An example to show the connection between cell damage and observable illness in the person exposed might help in understanding the problems posed by radionuclide (radioactive chemical) uptake, i.e. their ingestion, inhalation or absorption with food, air and water, into human bodies, with subsequent cell damage. The thyroid gland contains cells which produce thyroid hormone, which when released into the bloodstream causes the body functions such as breathing, digesting and reacting to stress to proceed at a certain rate. If the thyroid is `overactive', one might notice in the person increased pulse rate, nervousness, excitability, loss of body weight and, in females, more frequent menstruation. Such a person is often called `hyperactive' (hyper-thyroidism). A normal amount of thyroid hormone in the blood produces a normally active individual. An `underactive' or `hypoactive' thyroid can result in sluggishness, listlessness, weight gain and irregular and/or infrequent menstrual flow in women (hypothyroidism).
        If radioactive iodine (I 131 or I 129) is ingested with food it will enter the blood and tend to accumulate in the thyroid. Radioactive iodine emits high-energy gamma radiation which can destroy thyroid cells, thus reducing total thyroid hormone production in the individual so affected.
        A small amount of radioactive iodine would probably kill only a few cells and have little or no noticeable effect on health. However, if many cells are destroyed or altered, the hormone level would noticeably drop or the hormone itself would be slightly changed. The individual would become lethargic and gain weight. If properly diagnosed and severe enough to require medical intervention, this hypoactive thyroid condition can be controlled with artificially ingested thyroid hormone. A mild exposure experienced by a large population could cause a decrease in average thyroid hormone levels and an increase in average body weight, such as is occurring now in the North American population. The USA has been polluted with nuclear industries since 1943 and with radioactive iodine from weapon testing since 1951. Radioactive iodine is routinely released in small quantities by nuclear power plants and in large quantities by nuclear reprocessing plants. It is not part of the natural human environment. The connection between this pollution and the overweight problem has, unfortunately, never been seriously researched. There is no evidence to confirm or deny the hypothesis, but weight increase is a well-known biological response to radioactive iodine. The hypothesis is certainly plausible under the circumstances.
        It is possible for thyroid cells to be altered but not killed by the radiation. The cellular growth mechanism may be damaged, allowing a runaway proliferation of cells. This results in a thyroid tumour, either cancerous (malignant), or non-cancerous (benign). Other possible radiation damage includes changes in the chemical composition of the individual's thyroid hormone, altering its action in the body and causing clinically observable symptoms not easily diagnosed or corrected.
        There is an extremely remote possibility that these changes will be desirable, but the overall experience of randomly damaging a complex organism like the human body is that it is destructive of health.
        An atomic veteran who participated in the nuclear tests which were conducted by the USA in the Bikini atoll in the late 1940s reported that he gained 75 lbs in the four years following his participation. The doctor diagnosed his problem as hypothyroidism. He also suffered from high blood pressure, chronic asthma and frequent bouts of bronchitis and pneumonia. He has had six tumours diagnosed since 1949, when he returned home from military service. Four have been surgically removed.
        Damage to the thyroid of a developing foetus can cause mental retardation and other severe developmental anomalies.[15]
        Other radionuclides will lodge in other parts of the body. If the trachea, bronchus or lung are exposed, the damage eventually causes speech or respiratory problems. If radioactive particles lodge in the stomach or digestive tract, the heart, liver, pancreas or other internal organs or tissues, the health problems will be correspondingly different and characteristic of the organ damaged. Radionuclides which lodge in the bone marrow can cause leukaemia, depression of the immune system (i.e. the body's ability to combat infectious diseases) or blood diseases of various kinds.
        If the radiation dose is high, there is extensive cell damage and health effects are seen immediately. Penetrating radiation doses at 1,000 rad or more cause `frying of the brain' with immediate brain death and paralysis of the central nervous system. This is why no one dared to enter the crippled Three Mile Island nuclear reactor building during the 1979 accident. An average of 30,000 roentgens (or rads) per hour were being reported by instruments within the containment building. This would convert to a 1,000 rad exposure for two minutes spent inside the building. Such a dose to the whole body is invariably fatal.
        The radiation dose at which half the exposed group of people would be expected to die, i.e. the 50 percent lethal dose, is 250 rad. The estimate is somewhat higher if only young men in excellent health (e.g. soldiers) are exposed. Between 250 and 1,000 rad, death is usually due to gross damage to the stomach and gut. Below 250 rad death is principally due to gross damage to the bone marrow and blood vessels. A dose of about 200 rad to a foetus in the womb is almost invariably fatal.
        Penetrating radiation in doses above 100 rad inflicts severe skin burns. Lower doses produce burns in some people. Vomiting and diarrhoea are caused by doses above about 50 rad. There are some individuals who are more sensitive to radiation, however, showing typical vomiting and diarrhoea radiation sickness patterns with doses as low as 5 rad. An individual may react differently at different times of life or under different circumstances. Below 30 rad, for most individuals, the effects from external penetrating radiation are not immediately felt. The mechanism of cell damage is similar to that described for minute quantities of radioactive chemicals which lodge within the body itself, and our bodies are incapable of `feeling' damage to or death of cells. Only when enough cells are damaged to interfere with the function of an organ or a body system does the individual become conscious of the problem.
        By sharpening our perceptions more subtle radiation effects can often become observable where once they went unnoticed. For example, a series of X-rays received by a young child may cause temporary depression of the white blood cells, and ten days to two weeks after the exposure the child will get influenza or some other infectious disease. Ordinarily the parent views the two events as unconnected.
        Sometimes one can observe a mutation in a person who has experienced loss of hair after radiation therapy to kill tumour cells: hair that was formerly very straight can be curly when it grows again.
        A plant whose flowers are normally white with red tips but which begins to form uniformly red flowers has mutated. Such an event has been observed by persons living in the vicinity of Sellafield in the United Kingdom.
        The use of radiation therapy to destroy malignant cells also has observable results. It is rather like surgery in that it is deliberately used to kill the unwanted tumour cells.

Probable Health Effects resulting
from Exposure to Ionising Radiation