It is generally considered that the period required to reduce the amount of the original material to a point where its danger could be tolerated by life would be ten times the half-life for that element. It can be seen from the chart that uranium undergoes a very long decay series until it becomes the stable, but toxic, element - lead. The period of time involved, when compared to the lifetime of a generation, is virtually forever. Radiation can be of several types. In uranium mine wastes the elements which decay by producing alpha radiation are of particular concern.
Alpha radiation has a far greater potential to damage living tissue than other types of radiation.
Because the tailings contain elements like Thorium 230 with a half life radioactive danger of 76,000 years, they are hazardous virtually forever. Radon Gas - A Particular Hazard Radon gas, a prime source of alpha radiation, is continuously emitted from tailings piles. When radon gas is produced in an undisturbed ore body, it is relatively harmless since moist of it disintegrates long before it can escape from the rock formation in which it is trapped. However, the mining and milling process grinds the ore to the consistency of sand from which the radioactive dust and radon gas can easily spread into the environment. It is the decay products of radon gas which are responsible for many fatal lung cancers in uranium miners.