Researchers are starting to understand the reason why coral bleaches when exposed to chemicals from common sunscreens.
Oxybenzone is the most common active ingredient in sunscreen sold over the counter, and it absorbs UVA and UVB rays which protects us from skin cancer. However, oxybenzone is also harmful to coral reefs, and that’s why it has been banned in sunscreens sold in Hawaii and the US Virgin Islands, and a few other countries worldwide.
Scientists understand the effect of oxybenzone on reefs, but they don’t know the mechanism, which researchers at Sanford University wanted to investigate. Led by Djordje Vuckovic, a Ph.D. student in civil and environmental engineering at the university, the group published a paper on May 5 in Science Magazine explaining the mechanism by which oxybenzone can harm reefs.
Not understanding how these chemicals affect reefs can hinder the research and development of reef-safe sunscreen. With almost 6,000 tons of sunscreen washing into coral reefs near the US every year, this research is critical.
Since coral is challenging to research in lab settings, Stanford researchers used anemone as a model system in addition to mushroom coral. They exposed the reefs to oxybenzone in artificial seawater with or without sunlight and found that anemones exposed to light in the 290-370nm wavelength died within 17 days. This led to the puzzling discovery that oxybenzone alone was not toxic to coral but needed to be exposed to sunlight to cause damage—which is the opposite of what oxybenzone does to humans.
With sunlight, the anemone metabolized the oxybenzone into oxybenzone-glucoside conjugates, forming free radicals that damaged the coral. Through this discovery, the researchers also found an intrinsic defense mechanism of the coral: the symbiotic algae will protect the coral by isolating themselves within the toxins the coral produces.
However, when coral is stressed, it expels the algae, making the coral look bleached. This can leave them even more vulnerable to further harm from oxybenzone.
These researchers hope that their findings will help manufacturers develop safer sunscreen that doesn’t use oxybenzone or other potentially harmful ingredients— ones with a similar chemical structure to oxybenzone but aren’t currently under the same scrutiny. Additionally, they plan to research other coral-safe sunscreen ingredients like zinc and other metals to see if the products live up to their claims.
Sources: Stanford, Science, US National Park Service