Thorium-230 is the uranium decay product with the longest lifetime. It lasts for hundreds of thousands of years. It is especially toxic to the liver and the spleen, and 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.
Radium-226 is one of the more dangerous of the uranium decay products. It’s a radioactive heavy metal. 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 breast milk. It’s readily taken up by vegetation. In aquatic plants, it can be concentrated by factors of hundreds or thousands.
In the first half of the 20th 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’s 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. Radium is sometimes used in cancer therapy for this very reason – to destroy 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.
Radon-222 is a toxic gas created by the decay of radium-226. Radon is normally trapped in the ore-bearing rock deep within the earth. But when the rock is excavated and crushed, 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. Uranium tailings are constantly producing large amounts of radon gas through the decay of radium in the tailings. This gas can travel thousands of miles 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.
So, 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 vapor 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 lungs, where they bombard the delicate tissues with alpha and beta particles and gamma rays. The radon progeny are various radioactive forms – "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 bronchial tissues.
When radon gas is given off from uranium tailings 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.
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. 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.
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.
Thanks to Dr Gordon Edwards, Canadian Coalition for Nuclear Responsibility (CCNR) (http://ccnr.org/)
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