Uranium in the environment
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Uranium in the environment is a global health concern, and comes from both natural and man-made sources. Beyond naturally occurring uranium, mining, phosphates in agriculture, weapons manufacturing, and nuclear power are anthropogenic sources of uranium in the environment.[1]
In the natural environment, radioactivity of uranium is generally low,[1] but uranium is a toxic metal that can disrupt normal functioning of the kidney, brain, liver, heart, and numerous other systems.[2] Chemical toxicity can cause public health issues when uranium is present in groundwater, especially if concentrations in food and water are increased by mining activity.[1] 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.[3]
Uranium's radioactivity can present health and environmental issues in the case of nuclear waste produced by nuclear power plants or weapons manufacturing.
Uranium is weakly radioactive and remains so because of its long physical half-life (4.468 billion years for uranium-238). The use of depleted uranium (DU) in munitions is controversial because of questions about potential long-term health effects.[4][5]
Uranium is a naturally occurring element found at 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.[6]
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 (the most common uranium ore), autunite, uranophane, torbernite, and coffinite.[7] There are significant concentrations of uranium 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.) Coal fly ash from uranium-bearing coal is particularly rich in uranium, and there have been several proposals to "mine" this waste product for its uranium content.[8][9] Because some of the ash produced in a coal power plant escapes through the smokestack, the radioactive contamination released by coal power plants in normal operation is actually higher than that of nuclear power plants.[10][11]
Seawater contains about 3.3 parts per billion (3.3 μg/kg of uranium by weight or 3.3 micrograms per liter).[12]
Sources of uranium
Mining and milling
Mining is the largest source of uranium contamination in the environment.[1] Uranium milling creates 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".[13]
Seventy percent of global uranium resources are on or adjacent to traditional[clarification needed] lands belonging to Indigenous people, and perceived environmental risks associated with uranium mining have resulted in environmental conflicts involving multiple actors, in which local campaigns have become national or international debates.[14]
Some of these environmental conflicts have limited uranium exploration. Incidents at Ranger Uranium Mine in the Northern Territory of Australia and disputes over Indigenous land rights led to increased opposition to development of the nearby Jabiluka deposits and suspension of that project in the early 2000s. Similarly, environmental damage from Uranium mining on traditional Navajo lands in the southwestern United States resulted in restrictions on additional mining in Navajo lands in 2005.[14]
Occupational hazards
The radiation hazards of uranium mining and milling were not appreciated in the early years, resulting in workers being exposed to high levels of radiation. Inhalation of radon gas caused sharp increases in lung cancers among underground uranium miners employed in the 1940s and 1950s.[15]
Military activity
Military activity is a source of uranium, especially at nuclear or munitions testing sites. Depleted uranium (DU) is a byproduct of uranium enrichment that is used for defensive armor plating and armor-piercing projectiles. Uranium contamination has been found at testing sites in the UK, in Kazakhstan, and in several countries as a result of DU munitions used in the Gulf War and the Yugoslav wars.[1] During a three-week period of conflict in 2003 in Iraq, 1,000 to 2,000 tonnes of DU munitions were used.[16]
Combustion and impact of DU munitions can produce aerosols that disperse uranium metal into the air and water where it can be inhaled or ingested by humans.[17] A United Nations Environment Programme (UNEP) study has expressed concerns about groundwater contamination from these munitions.[18] Studies of DU aerosol exposure suggest that uranium particles would quickly settle out of the air,[19] and thus should not affect populations more than a few kilometres from target areas.[17]
Nuclear energy and waste
The nuclear power industry is also a source of uranium in the environment in the form of radioactive waste or through nuclear accidents such as Three Mile Island or the Chernobyl disaster.[14] Perceived risks of contamination associated with this industry contribute to the anti-nuclear movement.[14]
In 2020, there were over 250,000 metric tons of high-level radioactive waste being stored globally in temporary containers. This waste is produced by nuclear power plants and weapons facilities, and is a serious human health and environmental issue. There are plans to permanently dispose of high-level waste in deep geological repositories, but none of these are operational. Corrosion of aging temporary containers has caused some waste to leak into the environment.[20]
As spent uranium dioxide fuel is very insoluble in water, it is likely to release uranium (and fission products) even more slowly than borosilicate glass when in contact with water.[21]
