Photodegradation

Photo-degradation is the alteration of materials by light. Typically, the term refers to the combined action of sunlight and air. Photo-degradation is usually oxidation and hydrolysis. Often photo degradation is 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. Photo degradation does not apply to how materials may be aged or degraded via Infrared light or heat, but does include degradation in all of the ultraviolet light wavebands.

The protection of food from photodegradation is very important. Some nutrients, like beer for example, are affected by degradation when being exposed to sunlight. In the case of beer, the UV radiation causes a process, which entails the degradation of hop bitter compounds to 3-Methyl-2-buten-1-thiol and therefore changes the taste. As amber glass has the ability to absorb UV radiation, beer bottles are often made from this glass type to avoid this process.

Paints, inks and dyes that are organic are more susceptible to photodegradation than those that are not. Ceramics are almost universally coloured with non-organic origin materials so as to allow the material to retain its colour even with the most relentless photo -degradation.

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, additional modalities are implemented to enhance their photodegradation, including the use of photosensitizers, photocatalysts (e.g., titanium dioxide), and the addition of reagents such as hydrogen peroxide that would generate hydroxyl radicals that would attack the pesticides.

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. But also in the primary packaging material the photodegradation of pharmaceuticals has to be prevented. For this, amber glasses like Fiolax amber are commonly used to protect the pharmaceutical from UV radiations. Iodine (in the form of Lugol's solution) and collodial silver are universally used in packaging that lets through very little UV light so as to avoid degradation.

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