Editing Colloid (section)

==In the environment==
Colloidal particles can also serve as transport vectors <ref>{{Cite book
|last = Frimmel|first = Fritz H. |author2=Frank von der Kammer |author3=Hans-Curt Flemming
|year = 2007
|title = Colloidal transport in porous media
|edition = 1
|publisher = Springer
|page=292
|isbn = 978-3-540-71338-8|url = https://www.springer.com/earth+sciences/book/978-3-540-71338-8?detailsPage=toc}}</ref>
of diverse contaminants in the surface water (sea water, lakes, rivers, freshwater bodies) and in underground water circulating in fissured rocks<ref>{{Cite journal
| last = Alonso| first = U.
|author2=T. Missana |author3=A. Patelli |author4=V. Rigato
 | year = 2007
| title = Bentonite colloid diffusion through the host rock of a deep geological repository
| journal = Physics and Chemistry of the Earth, Parts A/B/C
| volume = 32
| issue = 1–7
| pages = 469–476
| doi = 10.1016/j.pce.2006.04.021|bibcode = 2007PCE....32..469A }}</ref>
(e.g. [[limestone]], [[sandstone]], [[granite]]). Radionuclides and heavy metals easily [[sorption|sorb]] onto colloids suspended in water. Various types of colloids are recognised: inorganic colloids (e.g. [[clay]] particles, silicates, [[ferrihydrite|iron oxy-hydroxide]]s), organic colloids ([[humic]] and [[fulvic]] substances). When heavy metals or radionuclides form pure colloids, the term "''[[eigencolloid]]''" is used to designate pure phases, i.e., pure Tc(OH)<sub>4</sub>, U(OH)<sub>4</sub>, or Am(OH)<sub>3</sub>. Colloids have been suspected for the long-range transport of plutonium on the [[Nevada Nuclear Test Site]]. They have been the subject of detailed studies for many years. However, the mobility of inorganic colloids is very low in compacted [[bentonite]]s and in deep clay formations<ref>{{Cite journal
|last1 = Voegelin
|first1 = A.
|last2 = Kretzschmar
|title = Stability and mobility of colloids in Opalinus Clay
|publisher = Institute of Terrestrial Ecology, ETH Zürich
|volume = Nagra Technical Report 02-14.
|date = December 2002
|issn = 1015-2636
|url = http://www.nagra.ch/documents/database/dokumente/%24default/Default%20Folder/Publikationen/e%5Fntb02%2D14.pdf
|page = 47
|first2 = R.
|journal = Technischer Bericht / NTB
|access-date = 22 February 2009
|archive-url = https://web.archive.org/web/20090309172632/http://www.nagra.ch/documents/database/dokumente/%24default/Default%20Folder/Publikationen/e%5Fntb02%2D14.pdf
|archive-date = 9 March 2009
|url-status = dead
}}</ref>
because of the process of [[ultrafiltration]] occurring in dense clay membrane.<ref>{{Cite web
 |title       = Diffusion of colloids in compacted bentonite
 |url         = http://www.kth.se/che/divisions/nuchem/research/1.19965?l=en_UK
 |access-date  = 12 February 2009
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20090304210603/http://www.kth.se/che/divisions/nuchem/research/1.19965?l=en_UK
 |archive-date = 4 March 2009
}}</ref>
The question is less clear for small organic colloids often mixed in porewater with truly dissolved organic molecules.<ref>{{Cite journal
| last = Wold | first = Susanna
|author2=Trygve Eriksen
| year = 2007
| title = Diffusion of humic colloids in compacted bentonite
| journal = Physics and Chemistry of the Earth, Parts A/B/C
| doi = 10.1016/j.pce.2006.05.002
| volume = 32
| issue = 1–7
| pages = 477–484|bibcode = 2007PCE....32..477W }}</ref>

In [[soil science]], the colloidal fraction in [[soil]]s consists of tiny [[clay]] and [[humus]] [[particle]]s that are less than 1μm in [[diameter]] and carry either positive and/or negative [[Electric charge|electrostatic charges]] that vary depending on the chemical conditions of the soil sample, i.e. [[soil pH]].<ref>{{Cite book|title=Elements of the nature and properties of soils|author1=Weil, Ray|author2=Brady, Nyle C.|isbn=9780133254594|edition= Fourth|location=New York, NY|oclc=1035317420|date = 11 October 2018}}</ref>