A few years ago, a group of researchers working in the Caribbean were talking to a local vendor who was waiting for the day’s invasion of tourists. He told them that the tourists would leave behind “a long oil slick” in the water. The scientists were intrigued, and wondered how this “oil slick” would affect the local coral reefs. Their recently published study suggests that the answer is bad news. [Downs, C.A., et al. 2015. Toxicopathological Effects of the Sunscreen UV Filter, Oxybenzone (Benzophenone-3), on Coral Planulae and Cultured Primary Cells and Its Environmental Contamination in Hawaii and the U.S. Virgin Islands. Archives of Environmental Contamination and Toxicology. DOI 10.1007/s00244-015-0227-7]
They observed several effects, all bad, affecting coral larvae. Larvae were deformed and transformed from a motile (free swimming) to a sessile (attached) state, they developed lesions, and ossification was induced, such that the larvae became encased in their own skeletons. The offending chemical is oxybenzone, a UV-absorbing compound that is a common ingredient in many sunscreen products. Perhaps most discouraging of all was the extremely low concentrations needed to cause adverse effects on coral: as low as 62 parts per trillion.
Coral bleaching also increased with increasing levels of oxybenzone in the water. Another nail in the coffin for coral reefs, which are undergoing worldwide bleaching at an alarming rate due to the effects of global warming.
In addition to swimmers and snorkelers being a source of oxybenzone, sewage may be an even bigger problem. Sewage outfalls in coastal communities commonly discharge into the ocean, and even when it is treated it can contribute a load of oxybenzone and many other chemicals to the near-shore environment. As one of the researchers put it: “People come inside and step into the shower. People forget it goes somewhere.”
Another reminder that so many of our actions, however benign they might appear to be, can have serious, unintended consequences. Who knew that taking steps to prevent sunburn and melanomas would be so devastating to coral reefs. There are sunscreen products that do not contain oxybenzone, and I’d encourage you to use them if you are traveling to areas with coral reefs.