UV filter

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An L39 UV filter with a 55mm filter thread UV Filter 6159.jpg
An L39 UV filter with a 55mm filter thread

UV filters are compounds, mixtures, or materials that block or absorb ultraviolet (UV) light. One of the major applications of UV filters is their use as sunscreens to protect skin from sunburn and other sun/UV related damage. After the invention of digital cameras changed the field of photography, UV filters have been used to coat glass discs fitted to camera lenses to protect hardware that is sensitive to UV light.

Contents

Background

Earlier types of photographic film were quite sensitive to UV light, which used to cause haziness or fogginess, and a bluish hue in color film. UV filters were used to filter out shorter ultraviolet wavelengths while remaining transparent to visible light. However, the modern-day photographic film and digital cameras are less sensitive to UV wavelengths.

UV filters are sometimes referred to as L37 or L39 filters, depending on the wavelengths of light they filter out. For example, an L37 filter removes ultraviolet light with wavelengths shorter than 370 nanometers (nm), whereas an L39 filter eliminates light with wavelengths shorter than 390 nm.

Applications in printing and photography

UV filters span[ clarification needed ] the color spectrum and are used for a wide variety of applications. So-called Ortho Red and Deep Ortho Red lights are commonly used in diffusion transfer, in typesetting film or paper, and other applications dealing with orthochromatic materials. Yellow Gold, Yellow, Lithostar Yellow, and Fuji Yellow filters or safelights provide safe workspaces for contact proofing applications like screen printing and plate making. Pan Green, Infrared Green, and Dark Green filters or safelights are commonly used in scanning applications, work with panchromatic film, papers, and x-rays.

Many photographers and cinematographers still use UV filters to protect their lenses' glass and coating. However, UV filters, as with any optical filter, may introduce lens flare and harm contrast and sharpness. Hoods can counteract this, as they offer some protection against impact and shade optical elements, thus preventing lens flare. Also, quality UV filters offer some protection against lens contamination while minimizing the inherent additional distortion.

In photography, the term "UV filter" can also be misused as a filter that passes UV light while blocking other wavelengths in the light spectrum, in the same way, the term "IR filter" is used for filtering the entire spectrum. The correct name for such filters are "UV pass filter" and "IR pass filter" respectively, and they are only used in very specialized photography.

Applications in personal care products

Since excessive UV radiation can cause sunburn, photoaging, and skin cancer, care products such as sunscreen usually include a classification for the specific wavelengths they filter. [1] UV classifications include UVA (320-400 nm), UVB (290-320 nm) and UVC (200-280 nm). UV-absorbing compounds are used not only in sunscreen, but also in other personal care products, such as lipstick, shampoo, hair spray, body wash, toilet soap, and insect repellent. [2] Chemical filters protect against UV radiation by absorbing, reflecting, or scattering it. [2] [3] Reflection and scattering are accomplished by inorganic physical UV filters, such as titanium dioxide (TiO2) and zinc oxide (ZnO). Absorption, mainly of UVB, is done by organic UV filters, which are known as chemical UV filters. [4] The levels of UV filters in sunscreens typically vary from 0.5% to 10%, although they sometimes reach 25%. [5]

Examples of organic UV filters

Many different organic compounds can serve as UV filters. They fall into several structural classes: [6]

Environmental aspects

The use of UV filters has increased recently due to growing concern about UV radiation and skin cancer, especially as a result of ozone depletion, which in turn has caused concern for its environmental impact. [3]

The filter material can enter the environment either directly, through industrial wastewater discharge, or indirectly, through domestic water discharge during showering, bathing, urine excretion or through wastewater treatment. Wastewater treatment plants (WWTP) are not very effective at removing these contaminants. [5] Several UV filters have been detected at ppb or ppt levels[ vague ] in surface water and wastewater, with maximum concentrations in the summertime. [7] [8]

Because most UV filters are lipophilic, they tend to bioaccumulate in aquatic environments and food chains originating from them. Confirming bioaccumulation, several studies have shown the presence of UV filters in aquatic organisms. The 4-methyl-benzylidene camphor was detected in the muscle tissue of trout in Swiss and German waters, while traces of Ethylhexyl methoxycinnamate and octocrylene were found in shellfish in the Mediterranean and Atlantic coasts of France. [9] [10] Furthermore, eighteen organic sunscreens were found in sediments of Japanese rivers and lakes, at concentrations ranging from 2 to about 3000 ng/g. [11] The accumulation of organic UV filters in living organisms is of major concern because some of them (and their metabolites) can act as endocrine disruptors both in vitro and in vivo. [12] Also, Goksøyr et al. (2009) reported concentrations of organic UV-filters in open waters of the Pacific Ocean, providing evidence of the persistence and wide dispersion of these components in the marine environment. [13]

Because UV-filters are not always stable under environmental conditions, it is common for them to transform into other compounds. Water in natural reservoirs, for example, is subjected to sun irradiation, while swimming-pool water is often disinfected by chlorination, bromination, ozonation, or UV irradiation. [14] These byproducts can often be more toxic than the original UV filter. For example, avobenzone transforms in the presence of chlorinated disinfection products and UV radiation, producing substituted chlorinated phenols and acetophenones, which are known for their toxicity. [5]

Some organic UV filters under UV radiation can generate reactive oxygen species (ROS) (OH, H2O2) (e.g. BP-3, octocrylene (OCR), octyl methoxycinnamate (OMC), phenyl benzimidazole sulphonic acid (PBS, PABA, etc.). Some studies have recorded increased hydrogen peroxide or H2O2 levels in beaches directly attributable to UV filter transformation. [15] H2O2 is responsible for damaging lipids, proteins and DNA, and generating high-stress levels in marine organisms. [16] Inorganic UV-filters (i.e. TiO2) can also generate ROS, another compound toxic for marine phytoplankton.

Coral bleaching

Dipsastraea pallida (hard coral) with signs of bleaching or crown-of-thorns starfish damage Favia pallida (hard coral) with signs of bleaching or crown-of-thorns starfish damage.jpg
Dipsastraea pallida (hard coral) with signs of bleaching or crown-of-thorns starfish damage

UV filters have shown severe effects on coral reefs due to the bleaching of corals at very low concentrations. As a result, small quantities of sunscreens result in the production of large amounts of coral mucous within 18-48 hrs and bleaching of hard corals within 96 hrs. Among the UV filters that result in coral bleaching according to studies are Ethylhexyl methoxycinnamate, benzophenone-3, and 4-methyl benzylidene camphor, even in very low concentrations. Bleaching was favored by higher temperatures which act as synergistic factors. Experiments showed that the coral bleaching was not dose-dependent, so it can occur upon exposure to very small amounts. [17]

According to the rough estimate of 78 million tourists per year in coral reef areas, the estimated amount of sunscreen used annually in tropical countries ranges between 16,000 and 25,000 tons. 25% of this amount is washed off during bathing activities, leading to a release of 4,000-6,000 tons/year in the reef areas. This results in threatening 10% of the world reefs by sunscreen induced coral bleaching alone. [17] Sunscreens can significantly enhance viral production in seawater. [17]

Mechanisms of transformation

Photolysis of Benzophenone-3 in presence of Benzotriazole Photolysis of Benzophenone-3 in presence of Benzotriazole.jpg
Photolysis of Benzophenone-3 in presence of Benzotriazole

Photolysis

Photolysis is the main abiotic route for the transformation of UV filters. Photolysis dissociates organic filters into free radicals. [6]

Photolysis can be direct or indirect. The direct way occurs when the chromophore of the organic filter absorbs sunlight at certain wavelengths. The indirect pathway occurs in the presence of a photo-sensitizer. Dissolved organic matter (DOM) in surface waters acts as a photo-sensitizer and produces reactive Photo-oxidation such as hydroxyl radicals, peroxyl radicals, and singlet oxygen.

The photolysis of sunscreen products is more complicated than the behavior of individual UV filters, as shown by this example. In the presence of other UV filters, Benzotriazole, and humic acids, Benzophenone -3 degradation was observed through the loss of hydroxyl and benzoyl functional groups resulting in the formation of 2,4 dimethyl anisole. [18]

Photoisomerism PhotoisomSolGel.png
Photoisomerism

Photoisomerization

Photoisomerization can result in products that absorb less UV light than their parent compound. [19] This is evidenced by cinnamates, salicylates, benzylidine camphor, and dibenzoylmethane derivatives. Octyl methoxycinnamate (OMC) can undergo photoisomerization, photodegradation, and photodimerization to obtain several dimers and cyclodimers isomers. Most commercial products are trans isomers but exist in the environment as a mixture of trans and cis isomers upon exposure to UV radiation due to the presence of the C=C double bond adjacent to the aromatic rings. The isomers may have identical physicochemical properties, but they may differ in biological behavior and effects. [6]

Disinfection by-product

Swimming pool water is usually disinfected by chlorination, bromination, ozonation or UV radiation. Upon the presence of some UV filters such as Avobenzone in swimming pools, these can break down and create disinfection by-products, including toxic products, as a result of the interaction between Avobenzone and the active chlorine and UV radiation. [5]

Fate of some Organic UV filters

Benzophenones

Metabolic pathway of Benzophenone-3 Metabolic pathway of Benzophenone-3.jpg
Metabolic pathway of Benzophenone-3

Benzophenones (BPs) are widely used in UV filters, fragrance enhancers, and plastic additives. The major sources of BP-3 are reported to be human recreational activities and wastewater treatment plant (WWTP) effluents. The anionic forms of both BP-3 and 4-OH-BP3 can undergo direct photodegradation. The photolytic rates of both compounds in natural waters are faster than those in pure water. Radical scavenging experiments revealed that triplet-excited dissolved organic matter (3DOM*) was responsible for the indirect photodegradation of BP-3 and 4-OH-BP3 in seawater, whereas, in freshwater, the indirect photodegradation of these two compounds was attributed to Dissolved Organic Matter and OH radical. [20]

P-aminobenzoic acid (PABA)

Indirect photolysis of p-aminobenzoic acid UV filter in water Photolysis of p-aminobenzoic acid UV filter in water.jpg
Indirect photolysis of p-aminobenzoic acid UV filter in water

P-amino benzoic acid was one of the earliest UV filters used in sunscreens (1943). It was used in concentrations up to 5%. It was discovered by 1982 that PABA increases the formation of a particular DNA defect in human cells.[ citation needed ] The photochemical fate of PABA may be impacted by water constituents, e.g., NO3, dissolved organic matter (DOM), and HCO3. [21] PABA undergoes both direct and indirect photolysis in the solution with the presence of NO3. Direct photolysis accounts for 25% of the degradation of PABA and is considered a secondary pathway. On the other hand, indirect photolysis was the dominant pathway.

Zhou and Mopper showed that nitrate enhanced the photodegradation of PABA by a factor of 2. However, in the presence of free radical scavengers such as carbonate forms and natural organic matter (NOM), the photodegradation of PABA decreased. It was proposed that the indirect photolysis of PABA was mainly due to the NO3 photolysis product •OH.[ citation needed ]

The Bicarbonate anion is abundant in water. Bicarbonate caused 10% of •OH scavenging. The reaction between bicarbonate and the •OH yields carbonate radical (•CO3), which is less reactive than •OH. In natural waters, •CO3 can reach a higher steady-state concentration than •OH because of its lower reactivity. The enhancement of PABA photolysis by bicarbonate is due to carbonate radicals. [21]

Water-soluble NOM is composed of organic acids. These organic acids are mainly humic substances, which can be categorized into a fulvic and humic acid fraction. NOM favors the indirect photolysis of PABA by absorbing the sunlight and weakening its intensity.

Two reactions can take place during the degradation of PABA in the presence of nitrate in water as shown in the figure. Three of the four products contain phenolic groups and may thus be estrogenic. So the hazardous byproducts generated during the PABA photoreaction should be concerned for its estrogenicity.

4-tert-butyl-4’-methoxydibenzoylmethane (avobenzone)

Avobenzone tautomeric forms Avobenzone Tautomeric Forms V1.svg
Avobenzone tautomeric forms

4-tert-Butyl-4’-methoxydibenzoylmethane, known as avobenzone, belongs to dibenzoylmethanes. It is one of the most common UVA (400-320 nm) filters used in sunscreens formulations. It is sold under the trade names Parsol 1789 or Eusolex 9020. Avobenzone exists in two tautomeric forms: enol and keto. In sunscreen formulations, avobenzone exists predominantly in the enol form, which has a maximum absorption at wavelengths ranging from 350 to 365 nm depending on the solvent used. The double bond of the enolic form was shown to be more reactive in conditions of aquatic chlorination than the aromatic ring. In a chlorinated aquatic environment, Avobenzone transforms to two corresponding aldehydes and acids, as shown in the figure. Both aldehydes are formed as a result of the CO-CH2 bond. They are less stable in the oxidative conditions and easily transform into the corresponding acids.

Chlorinated acetophenone derivatives are also formed due to the cleavage of the same CO-CH2 bond. Chlorinated acetophenone derivatives are tear gases, trigger dermatitis, and some other health problems. It was reported that chlorination of the original avobenzone into the aromatic ring position is less possible. The cleavage of the CO-Ar bond results in the formation of 4-chloroanisole. [5]

Avobenzone transformation products in chlorinated aquatic systems Avobenzone transformation products in chlorinated aquatic systems.gif
Avobenzone transformation products in chlorinated aquatic systems

Ethylhexyl methoxycinnamate (EHMC)

Ethylhexyl methoxycinnamate (EHMC) is one of the most common UVB filters used worldwide. It is known as Eusolex 2292 and Uvinul MC80. It is included in the High Production Volume Chemicals (HPVC) list, which includes chemicals produced or imported in the EU at a rate of more than 1000 tons per year. The lifetime of the EHMC was predicted to be from hours to a few days. EHMC is well tolerated by the skin. However, it has some side effects, including its ability to produce reactive oxygen species (ROS) and penetrate the human skin after exposure to UV light. EHMC has also been found in shellfish, fish, and cormorants at ng/g levels, which suggests that it can be accumulated in the food chain. [22] EHMC was proved to be responsible for coral bleaching by promoting viral infections. [17] From the toxicological point of view, EHMC has estrogenic properties both in vitro and in vivo. For instance, exposure to this compound caused the increase of the uterus' weight for rats. Prenatal exposure to EHMC can affect both the reproductive and neurological development in the offspring of rats, which can be a cause for concern because humans are routinely exposed to this compound through the use of sunscreens and other cosmetics.

The main transformation pathway for EHMC is photolysis. Direct photolysis represents the dominant transformation pathway. On the other hand, the indirect photolysis due to OH is negligible and, due to dissolved organic matter, will be a secondary route. Four transformation products were detected for EHMC upon exposure to UV radiation. 4-methoxy benzaldehyde (MOBA) and 4-methoxy cinnamic acid are two transformation products of EHMC via dealkylation. The intermediate MOBA is more toxic than EHMC towards the bacteria.

See also

Related Research Articles

Ultraviolet Electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays

Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules.

Benzophenone chemical compound

Benzophenone is the organic compound with the formula (C6H5)2CO, generally abbreviated Ph2CO. It is a white solid that is soluble in organic solvents. Benzophenone is a widely used building block in organic chemistry, being the parent diarylketone.

Oxybenzone chemical compound

Oxybenzone or benzophenone-3 or BP-3 is an organic compound. It is a pale-yellow solid that is readily soluble in most organic solvents. Oxybenzone belongs to the class of aromatic ketones known as benzophenones. It is a naturally occurring chemical found in various flowering plants as well as being an organic component of many sunscreen lotions. It is also in widespread use in things like plastics, toys, furniture finishes, and more to limit UV degradation.

Sunscreen Topical skin product that helps protect against sunburn

Sunscreen, also known as sunblock, is a lotion, spray, gel, foam, stick or other topical product that absorbs or reflects some of the sun's ultraviolet (UV) radiation and thus helps protect against sunburn. Diligent use of sunscreen can also help to slow or temporarily prevent the development of wrinkles, dark spots and sagging skin.

4-Aminobenzoic acid (also known as para-aminobenzoic acid or PABA because the number 4 carbon in the benzene ring is also known as the para position) is an organic compound with the formula H2NC6H4CO2H. PABA is a white solid, although commercial samples can appear gray. It is slightly soluble in water. It consists of a benzene ring substituted with amino and carboxyl groups. The compound occurs extensively in the natural world.

Photochemistry Sub-discipline of chemistry

Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet, visible light (400–750 nm) or infrared radiation (750–2500 nm).

Ecamsule chemical compound

Ecamsule is an organic compound which is added to many sunscreens to filter out UVA rays. It is a benzylidene camphor derivative, many of which are known for their excellent photostability.

Avobenzone Oil-soluble ingredient used in sunscreen products

Avobenzone is an oil-soluble ingredient used in sunscreen products to absorb the full spectrum of UVA rays.

Octyl methoxycinnamate Organic chemical compound

Octyl methoxycinnamate or ethylhexyl methoxycinnamate (INCI) or octinoxate (USAN), trade names Eusolex 2292 and Uvinul MC80, is an organic compound that is an ingredient in some sunscreens and lip balms. It is an ester formed from methoxycinnamic acid and 2-ethylhexanol. It is a liquid that is insoluble in water.

Photodegradation alteration of materials by light

Photodegradation is the alteration of materials by light. Typically, the term refers to the combined action of sunlight and air. Photodegradation is usually oxidation and hydrolysis. Often photodegradation 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. Photodegradation 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.

Padimate O Water-insoluble oily ingredient used in some sunscreens

Padimate O is an organic compound related to the water-soluble compound PABA that is used as an ingredient in some sunscreens. This yellowish water-insoluble oily liquid is an ester formed by the condensation of 2-ethylhexanol with dimethylaminobenzoic acid. Other names for padimate O include 2-ethylhexyl 4-dimethylaminobenzoate, Escalol 507, octyldimethyl PABA, and OD-PABA.

Octocrylene chemical compound

Octocrylene is an organic compound used as an ingredient in sunscreens and cosmetics. It is an ester formed by the reaction of 3,3-diphenylcyanoacrylate with 2-ethylhexanol. It is a viscous, oily liquid that is clear and colorless.

Photoprotection is the biochemical process that helps organisms cope with molecular damage caused by sunlight. Plants and other oxygenic phototrophs have developed a suite of photoprotective mechanisms to prevent photoinhibition and oxidative stress caused by excess or fluctuating light conditions. Humans and other animals have also developed photoprotective mechanisms to avoid UV photodamage to the skin, prevent DNA damage, and minimize the downstream effects of oxidative stress.

Homosalate chemical compound

Homosalate is an organic compound used in some sunscreens. It is made by the Fischer–Speier esterification of salicylic acid and 3,3,5-trimethylcyclohexanol, the latter being a hydrogenated derivative of isophorone. Contained in 45% of U.S. sunscreens, it is used as a chemical UV filter. The salicylic acid portion of the molecule absorbs ultraviolet rays with a wavelength from 295 nm to 315 nm, protecting the skin from sun damage. The hydrophobic trimethyl cyclohexane functional group provides greasiness that prevents it from dissolving in water.

Bemotrizinol chemical compound

Bemotrizinol is an oil-soluble organic compound that is added to sunscreens to absorb UV rays. It is marketed as Parsol Shield, Tinosorb S, and Escalol S.

Bisoctrizole chemical compound

Bisoctrizole is a benzotriazole-based organic compound that is added to sunscreens to absorb UV rays.

Colored dissolved organic matter The optically measurable component of the dissolved organic matter in water

Colored dissolved organic matter (CDOM) is the optically measurable component of dissolved organic matter in water. Also known as chromophoric dissolved organic matter, yellow substance, and gelbstoff, CDOM occurs naturally in aquatic environments and is a complex mixture of many hundreds to thousands of individual, unique organic matter molecules, which are primarily leached from decaying detritus and organic matter. CDOM most strongly absorbs short wavelength light ranging from blue to ultraviolet, whereas pure water absorbs longer wavelength red light. Therefore, water with little or no CDOM, such as the open ocean, appears blue. Waters containing high amounts of CDOM can range from brown, as in many rivers, to yellow and yellow-brown in coastal waters. In general, CDOM concentrations are much higher in fresh waters and estuaries than in the open ocean, though concentrations are highly variable, as is the estimated contribution of CDOM to the total dissolved organic matter pool.

Personal care or toiletries are consumer products used in personal hygiene and for beautification.

Mycosporine-like amino acids (MAAs) are small secondary metabolites produced by organisms that live in environments with high volumes of sunlight, usually marine environments. The exact number of compounds within this class of natural products is yet to be determined, since they have only relatively recently been discovered and novel molecular species are constantly being discovered; however, to date their number is around 30. They are commonly described as “microbial sunscreens” although their function is believed not to be limited to sun protection.

Scytonemin chemical compound

Scytonemin is a secondary metabolite and an extracellular matrix (sheath) pigment synthesized by many strains of cyanobacteria, including Nostoc, Scytonema, Calothrix, Lyngbya, Rivularia, Chlorogloeopsis, Hyella etc. Scytonemin-synthesizing cyanobacteria often inhabit highly insolated terrestrial, freshwater and coastal environments such as deserts, semideserts, rocks, cliffs, marine intertidal flats, hot springs, etc.

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