From Wikipedia, the free encyclopedia
Jump to: navigation, search
Good article Selenium has been listed as one of the Natural sciences good articles under the good article criteria. If you can improve it further, please do so. If it no longer meets these criteria, you can reassess it.
June 17, 2012 Good article nominee Listed
          This article is of interest to the following WikiProjects:
Version 0.5      (Rated GA-Class)
Peer review This Natsci article has been selected for Version 0.5 and subsequent release versions of Wikipedia. It has been rated GA-Class on the assessment scale (comments).
WikiProject Elements (Rated GA-class, Top-importance)
WikiProject icon This article is supported by WikiProject Elements, which gives a central approach to the chemical elements and their isotopes on Wikipedia. Please participate by editing this article, or visit the project page for more details.
 GA  This article has been rated as GA-Class on the quality scale.
 Top  This article has been rated as Top-importance on the importance scale.

This article has comments here.

This article has an assessment summary page.

Article change[edit]

Article changed over to new Wikipedia:WikiProject Elements format by Dwmyers, Maveric149 and Malcolm Farmer. Elementbox converted 13:54, 1 July 2005 by Femto (previous revision was that of 02:42, 18 June 2005).

Information Sources[edit]

Some of the text in this entry was rewritten from Los Alamos National Laboratory - Selenium. Additional text was taken directly from USGS Selenium Statistics and Information, USGS Periodic Table - Selenium, from the Elements database 20001107 (via, Webster's Revised Unabridged Dictionary (1913) (via and WordNet (r) 1.7 (via Data for the table was obtained from the sources listed on the subject page and Wikipedia:WikiProject Elements but was reformatted and converted into SI units.

Nonmetal vs Metalloid[edit]

Is Selenium a nonmetal (as per this article) or a metalloid (as per Chalcogen)? Ian Cairns 01:16, 6 Mar 2005 (UTC)

Hi. I also have noticed a discrepancy:

so, if you have came to some conclusions, could you share them?

It is a non-metal according to the Periodic table, so I'm gonna think that's right.-- (talk) 07:28, 18 September 2008 (UTC)
According to Chemical Priciples by Atkins and Jones Selenium is a nonmetal. A Swedish encyclopedia supports this so the article is wrong.

Zotamedu (talk) 14:06, 4 February 2009 (UTC)

Selenium as a metalloid

It is reasonable that the term metalloid is meant to denote a group of chemical elements which exhibit characteristics roughly intermediate between metals and nonmetals. Although the famous metalloid stair step is a starting place, that line, traditionally drawn under B, on the right side of Al, under Si on the left side of As, etc. clearly doesn't define metalloids as all elements that lie symmetrically along that line. For instance, the unbroken diagonal of At Te As Si and B above the line isn't mirrored by Po Sb Ge and Al below the line: Al is not considered a metalloid; it clearly acts as a metal. Nor is At diagonally below Te, considered a metalloid.

Selenium is often referred to as a metalloid in the literature:

Here are a few articles that note that selenium is a metalloid:

Quote: “Selenium is a metalloid which is an essential micronutrient at low concentrations but becomes toxic at higher concentrations, with the range between being very narrow.”

Citation: David F. Lambert, Nicholas J. Turoczy; Comparison of digestion methods for the determination of selenium in fish tissue by cathodic stripping voltammetry; Analytica Chimica Acta 408 (2000) 97–102.

Quote: “The mobility and availability of the toxic metalloid selenium in the environment are largely controlled by sorption and redox reactions, which may proceed at temporal scales similar to that of subsurface water movement under saturated or unsaturated conditions.”

Citation: L. Charlet, A.C. Scheinost, C. Tournassat, J.M. Greneche, A. Géhin, A. Fernández-Martı´nez, S. Coudert, D. Tisserand, J. Brendle; Electron transfer at the mineral/water interface: Selenium reduction by ferrous iron sorbed on clay; Geochimica et Cosmochimica Acta, Volume 71; 2007; 5731-5749.

Quote: “The metalloid selenium is a required micronutrient in mammals needed for insertion into specific selenoproteins.”

Citation: Dennis Ganyc, William T. Self; High affinity selenium uptake in a keratinocyte model; FEBS Letters, Volume 582; 2008; 299-304.

Quote: “However, anodic stripping voltammetry (ASV), usually carried out with gold electrodes, is not so often applied to determination of Se because the stripping of this metalloid is accompanied by multiple peaks, which impair the reproducibility of the curves to be obtained.”

Citation: Claudete Fernandes Pereira, Fabiano Barbieri Gonzaga, Antonio Moraes Guarita-Santos, Jurandir Rodrigues SouzaDe, Determination of Se(IV) by anodic stripping voltammetry using gold electrodes made from recordable CDs, Talanta, Volume 69; 2006; 877-881.

Quote: “There is an increasing recognition that selenium is an important metalloid with industrial, environmental, biological and toxicological significance.”

Citation: F. Hellal, M. Dachraoui, Application of Doehlert matrix to the study of flow injection procedure for selenium (IV) determination, Talanta, Volume 63; 2004; 1089-1094.

Quote: “Selenium (Se) is a metalloid. It is essential for animals and humans.”

Citation: Lin Wu, Review of 15 years of research on ecotoxicology and remediation of land contaminated by agricultural drainage sediment rich in selenium, Ecotoxicology and Environmental Safety, Volume 57; 2004; 257-269.

Quote: “Selenium is a metalloid that in recent decades has gained international importance because of elevated residues found in fish and wildlife.” Citation: Steven J. Hamilton, Rationale for a tissue-based selenium criterion for aquatic life, Aquatic Toxicology, Volume 57; 2002; 85-100. put an unsupported unsigned objection to this quote and citation. I undid that. --Eldin raigmore (talk) 20:06, 8 November 2009 (UTC)

Quote: “Urinary levels of another metalloid, selenium (Se), have recently been shown to be associated with increased As excretion and altered metabolite distribution.”

Citation: W. Jay Christian, Claudia Hopenhayn, Jose´ A. Centeno, Todor Todorov; Distribution of urinary selenium and arsenic among pregnant women exposed to arsenic in drinking water; Environmental Research 100 (2006) 115–122.

I propose adding the description in this article of selenium as a metalloid. Redchasteen (talk) 19:56, 27 April 2009 (UTC)

Why selenium is named as metalloid (really often), but very similar in metallicity carbon and phosphorus are almost always named as (ordinary) metalloids? Maybe grey selenium looks more metallic than black (metallic, grey) phosphorus and graphite and more selenides have metallic appearance than phosphides and carbides, but it not justify naming selenium as (half-)metalloid and carbon and phosphorus only as nonmetals! Graphite and black phosphorus, metallic allotropes of C and P, have much higher melting point than gray Se and are probably better conductors of heat (black P - 12.1 W·m−1·K−1, graphite - 119-165 W·m−1·K−1 (better than some metals), tellurium (element more metallic than Se) - (1.97–3.38) W·m−1·K−1). (talk) 19:18, 14 October 2013 (UTC)

Possibly a featured article?[edit]

I find this article pretty comprehensive and think would make a good candidate for a featured article. However, it seems to be lacking in a few things which I can't quite pin-point. Leftist 14:56, 21 March 2006 (UTC)

Maybe a hint of garlic? SBHarris 19:40, 7 September 2006 (UTC)
I'd like to see a list of foods in which selenium is naturally occurring. / LNelson, 27 Aug 2007 —Preceding unsigned comment added by (talk) 12:55, August 27, 2007 (UTC)


I don't have strong opinions about this, and I can understand why most people would never think of representing mu the way I originally did, but I think 100\mug is rather clearer than 100μg . I think it must be the lack of curved lines on the standard μ . Elroch 16:47, 10 April 2006 (UTC)

The <math> markup is altogether undefined with respect to the standard browser fonts; 100 \mug looks horrible on my system. The micro sign µ is typographically unambiguos. It's a different beast from the character entity &mu; (in any coding) for the Greek language letter μ, which should not be used as a substitute for the micro prefix for this reason. Femto 18:51, 10 April 2006 (UTC)
The mu I used, \mu, just looks like a more curvy mu in Internet Explorer 6.0 and Firefox 1.5: presumably you are using a different browser. I was not aware there was a separate symbol for "micro". I thought the use of a lower case Greek letter was standard - did you not use the letter from the Greek alphabet at the bottom of the editor window? Elroch 20:31, 10 April 2006 (UTC)
No I don't have JavaScript enabled. Around here, I can enter the ISO 8859-1 code $B5 directly from my keyboard (Want some € too? :). You can always substitute with the HTML entity &micro; (µ). Theoretically, the lower case Greek mu &mu; (μ) is standard; it should also appear typographically consistent with the ordinary text for everybody, though for historical coding reasons the separate micro is kept for the units. Femto 21:17, 10 April 2006 (UTC)
It certainly looks exactly the same on my two browsers. Whether it would on all others is another matter. Elroch 00:41, 11 April 2006 (UTC)

Selenium and Mercury[edit]

Should information that selenium counteracts the negative effects of mercury be added?

MSTCrow 12:11, 17 June 2006 (UTC)


While it's true that people have existed in sub-Saharan Africa for longer than the AIDS epidemic, it does not follow that they have had selenium deficiency since before the AIDS epidemic. Furthermore, assuming that they did, it does not follow that they should have had AIDS then; the HIV virus is a necessary condition for AIDS and lacking (or predating) its existence, the contributory selenium factor (assuming it exists) is rendered moot.

The "fact" that copper-mining produces selenium as a by-product (source? I find it implausible that the existence of one raw element necessarily requires the existence of another) doesn't imply that said by-product is sufficiently present in agricultural soil and therefore in food. Therefore, nothing about copper-mining necessarily has any effect on selenium deficiency in areas in which it exists.

The lack of a published standard of what is subjectively considered "low" has no bearing on the fact that selenium, as a physical and measurable element, can be objetively found to be lower or higher in the diets of some regions. This is all that is needed to establish a negative correlation between dietary selenium and severity of the AIDS epidemic. 12:09, 7 September 2006 (UTC)

Actually, a study was just published about the effects of Selenium on the HIV virus [1]. I'm not sure if it's totally accurate, as the server that hosts the study is down for an hour or so, but it would certainly be worth looking into.Ahudson 18:13, 23 January 2007 (UTC)
It's all over Google News, so it can at least be referenced in a preliminary fashion from journalistic sources. Elijahmeeks 06:40, 24 January 2007 (UTC)
Perhaps this one could be interesting in selenium/HIV context [2] ??

Need this info[edit]

Whats the cost per gram??? and the number of electrons at solid state??? i needed this for project and couldn't find it —The preceding unsigned comment was added by (talkcontribs) 23:41, 3 December 2006 (UTC).

Prices are usually not given for elements, since they vary greatly according to purity and form. And change with time and supplier. I don't understand your question on electrons. What does solid state have to do with it? Generally the number of electrons her atom for isolated elements is the same as the atomic number. SBHarris 01:11, 4 December 2006 (UTC)

Early reference to photovoltaic effects[edit]

I was doing some research in The Times of 1921, and on 24 September 1921 pages 6 and 8 there are articles on the use of selenium in an early "talkie" (film + phonograph recording). Jackiespeel 18:14, 12 February 2007 (UTC)

Fact tag to Isotope section[edit]

Hi there,

I have just been dealing with some vandalism at Badminton where I noticed the only other contribution of the anon IP was some time ago on this article see [3]. Basically I have added fact tag because the information on the number of isotopes and how many are stable needs referencing and of course the edit by the anon IP may have added incorrect information, and need verification.

Cheers Lethaniol 15:39, 15 February 2007 (UTC)

Gave the section an overhaul, reference is isotopes of selenium. Femto 16:14, 15 February 2007 (UTC)


Is the red form really an allotrope, or an oxide?--THobern 10:24, 23 April 2008 (UTC)

Reference to Evolution_(film)[edit]

I added the reference to the movie Evolution as i felt that selenium was such a key component and the 'savior of the day'. I hope this doesn't need a spoiler warning! Megatonman (talk) 18:46, 14 May 2008 (UTC)

Points to reference that does not mention it[edit]

In this page it says, "Natural sources of selenium include certain selenium-rich soils, and selenium that has been bioconcentrated by certain toxic plants such as locoweed. Anthropogenic sources of selenium include coal burning and the mining and smelting of sulfide ores.[3]"

The link to locoweed points to the locoweed page -- which does not mention selenium. That's a shame, because selenium poisoning is a big time problem in the state of Wyoming.

Probably the locoweed page needs this added.

Thanks, David Small Sept. 29 2008 (talk) 22:08, 28 September 2008 (UTC) (talk) 22:08, 28 September 2008 (UTC)

Shouldn't Selenium be in Category:Biology and pharmacology of chemical elements ?[edit]

Shouldn't Selenium be in Category:Biology and pharmacology of chemical elements ? Eldin raigmore (talk) 20:42, 16 May 2009 (UTC)

The article should mention mitochondria.[edit]

The article should mention that, in eukaryotic cells, selenocysteine is found mostly in organelles that have their own extra-nuclear genetic material, such as mitochondria. It should mention that the evolution of mitochondria was a necessary step towards tolerating the high-oxygen atmosphere caused by the evolution of photosynthes. Eldin raigmore (talk) 23:34, 29 June 2009 (UTC)

Makes sense to some gibberish to others[edit]

Someone one should really consider finding a way to simplify pages like these so those without a master's degree in the subject can understand it. Pyrolord777 (talk) 17:01, 30 December 2009 (UTC)

Lacks an etymology section[edit]

most "element" articles have a section about where the word comes from. This one doesn't. (talk) 20:27, 2 January 2010 (UTC)

Has a sentence in History and global demand.--Stone (talk) 19:55, 5 March 2010 (UTC)

The Venturi view[edit]

Comment left in the article section by an IP user:

"This article contains a number of citations (regarding iodine as an antioxidant) to non-peer reviewed articles, expressing views that are not widely shared in teh scientific community. It would seem that a certain author (VEnturi) is using wikipedia to push his views, rather than go through the conventional route."

There may be something to this. Although the journals are peer-reviewed, so far as I can tell, at the same time, the Venturis are nearly the only authors writing about the evolution of iodine's role in biology. So what do we do? Perhaps summarize more in the main iodine article, offload even more to the main article on iodine in evolution, and there note that these views are those held by one major camp. Here's another example, cited elsewhere. It's a perfectly good article, but like most such things, contains a lot of hypothesis. What is NOT hypothesis is that iodine is heavily and actively concentrated in many non thryoid tissues, so it's surely doing something important there.

Nutr Health. 2009;20(2):119-34. Iodine in evolution of salivary glands and in oral health. Venturi S, Venturi M.

Servizio di Igiene, ASL n. 1, Regione Marche, Pennabilli (PU), Italy.

The authors hypothesize that dietary deficiency or excess of iodine (I) has an important role in oral mucosa and in salivary glands physiology. Salivary glands derived from primitive I-concentrating oral cells, which during embryogenesis, migrate and specialize in secretion of saliva and iodine. Gastro-salivary clearance and secretions of iodides are a considerable part of "gastro-intestinal cycle of iodides", which constitutes about 23% of iodides pool in the human body. Salivary glands, stomach and thyroid share I-concentrating ability by sodium iodide symporter (NIS) and peroxidase activity, which transfers electrons from iodides to the oxygen of hydrogen peroxide and so protects the cells from peroxidation. Iodide seems to have an ancestral antioxidant function in all I-concentrating organisms from primitive marine algae to more recent terrestrial vertebrates. The high I-concentration of thymus supports the important role of iodine in the immune system and in the oral immune defence. In Europe and in the world, I-deficiency is surprisingly present in a large part of the population. The authors suggest that the trophic, antioxidant and apoptosis-inductor actions and the presumed antitumour activity of iodides might be important for prevention of oral and salivary glands diseases, as for some other extrathyroidal pathologies.PMID: 19835108 [PubMed - indexed for MEDLINE]

Anybody else have thoughts on this mattter? If not, I'll cut down and summarize the evolutionary section in this main element article a bit more, to reflect the lack of scientific concensus. Though (as a personal matter) I suspect the Venturis are probably more right than wrong. SBHarris 19:06, 5 March 2010 (UTC)

Nano selenium[edit]

1)Does the sentence really need 5 refs and 2) for me nano size selenium is not notable enough to be mentioned in the elements article itself.

Nano-size selenium has equal efficacy, but much lower toxicity.26,27,28,29,30,31

--Stone (talk) 20:10, 5 March 2010 (UTC)

All refs come from same author (COI). Thus I removed all but one (most recent). Can't evaluate the validity of this. As to nano-Se (and other "nano" elemental solids), IMO it is notable enough for an element article. Materialscientist (talk) 04:58, 6 March 2010 (UTC)

Really ugly element box photo replaced[edit]

Melted, fused selenium comes out as a shiny semi-metal when broken, with facets that look rather like those of silicon crystals. This photo was just ugly in the extreme. I've replaced it with the allotrope photo (yes, I know that's duplicated now), until somebody can come up with something better. SBHarris 04:21, 8 April 2010 (UTC)


I can't find any orthoepic authority for the pronunciation sih-LEN-ee-um. Every dictionary I checked, American and British, only lists sih-LEE-nee-um as a pronunciation. I have therefore removed that pronunciation. Someone can restore it if they can provide any authority for it. nohat (talk) 13:53, 19 November 2010 (UTC)

selenium ref upgrade[edit]

--Stone (talk) 21:32, 11 March 2012 (UTC)


Review on role in health doi:10.1016/S0140-6736(11)61452-9 JFW | T@lk 20:28, 29 April 2012 (UTC)

Electron configuration[edit]

It should be 3 4 4, and not 4 3 4. Why do you write it in that random order? First the 3rd orbit and then 4th. — Preceding unsigned comment added by (talk) 20:29, 25 May 2012 (UTC)

Well, some people believe that the 4s orbital will be filled up before 3d orbital, which is unpredictable in general, and we better follow simple rules of increasing orbital number. Changed. Materialscientist (talk) 23:44, 25 May 2012 (UTC)

Se and impotency[edit]

I rolled back edits by Horoporo because the topic, sexual impotency, is always topical but the citations seemed specialized. We probably should follow WP:MEDRS in this area. In general, my impression is that the media are filled with advice on Se in the diet. IMHO, we should be cautious with well intentioned but potentially misleading/incomplete information that overlaps with the nutritional supplements business.--Smokefoot (talk) 12:54, 6 June 2012 (UTC)

GA Review[edit]


for dead URLs

This review is transcluded from Talk:Selenium/GA1. The edit link for this section can be used to add comments to the review.

Reviewer: Pyrotec (talk · contribs) 13:35, 12 June 2012 (UTC)

I will review. Pyrotec (talk) 13:35, 12 June 2012 (UTC)

Initial comments[edit]

I'm done an initial quick read of the article. On this basis, it looks a very strong contender for GA; and I would expect to be awarding GA at the end of this review. Having said that, I've not yet checked any of the references, so there may be some corrective actions - we will see. Pyrotec (talk) 15:53, 14 June 2012 (UTC)

I'm now reviewing the article against WP:WIAGA section by section, starting from Characteristics and then doing the WP:Lead last. Here I will be mostly highlighting "problems", so a section that is OK is likely to have few comments here. There will be an overall summary at the end of the review. Pyrotec (talk) 16:19, 14 June 2012 (UTC)

  • Characteristics -
    • Physical properties -
  • Appears compliant. I had a look at one of my old course books (Cotton & Wilkinson, 3rd ed, 1972) - Se8 made by evaporation of solutions below 72 C, stable gray form can be grown from hot solutions of Se in aniline or from melts: worth mentioning?
    • Isotopes & Occurrence -
  • These two subsections appear to be compliant.

Pyrotec (talk) 18:13, 15 June 2012 (UTC)

  • History -
  • YesY Pyrotec (talk) - Ref 21 (Trofast, Jan. Berzelius' Discovery of Selenium) has not been fully cited. The article comes from a journal, which has a publisher, journal title, volume & no., date of publication, pages and ISSN: none of these are given in the citation.
  • YesY Pyrotec (talk) - Ref 28 (The need for selenite and molybdate in the formation of formic dehydrogenase by members of the Coli-aerogenes group of bacteria. 57. 1954.) has not been fully cited. The article comes from a journal, which has a personal author, journal title, and page numbers: none of these are given in the citation.
  • Otherwise OK.
  • Production -
  • Appears compliant.
  • Chemical compounds -
    • Chalcogen compounds -
  • The text appears to contradict itself in respect of SeO3: i.e. "Selenium forms two stable oxides: selenium dioxide (SeO2) and selenium trioxide (SeO3). .... Unlike sulfur, which forms a stable trioxide, selenium trioxide is unstable and decomposes to the dioxide above 185 °C". I suspect that the problem lies in the wording of the "Unlike sulfur, ..." sentence.
    Yes check.svg Done SO3 is stable, but SeO3 isn't. I've fixed it. Double sharp (talk) 15:47, 16 June 2012 (UTC)
  • There is no mention of how selenium trioxide is made (I looked it up and also when it was first prepared - 1930, by the way).
    Yes check.svg Done Would that be enough? Double sharp (talk) 15:47, 16 June 2012 (UTC)
  • YesY Pyrotec (talk) - The equation: "3 Se + 4 HNO3 → 3 H2SeO3 + 4 NO" is balanced for Se and N but not H and O; there appears to be one molecule of water missing.
    • Halogen compounds -

...stopping for now. To be continued. Pyrotec (talk) 19:24, 15 June 2012 (UTC)

In passing, I've completed refs. 21 and 28 and the HNO3 reaction (water is also missing in the source book), though don't expect much from me on more time-consuming issues :-). Materialscientist (talk) 01:22, 16 June 2012 (UTC)
Thanks Materialscientist. Pyrotec (talk) 13:45, 16 June 2012 (UTC)
    • Selenides -
  • The reaction: "Al2Se3 + 6 H2O → 8 Al2O3 + H2Se" is clearly wrong (or perhaps the vandals have struck?).
    Yes check.svg Done Double sharp (talk) 16:06, 16 June 2012 (UTC)
    • Other compounds -
  • I find the wikilink on the chemical compound S4N4 visually distracting. I would prefer the link to be on its proper name Tetrasulfur tetranitride with the chemical formula afterwards. It has been done below for "(sulfur hexafluoride), SeF6", why the inconsistency?
    Yes check.svg Done Double sharp (talk) 16:06, 16 June 2012 (UTC)
    • Organoselenium compounds -
  • Looks OK.
  • Applications -
  • Ref 54 (^ Davis, Joseph R. (2001). %7C page 278 Copper and Copper Alloys. ISBN 978-0-87170-726-0.) is strangely cited. It's a book, but the publisher is not cited; the page number appears to be 278, but its not clear what the "%7C page 278" means.
    Yes check.svg Done Double sharp (talk) 16:11, 16 June 2012 (UTC)
  • Refs 58, 59, 60 and 66 are books, but the publishers are not cited.
  • Biological role -

...stopping for now. To be continued. Pyrotec (talk) 15:08, 16 June 2012 (UTC)

  • I'm not sure I understand "2 GSH + H2O2----GSH-Px → GSSG + 2 H2O". The equation "2 GSH + H2O2 → GSSG + 2 H2O" seems to make more sense and its almost identical to the equation in Glutathione peroxidase.
  • Otherwise, OK.
  • Looks OK.

Pyrotec (talk) 08:27, 17 June 2012 (UTC)

Overall summary[edit]

GA review – see WP:WIAGA for criteria

  1. Is it reasonably well written?
    A. Prose quality:
    B. MoS compliance for lead, layout, words to watch, fiction, and lists:
  2. Is it factually accurate and verifiable?
    A. References to sources:
    Well referenced.
    B. Citation of reliable sources where necessary:
    Well referenced.
    C. No original research:
  3. Is it broad in its coverage?
    A. Major aspects:
    B. Focused:
  4. Is it neutral?
    Fair representation without bias:
  5. Is it stable?
    No edit wars, etc:
  6. Does it contain images to illustrate the topic?
    A. Images are copyright tagged, and non-free images have fair use rationales:
    B. Images are provided where possible and appropriate, with suitable captions:
  7. Overall:
    Pass or Fail:

I'm awarding this article GA status. Having looked at other chemical/element articles, such as Oxygen which is now an FA, I suspect that Selenium could in due course become a strong candidate for WP:FAC. Congratulations on a fine article. Pyrotec (talk) 08:27, 17 June 2012 (UTC)

Selenium health effects and RCTs[edit]

The section on controversial health effects currently says the following:

A number of correlative epidemiological studies have implicated selenium deficiency (as measured by blood levels) in a number of serious or chronic diseases, such as cancer,[110] diabetes,[110] HIV/AIDS,[111] and tuberculosis. In addition, selenium supplementation has been found to be a chemopreventive for some types of cancer in some types of rodents. However, in randomized, blinded, controlled prospective trials in humans, selenium supplementation has not succeeded in reducing the incidence of any disease, nor has a meta-analysis of such selenium supplementation studies detected a decrease in overall mortality.

This is factually incorrect or at best misleading; health benefits, including a statistically significant reduced mortality from cancer, has been found in at least one RCT and not only in epidemiological and laboratory studies. The overall picture when averaging a bunch of trials appears to show a mortality RR 0.97 per the Cochrane review, which is a nonstatistically significant decrease. However, this may mislead the reader as to what the research actually shows. The most notable RCT which reduced cancer is the NPC study (see, e.g., Hatfield & Gladyshev 2009 for commentary). This is commonly viewed as being "disproved" by a larger trial called SELECT by the press and unsurprisingly is not going to show up in an abstract (perhaps not even in the full-text of the Cochrane review covering all antioxidants, which I don't have); however, researchers commenting often acknowledge that NPC was relatively focused on those with low serum selenium (for example, Hatfield & Gladyshev mention that "subjects in the NPC trial were selected, in part, on the basis of their having relatively low serum selenium levels (5); it was in this cohort that selenium supplementation was effective in reducing cancer risks") whereas I recall that in the SELECT, subjects were generally replete (an odd decision on the part of researchers, given that selenium was widely-regarded as toxic for many years). This needs to be corrected in the article. II | (t - c) 09:26, 21 April 2013 (UTC)

Grey selenium[edit]

What is electrical resistnce of grey selenium?

That page informs that only 12 μΩcm (20 °C). It would be lower than resistivity of many metals.

What is thermal conductivity of grey allotrope of Se?

The same page informs that 2,04 W m-1K-1.

Is grey selenium ductile, malleable or elastic, or it is brittle? (talk) 20:41, 23 October 2013 (UTC)

Why grey selenium is really often counts as metalloid (sometimes even (heavy) metal)) but black phosphorus and graphite only to nonmetals? They are much so similar to classify them separately in metallic character. Grey Se is famous photoconductor, but has wider band gap (about 1.8 eV) than black phosphorus (0.34 eV, narrower even than germanium and silicon). Carbon and phosphorus are associated with biology, but selenium is associated with toxicity. Maybe it is a source of that prejudice? Black P has thermal conductivity much over four times better than Se "metal". (talk) 10:49, 26 October 2013 (UTC)

I suppose it's a case of books parroting each other out of context without thinking about the subject at hand? Se does behave like As in aquatic environments IIRC, so a metalloid classification of Se and not C and P isn't wholly unwarranted in that field. But I would say that if you're going to classify Se generally as a metalloid, C, P, and I should also be counted as metalloids. On Wikipedia we do not put any of them as metalloids, which is also consistent. See Metalloid for more info. On Wikipedia we have tried to use a better classification of metalloids, but we don't have control over what authors write and have to just report what they say (not that we have to follow their classification without question!). Double sharp (talk) 11:54, 26 October 2013 (UTC)

I agree that C, P and Se are too similar to make a difference in "metallicity class" among them (in Wikipedia they are named as "polyatomic nonmetals" (along with sulfur), which border to typical metalloids (they are on the left of them)). I am irritating when I see a periodic table in which only selenium (from these three elements) is classified as a metalloid. In German Wikipedia this flawful classification occurs. (talk) 15:48, 26 October 2013 (UTC)

I am asking qustions gain: what is electrical conductivity of pure hexgonal selenium (especilly internally stressed, in darkness)? What is its coordination number? (talk) 00:34, 13 November 2013 (UTC)

Is there a difference between trigonal and hexagonal Se? Hexagonal (metallic, grey form) probably looks even silvery, but has far much lower melting and boiling point than graphite and diamond. I think that grey form can be confused with black allotrope, which is significantly darker. What is band gap and electrical conductivity of GREY (not trigonal or black) allotrope of Se?

There are many pages in which is written that hexagonal Se is the same as hexagonal form of its element.

Because trigonal tellurium has a much higher conductivity than trigonal selenium does (in the dark, 3 - 5 x 10-5 S/cm) this demonstration provides a potentially useful way for tuning the electrical conductivity of these nanostructures...

It would be not so large conductivity, similar to that of pure fullerenes. Band gap of trigonal Se is about 1,6 - 1,8 eV (from Internet), also similar to band gaps of fullerenes.

But there are also pages in which "selenium metal" looks really like a metal - shiny, silvery-white substance:

In the lower part of that page there is many about lead, not about Se and it looks that on the page there is probably a picture of pure Pb, not pure Se. (talk) 11:48, 16 November 2013 (UTC)

questions about numbers[edit]

Just a couple of notes. The percentages in the section of the different uses of Se don't add up to 100%, they make 90%. Perhaps the other 10% is used in processes in industry that are to small and numerous to go through individually or perhaps this is a mistake. If it is the former, then a note could be added to say this. — Preceding unsigned comment added by (talk) 12:13, 25 March 2014 (UTC)