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 sulphonic 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 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. 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. Sunscreens can significantly enhance viral production in seawater. Mechanisms of transformation Photolysis Photolysis is the main abiotic route for the transformation of UV filters. Photolysis dissociates organic filters into free radicals. 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