Sunscreens makes corals pale

More than 10,000 tons of UV filters are produced annually for the global market and consumption of cosmetic sun products associated with tourism in marine coastal areas is rapidly increasing worldwide. To evaluate the potential impact of sunscreens on hard corals and their symbiotic algae, the authors conducted in situ and laboratory experiments in several tropical regions (Atlantic, Indian, and Pacific Oceans and the Red Sea) supplementing coral branches of Acropora spp., Stylophora pistillata, and Millepora complanata with different concentrations (10, 33, 50, and 100 μL/L) of several common ultraviolet filters contained in sunscreens formula.

In all replicates and at all sampling sites, sunscreen addition, even in very low concentrations, resulted in the release of large amounts of coral mucous (composed of zooxanthellae and coral tissue) within 18–48hr and complete bleaching of the coral within 96hr. Bleaching was faster in systems subjected to higher temperature, suggesting synergistic effects with this variable. The coral response to sunscreen exposure was not dose dependent, as the same effects were observed at low and high sunscreen concentrations. Therefore, UV filters can have potentially negative impacts even at concentrations lower than those used in the study.

Sunscreens typically comprise up to 20 or more chemical compounds. To identify the organic UV filters or preservatives possibly responsible for coral bleaching, seven compounds typically present in sunscreens were selected by the authors (i.e., butylparaben, ethylhexylmethoxycinnamate, benzophenone-3, 4-methylbenzylidene camphor, octocrylene, ethylhexylsalicylate, 4-tert-butyl-4-methoxydibenzoylmethane and propylene glycol) and each single ingredient was tested on Acropora spp. The results showed that sunscreens containing parabens, cinnamates, benzophenones, and camphor derivatives noticeably contribute to hard-coral bleaching even in very low concentrations.

In addition, TEM and epifluorescence microscopy analyses revealed a loss of photosynthetic pigments and membrane integrity in the zooxanthellae released from treated corals, whereas zooxanthellae membranes from untreated corals were intact suggesting that sunscreens were somehow capable of damaging the symbiotic algae. Furthermore, after the addition of sunscreens, viral abundance in seawater surrounding coral branches increased by a factor of 15 than in controls. Because, prior to any treatment, the hard corals were washed and incubated in virus-free seawater and because TEM analysis of treated corals showed the presence of roundhycosahedral virus-like particles around and inside the zooxanthellae, the authors concluded that viruses were directly released  from the symbiotic algae and that the bleaching effect of sunscreens was due to organic ultraviolet filters, which are capable to induce the lytic viral cycle in symbiotic zooxanthellae with latent infections.

Hence sunscreens, by promoting zooxanthellae viral infection, are likely to play an important role in coral bleaching. Considering a rough estimate of 78 million of tourists per year in areas hosting reefs, two daily applications per tourist traveling on a 5-day tourist package, an average usage of 20g per application and given that at least 25% of the amount applied is washed off during swimming and bathing, the authors calculated that between 4,000 and 6,000 tons of sunscreens are released every year in tropical reef areas. Because human recreational use of tropical ecosystems is steadily increasing worldwide, the global impact of sunscreens on coral bleaching will considerably grow in the future and actions are therefore needed to stimulate the research and utilization of UV filters that do not threaten the survival of coral reefs.

Reference

Danovaro R, Bongiorni L, Corinaldesi C, Giovannelli D, Damiani E, Astolfi P, Greci L, Pusceddu A (2008). Sunscreens cause coral bleaching by promoting viral infections. Environ Health Perspect 116:441–447