Sunscreen may be an important defense against skin cancer, but it also has a dark side. As if coral reefs do not already have enough problems, sunscreen from tourists is creating an additional threat to popular reefs worldwide.
“Wear sunscreen,” began the late 90s hit, adding, “The long-term benefits of sunscreen have been proved by scientists.” Science, however, is constantly evolving and while sunscreen's benefits for the wearer are well established, it may not be so good for the environment.
Powerful evidence for these fears are published in the Archives of Environmental Contamination and Toxicology.
Oxybenzone (also known as benzophenone-3) is a common component of sunscreens. It combines the capacity to protect against ultraviolet light with easy solubility in organic solvents.
Concerns have been raised about oxybenzone's effects on wearers, but so far evidence for its dangers to humans is limited. Certainly any risks are low compared to sunburn and skin cancer. Unfortunately, the same cannot be said for coral reefs when the sunscreen washes off our skin.
“The chemical, oxybenzone, is found in more than 3,500 sunscreen products worldwide. It pollutes coral reefs via swimmers who wear sunscreen or wastewater discharges from municipal sewage outfalls and coastal septic systems," said co-author Dr. Omri Bronstein of Tel Aviv University in a statement.
The authors examined the effect of oxybenzone on seven coral species in the lab, and compared the health concentrations of the chemical in coral reefs off Hawaii, the Virgin Islands and Eilat, Israel.
Laboratory testing showed sufficient doses could kill coral larvae by deforming the skeleton so that they don't float properly. Adults become stressed and expel the symbiotic zooxanthellae that give coral its color and nutrients, leading to the bleaching that signifies a reef in danger.
Ironically, considering the reason for oxybenzone's use, its effects are worse on cells exposed to sunlight.
Contamination was almost 100 times worse in the American Virgin Islands than in Hawaii, and well within the ranges where some species suffered cell death in the lab. The effects are thought to be worse when combined with other sources of stress, such as heat.
“Oxybenzone poses a hazard to coral reef conservation, and threatens the resiliency of coral reefs to climate change,” the paper concludes.
“The use of oxybenzone-containing products needs to be seriously deliberated in islands and areas where coral reef conservation is a critical issue,” said first author Professor Craig Downs of the Haereticus Environmental Laboratory, Virginia. “We have lost at least 80 percent of the coral reefs in the Caribbean. Any small effort to reduce oxybenzone pollution could mean that a coral reef survives a long, hot summer, or that a degraded area recovers.”
The authors encourage anyone diving or snorkeling around reefs to avoid wearing sunscreen in the water, but this will not solve the whole problem. "Oxybenzone pollution predominantly occurs in swimming areas, but it also occurs on reefs 5-20 miles from the coastline as a result of submarine freshwater seeps that can be contaminated with sewage," Bronstein said.