Part F : URANIUM TAILINGS F.1. What are uranium tailings?
F.2. What is thorium-230?
F.3. What is radium-226?
F.4. What is radon-222?
F.5. What are the radon progeny?
F.6. What is polonium?
F.1. What are uranium tailings? In mining, the uranium and its decay products buried deep in the earth are brought to the surface, and the rock containing them is crushed into a fine sand. After the uranium is chemically removed, the sand is stored in huge reservoirs. These left-over piles of radioactive sand are called "uranium tailings".Uranium tailings contain over a dozen radioactive materials which are all extremely harmful to living things. The most important of these are thorium-230, radium-226, radon-222 (radon gas) and the radon progeny, including polonium-210.
If this radioactive sand is left on the surface and allowed to dry out, it can blow in the wind and be deposited on vegetation far away, entering the food chain. Or it can wash into rivers and lakes and contaminate them.
F.2. What is thorium-230? Thorium-230 is the uranium decay product with the longest lifetime. It lasts for hundreds of thousands of years -- in human terms, forever. Thorium is especially toxic to the liver and the spleen. It has been known to cause leukemias and other blood diseases. It decays to produce radium-226, which in turn produces radon gas (radon-222).
So the amount of radium in the waste, and the quantities of radon gas produced by it, will not diminish for a long time, because they are constantly being replenished by the decay of the very long-lived thorium-230.
F.3. What is radium-226? Radium-226 is one of the more dangerous of the uranium decay products. It is a radioactive heavy metal, and a potent alpha emitter. As it decays, it produces radon gas as a byproduct. Radium is chemically similar to calcium, so when ingested, it migrates to the bones, the teeth and the milk. It is readily taken up by vegetation. In aquatic plants, it can be concentrated by factors of hundreds or even thousands.
In the first half of the twentieth century, radium was used to make a paint that glows in the dark. Radium is now considered too dangerous to use for such purposes. Many young women who used the paint in their work died from cancers of the bone or of the head. The bone cancers were caused by microscopic amounts of radium which were unintentionally swallowed. The head cancers resulted from radon gas generated inside the women's bodies which collected in their sinus and mastoid cavities.
Today, it is considered dangerous to wear a watch whose numerals have been painted with radium paint, because some of the decay products give off intense gamma rays, even more powerful than x-rays. This type of radiation can damage the body by sending rays right through it, even from a distance. Indeed, radium is sometimes used in cancer therapy for this very reason, to destroy unwanted tumours.
While some radium is still used for medical purposes, only small quantities are needed. Most of the world's radium is now discarded with the crushed rock left over from uranium mining, despite the fact that it is known to be a hazard.
Several U.S. studies have reported higher rates of cancer and leukemia in communities having elevated levels of radium in the drinking water, although the cause-and-effect relationship in these cases is still a matter of dispute.
F.4. What is radon-222? Radon-222 is a toxic gas created by the decay of radium-226. Most of the radon is normally trapped in the ore-bearing rock deep within the earth. But when the rock is excavated and crushed, a lot of radon gas is released into the air. The uranium miners breathe this radioactive gas and its progeny into their lungs.
Radon (the gas and its progeny) is a very powerful cancer-causing agent. Even small doses inhaled repeatedly over a long time can cause lung cancer.
Uranium tailings are constantly producing large amounts of radon gas through the decay of radium in the tailings. This gas can travel thousands of kilometers in a light breeze in just a few days. As it travels, it continually deposits solid radon progeny on the ground, water and vegetation below.
Radon also dissolves readily in water, and can be transported by ground water into wells and streams.
F.5. What are the radon progeny? 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.
By itself, 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 F.4) the radon progeny eventually come to earth as radioactive fallout, in the form of rain, snow or dust, entering aquatic and terrestrial food chains. A few days following deposition, the only progeny left are lead-210 and polonium-210; the others have decayed away to almost nothing.
When lead-210 and polonium-210 are ingested in contaminated vegetables, fruits, fish or meat, they are incorporated into the body just as non-radioactive materials are.
F.6. What is polonium? Three different isotopes of polonium are included among the radon progeny. They are polonium-218, polonium-214 and polonium-210. 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 (mentioned in C.3), 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.
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for permission to adapt this discussion guide from his original version.