# Photodegradation > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Photodegradation > Markdown URL: https://mediated.wiki/source/Photodegradation.md > Source: https://en.wikipedia.org/wiki/Photodegradation > Source revision: 1344138804 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) Alteration of materials by light A plastic bucket used as an open-air flowerpot photodegraded after some years. **Photodegradation** is the alteration of materials by light. Commonly, the term is used loosely to refer to the combined action of [sunlight](/source/Sunlight) and [air](/source/Air), which cause [oxidation](/source/Oxidation) and [hydrolysis](/source/Hydrolysis). Often photodegradation is intentionally avoided, since it destroys paintings and other artifacts. It is, however, partly responsible for remineralization of biomass and is used intentionally in some disinfection technologies. Photodegradation does not apply to how materials may be aged or degraded via [infrared](/source/Infrared) light or heat, but does include degradation in all of the [ultraviolet](/source/Ultraviolet) light wavebands. ## Applications ### Foodstuffs The protection of food from photodegradation is very important. Some nutrients, for example, are affected by degradation when exposed to sunlight. In the case of [beer](/source/Beer), UV radiation causes a process that entails the degradation of hop bitter compounds to 3-methyl-2-buten-1-thiol and therefore changes the taste. As amber-colored glass has the ability to absorb UV radiation, beer bottles are often made from such glass to prevent this process. ### Paints, inks, and dyes Further information: [Lightfastness](/source/Lightfastness) Paints, inks, and dyes that are organic are more susceptible to photodegradation than those that are not. Ceramics are almost universally colored with non-organic origin materials so as to allow the material to resist photodegradation even under the most relentless conditions, maintaining its color. ### Pesticides and herbicides The photodegradation of pesticides is of great interest because of the scale of agriculture and the intensive use of chemicals. Pesticides are however selected in part not to photodegrade readily in sunlight in order to allow them to exert their biocidal activity. Thus, more modalities are implemented to enhance their photodegradation, including the use of photosensitizers, photocatalysts (e.g., [titanium dioxide](/source/Titanium_dioxide)), and the addition of reagents such as [hydrogen peroxide](/source/Hydrogen_peroxide) that would generate hydroxyl radicals that would attack the pesticides.[1] ### Pharmaceuticals The photodegradation of pharmaceuticals is of interest because they are found in many water supplies. They have deleterious effects on aquatic organisms including toxicity, endocrine disruption, genetic damage.[2] But also in the primary packaging material the photodegradation of pharmaceuticals has to be prevented. For this, amber glasses like [Fiolax](/source/Fiolax) amber and Corning 51-L are commonly used to protect the pharmaceutical from UV radiations. Iodine (in the form of [Lugol's solution](/source/Lugol's_solution)) and [colloidal silver](/source/Colloidal_silver) are universally used in packaging that lets through very little UV light so as to avoid degradation. ### Polymers Main article: [Photo-oxidation of polymers](/source/Photo-oxidation_of_polymers) Effect of UV exposure on [polypropylene](/source/Polypropylene) rope A plastic bag photodegraded into approximately 2,000 pieces, 1 to 25 mm each, after three months' exposure outdoors. Photodegradation made a plastic straw brittle. Common synthetic polymers that can be attacked include [polypropylene](/source/Polypropylene) and [LDPE](/source/LDPE), where [tertiary carbon](/source/Tertiary_carbon) bonds in their chain structures are the centres of attack. Ultraviolet rays interact with these bonds to form [free radicals](/source/Free_radicals), which then react further with [oxygen](/source/Oxygen) in the atmosphere, producing [carbonyl](/source/Carbonyl) groups in the main chain. The exposed surfaces of products may then discolour and crack, and in extreme cases, complete product disintegration can occur. In fibre products like [rope](/source/Rope) used in outdoor applications, product life will be low because the outer fibres will be attacked first, and will easily be damaged by [abrasion](/source/Abrasion_(mechanical)) for example. Discolouration of the rope may also occur, thus giving an early warning of the problem. Polymers which possess UV-absorbing groups such as [aromatic rings](/source/Aromatic_ring) may also be sensitive to UV degradation. [Aramid](/source/Aramid) fibres like [Kevlar](/source/Kevlar), for example, are highly UV-sensitive and must be protected from the deleterious effects of sunlight. ## Mechanism Many organic chemicals are thermodynamically unstable in the presence of oxygen; however, their rate of spontaneous oxidation is slow at room temperature. In the language of physical chemistry, such reactions are kinetically limited. This kinetic stability allows the accumulation of complex environmental structures in the environment. Upon the absorption of light, triplet oxygen converts to [singlet oxygen](/source/Singlet_oxygen), a highly reactive form of the gas, which effects spin-allowed oxidations. In the atmosphere, the organic compounds are degraded by [hydroxyl radicals](/source/Hydroxyl_radical), which are produced from water and ozone.[3] Photochemical reactions are initiated by the absorption of a photon, typically in the wavelength range 290–700 nm (at the surface of the Earth). The energy of an absorbed photon is transferred to electrons in the molecule and briefly changes their configuration (i.e., promotes the molecule from a [ground state](/source/Ground_state) to an [excited state](/source/Excited_state)). The excited state represents what is essentially a new molecule. Often excited state molecules are not kinetically stable in the presence of O2 or H2O and can spontaneously decompose ([oxidize](/source/Oxidize) or [hydrolyze](/source/Hydrolyze)). Sometimes molecules decompose to produce high energy, unstable fragments that can react with other molecules around them. The two processes are collectively referred to as direct photolysis or indirect [photolysis](/source/Photolysis), and both mechanisms contribute to the removal of pollutants. The United States federal standard for testing plastic for photodegradation is 40 CFR Ch. I (7–1–03 Edition) PART 238. ## Protection against photodegradation Photodegradation of plastics and other materials can be inhibited with [polymer stabilizers](/source/Polymer_stabilizers), which are widely used. These additives include [antioxidants](/source/Antioxidant), which interrupt degradation processes. Typical antioxidants are derivatives of [aniline](/source/Aniline). Another type of additive are UV-absorbers. These agents capture the photon and convert it to heat. Typical UV-absorbers are hydroxy-substituted [benzophenones](/source/Benzophenone), related to the chemicals used in [sunscreen](/source/Sunscreen).[4] Restoration of yellowed plastic of old toys[5] is nicknamed [retrobright](/source/Retrobright). See also: [Biodegradable plastic](/source/Biodegradable_plastic) ## See also - [Plastic bag](/source/Plastic_bag) - [Polymer degradation](/source/Polymer_degradation) - [UV degradation](/source/UV_degradation) ## References 1. **[^](#cite_ref-burrows_1-0)** Burrows, H.D.; Canle L, M.; Santaballa, J.A.; Steenken, S. (June 2002). "Reaction pathways and mechanisms of photodegradation of pesticides". *Journal of Photochemistry and Photobiology B: Biology*. **67** (2): 71–108. [Bibcode](/source/Bibcode_(identifier)):[2002JPPB...67...71B](https://ui.adsabs.harvard.edu/abs/2002JPPB...67...71B). [doi](/source/Doi_(identifier)):[10.1016/S1011-1344(02)00277-4](https://doi.org/10.1016%2FS1011-1344%2802%2900277-4). [hdl](/source/Hdl_(identifier)):[10316/5187](https://hdl.handle.net/10316%2F5187). [PMID](/source/PMID_(identifier)) [12031810](https://pubmed.ncbi.nlm.nih.gov/12031810). 1. **[^](#cite_ref-boreen_2-0)** Boreen, Anne L.; Arnold, William A.; McNeill, Kristopher (1 December 2003). "Photodegradation of pharmaceuticals in the aquatic environment: A review". *Aquatic Sciences*. **65** (4): 320–341. [Bibcode](/source/Bibcode_(identifier)):[2003AqSci..65..320B](https://ui.adsabs.harvard.edu/abs/2003AqSci..65..320B). [doi](/source/Doi_(identifier)):[10.1007/s00027-003-0672-7](https://doi.org/10.1007%2Fs00027-003-0672-7). [S2CID](/source/S2CID_(identifier)) [34188238](https://api.semanticscholar.org/CorpusID:34188238). 1. **[^](#cite_ref-Simmler_3-0)** Walter Simmler "Air, 6. Photochemical Degradation" in Ullmann's Encyclopedia of Industrial Chemistry 2011, Wiley-VCH, Weinheim. 1. **[^](#cite_ref-Wolf_4-0)** Rainer Wolf, Bansi Lal Kaul "Plastics, Additives" in Ullmann's Encyclopedia of Industrial Chemistry 2000, Wiley-VCH, Weinheim. 1. **[^](#cite_ref-5)** ["Shining light on why plastics turn yellow - American Chemical Society"](https://www.acs.org/pressroom/newsreleases/2022/september/shining-light-on-why-plastics-turn-yellow.html). 6 September 2022. Retrieved 4 March 2022. ### Sources - Castell, JV; Gomez-L, MJ; Miranda, MA; Morera, IM (2008), "Photolytic degradation of Ibuprofen. Toxicity of the isolated photoproducts on fibroblasts and erythrocytes", *Photochemistry and Photobiology*, **46** (6): 991–96, [doi](/source/Doi_(identifier)):[10.1111/j.1751-1097.1987.tb04882.x](https://doi.org/10.1111%2Fj.1751-1097.1987.tb04882.x), [hdl](/source/Hdl_(identifier)):[10251/150607](https://hdl.handle.net/10251%2F150607), [PMID](/source/PMID_(identifier)) [3438349](https://pubmed.ncbi.nlm.nih.gov/3438349), [S2CID](/source/S2CID_(identifier)) [41693238](https://api.semanticscholar.org/CorpusID:41693238) - Salgado, R; Pereira, VJ; Carvalho, G; Soeiro, R; Gaffney, V; Almeida, C; Vale Cardoso, V; Ferreira, E; Benoliel, MJ; Ternes, TA; Oehmen, A; Reis, MAM; Noronha, JP (2013), "Photodegradation kinetics and transformation products of ketoprofen, diclofenac and atenolol in pure water and treated wastewater", *Journal of Hazardous Materials*, 244–245: 516–52, [Bibcode](/source/Bibcode_(identifier)):[2013JHzM..244..516S](https://ui.adsabs.harvard.edu/abs/2013JHzM..244..516S), [doi](/source/Doi_(identifier)):[10.1016/j.jhazmat.2012.10.039](https://doi.org/10.1016%2Fj.jhazmat.2012.10.039), [PMID](/source/PMID_(identifier)) [23177274](https://pubmed.ncbi.nlm.nih.gov/23177274) - Boltres, Bettine, "When glass meets pharma", ECV Editio Cantor, 2015, [ISBN](/source/ISBN_(identifier)) [978-3-87193-432-2](https://en.wikipedia.org/wiki/Special:BookSources/978-3-87193-432-2) v t e Biosolids, waste, and waste management Major types Agricultural wastewater Biodegradable waste Biomedical waste Brown waste Chemical waste Construction waste Demolition waste Electronic waste by country Food waste Green waste Hazardous waste Heat waste Industrial waste Industrial wastewater Litter Marine debris Mining waste Municipal solid waste Open defecation Packaging waste Post-consumer waste Radioactive waste Scrap metal Sewage Sharps waste Surface runoff Toxic waste Processes Anaerobic digestion Balefill Biodegradation Composting Durable good Ecological design Garden waste dumping Illegal dumping Incineration Landfill Landfill mining Mechanical biological treatment Mechanical sorting Photodegradation Reclaimed lumber Recycling appliance recycling battery recycling bottle recycling fluorescent lamp recycling land recycling plastic recycling textile recycling timber recycling tire recycling water heat recycling water recycling shower Repurposing Resource recovery Reusable packaging Right to repair Sewage treatment Urban mining Waste characterisation Waste collection Waste transfer station Waste sorting Waste trade Waste treatment Waste-to-energy Countries Afghanistan Albania Armenia Australia Belgium Bangladesh Brazil Bosnia and Herzegovina Egypt Georgia Hong Kong India Israel Japan Kazakhstan New Zealand Russia South Korea Sri Lanka Switzerland Syria Tanzania Taiwan Thailand Turkey United Kingdom United States Agreements Bamako Convention Basel Convention EU directives batteries Recycling framework incineration landfills RoHS vehicles waste water WEEE London Convention Oslo Convention OSPAR Convention Occupations Sanitation worker Street sweeper Waste collector Waste picker Other topics Blue Ribbon Commission on America's Nuclear Future China's waste import ban Cleaner production Downcycling Eco-industrial park Extended producer responsibility Garbology High-level radioactive waste management History of waste management Landfill fire Sewage regulation and administration Supervised injection site Toxic colonialism Upcycling Waste hierarchy Waste legislation Waste management industry Waste minimisation Zero waste Environment portal Category: Waste Index Journals Lists Organizations --- Adapted from the Wikipedia article [Photodegradation](https://en.wikipedia.org/wiki/Photodegradation) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Photodegradation?action=history)). 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