The biological integrity of about 60% of the world's coral reefs is under assault, and the percentage of threatened reefs is expected to continue rising. Coral bleaching, which indicates the death of colored symbiotic algae that provide nutrients to coral, is a visible sign of this damage.

New suspects in the bleaching process include four commonly used sunscreen ingredients that routinely wash off into water, according to a team of Italian researchers who published their study online January 3 in Environmental Health Perspectives (2008, DOI 10.1289/ehp.10966). The ingredients killed the algae within just 4 days at very low levels, at or below what would be observed with typical usage by swimmers worldwide. The team says this is the first evidence linking sunscreens to coral bleaching.

The problematic ingredients included a paraben preservative and three types of UV filters-a cinnamate, a benzophenone, and a camphor derivative. The researchers conclude that these compounds likely kill algae by stimulating latent viruses that have been found in almost all classes of coral-inhabiting algae. The number of viruses in seawater surrounding coral samples exposed to the ingredients increased as much as 15-fold, and viruslike particles were found in and around the algae. All sunscreen brands, sun-protection factors, and concentrations tested bleached the coral.

The researchers used field and laboratory analyses to evaluate more than half a dozen coral species from sites in the Red Sea, the Caribbean Sea, the Andaman Sea in the Indian Ocean, and the Celebes Sea in Indonesia. They calculate that approximately 10% of the world's coral reefs are potentially threatened by about 4000-6000 metric tons of sunscreen that annually wash off swimmers in these and other reef waters. The rapid expansion of tourism in reef areas suggests to the researchers that destruction is likely to worsen unless sunscreen formulations that are safer for the coral are developed.

Copyright © 2008 American Chemical Society