Uranium in the environment resulting in workers exposed to high levels of radiation. Conventional uranium ore treatment mills create radioactive waste in the form of tailings, which contain uranium, radium, and polonium. Consequently, uranium mining results in "the unavoidable radioactive contamination of the environment by solid, liquid and gaseous wastes". Inhalation of radon gas caused sharp increases in lung cancers among underground uranium miners employed in the 1940s and 1950s. In the 1940s and 1950s, uranium mill tailings were released with impunity into water sources, and the radium leached from these tailings contaminated thousands of miles of the Colorado River system. Between 1966 and
Uranium Uranium is a naturally occurring element that can be found in low levels within all rock, soil, and water. Uranium is the 51st element in order of abundance in the Earth's crust. Uranium is also the highest-numbered element to be found naturally in significant quantities on Earth and is almost always found combined with other elements. The decay of uranium, thorium, and potassium-40 in the Earth's mantle is thought to be the main source of heat that keeps the outer core liquid and drives mantle convection, which in turn drives plate tectonics. Uranium's average concentration in the Earth's crust is