Uranium in the environment

Uranium in the environment refers to the science of the sources, environmental behaviour, and effects of uranium on humans and other animals. Uranium is weakly radioactive and remains so because of its long physical half-life (4.468 billion years for uranium-238). The biological half-life (the average time it takes for the human body to eliminate half the amount in the body) for uranium is about 15 days. Normal functioning of the kidney, brain, liver, heart, and numerous other systems can be affected by uranium exposure, because uranium is a toxic metal. The use of depleted uranium (DU) in munitions is controversial because of questions about potential long-term health effects. Uranium in the environment refers to the science of the sources, environmental behaviour, and effects of uranium on humans and other animals. Uranium is weakly radioactive and remains so because of its long physical half-life (4.468 billion years for uranium-238). The biological half-life (the average time it takes for the human body to eliminate half the amount in the body) for uranium is about 15 days. Normal functioning of the kidney, brain, liver, heart, and numerous other systems can be affected by uranium exposure, because uranium is a toxic metal. The use of depleted uranium (DU) in munitions is controversial because of questions about potential long-term health effects. Uranium is a naturally occurring element found in low levels within all rock, soil, and water. This is the highest-numbered element to be found naturally in significant quantities on earth. According to the United Nations Scientific Committee on the Effects of Atomic Radiation the normal concentration of uranium in soil is 300 μg/kg to 11.7 mg/kg. It is considered to be more plentiful than antimony, beryllium, cadmium, gold, mercury, silver, or tungsten and is about as abundant as tin, arsenic or molybdenum. It is found in many minerals including uraninite (most common uranium ore), autunite, uranophane, torbernite, and coffinite. Significant concentrations of uranium occur in some substances such as phosphate rock deposits, and minerals such as lignite, and monazite sands in uranium-rich ores (it is recovered commercially from these sources). Seawater contains about 3.3 parts per billion of uranium by weight, approximately (3.3 µg/kg) or, 3.3 micrograms per liter of seawater. as uranium(VI) forms soluble carbonate complexes. The extraction of uranium from seawater has been considered as a means of obtaining the element. The radiation hazards of uranium mining and milling were not appreciated in the early years, 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 1971, thousands of homes and commercial buildings in the Colorado Plateau region were 'found to contain anomalously high concentrations of radon, after being built on uranium tailings taken from piles under the authority of the Atomic Energy Commission'. Depleted uranium (DU) is useful because of its very high density of 19.1 g/cm3 (68.4% denser than lead). Civilian uses include counterweights in aircraft, radiation shielding in medical radiation therapy and industrial radiography equipment, and containers used to transport radioactive materials. Military uses include defensive armor plating and armor-piercing projectiles. Uranium metal can disperse into the air and water, United Nations Environment Programme (UNEP) study says in part: Studies of depleted uranium aerosol exposure suggest that uranium combustion product particles would quickly settle out of the air, and thus could not affect populations more than a few kilometres from target areas.