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 sunlight- or UV-related damage. UV filters have been used to coat glass discs fitted to camera lenses to protect hardware that is sensitive to UV light.
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 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. 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. Chemical filters protect against UV radiation by absorbing, reflecting, or scattering it. 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. The levels of UV filters in sunscreens typically vary from 0.5% to 10%, although they sometimes reach 25%.
Examples of organic UV filters Many different organic compounds can serve as UV filters. They fall into several structural classes:
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. 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. Several UV filters have been detected at ppb or ppt levels in surface water and wastewater, with maximum concentrations in the summertime. 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. Furthermore, eighteen organic sunscreens were found in sediments of Japanese rivers and lakes, at concentrations ranging from 2 to about 3000 ng/g. 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. 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. 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. 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. 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 sulfonic acid (PBS, PABA, etc.). Some studies have recorded increased hydrogen peroxide or H2O2 levels in beaches directly attributable to UV filter transformation. H2O2 is responsible for damaging lipids, proteins, and DNA, and generating high stress levels in marine organisms. Inorganic UV-filters (i.e. TiO2) can also generate ROS, another compound toxic for marine phytoplankton.
Coral bleaching
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