Editing Biodegradation (section)

== Plastics ==
{{Main|Biodegradable plastic#Examples of biodegradable plastics}}

The term Biodegradable Plastics refers to materials that maintain their mechanical strength during practical use but break down into low-weight compounds and non-toxic byproducts after their use.<ref name = "Ikada_2000">{{cite journal|last1=Ikada|first1=Yoshito|last2=Tsuji|first2=Hideto|name-list-style=vanc|date=February 2000|title=Biodegradable polyesters for medical and ecological applications|journal=Macromolecular Rapid Communications|volume=21|issue=3|pages=117–132|doi=10.1002/(sici)1521-3927(20000201)21:3<117::aid-marc117>3.0.co;2-x|url=http://web.mit.edu/course/10/10.569/www/ikadaPEreview.pdf|access-date=2011-03-08|archive-date=2016-03-05|archive-url=https://web.archive.org/web/20160305143418/http://web.mit.edu/course/10/10.569/www/ikadaPEreview.pdf|url-status=live}}</ref> This breakdown is made possible through an attack of microorganisms on the material, which is typically a non-water-soluble polymer.<ref name=":1" /> Such materials can be obtained through chemical synthesis, fermentation by microorganisms, and from chemically modified natural products.<ref>{{cite journal|vauthors=Flieger M, Kantorová M, Prell A, Rezanka T, Votruba J|title=Biodegradable plastics from renewable sources|journal=Folia Microbiologica|volume=48|issue=1|pages=27–44|date=January 2003|pmid=12744074|doi=10.1007/bf02931273|s2cid=32800851}}</ref>

[[Plastics]] biodegrade at highly variable rates.  [[Polyvinylchloride|PVC]]-based plumbing is selected for handling [[sewage]] because PVC resists biodegradation.  Some packaging materials on the other hand are being developed that would degrade readily upon exposure to the environment.<ref>{{cite journal|last1=Kyrikou|first1=Ioanna|last2=Briassoulis|first2=Demetres|name-list-style=vanc|date=12 Apr 2007|title=Biodegradation of Agricultural Plastic Films: A Critical Review|journal=Journal of Polymers and the Environment|volume=15|issue=2|pages=125–150|doi=10.1007/s10924-007-0053-8|bibcode=2007JPEnv..15..125K |s2cid=195331133}}</ref> Examples of [[synthetic polymer]]s that biodegrade quickly include [[polycaprolactone]], other [[polyesters]] and aromatic-aliphatic esters, due to their ester bonds being susceptible to attack by water. A prominent example is [[poly-3-hydroxybutyrate]], the renewably derived [[polylactic acid]]. Others are the cellulose-based cellulose acetate and celluloid (cellulose nitrate).

[[File:Polylactid sceletal.svg|thumb|upright|[[Polylactic acid]] is an example of a plastic that biodegrades quickly.]]

Under [[anaerobic decomposition|low oxygen]] conditions plastics break down more slowly. The breakdown process can be accelerated in specially designed [[compost | compost heap]]. Starch-based plastics will degrade within two to four months in a home compost bin, while polylactic acid is largely undecomposed, requiring higher temperatures.<ref>{{cite web|url=http://www3.imperial.ac.uk/pls/portallive/docs/1/33773706.PDF|archive-url=https://web.archive.org/web/20130602155241/http://www3.imperial.ac.uk/pls/portallive/docs/1/33773706.PDF|archive-date=2013-06-02|url-status=live|title=Section 6: Biodegradability of Packaging Waste|publisher=Imperial College London|access-date=2014-03-02}}</ref> Polycaprolactone and polycaprolactone-starch composites decompose slower, but the starch content accelerates decomposition by leaving behind a porous, high surface area polycaprolactone. Nevertheless, it takes many months.<ref>{{cite journal|last1=Wu|first1=Chin-San|name-list-style=vanc|title=Physical properties and biodegradability of maleated-polycaprolactone/starch composite|journal=Polymer Degradation and Stability|date=January 2003|volume=80|issue=1|pages=127–134|doi=10.1016/S0141-3910(02)00393-2|url=http://www.kyu.edu.tw/93/epaperv6/93-129.pdf|citeseerx=10.1.1.453.4220|access-date=2012-06-23|archive-date=2016-03-04|archive-url=https://web.archive.org/web/20160304072701/http://www.kyu.edu.tw/93/epaperv6/93-129.pdf|url-status=dead}}</ref>

In 2016, a bacterium named ''[[Ideonella sakaiensis]]'' was found to biodegrade [[Polyethylene terephthalate|PET]]. In 2020, the PET degrading enzyme of the bacterium, [[PETase]], has been genetically modified and combined with [[MHETase]] to break down PET faster, and also degrade [[Polyethylene 2,5-furandicarboxylate|PEF]].<ref>{{cite news|last1=Carrington|first1=Damian|title=New super-enzyme eats plastic bottles six times faster|url=https://www.theguardian.com/environment/2020/sep/28/new-super-enzyme-eats-plastic-bottles-six-times-faster|access-date=12 October 2020|work=The Guardian|date=28 September 2020|archive-date=12 October 2020|archive-url=https://web.archive.org/web/20201012004245/https://www.theguardian.com/environment/2020/sep/28/new-super-enzyme-eats-plastic-bottles-six-times-faster|url-status=live}}</ref><ref>{{cite news|title=Plastic-eating enzyme 'cocktail' heralds new hope for plastic waste|url=https://phys.org/news/2020-09-plastic-eating-enzyme-cocktail-heralds-plastic.html|access-date=12 October 2020|work=phys.org|language=en|archive-date=11 October 2020|archive-url=https://web.archive.org/web/20201011210353/https://phys.org/news/2020-09-plastic-eating-enzyme-cocktail-heralds-plastic.html|url-status=live}}</ref><ref>{{cite journal|last1=Knott|first1=Brandon C.|last2=Erickson|first2=Erika|last3=Allen|first3=Mark D.|last4=Gado|first4=Japheth E.|last5=Graham|first5=Rosie|last6=Kearns|first6=Fiona L.|last7=Pardo|first7=Isabel|last8=Topuzlu|first8=Ece|last9=Anderson|first9=Jared J. |last10=Austin |first10=Harry P.|last11=Dominick|first11=Graham|last12=Johnson|first12=Christopher W.|last13=Rorrer|first13=Nicholas A.|last14=Szostkiewicz|first14=Caralyn J.|last15=Copié|first15=Valérie|last16=Payne|first16=Christina M.|last17=Woodcock|first17=H. Lee|last18=Donohoe|first18=Bryon S.|last19=Beckham|first19=Gregg T. |last20=McGeehan |first20=John E.|title=Characterization and engineering of a two-enzyme system for plastics depolymerization|journal=Proceedings of the National Academy of Sciences|date=24 September 2020|volume=117|issue=41|pages=25476–25485|doi=10.1073/pnas.2006753117|pmid=32989159|pmc=7568301|bibcode=2020PNAS..11725476K|language=en|issn=0027-8424|doi-access=free}}</ref> In 2021, researchers reported that a mix of microorganisms from [[Cattle#Digestive system|cow stomachs]] could break down three types of plastics.<ref>{{cite news|last1=Spary|first1=Sara|title=Cows' stomachs can break down plastic, study finds|url=https://edition.cnn.com/2021/07/02/world/cows-plastic-scli-intl-scn/index.html|access-date=14 August 2021|work=CNN|archive-date=14 August 2021|archive-url=https://web.archive.org/web/20210814141350/https://edition.cnn.com/2021/07/02/world/cows-plastic-scli-intl-scn/index.html|url-status=live}}</ref><ref>{{cite journal|last1=Quartinello|first1=Felice|last2=Kremser|first2=Klemens|last3=Schoen|first3=Herta|last4=Tesei|first4=Donatella|last5=Ploszczanski|first5=Leon|last6=Nagler|first6=Magdalena|last7=Podmirseg|first7=Sabine M.|last8=Insam|first8=Heribert|last9=Piñar|first9=Guadalupe |last10=Sterflingler |first10=Katja|last11=Ribitsch|first11=Doris|last12=Guebitz|first12=Georg M.|title=Together Is Better: The Rumen Microbial Community as Biological Toolbox for Degradation of Synthetic Polyesters|journal=Frontiers in Bioengineering and Biotechnology|date=2021|volume=9|doi=10.3389/fbioe.2021.684459|language=English|issn=2296-4185|doi-access=free}}</ref>

Many [[plastic producer]]s have gone so far even to say that their plastics are compostable, typically listing [[corn starch]] as an ingredient. However, these claims are questionable because the [[plastics industry]] operates under its own definition of compostable:
:"that which is capable of undergoing biological decomposition in a compost site such that the material is not visually distinguishable and breaks down into carbon dioxide, water, inorganic compounds and biomass at a rate consistent with known compostable materials." (Ref: [[ASTM]] D 6002)<ref>{{cite web|url=http://www.compostable.info/compostable.htm|title=Compostable|publisher=Compostable.info|access-date=2014-03-02|archive-date=2020-11-12|archive-url=https://web.archive.org/web/20201112012056/http://www.compostable.info/compostable.htm|url-status=live}}</ref>

The term "composting" is often used informally to describe the biodegradation of packaging materials. Legal definitions exist for compostability, the process that leads to compost.  Four criteria are offered by the European Union:<ref name="EN 13432">{{cite web|title=Requirements of the EN 13432 standard|url=https://docs.european-bioplastics.org/publications/bp/EUBP_BP_En_13432.pdf|archive-url=https://web.archive.org/web/20180924190657/https://docs.european-bioplastics.org/publications/bp/EUBP_BP_En_13432.pdf|archive-date=2018-09-24|url-status=live|date=April 2015|work=European Bioplastics|access-date=July 22, 2017|location=Brussels, Belgium}}</ref><ref>{{cite book |vauthors=Breulmann M, Künkel A, Philipp S, Reimer V, Siegenthaler KO, Skupin G, Yamamoto M |chapter=Polymers, Biodegradable |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2012 |publisher=Wiley-VCH |location=Weinheim |doi=10.1002/14356007.n21_n01 |isbn=978-3527306732 }}</ref>
#'''Chemical composition''': volatile matter and heavy metals as well as fluorine should be limited.
#'''Biodegradability''': the conversion of >90% of the original material into {{CO2}}, water and minerals by biological processes within 6 months.
#'''Disintegrability''': at least 90% of the original mass should be decomposed into particles that are able to pass through a 2x2 mm sieve.
#'''Quality''': absence of toxic substances and other substances that impede composting.