Editing Uranium (section)

===Biotic and abiotic===
{{Main|Uranium in the environment}}
[[File:Pichblende.jpg|thumb|Uraninite, also known as pitchblende, is the most common ore mined to extract uranium.|alt=A shiny gray 5-centimeter piece of matter with a rough surface.]]

[[File:Evolution of Earth's radiogenic heat.svg|thumb|right|The evolution of Earth's [[radiogenic heat]] flow over time: contribution from {{sup|235}}U in red and from {{sup|238}}U in green]]

Some bacteria, such as ''[[Shewanella putrefaciens]]'', ''[[Geobacter metallireducens]]'' and some strains of ''[[Burkholderia fungorum]]'', can use uranium for their growth and convert U(VI) to U(IV).<ref>{{cite journal |doi=10.1016/j.oregeorev.2004.10.003 |title=Evidence of uranium biomineralization in sandstone-hosted roll-front uranium deposits, northwestern China |date=2005 |last1=Min |first1=M. |last2=Xu |first2=H. |last3=Chen |first3=J. |last4=Fayek |first4=M. |journal=Ore Geology Reviews |volume=26 |page=198 |issue=3–4 |bibcode=2005OGRv...26..198M}}</ref><ref>{{cite journal |doi=10.1371/journal.pone.0123378 |pmid=25874721 |pmc=4395306 |year=2015 |last1=Koribanics |first1=N. M. |title=Spatial Distribution of an Uranium-Respiring Betaproteobacterium at the Rifle, CO Field Research Site |journal=PLOS ONE |volume=10 |issue=4 |pages=e0123378 |last2=Tuorto |first2=S. J. |last3=Lopez-Chiaffarelli |first3=N. |last4=McGuinness |first4=L. R. |last5=Häggblom |first5=M. M. |last6=Williams |first6=K. H. |last7=Long |first7=P. E. |last8=Kerkhof |first8=L. J. |bibcode=2015PLoSO..1023378K |doi-access=free}}</ref> Recent research suggests that this pathway includes reduction of the soluble U(VI) via an intermediate U(V) pentavalent state.<ref name="Renshaw">{{cite journal |last1=Renshaw |first1=J. C. |last2=Butchins |first2=L. J. C. |last3=Livens |first3=F. R. |last4=May |first4=I. |last5=Charnock |first5=J. M. |last6=Lloyd |first6=J. R. |display-authors=3 |title=Bioreduction of uranium: environmental implications of a pentavalent intermediate |journal=Environmental Science & Technology |date=June 2005 |volume=39 |issue=15 |pages=5657–5660 |doi=10.1021/es048232b |pmid=16124300|bibcode=2005EnST...39.5657R }}</ref><ref name="Vitesse">{{cite journal |last1=Vitesse |first1=GF |last2=Morris |first2=K |last3=Natrajan |first3=LS |last4=Shaw |first4=S |title=Multiple Lines of Evidence Identify U(V) as a Key Intermediate during U(VI) Reduction by Shewanella oneidensis MR1 |journal=Environmental Science & Technology |date=January 2020 <!--|volume=preprint--> |volume=54 |issue=4 |pages=2268–2276 |doi=10.1021/acs.est.9b05285 |pmid=31934763 |bibcode=2020EnST...54.2268V |doi-access=free }}</ref>
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Some recent work at [[Manchester]] has shown that [[bacteria]] can reduce and fix uranium in [[soil]]s. This research is continuing at the [[University of Plymouth]] by Dr. Keith Roach and S. Handley.
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Other organisms, such as the [[lichen]] ''Trapelia involuta'' or [[microorganism]]s such as the [[bacterium]] ''[[Citrobacter]]'', can absorb concentrations of uranium that are up to 300 times the level of their environment.{{sfn|Emsley|2001|pp=476 and 482}} ''Citrobacter'' species absorb [[uranyl]] ions when given [[glycerol phosphate]] (or other similar organic phosphates). After one day, one gram of bacteria can encrust themselves with nine grams of uranyl phosphate crystals; this creates the possibility that these organisms could be used in [[bioremediation]] to [[radioactive contamination|decontaminate]] uranium-polluted water.{{sfn|Emsley|2001|p=477}}<ref>{{cite journal
| title = Uranium bioaccumulation by a ''Citrobacter'' sp. as a result of enzymically mediated growth of polycrystalline {{chem|HUO|2|PO|4}}
| author = Macaskie, L. E.
| author2 = Empson, R. M.
| author3 = Cheetham, A. K.
| author4 = Grey, C. P.
| author5 = Skarnulis, A. J.
| name-list-style = amp
| journal = Science
| volume = 257
| issue = 5071
| date = 1992
| pages = 782–784
| doi = 10.1126/science.1496397
| pmid = 1496397 |bibcode = 1992Sci...257..782M}}</ref>
The proteobacterium ''[[Geobacter]]'' has also been shown to bioremediate uranium in ground water.<ref name="AndersonVrionis2003">{{cite journal |last1=Anderson |first1=R. T. |last2=Vrionis |first2=H. A. |last3=Ortiz-Bernad |first3=I. |last4=Resch |first4=C. T. |last5=Long |first5=P. E. |last6=Dayvault |first6=R. |last7=Karp |first7=K. |last8=Marutzky |first8=S. |last9=Metzler |first9=D. R. |last10=Peacock |first10=A. |last11=White |first11=D. C. |last12=Lowe |first12=M. |last13=Lovley |first13=D. R. |title=Stimulating the ''in situ'' activity of ''Geobacter'' species to remove uranium from the groundwater of a uranium-contaminated aquifer |journal=Applied and Environmental Microbiology |volume=69 |issue=10 |date=2003 |pages=5884–5891 |doi=10.1128/AEM.69.10.5884-5891.2003 |pmc=201226 |pmid=14532040|bibcode=2003ApEnM..69.5884A }}</ref> The mycorrhizal fungus ''[[Glomus intraradices]]'' increases uranium content in the roots of its symbiotic plant.<ref>{{Cite journal |title=Metals, minerals and microbes: geomicrobiology and bioremediation |journal=Microbiology |author=Gadd, G. M. |volume=156 |issue=Pt 3 |date=March 2010 |pages=609–643|pmid=20019082 |doi=10.1099/mic.0.037143-0 |doi-access=free }}</ref>

In nature, uranium(VI) forms highly soluble carbonate complexes at alkaline pH. This leads to an increase in mobility and availability of uranium to groundwater and soil from nuclear wastes which leads to health hazards. However, it is difficult to precipitate uranium as phosphate in the presence of excess carbonate at alkaline pH. A ''[[Sphingomonas]]'' sp. strain BSAR-1 has been found to express a high activity [[alkaline phosphatase]] (PhoK) that has been applied for bioprecipitation of uranium as uranyl phosphate species from alkaline solutions. The precipitation ability was enhanced by overexpressing PhoK protein in ''[[E. coli]]''.<ref>
{{cite journal
|author=Nilgiriwala, K.S.
|author2=Alahari, A.
|author3=Rao, A. S.
|author4=Apte, S.K.
|name-list-style=amp
|date=2008
|title=Cloning and Overexpression of Alkaline Phosphatase PhoK from ''Sphingomonas'' sp. Strain BSAR-1 for Bioprecipitation of Uranium from Alkaline Solutions
|journal=Applied and Environmental Microbiology
|volume=74
|issue=17
|pages=5516–5523
|doi=10.1128/AEM.00107-08
|pmid=18641147
|pmc=2546639
|bibcode=2008ApEnM..74.5516N
}}</ref>

[[Plant]]s absorb some uranium from soil. Dry weight concentrations of uranium in plants range from 5 to 60 parts per billion, and ash from burnt wood can have concentrations up to 4 parts per million.{{sfn|Emsley|2001|p=477}} Dry weight concentrations of uranium in [[food]] plants are typically lower with one to two micrograms per day ingested through the food people eat.{{sfn|Emsley|2001|p=477}}