Understanding the Effects of Sunscreen on Coral

Understanding the Effects of Sunscreen on Coral

The world’s coral reefs are in trouble, and chemicals found in sunscreen are contributing to the situation. The problem appears to be formidable when seen numerically: Each year, 14,000 tons of sunscreen are thought to wash into the oceans; 82,000 chemicals from personal-care items may be contaminating the seas; and 80 percent of Caribbean corals have been destroyed in the previous 50 years owing to pollution, coastal development, and warmer waters.

Researchers have discovered how oxybenzone, a common sunscreen component, harms corals. The unexpected discoveries may aid in the development and marketing of effective, coral-safe sunscreens.

You can fall madly in love with something. That is one way to interpret a new Stanford University study that demonstrates how a common component of many sunscreens worn by coral reef tourists may expedite the extinction of these vulnerable ecosystems. The unexpected findings, reported in Science on May 6, could aid in the development and marketing of effective, coral-safe sunscreens.

“It would be a tragic irony if ecotourism aimed at conserving coral reefs was actually increasing their loss,” said Djordje Vuckovic, a Ph.D. student in civil and environmental engineering. “My aim is that our research will pave the road for the development of coral-safe sunscreens.”

It would be a tragic irony if ecotourism aimed at conserving coral reefs was actually increasing their loss. My aim is that our research will pave the road for the development of coral-safe sunscreens.

Djordje Vuckovic

According to the National Park Service, up to 6,000 tons of sunscreen – the weight of 50 blue whales – wash across U.S. reef regions each year. For some years, scientists have known that oxybenzone, an organic chemical contained in many sunscreens, might harm corals. As a result, sunscreens containing this molecule have been banned in the United States Virgin Islands and Hawaii, the island nation of Palau, and Bonaire, a Dutch island municipality, among other places.

Djordje Vuckovic

However, the mechanisms through which oxybenzone causes harm are largely unknown, making it difficult to confirm that sunscreen ingredients recommended as substitutes are genuinely safer for corals.

William Mitch, a professor of civil and environmental engineering at Stanford, became interested in the issue several years ago when he heard about Hawaii’s then-pending ban. With funding from the Stanford Woods Institute for the Environment, he and John Pringle, a professor of genetics in the Stanford School of Medicine, began work to characterize the chemical and biological mechanisms by which oxybenzone harms corals.

Understanding how sunscreens damage coral

Protection for humans, damage for corals

Mitch, Pringle, Vuckovic, and other Stanford researchers used anemones as surrogates for corals, which are more difficult to experiment with, as well as mushroom corals, in their latest study. The anemones died after being exposed to oxybenzone in artificial seawater under simulated sunlight for 17 days, whereas anemones subjected to oxybenzone in the absence of simulated sunlight survived.

“It was strange to discover that oxybenzone rendered sunlight hazardous to corals, which is the contrary of what it is supposed to accomplish,” Mitch added. “Because the chemical absorbs light well within the waveband we studied, it’s widely used in sunscreens.”

Following absorption of UV light, oxybenzone is meant to release the light energy as heat, so preventing sunburn. However, when exposed to sunlight, anemones and corals metabolized oxybenzone in such a way that the resulting compound generated harmful radicals.

Aside from this weakness, the researchers discovered evidence for a coral defense mechanism. Symbiotic algae in corals appeared to protect their hosts by sequestering the toxins produced by corals from oxybenzone.

As ocean waters warm, stressed corals expel their algae partners, exposing bone-white coral skeletons. Thus, in addition to being more vulnerable to disease and environmental shocks, such “bleached” corals would be more vulnerable to the depredations of oxybenzone without their algae to protect them.

Ensuring sunscreens are safe for corals and other marine species

The researchers caution that oxybenzone may not be the only sunscreen component to be concerned about. The same metabolic processes that appear to transform oxybenzone into a strong toxin for corals may also do so with other common sunscreen chemicals, many of which have similar chemical structures and hence may generate similar phototoxic metabolites.

Many coral-safe sunscreens are made from metals like zinc and titanium, rather than chemical components like oxybenzone. Although these sunscreens work in fundamentally different ways, it is unclear whether they are genuinely safer for corals, according to the researchers, who aim to examine further.

“In environmental research, like in medicine, a thorough grasp of underlying systems should provide the greatest direction for the creation of practical solutions,” Pringle added. “Our work also demonstrates the huge impact of cooperation among scientists with quite different backgrounds and experience,” Mitch remarked.