Editing Selenium (section)

===Toxicity===
[[File:Selenium paradox.jpg|thumb|upright=1.3|Selenium at nutritional levels or low concentrations is required for cell [[homeostasis]], playing a role as an [[Antioxidant|anti-oxidant]] through [[selenoprotein]]s, thus, act chemo-preventive against cancer. In contrast, supra-nutritional levels or higher concentrations act as [[pro-oxidant]] in tumour cells, thus can be exploited as chemo-therapeutic against [[cancer]].<ref name=":0">{{Cite journal|last1=Razaghi|first1=Ali|last2=Poorebrahim|first2=Mansour|last3=Sarhan|first3=Dhifaf|last4=Björnstedt|first4=Mikael|date=2021-09-01|title=Selenium stimulates the antitumour immunity: Insights to future research|url=https://www.ejcancer.com/article/S0959-8049(21)00462-7/abstract|journal=European Journal of Cancer|language=English|volume=155|pages=256–267|doi=10.1016/j.ejca.2021.07.013|pmid=34392068|issn=0959-8049|doi-access=free}}</ref>]]
Although selenium is an essential [[dietary mineral|trace element]], it is toxic if taken in excess. Exceeding the [[Dietary Reference Intake|Tolerable Upper Intake Level]] of 400 micrograms per day can lead to selenosis.<ref>{{cite web |url= http://ods.od.nih.gov/factsheets/selenium.asp#h7 |title= Dietary Supplement Fact Sheet: Selenium |publisher= National Institutes of Health; Office of Dietary Supplements |access-date= 2009-01-05}}</ref> This 400&nbsp;μg Tolerable Upper Intake Level is based primarily on a 1986 study of five Chinese patients who exhibited overt signs of selenosis and a follow-up study on the same five people in 1992.<ref>{{cite book |title= Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids |publisher= Institute of Medicine |date= August 15, 2000 |pages= 314–315 |url= http://www.nap.edu/openbook.php?record_id=9810&page=315 |isbn= 978-0-309-06949-6 |author=((Panel on Dietary Antioxidants and Related Compounds, Subcommittees on Upper Reference Levels of Nutrients and Interpretation and Uses of DRIs, Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, Institute of Medicine))|doi= 10.17226/9810 |pmid= 25077263 }}</ref> The 1992 study found the maximum safe dietary selenium intake to be approximately 800 micrograms per day (15 micrograms per kilogram body weight), but suggested 400 micrograms per day to avoid creating an imbalance of nutrients in the diet and to accord with data from other countries.<ref>{{cite journal |last1= Yang |first1=G.|last2= Zhou |first2=R.|date= 1994 |title= Further Observations on the Human Maximum Safe Dietary Selenium Intake in a Seleniferous Area of China |journal= Journal of Trace Elements and Electrolytes in Health and Disease |volume= 8 |issue= 3–4 |pages= 159–165 |pmid=7599506
}}</ref> In China, people who ingested corn grown in extremely selenium-rich stony coal (carbonaceous [[shale]]) have suffered from selenium toxicity. This coal was shown to have selenium content as high as 9.1%, the highest concentration in coal ever recorded.<ref>{{cite journal |last1= Yang |first1=Guang-Qi|last2= Xia |first2=Yi-Ming|date= 1995 |title= Studies on Human Dietary Requirements and Safe Range of Dietary Intakes of Selenium in China and Their Application in the Prevention of Related Endemic Diseases |journal= Biomedical and Environmental Sciences |volume= 8 |issue= 3|pages= 187–201 |pmid= 8561918}}</ref>

Signs and symptoms of selenosis include a garlic odor on the breath, gastrointestinal disorders, hair loss, [[sloughing]] of nails, fatigue, irritability, and neurological damage. Extreme cases of selenosis can exhibit [[cirrhosis]] of the liver, [[pulmonary edema]], or death.<ref>{{cite web |url= http://www.atsdr.cdc.gov/toxprofiles/tp92-c3.pdf |publisher= Agency for Toxic Substances and Disease Registry |title= Public Health Statement: Health Effects |access-date= 2009-01-05}}</ref> Elemental selenium and most metallic [[selenide]]s have relatively low toxicities because of low [[bioavailability]]. By contrast, [[selenate]]s and [[Selenite (ion)|selenites]] have an oxidant mode of action similar to that of [[arsenic trioxide]] and are very toxic. The chronic toxic dose of selenite for humans is about 2400 to 3000 micrograms of selenium per day.<ref>{{cite journal |last= Wilber |first=C. G. |title= Toxicology of selenium |date= 1980 |journal= Clinical Toxicology |volume= 17 |pages= 171–230 |doi= 10.3109/15563658008985076 |pmid= 6998645| issue= 2}}</ref> [[Hydrogen selenide]] is an extremely toxic, corrosive gas.<ref>{{cite journal |doi= 10.3109/10915818609140736 |title= Selenium Toxicity in Animals with Emphasis on Man |date= 1986 |journal= International Journal of Toxicology |volume= 5 |pages= 45–70 |last= Olson |first=O. E.|s2cid= 74619246 |doi-access= free }}</ref> Selenium also occurs in organic compounds, such as dimethyl selenide, [[selenomethionine]], [[selenocysteine]] and [[methylselenocysteine]], all of which have high [[bioavailability]] and are toxic in large doses.

On 19 April 2009, 21 [[Polo pony|polo ponies]] died shortly before a match in the United States Polo Open. Three days later, a pharmacy released a statement explaining that the horses had received an incorrect dose of one of the ingredients used in a vitamin/mineral supplement compound that had been incorrectly prepared by a [[compounding pharmacy]]. Analysis of blood levels of [[inorganic compound]]s in the supplement indicated the selenium concentrations were 10 to 15 times higher than normal in the [[blood sample]]s and 15 to 20 times higher than normal in the liver samples. Selenium was later confirmed to be the toxic factor.<ref>{{cite web| date= 2009-05-06| url= http://www.horsetalk.co.nz/news/2009/05/033.shtml| title= Polo pony selenium levels up to 20 times higher than normal| access-date= 2009-05-05| archive-date= 2016-08-19| archive-url= https://web.archive.org/web/20160819235242/http://www.horsetalk.co.nz/news/2009/05/033.shtml| url-status= dead}}</ref>

[[File:Se dose-response curve for juvenile salmon mortality - percent scale.jpg|thumb|Relationship between survival of juvenile salmon and concentration of selenium in their tissues after 90 days (Chinook salmon<ref name="Hamilton" />) or 45 days (Atlantic salmon<ref name="Poston" />) exposure to dietary selenium. The 10% lethality level (LC10=1.84 μg/g) was derived by applying the biphasic model of Brain and Cousens<ref>{{cite journal|last1=Brain |first1=P.|title=An equation to describe dose responses where there is stimulation of growth at low doses|journal=Weed Research|last2=Cousens |first2=R.|date=1989|doi=10.1111/j.1365-3180.1989.tb00845.x|volume= 29|pages= 93–96|issue=2|bibcode=1989WeedR..29...93B }}</ref> to only the Chinook salmon data. The Chinook salmon data comprise two series of dietary treatments, combined here because the effects on survival are indistinguishable.]]

In fish and other wildlife, selenium is necessary for life but toxic in high doses. For [[salmon]], the optimal selenium concentration is about 1 microgram selenium per gram of whole body weight. Much below that level, young salmon die from deficiency;<ref name="Poston">{{cite journal| last1= Poston|first1=H. A.| date= 1976| title= Vitamin E and selenium interrelations in the diet of Atlantic salmon (''Salmo salar''): gross, histological and biochemical signs|pmid=932827|journal= Journal of Nutrition|volume= 106|pages= 892–904| last2= Combs| first2=G. F. Jr.| last3= Leibovitz| first3=L.| issue= 7|doi=10.1093/jn/106.7.892}}</ref> much above, they die from toxic excess.<ref name="Hamilton">{{cite journal| last1= Hamilton|first1= Steven J. |date= 1990| title= Toxicity of organic selenium in the diet to chinook salmon|journal= Environ. Toxicol. Chem.|volume= 9|issue = 3| pages= 347–358|doi =10.1002/etc.5620090310| last2= Buhl| first2= Kevin J.| last3= Faerber| first3= Neil L.| last4= Bullard| first4= Fern A.| last5= Wiedmeyer| first5= Raymond H. |bibcode= 1990EnvTC...9..347H |display-authors=3}}</ref>

The [[Occupational Safety and Health Administration]] (OSHA) has set the legal limit ([[permissible exposure limit]]) for selenium in the workplace at 0.2&nbsp;mg/m<sup>3</sup> over an 8-hour workday. The [[National Institute for Occupational Safety and Health]] (NIOSH) has set a [[Recommended exposure limit]] (REL) of 0.2&nbsp;mg/m<sup>3</sup> over an 8-hour workday. At levels of 1&nbsp;mg/m<sup>3</sup>, selenium is [[IDLH|immediately dangerous to life and health]].<ref>{{Cite web|title = NIOSH Pocket Guide to Chemical Hazards – Selenium|url = https://www.cdc.gov/niosh/npg/npgd0550.html|publisher = National Institute for Occupational Safety & Health|location=United States|access-date = 2015-11-21}}</ref>

==== Detection in biological fluids ====
Selenium may be measured in blood, plasma, serum, or urine to monitor excessive environmental or occupational exposure, to confirm a diagnosis of poisoning in hospitalized victims, or to investigate a suspected case of fatal overdose. Some analytical techniques can distinguish organic from inorganic forms of the element. Both organic and inorganic forms of selenium are largely converted to monosaccharide conjugates (selenosugars) in the body before elimination in the urine. Cancer patients receiving daily oral doses of selenothionine may achieve very high plasma and urine selenium concentrations.<ref>{{cite book |last=Baselt |first=R. |title=Disposition of Toxic Drugs and Chemicals in Man |date=2008 |publisher=Biomedical Publications |isbn=978-0-9626523-5-6 |edition=8th |place=Foster City, California |pages=1416–1420}}</ref>