Editing Hydrogen sulfide (section)

==Hydrogen sulfide in the natural environment==
===Microbial: The sulfur cycle===
{{Anchor|Microbial|Sulfur cycle}}
{{main|Sulfur cycle}}
[[File:Teichschlamm1.jpg|thumb|left|A drained pond, showing the layer of [[sludge]] on the bottom; its black colour is due to the presence of metal sulfides, the result of reactions with hydrogen sulfide produced by bacteria]]

Hydrogen sulfide is a central participant in the [[sulfur cycle]], the [[biogeochemical cycle]] of sulfur on Earth.<ref>{{cite book |doi=10.1007/978-94-017-9269-1_10 |chapter=Hydrogen Sulfide: A Toxic Gas Produced by Dissimilatory Sulfate and Sulfur Reduction and Consumed by Microbial Oxidation |title=The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment |series=Metal Ions in Life Sciences |year=2014 |last1=Barton |first1=Larry L. |last2=Fardeau |first2=Marie-Laure |last3=Fauque |first3=Guy D. |volume=14 |pages=237–277 |pmid=25416397 |isbn=978-94-017-9268-4 }}</ref>

In the absence of [[oxygen]], [[Sulfur-reducing bacteria|sulfur-reducing]] and [[Sulfate-reducing bacteria|sulfate-reducing]] bacteria derive energy from [[redox|oxidizing]] hydrogen or organic molecules by reducing elemental sulfur or sulfate to hydrogen sulfide. Other bacteria liberate hydrogen sulfide from sulfur-containing [[amino acid]]s; this gives rise to the odor of rotten eggs and contributes to the odor of [[flatulence]].

As organic matter decays under low-oxygen (or [[Hypoxia (environmental)|hypoxic]]) conditions (such as in swamps, [[eutrophic]] lakes or [[Dead zone (ecology)|dead zones]] of oceans), sulfate-reducing bacteria will use the sulfates present in the water to oxidize the organic matter, producing hydrogen sulfide as waste. Some of the hydrogen sulfide will react with metal ions in the water to produce metal sulfides, which are not water-soluble. These metal sulfides, such as ferrous sulfide FeS, are often black or brown, leading to the dark color of [[sludge]].

Several groups of bacteria can use hydrogen sulfide as fuel, oxidizing it to elemental sulfur or to sulfate by using dissolved oxygen, metal oxides (e.g., [[Iron(III) oxide-hydroxide|iron oxyhydroxides]] and [[manganese oxide]]s), or nitrate as electron acceptors.<ref>{{cite book|last1=Jørgensen |first1=B. B. |first2=D. C. |last2=Nelson |date=2004 |chapter=Sulfide oxidation in marine sediments: Geochemistry meets microbiology |pages=36–81 |editor1-first=J. P. |editor1-last=Amend |editor2-first=K. J. |editor2-last=Edwards |editor3-first=T. W. |editor3-last=Lyons |title=Sulfur Biogeochemistry – Past and Present |publisher=Geological Society of America}}</ref>

The [[purple sulfur bacteria]] and the [[green sulfur bacteria]] use hydrogen sulfide as an [[electron donor]] in [[photosynthesis]], thereby producing elemental sulfur. This mode of photosynthesis is older than the mode of [[cyanobacteria]], [[algae]], and [[plant]]s, which uses water as electron donor and liberates oxygen.

The biochemistry of hydrogen sulfide is a key part of the chemistry of the [[Iron-sulfur world theory|iron-sulfur world]]. In this model of the [[origin of life]] on Earth, geologically produced hydrogen sulfide is postulated as an electron donor driving the reduction of carbon dioxide.<ref>{{cite journal |last1=Wächtershäuser |first1=G |title=Before enzymes and templates: theory of surface metabolism. |journal=Microbiological Reviews |date=December 1988 |volume=52 |issue=4 |pages=452–484 |doi=10.1128/MMBR.52.4.452-484.1988 |pmid=3070320 |pmc=373159 }}</ref>

===Animals===
Hydrogen sulfide is lethal to most animals, but a few highly specialized species ([[extremophile]]s) do thrive in habitats that are rich in this compound.<ref name=Tobler2008>{{cite journal |last1=Tobler |first1=M |last2=Riesch |first2=R. |last3=García de León |first3=F. J. |last4=Schlupp |first4=I. |last5=Plath |first5=M. |date=2008 |title=Two endemic and endangered fishes, ''Poecilia sulphuraria'' (Álvarez, 1948) and ''Gambusia eurystoma'' Miller, 1975 (Poeciliidae, Teleostei) as only survivors in a small sulphidic habitat |journal=Journal of Fish Biology |volume=72 |issue=3 |pages=523–533 |doi=10.1111/j.1095-8649.2007.01716.x |bibcode=2008JFBio..72..523T |s2cid=27303725 }}</ref>

In the deep sea, [[hydrothermal vent]]s and [[cold seep]]s with high levels of hydrogen sulfide are home to a number of extremely specialized lifeforms, ranging from bacteria to fish.{{which|date=June 2015}}<ref>{{cite journal|last1=Bernardino|first1=Angelo F. |last2=Levin|first2=Lisa A. |last3=Thurber|first3=Andrew R. |last4=Smith|first4=Craig R. |date=2012 |title=Comparative Composition, Diversity and Trophic Ecology of Sediment Macrofauna at Vents, Seeps and Organic Falls. |journal=PLOS ONE |volume=7|issue=4|page=e33515|doi=10.1371/journal.pone.0033515 |pmid=22496753 |pmc=3319539|bibcode=2012PLoSO...733515B|doi-access=free }}</ref> Because of the absence of sunlight at these depths, these ecosystems rely on [[chemosynthesis]] rather than [[photosynthesis]].<ref>{{cite web|work=Marine Society of Australia|url=http://www.mesa.edu.au/deep_sea/hydrothermal_vents.asp|title=Hydrothermal Vents|access-date=28 December 2014}}</ref>

Freshwater springs rich in hydrogen sulfide are mainly home to invertebrates, but also include a small number of fish: ''[[Cyprinodon bobmilleri]]'' (a [[pupfish]] from Mexico), ''[[Limia sulphurophila]]'' (a [[poeciliid]] from the [[Dominican Republic]]), ''[[Gambusia eurystoma]]'' (a poeciliid from Mexico), and a few ''[[Poecilia]]'' (poeciliids from Mexico).<ref name=Tobler2008/><ref>{{cite journal|last1=Palacios|first1=Maura |last2=Arias-Rodríguez|first2=Lenín |last3=Plath|first3=Martin |last4=Eifert|first4=Constanze |last5=Lerp|first5=Hannes |last6=Lamboj|first6=Anton |last7=Voelker |first7=Gary|last8=Tobler|first8=Michael |date=2013 |title=The Rediscovery of a Long Described Species Reveals Additional Complexity in Speciation Patterns of Poeciliid Fishes in Sulfide Springs.|journal=PLOS ONE |volume=8|issue=8 |page=e71069|doi=10.1371/journal.pone.0071069 |pmid=23976979 |pmc=3745397|bibcode=2013PLoSO...871069P|doi-access=free }}</ref> Invertebrates and microorganisms in some cave systems, such as [[Movile Cave]], are adapted to high levels of hydrogen sulfide.<ref>{{cite journal |last1=Kumaresan |first1=Deepak |last2=Wischer |first2=Daniela |last3=Stephenson |first3=Jason |last4=Hillebrand-Voiculescu |first4=Alexandra |last5=Murrell |first5=J. Colin |title=Microbiology of Movile Cave—A Chemolithoautotrophic Ecosystem |journal=Geomicrobiology Journal |date=16 March 2014 |volume=31 |issue=3 |pages=186–193 |doi=10.1080/01490451.2013.839764 |bibcode=2014GmbJ...31..186K |s2cid=84472119 }}</ref>

===Interstellar and planetary occurrence===
Hydrogen sulfide has often been detected in the interstellar medium.<ref>{{cite journal |last1=Despois |first1=D. |title=Radio Line Observations Of Molecular And Isotopic Species In Comet C/1995 O1 (Hale-Bopp) |journal=Earth, Moon, and Planets |date=1997 |volume=79 |issue=1/3 |pages=103–124 |doi=10.1023/A:1006229131864 |bibcode=1997EM&P...79..103D |s2cid=118540103 }}</ref> It also occurs in the clouds of planets in our solar system.<ref>{{cite journal |last1=Irwin |first1=Patrick G. J. |last2=Toledo |first2=Daniel |last3=Garland |first3=Ryan |last4=Teanby |first4=Nicholas A. |last5=Fletcher |first5=Leigh N. |last6=Orton |first6=Glenn A. |last7=Bézard |first7=Bruno |title=Detection of hydrogen sulfide above the clouds in Uranus's atmosphere |journal=Nature Astronomy |date=May 2018 |volume=2 |issue=5 |pages=420–427 |doi=10.1038/s41550-018-0432-1 |bibcode=2018NatAs...2..420I |hdl=2381/42547 |s2cid=102775371 |url=https://research-information.bris.ac.uk/en/publications/detection-of-hydrogen-sulfide-above-the-clouds-in-uranuss-atmosphere(099d2fdd-8d3d-4e78-b009-bebffdece302).html |hdl-access=free }}</ref><ref name=lissauer2019>{{Cite book |title=Fundamental Planetary Sciences : physics, chemistry, and habitability |last1=Lissauer|first1=Jack J. |last2=de Pater|first2=Imke |year=2019 |publisher=Cambridge University Press |pages=149–152|isbn=9781108411981 |location=New York, NY, USA }}{{page needed|date=September 2020}}</ref>

===Mass extinctions===
{{main|Anoxic event}}
[[File:Hydrogen Sulfide Emissions off of Africa.jpg|thumb|A hydrogen sulfide bloom (green) stretching for about 150km along the coast of Namibia. As oxygen-poor water reaches the coast, bacteria in the organic-matter rich sediment produce hydrogen sulfide, which is toxic to fish.]]
Hydrogen sulfide has been implicated in several [[Extinction event|mass extinctions]] that have occurred in the Earth's past. In particular, a buildup of hydrogen sulfide in the atmosphere may have caused, or at least contributed to, the [[Permian-Triassic extinction event]] 252 million years ago.<ref name="sciam" /><ref>{{cite journal |last1=Lamarque |first1=J.-F. |last2=Kiehl |first2=J. T. |last3=Orlando |first3=J. J. |date=16 January 2007 |title=Role of hydrogen sulfide in a Permian-Triassic boundary ozone collapse |journal=[[Geophysical Research Letters]] |volume=34 |issue=2 |pages=1–4 |doi=10.1029/2006GL028384 |bibcode=2007GeoRL..34.2801L |s2cid=55812439 |doi-access=free }}</ref><ref name=Kump2005>{{cite journal |last1=Kump |first1=Lee |last2=Pavlov |first2=Alexander |first3=Michael A. |last3=Arthur |title=Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia |journal=[[Geology (journal)|Geology]] |date=1 May 2005 |volume=33 |issue=5 |pages=397–400 |url=https://www.researchgate.net/publication/253144294 |doi=10.1130/G21295.1 |bibcode=2005Geo....33..397K |access-date=2 April 2023}}</ref>

Organic residues from these extinction boundaries indicate that the oceans were anoxic (oxygen-depleted) and had species of shallow plankton that metabolized {{chem2|H2S}}. The formation of {{chem2|H2S}} may have been initiated by massive volcanic eruptions, which emitted [[carbon dioxide]] and [[methane]] into the atmosphere, which warmed the oceans, lowering their capacity to absorb oxygen that would otherwise oxidize {{chem2|H2S}}. The increased levels of hydrogen sulfide could have killed oxygen-generating plants as well as depleted the ozone layer, causing further stress. Small {{chem2|H2S}} blooms have been detected in modern times in the [[Dead Sea]] and in the [[Atlantic Ocean]] off the coast of [[Namibia]].<ref name="sciam">{{cite magazine|url=https://www.scientificamerican.com/article/impact-from-the-deep/|title=Impact from the Deep|magazine=Scientific American | date = October 2006 }}</ref>