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03/30/09 |
               
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Radiation Facts about Uranium: (Uranium 101) Health Concerns: What is uranium? [top of page] Uranium is the heaviest metal that occurs in nature. It is an unstable material which gradually breaks apart or decays at the atomic level (as described in the next section). Any such material is said to be radioactive. As uranium slowly decays, it gives off invisible bursts of penetrating energy called atomic radiation. It also produces more than a dozen other radioactive substances as by-products. See Figure 2. These unstable by-products, having little or no commercial value, are called uranium decay products. One of them is a toxic radioactive gas called radon. The others are radioactive solids. They are discarded as waste when uranium is mined. What is radioactivity? [top of page] Science teaches us that everything is made of tiny little particles called atoms. They are too small to be seen even under a powerful microscope. When a substance is radioactive, it means that its atoms are exploding (sub-microscopically) and throwing off pieces of themselves with great force. This process is called radioactive decay. During radioactive decay, two types of tiny electrically charged particles are given off, travelling very fast. They are called alpha and beta particles. Some radioactive materials are alpha emitters, and others are beta emitters. In addition, highly energetic rays called gamma rays are often emitted. Gamma rays are not material particles at all, but a form of pure energy very similar to x-rays, travelling at the speed of light. Can atomic radiation penetrate living tissue? [top of page] Gamma rays penetrate through soft tissue just as light shines through a window. Beta particles have less penetrating power, travelling less than two centimeters in soft tissue. Alpha particles have the least penetrating power, travelling just a few micrometers in soft tissue, equivalent to a few cell diameters.
Is radioactivity dangerous? [top of page] Alpha particles, beta particles and gamma rays can do great harm to a living cell by breaking its chemical bonds at random and disrupting the cell's genetic instructions. Massive exposure to atomic radiation can cause death within a few days or weeks. Smaller doses can cause burns, loss of hair, nausea, loss of fertility and pronounced changes in the blood. Still smaller doses, too small to cause any immediate visible damage, can result in cancer or leukemia in the person exposed, congenital abnormalities in his or her children (including physical deformities, diseases and mental retardation), and possible genetic defects in future generations. Outside the body, because of their low penetrating power, alpha emitters are the least harmful, while gamma emitters are more dangerous than beta emitters. Inside the body, however, alpha emitters are the most dangerous. They are about 20 times more damaging than beta emitters or gamma emitters. Thus, although alpha radiation cannot penetrate through a sheet of paper or a dead layer of skin, alpha emitters are extremely hazardous when taken into the body by inhalation or ingestion, or through a cut or open sore. Uranium and most of its decay products are alpha emitters. As such, the uranium decay products are among the most toxic materials known to science. How do radioactive elements produce other radioactive elements? [top of page] When atoms undergo radioactive decay, they change into new substances, because they have lost something of themselves. These by-products of radioactive decay are called decay products or progeny. In many cases, the decay products are also radioactive. If so, they too will disintegrate, producing further decay products and giving off even more atomic radiation.
The number which appears after the name of a substance helps to indicate its place in the list of decay products. When the numbers go down by four, an alpha particle has been emitted. When the numbers stay the same, a beta particle has been emitted. Most of the time, but not always, there is a gamma ray emitted to accompany the alpha or beta emission. Thus uranium-238 changes into thorium-230 (in three stages), which then changes into radium-226, and thence into radon-222. The numbers keep getting smaller because the atoms are losing a part of themselves. Are the peaceful and military uses of uranium incompatible? [top of page] Any nuclear reactor fuelled with uranium automatically produce plutonium as a byproduct. If that plutonium is chemically separated from the rest of the radioactive garbage in the spent reactor fuel, it can be used as a nuclear explosive. So, the spread of nuclear power around the world gives more and more countries the option of producing nuclear weapons at some future time. In 1974, India exploded a bomb that was made from plutonium produced in a reactor given to the Indian government as a gift by the Canadian government. It was not an electricity-producing reactor, but a smaller machine called a research reactor. Canada has also given or sold reactors to Taiwan, Pakistan, South Korea,
Argentina and Romania. Some regimes in these client countries have displayed an
interest in either developing nuclear weapons themselves, or in sharing their
nuclear technology with other countries having such ambitions (e.g. Iraq and
Libya). What is "nuclear weapons fallout"? [top of page] When an atomic bomb explodes in the atmosphere, fission products are dispersed into the environment. They contaminate air, water and soil, as well as plants and animals. They attach themselves to dust particles and water droplets, and come down as rain or snow. Some are sent high up into the stratosphere; they descend very slowly for many years thereafter, all over the globe, as radioactive fallout. If the bomb explodes at ground level, huge quantities of earth are scooped up
into the fireball. Many of these materials, originally non-radioactive, become
radioactive by absorbing stray neutrons from the fission process. These new
radioactive substances, caused by neutron absorption, are not fission products;
they are called activation products. They can contribute significantly to the
fallout from an atomic explosion. What are the health hazards of uranium mining? [top of page] Uranium mining is hazardous. In addition to the usual risks of mining,
uranium miners worldwide have experienced a much higher incidence of lung cancer
and other lung diseases. Several studies have also indicated an increased
incidence of skin cancer, stomach cancer and kidney disease among uranium
miners. How did we learn that radioactivity causes lung cancer? [top of page] In 1897 it was learned that uranium ores are radioactive. By 1900 it was found that severe skin damage can be caused by prolonged contact with some of the radioactive decay products of uranium. By 1920 it was well established that chronic exposure to atomic radiation, even without any visible damage to skin or other bodily tissues, can cause cancers and leukemias, years later, in both humans and animals. By the 1930s, scientists were convinced that the centuries-old lung cancer epidemic among German and Czechoslovakian miners was caused by the men inhaling airborne radioactive materials in the underground mines. Decades later, Japanese atomic bomb survivors were found to have an abnormally high rate of lung cancer. Which radioactive materials cause lung cancer among miners? [top of page] In the 1950's it was pointed out that the radon gas, hovering in the stagnant air of the mine, produces radioactive decay products called radon progeny (formerly called radon daughters). These solid radioactive byproducts (see figure 3) produced a single atom at a time, hang in the air along with radon gas. When radon gas is inhaled, the radon progeny are also inhaled, resulting in a much larger dose of alpha radiation to the lungs than would be delivered by the gas alone. Is radon in homes a problem? [top of page] In places, such as Port Hope, Ontario, and Grand Junction, Colorado, elevated radon levels in homes and schools resulted from the careless use of abandoned uranium tailings or other uranium wastes in construction. In other places, such as Oka, Quebec, and St. Johns, Newfoundland, other radium-contaminated materials have been sold to unsuspecting builders, leading to high radon levels in many homes. A British medical study (published in The Lancet in April 1990) has found a significant correlation between elevated radon levels in homes and serious illnesses like myeloid leukemia, kidney cancer, melanoma, and a variety of cancers among children. This study uses published statistics from fifteen countries, including Canada.
Can the health dangers be alleviated by using more miners for shorter times? [top of page] The 1976 Ontario Ham Commission Report warned that using more miners for shorter times, without reducing the total exposure to inhaled radon, will not reduce the number of cancer victims. If anything, it could increase the number of excess lung cancers. The Ham Commission Report, the BCMA Report, the Thomas/MacNeill Report, and the 1988 BEIR-IV Report (published by the U.S. National Research Council) have all pointed out that at lower radon exposure levels the number of cancers caused per unit dose may actually increase. In other words, spreading the same total dose out over a larger population, so that each individual gets a smaller dose, may increase the total number of cancers caused. The BEIR-IV Report observes that this phenomenon is well-known for laboratory animals, but is less clearly established in the case of human populations. What are the radon progeny? [top of page] Because radon gas is radioactive, it decays, producing seven radioactive decay products called radon progeny. These solid radioactive materials attach themselves to tiny dust particles and droplets of water vapour floating in the air. When breathed, radon gas is exhaled as easily as it is inhaled; but when the accompanying radon progeny are inhaled, they lodge in the lining of the lung. There they bombard the delicate tissues with alpha particles, beta particles and gamma rays. The radon progeny are various radioactive forms (or isotopes) of bismuth, polonium and lead. The bismuth and lead isotopes emit beta particles and intense gamma rays, while the polonium isotopes emit alpha particles which irreparably damage the bronchial tissue. When radon gas is given off from uranium tailings (see figure 3) the radon progeny eventually come to earth as radioactive fallout in the form of rain, snow or dust, thus entering aquatic and terrestrial food chains. A few days following deposition, the main radioactive progeny left are lead-210 and polonium-210; the others have decayed away to non-radioactive atoms. When lead-210 and polonium-210 are ingested via contaminated vegetables, fruits, fish or meat, they are incorporated into the body just like non-radioactive materials.
What is polonium? [top of page] Three different isotopes of polonium are included among the radon progeny. These pernicious substances are responsible for most of the biological damage attributed to radon. In particular, polonium-214 and polonium-218, when inhaled, deliver massive doses of alpha radiation to the lungs, causing fibrosis of the lungs as well as cancer. Animal studies have confirmed that polonium is extremely harmful, even in minute quantities. The 1988 BEIR-IV report states that polonium-210 is far more dangerous than plutonium at high exposure levels, is more or less equivalent to plutonium (which is five times more damaging than radium) at intermediate exposure levels, and approaches the toxicity of radium at very low exposure levels. Because of the lichen-caribou food chain, caribou in the arctic and in northern Saskatchewan have much higher levels of polonium-210 in their flesh than any other animals in North America. As a result, the Canadian Inuit have up to 80 times more polonium-210 in their bodies than other North American people do. Uranium mining can only exacerbate this situation, because increased amounts of airborne polonium-210 will be deposited on the lichen as fallout from the tailings and from abandoned ore bodies. There is growing evidence that polonium-210 inhaled in tobacco smoke is
responsible for much of the biological damage caused by cigarettes. Autopsies
show that smokers have higher levels of polonium-210 in their lungs than
non-smokers. Animal studies show that polonium-210 in the lungs is a superb
carcinogen. From the lungs, polonium can also enter the bloodstream; the
resulting radiation damage to blood vessels can eventually lead to blocked
arteries, causing strokes and heart attacks. What dangers do tailings pose to humans, wildlife and the environment? [top of page] Unless uranium tailing are perfectly contained in some kind of storage system which has yet to be devised, humans and animals who come close to the tailings cannot help ingesting or inhaling some of this radioactive material, which seeps into the air, the food and the water. In this way, damage can be done to the lungs, skin, kidneys, blood, bones and reproductive organs. Over a period of years, that damage can lead to many types of illnesses, including cancers and leukemia. It can also lead to diseases and malformations in children, even before they are born. A major study of Navajo Indians who worked as uranium miners, and those living near uranium tailings on the Colorado plateau, is almost finished. The children of these people have a very high rate of birth defects. A study in Malaysia is currently documenting changes in blood and ill health among children exposed to thorium and uranium waste. Radioactive materials in the tailings can also be carried very far away in
the bodies of animals, fish, birds, and insects. Anybody eating the meat from
contaminated animals will get the radioactive material inside his or her own
body. What do scientists know about the long-term effects of uranium mining on the environment? [top of page] What is known:
What is unknown:
Can radioactivity be detected by human senses? [top of page]
At much lower doses, such as those experienced in uranium mining,
atomic radiation cannot be detected by any of our human senses. Special
instruments are needed. Alpha radiation, the kind associated with radon gas and
most of the other uranium decay products, is difficult to detect even with
instruments. How does atomic radiation cause genetic defects in children? [top of page] Radiation damage to the father's sperm or the mother's eggs can result in a damaged child. Atomic radiation workers take the greatest risk of having a damaged child because they are in closest contact with radioactive materials. A child suffering from genetic damage can pass that damage on to future generations. Since the father's sperm is replaced every three or four months, he could theoretically wait for some time after working in a radiation environment before fathering a child. However, if his body is contaminated with long-lived radioactive materials, his sperm could continue to be damaged by internal exposure to radiation even after quitting his mining job. Women carry in their bodies from birth, all the eggs they will ever have. Damage to a woman's eggs at any one time can result in a damaged baby many years later. What is an acceptable level of exposure to atomic radiation? [top of page] There is no convincing scientific evidence that there is a safe dose of atomic radiation. The evidence points strongly to the opposite conclusion; that every dose of atomic radiation administered to a large population, no matter how small it may be, will cause a corresponding increase in the numbers of cancers, genetic defects in offspring and other diseases. The increase in the incidence of cancers and genetic defects seems to be roughly proportional to the total radiation dose received by the entire population. If the radiation dose is cut in half, the increase in the number of people dying of cancer or having defective children will also be cut in half, but the degree of damage to each affected individual is undiminished. Lowering the dose reduces the frequency but not the severity of the medical consequences. Every regulatory body in the world uses this principle as the basis for regulating radiation exposures. Since no dose can be proven safe, there is no objective or scientific way to decide what dose is acceptable. It is a social or political choice, not a technical or scientific one. Science can only help us to estimate the risks; how many people are likely to get cancer, how many children are likely to be born defective, or what other types of illnesses might increase as a result of a given exposure to radiation. But to judge whether or not these consequences are acceptable is beyond the scope of science. The situation is further complicated when the people who receive the financial or other benefits of nuclear power or uranium mining are not the only ones exposed to the risks. What is the basis for setting radiation standards? [top of page] In a very real sense, radiation standards are arbitrary. While maximum permissible levels of radiation exposure have been defined for workers and the general population, these exposures should not be regarded as safe, or even acceptable. The International Commission on Radiological Protection (ICRP) warns that it would be unacceptable for workers or for members of the general public to be exposed continuously to the maximum permissible dose levels. What is "background radiation"? [top of page] Some radiation exposure is unavoidable, even in the absence of uranium mining and nuclear technology. This background radiation is due to small quantities of radioactive materials in the natural environment -- food, water and air -- as well as penetrating rays from outer space to which we are all exposed. Background radiation is higher in some places than in other, depending on the altitude, the nature of the soil, and the type of building materials used. In recent years, it has become clear that the largest and most dangerous single source of exposure to background radiation is in the form of naturally-occurring radon gas produced by the radioactive decay of uranium in the soil. Radon is responsible for more than 50 percent of all human exposure to background radiation. Most scientists consider that a fraction of the spontaneous cancers or birth
defects that occur in human populations are caused by our unavoidable exposure
to background radiation. Radon is thought to be the most potent cancer causing
agent in the natural environment. Is background radiation increasing? [top of page] Because of man's activities, background radiation exposure is gradually increasing as greater quantities of naturally ocurring radioactive materials are being released into the biosphere (for example, through uranium mining). We have added significantly to the unavoidable radiation exposure of all people on earth because of fallout from nuclear weapons testing and nuclear power plant discharges, particularly in the case of a large-scale accident like Chernobyl. The medical profession has also added to our average radiation exposure through the use of x-rays. In addition, small quantities of medical and industrial radioisotopes (man-made radioactive substances used for "tracers" or therapeutic purposes) often end up in soil, water or air. Although the term "background radiation" is not meant to include bomb fallout, reactor discharges, medical exposures or environmental contamination from radioisotopes, it is nevertheless a fact that people all over the world are being exposed to increasing doses of radiation because of these factors. The text was written by Dr. Gordon Edwards, with the exception of the question "what do scientists know about long-term effects of uranium mining on the environment", which was written by Dr. Stella Swanson. The text appears in URANIUM: a discussion guide, 1991 Dr Robert Woollard, Dr. Rosalie Bertell, Dr. Harding and Dr. Swanson provided editorial consultation.
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