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Uranium in the environment

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Uranium in the environmentis a global health concern, and comes from both natural and man-made sources. Beyond naturally occurring uranium, mining,phosphates in agriculture,weapons manufacturing, andnuclear powerare anthropogenic sources ofuraniumin the environment.[1]

In the natural environment,radioactivityof uranium is generally low,[1]but uranium is atoxic metalthat can disrupt normal functioning of the kidney, brain, liver, heart, and numerous other systems.[2]Chemical toxicity can causepublic healthissues when uranium is present in groundwater, especially if concentrations in food and water are increased by mining activity.[1]Thebiological 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 ofnuclear wasteproduced by nuclear power plants or weapons manufacturing.

Uranium is weaklyradioactiveand remains so because of its longphysical half-life(4.468 billion years foruranium-238). The use of depleted uranium (DU) inmunitionsis controversial because of questions about potential long-term health effects.[4][5]

Natural occurrence

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Uranium ore

Uraniumis 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 theUnited Nations Scientific Committee on the Effects of Atomic Radiationthe normal concentration of uranium in soil is 300 μg/kg to 11.7 mg/kg.[6]

It is considered to be more plentiful thanantimony,beryllium,cadmium,gold,mercury,silver,ortungstenand is about as abundant astin,arsenicormolybdenum.It is found in many minerals includinguraninite(the most common uranium ore),autunite,uranophane,torbernite,andcoffinite.[7]There are significant concentrations of uranium in some substances, such asphosphaterock deposits, and minerals such aslignite,andmonazitesands in uranium-richores.(It is recovered commercially from these sources.)Coal fly ashfrom 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]

Seawatercontains about 3.3parts per billion(3.3 μg/kg of uranium by weight or 3.3 micrograms perliter).[12]

Sources of uranium

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Mining and milling

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Main article:Uranium mining

Mining is the largest source of uranium contamination in the environment.[1]Uranium milling createsradioactive wastein the form oftailings,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 inenvironmental conflictsinvolving multiple actors, in which local campaigns have become national or international debates.[14]

Some of these environmental conflicts have limited uranium exploration. Incidents atRanger Uranium Minein theNorthern Territoryof Australia and disputes overIndigenous land rightsled to increased opposition to development of the nearbyJabilukadeposits and suspension of that project in the early 2000s. Similarly, environmental damage fromUranium mining on traditional Navajo landsin the southwestern United States resulted in restrictions on additional mining in Navajo lands in 2005.[14]

Occupational hazards

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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 ofradongas caused sharp increases in lung cancers among underground uranium miners employed in the 1940s and 1950s.[15]

Military activity

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See also:Depleted uranium
DU penetrator from the PGU-14/B incendiary 30 mm round

Military activity is a source of uranium, especially at nuclear or munitions testing sites.Depleted uranium(DU) is a byproduct ofuranium enrichmentthat is used for defensive armor plating andarmor-piercingprojectiles.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 theGulf Warand theYugoslav wars.[1]During a three-week period of conflict in 2003 inIraq,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]AUnited Nations Environment Programme (UNEP)study has expressed concerns aboutgroundwater contaminationfrom 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]

Sites in Kosovo and southern Central Serbia where NATO aviation used depleted uranium munitions during 1999 bombing

Nuclear energy and waste

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Thenuclear powerindustry is also a source of uranium in the environment in the form of radioactive waste or throughnuclear accidentssuch asThree Mile Islandor theChernobyl disaster.[14]Perceived risks of contamination associated with this industry contribute to theanti-nuclear movement.[14]

In 2020, there were over 250,000 metric tons ofhigh-level radioactive wastebeing stored globally in temporary containers. This waste is produced bynuclear power plantsand weapons facilities, and is a serious human health and environmental issue. There are plans to permanently dispose of high-level waste indeep geological repositories,but none of these are operational. Corrosion of aging temporary containers has caused some waste to leak into the environment.[20]

As spenturanium dioxidefuel is very insoluble in water, it is likely to release uranium (andfission products) even more slowly than borosilicate glass when in contact with water.[21]

Health effects

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Tiron
Further information:Uranium § Human exposure

Soluble uranium salts are toxic, though less so than those of other heavy metals such asleadormercury.The organ which is most affected is thekidney.Soluble uranium salts are readily excreted in theurine,although some accumulation in the kidneys does occur in the case of chronic exposure. TheWorld Health Organizationhas established a daily "tolerated intake" of soluble uranium salts for the general public of 0.5 μg/kg body weight (or 35 μg for a 70 kg adult): exposure at this level is not thought to lead to any significant kidney damage.[22][23]

Tironmay be used to remove uranium from the human body, in a form ofchelation therapy.[24]Bicarbonatemay also be used as uranium (VI) forms complexes with thecarbonateion.

Public health

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Uranium mining producestoxic tailingsthat are radioactive and may contain other toxic elements such asradon.Dust and water leaving tailing sites may carry long-lived radioactive elements that enter water sources and the soil, increasebackground radiation,and eventually be ingested by humans and animals. A 2013 analysis in a medical journal found that, "The effects of all these sources of contamination on human health will be subtle and widespread, and therefore difficult to detect both clinically and epidemiologically."[25]A 2019 analysis of the global uranium industry said that the industry was shifting mining activities toward theGlobal Southwhere environmental regulations are typically less stringent; and that people in impacted communities would "surely experience adverse environmental consequences" andpublic healthissues arising from mining activities carried out by powerful multi-national corporations or mining companies based in foreign countries.[26]

Cancer

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In 1950, the US Public Health service began a comprehensive study of uranium miners, leading to the first publication of a statistical correlation between cancer and uranium mining, released in 1962.[27]The federal government eventually regulated the standard amount ofradonin mines, setting the level at 0.3WLon January 1, 1969.[28]

Out of 69 present and former uranium milling sites in 12 states, 24 have been abandoned, and are the responsibility of theUS Department of Energy.[29]Accidental releases from uranium mills include the 1979Church Rock uranium mill spillin New Mexico, called the largest accident of nuclear-related waste in US history, and the 1986Sequoyah Corporation Fuels Releasein Oklahoma.[30]

In 1990,Congresspassed theRadiation Exposure Compensation Act(RECA), grantingreparationsfor those affected by mining, withamendmentspassed in 2000 to address criticisms with the original act.[27]

Depleted uranium exposure studies

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See also:Depleted uranium

The use of depleted uranium (DU) inmunitionsis controversial because of questions about potential long-term health effects.[4][5][31]Normal functioning of thekidney,brain,liver,heart,and numerous other systems can be affected by uranium exposure, because uranium is atoxic metal.[2]Some people have raised concerns about the use of DU munitions because of its mutagenicity,[32]teratogenicity in mice,[33][34]neurotoxicity,[35]and its suspected carcinogenic potential. Additional concerns address unexploded DU munitions leeching into groundwater over time.[36]

The toxicity of DU is a point of medical controversy. Multiple studies using cultured cells and laboratory rodents suggest the possibility ofleukemogenic,genetic,reproductive,andneurologicaleffects from chronic exposure.[4] A 2005epidemiologyreview concluded: "In aggregate the human epidemiological evidence is consistent with increased risk of birth defects in offspring of persons exposed to DU."[37]TheWorld Health Organizationstates that no risk of reproductive, developmental, or carcinogenic effects have been reported in humans due to DU exposure.[38][39]This report has been criticized by Dr. Keith Baverstock for not including possible long-term effects.[40]

Birth defects

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Most scientific studies have found no link between uranium and birth defects, but some claim statistical correlations between soldiers exposed to DU, and those who were not, concerning reproductive abnormalities.

One study found epidemiological evidence for increased risk of birth defects in the offspring of persons exposed to DU.[37]Several sources have attributed an increased rate of birth defects in the children ofGulf Warveterans and in Iraqis to inhalation of depleted uranium.[34][41]A 2001 study of 15,000 Gulf War combat veterans and 15,000 control veterans found that the Gulf War veterans were 1.8 (fathers) to 2.8 (mothers) times more likely to have children with birth defects.[42] A study of Gulf War Veterans from the UK found a 50% increased risk of malformed pregnancies reported by men over non-Gulf War veterans. The study did not find correlations between Gulf war deployment and other birth defects such as stillbirth, chromosomal malformations, or congenital syndromes. The father's service in the Gulf War was associated with increased rate of miscarriage, but the mother's service was not.[43]

In animals

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Uranium causesreproductivedefects and other health problems inrodents,frogsand other animals. Uranium was also shown to have cytotoxic, genotoxic and carcinogenic effects in animals.[44][45]It has been shown inrodentsandfrogsthat water-soluble forms of uranium areteratogenic.[37][33][34]

In soil and microbiology

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Bacteria andPseudomonadota,such asGeobacterandBurkholderia fungorum(strain Rifle), canreduceand fix uranium in soil andgroundwater.[46][47][48]These bacteria change soluble U(VI) into the highly insoluble complex-forming U(IV) ion, hence stoppingchemical leaching.

It has been suggested that it is possible to form areactive barrierby adding something to the soil which will cause the uranium to become fixed. One method of doing this is to use a mineral (apatite)[49]while a second method is to add a food substance such asacetateto the soil. This will enable bacteria to reduce the uranium(VI) to uranium(IV), which is much less soluble. Inpeat-like soils, the uranium will tend to bind to thehumic acids;this tends to fix the uranium in the soil.[50]

References

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