Organic UV filters and preservatives used in sun care products could contribute to the bleaching of hard-coral if released into natural systems, say the researchers led by Roberto Danovaro. Coral bleaching refers to the loss of the zooxanthellae algae that live in a symbiotic relationship with the coral. The algae provided nutrients and energy for the organism by photosynthesis and in return they benefit from a protected environment in which to live and a constant supply of carbon dioxide to use for photosynthesis. Without the zooxanthellae the coral host eventually dies with negative impacts on the reef ecosystem. Coral bleaching is an increasing problem worldwide and can be caused by unexpected changes in temperature, an increase in UV radiation and pollution. Organic UV filters lead to bleaching Danovaro and the team claim that the chemicals found in sunscreen products also lead to coral bleaching, and that the increased number of sunscreen wearing tourists bathing in reef areas represents a significant danger to the health of reef ecosystems. The team performed in situ and laboratory experiments in Indonesia, Mexico, Thailand and Egypt, supplementing the coral with various compounds found in sunscreen products and measuring the level of bleaching that occurred. The team found that the addition of sunscreen to the sampling sites, even in very low concentrations resulted in the release of large amounts of zooxanthellae within 18-48 hours and complete bleaching of hard coral within 96 hours. In order to identify the compounds responsible for the bleaching the researchers tested seven compounds typically present in sunscreens, four of which lead to complete bleaching even at very low concentrations. "These results suggest that sunscreens containing parabens, cinnamates, benzophenones and camphor derivatives can contribute to hard coral bleaching if released into natural systems," wrote the authors of the study. Large quantities of sunscreen released every year Furthermore, the team estimate that 25 per cent of the sunscreen applied to the skin is released in the water over the course of 20 minutes. Using sunscreen application guidelines released by the FDA, and estimated numbers of tourists visiting coral reef areas, the study claims that a potential 4,000 - 6,000 tons of sunscreen could be released into reef areas per year. The researchers hypothesize that the compounds induce viral infections that were previously dormant in the coral, leading to the death of the zooxanthellae and its consequent release from the organism. As the human use of tropical ecosystems and coral reef areas is increasing the impact of sunscreens on coral bleaching will become a worldwide problem, say the scientists. "Actions are therefore needed to stimulate the research and utilization of UV filters that do not threaten the survival of these endangered tropical ecosystems," they conclude.