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 mining to extract the uranium by chemical leaching. The milling process commonly yields dry powder-form material consisting of natural uranium, "yellowcake," which is sold on the uranium market as UO. Uranium minerals were noticed by miners for a long time prior to the discovery of uranium in 1789. The uranium mineral pitchblende, also known as uraninite, was reported from the Krušné hory (Ore Mountains), Saxony, as early as 1565. Other early reports of pitchblende date from 1727 in Jáchymov and 1763 in Schwarzwald. In the early 19th century, uranium ore was recovered as a byproduct of mining in Saxony, Bohemia, and