Editing Hydrogen peroxide (section)

==Natural occurrence==
Hydrogen peroxide is produced by various biological processes mediated by [[enzyme]]s.

Hydrogen peroxide has been detected in surface water, in groundwater, and in the [[atmosphere]]. It can also form when water is exposed to UV light.<ref>{{Cite journal |last1=Li |first1=Juan |last2=Zhang |first2=Qi |last3=Chen |first3=Baiyang |last4=Wang |first4=Lei |last5=Zhu |first5=Rongshu |last6=Yang |first6=Jie |date=2021 |title=Hydrogen peroxide formation in water during the VUV/UV irradiation process: Impacts and mechanisms of selected anions |url=https://linkinghub.elsevier.com/retrieve/pii/S0013935121000451 |journal=Environmental Research |language=en |volume=195 |pages=110751 |doi=10.1016/j.envres.2021.110751|pmid=33472042 |bibcode=2021ER....19510751L }}</ref> Sea water contains 0.5 to 14&nbsp;μg/L of hydrogen peroxide, and freshwater contains 1 to 30&nbsp;μg/L.<ref name="offer"/> Concentrations in air are about 0.4 to 4&nbsp;μg/m<sup>3</sup>, varying over several [[orders of magnitude]] depending in conditions such as season, altitude, daylight and water vapor content. In rural nighttime air it is less than 0.014&nbsp;μg/m<sup>3</sup>, and in moderate [[Smog#Photochemical smog|photochemical smog]] it is 14 to 42&nbsp;μg/m<sup>3</sup>.<ref name="OEL 1996">[https://www.ecetoc.org/wp-content/uploads/2021/10/SR-10.pdf Special Report No. 10. Hydrogen Peroxide. OEL Criteria Document.] CAS No. 7722-84-1. July 1996.</ref>

The amount of hydrogen peroxide in biological systems can be assayed using a [[Enzyme assay|fluorometric assay]].<ref name="pmid8074285">{{cite journal |vauthors = Rapoport R, Hanukoglu I, Sklan D |title = A fluorimetric assay for hydrogen peroxide, suitable for NAD(P)H-dependent superoxide generating redox systems |journal = Analytical Biochemistry |volume = 218 |issue = 2 |pages = 309–313 |date = May 1994 |pmid = 8074285 |doi = 10.1006/abio.1994.1183 |url = https://zenodo.org/record/890715 |access-date = 1 July 2019 |url-status = live |s2cid = 40487242 |archive-url = https://web.archive.org/web/20200318091435/https://zenodo.org/record/890715 |archive-date = 18 March 2020}}</ref>