by ultraviolet irradiation. This type of cancer is potentially deadly, quite unpredictable and can metastasize rapidly.
The radiation produced by x-ray machines, radioactive substances, and cosmic rays appears to act in a similar enough manner so that we can deal with them together. What I say about x-rays also applies to other forms of radioactivity.
The first people to use x-rays were not aware of its harmful effects. Some had their fingers burned off by the effects of the rays, and a number of users developed cancer. There is no question that x-rays, or any other form of atomic radiation, will cause cancer, but there is a considerable void in our information about exactly how much it takes to produce it.
The incidence of leukemia in radiologists was higher than in other groups of physicians, and higher than in the general population. The induction of leukemia by radiation has been confirmed in animals and people.
Shrinking the thymus of newborn infants with x-ray was once a medical fad, and children so treated have an increased incidence of both thyroid cancer and leukemia. The incidence of leukemia in the survivors of the atomic bomb blast at Hiroshima and Nagasaki was very high.
There is a form of arthritis of the spine called ankylosing spondylitis which, in its early stages, is painful and results in the fusion (loss of flexibility) of the spine (the pain goes away when the fusion is complete). This condition was treated with large amounts of x-ray, particularly in England. The leukemia incidence in people so treated was high in comparison with untreated patients. Both ankylosing spondylitis and tuberculosis were treated with repeated injections of radium. Shortly after World War II about 2,000 German patients, children and Adults, were given repeated injections of radium. By 1950 it was shown that the treatment was ineffective for tuberculosis and the use of radium for this disease was discontinued. Unfortunately, no one could prove that it was ineffective for ankylosing spondylitis so it is still being used. Charles W. Mays states that "at the present time (1973) about 100 new spondylitic patients are being injected with 224Ra each year in Germany, because of the belief by some physicians then 224Ra treatments may partially alleviate 'this disease." So far there have been 53 cases of bone cancer caused by this treatment (47 cases from the tuberculosis treatment, 5 from treating ankylosing spondylitis, and 1 from other uses). What a way to cure arthritis!
The inhalation of radioactive substances can cause lung cancer. The deaths due to lung cancer in uranium miners, in the unventilated mines of Europe, appears to be about 50 percent. This may not be due entirely to the radiation, because the incidence of lung cancer is ten times higher in American uranium miners who smoke cigarettes. The cigarette may account for the increase in the deaths due to lung cancer in European miners of radioactive ores from 25 percent in 1875-1912 to about 50 percent thereafter.
A certain amount of radiation is with us that we cannot possibly avoid; this is referred to as "background radiation." Some of it comes from outer space as cosmic rays, some from the radioactive elements in the soil, and some from isotopes in the air and water. One of the problems in evaluating the effects of low-dose radiation is that it is extremely difficult to experimentally achieve levels of radiation that would be below background.
One of the scientific controversies with regard to the production of cancer by radiation is whether any amount of radiation will produce cancer, or if a certain minimum quantity must be applied. If a minimum number of rads (a unit of measurement of radiation) per individual is required to produce a cancer, then maintaining the amount of radiation exposure below that level will result in no radiation-induced cancers. If, on the other hand, effect is proportional to dose, halving the amount of radiation will halve the incidence of tumors. If x amount of radiation per person produced one cancer in 100 individuals, 1/10 X would produce one cancer in 1,000 individuals; 1/100 X would Produce one cancer in 10,000, and 1/10,000 X would produce one cancer in 1,000,000 individuals. In other words, a small amount of radiation would produce a tumor in someone, if there is no threshold and the population is large enough.
With regard to the production of genetic changes with radiation, there appears to be no threshold. Any amount of radiation --no matter how small-- can produce genetic change in at least one individual, if the population is large enough. With regard to some tumors (such as cancer of the bone), which require large amounts of radiation, there may be a "practical threshold." The amount of radiation required to produce one of these tumors in a very large population is so large that one would have to have an immense number of either experimental animals or people to produce even one tumor with a lesser amount of radiation.
The so-called bone seeking radioisotopes, such as strontium and radium, are able to deliver very large amounts of radiation to bone over a long period of time, The ladies who used to paint radium onto radium dial watches received very heavy exposure. They received this heavy exposure simply by wetting the tip of the paint brush that they used, with their tongues. Radioactive isotopes are extremely powerful. Think of what 33 pounds of uranium235 did to Hiroshima and 11 pounds of plutonium did to Nagasaki). The amounts of strontium90 delivered to people by the fallout from atomic explosions has been considerable, when compared with the amount of that isotope that was present before the advent of the atomic age.
The argument has been presented that, since we do not know for sure whether this threshold exists, we cannot talk about possible "safe" levels and that a certain amount of environmental pollution with radiation can be justifed. At the present time, it is possible to justify a certain amount of medical x-ray because we can equate it against its potential life-saving value. With regard to environments pollution with long-lived radioisotopes, we have to consider the very important argument: What are the consequences of polluting our environment if there is no threshold? Once you turn off an x-ray machine, the radiation ceases.There is no way of turning off a radioactive isotope.
There is no doubt that any form of ionizing radiation can cause cancer. It will take a considerable amount of research to find out the relationship of the dose of radiation to the cancer incidence in animals, and we are probably unwilling to perform the corresponding experiments in human beings; at least I hope so. In terms of personal safety, I think that we have to proceed on the conservative assumption that there is no threshold and that any amount of radiation may produce tumors. On this basis, the risk, however small, of using radiation must be weighed against the benefits derived from it. The benefits of the medical use of x-ray outweighs the risk in many cases, contingent on the person using the x-ray taking precautions to make sure that as little x-ray as possible is used to achieve the necessary result, and that parts of the body that do not have to be exposed are not exposed. It is very hard to justify polluting our environment with long-lived radioactive isotopes.
The argument ranges between people who claim that there is no threshold and that any amount of exposure will do damage, and those who claim that there is a threshold and that we could tolerate a certain amount of increased radioactivity in our environment. The important question is not which side is correct, but what is the consequences of our making the wrong guess: If we assume that there is no threshold, then the amount of radiation added to the environment must be kept at minimal levels. This means the complete cessation of atomic testing and the use of extreme caution when using atomic energy. The consequences of the cessation of atomic testing have to be measured in political, rather than biological, terms. If we assume that there is a threshold and continue to add long lived radioactive isotopes to our environment, the consequences will be measured in more deformed children and both children and adults with cancer.