We finally know why sunscreen kills coral reefs

While researchers have known for some time that oxybenzone, an organic ingredient in sunscreens, can damage coral reefs, the exact mechanism behind How? ‘Or’ What oxybenzone kills coral was unknown.

Stanford civil and environmental engineering professor William Mitch began to ponder this problem when he learned that Hawaii had banned common sunscreens to save his reefs.

Mitch, doctoral student Djordje Vuckovic and geneticist John Pringle went after the answer.

Their study, published in the leading journal Science, found that oxybenzone only kills sea anemones and mushroom corals when exposed to wavelengths of sunlight. Without the sun’s rays, sea creatures would stay healthy.

Researchers know that oxybenzone, an organic ingredient in sunscreens, can damage coral reefs, but exactly How? ‘Or’ What was unknown.

“It was strange to see that oxybenzone made sunlight toxic to corals – the opposite of what it’s supposed to do,” Mitch said in a statement.

Knowledge Why topical sunscreens are dangerous to marine life will help researchers design a better reef-safe sunscreen. There are plenty of sunscreens that qualify as ‘reef safe’, but the science to back that up is still murky, according to consumer reports.

“In environmental science, as in medicine, a good understanding of basic mechanisms should provide the best guidance for developing practical solutions,” said Pringle, professor of genetics at Stanford School of Medicine.

Bleached by the toxic sun: Coral reefs are under anthropogenic attack.

Rising sea temperatures driven by climate change, nutrient runoff from human agriculture and overfishing are all having adverse consequences, wrote Colleen M. Hansel, senior scientist in marine chemistry at the Woods Hole Oceanographic Institute. comment on the Stanford study.

But perhaps most unfortunate of all are the chemical compounds in thousands of commonly used sunscreens that wipe us out when we swim, dive and surf near reefs.

According NOAAthese chemicals can harm marine life throughout the marine ecosystem, including interfering with algal growth and photosynthesis, deforming baby sea urchins and mussels, reducing fish fertility, and causing males to show female characteristics, and being absorbed into the food chain by dolphins, then transmitted to the calves.

Chemicals can also cause coral bleachinga phenomenon where corals expel the symbiotic algae that live there and provide food and color, leaving behind hungry ghostly skeletons, which also become susceptible to disease.

Marine life metabolizes the compound in sun-damaging ways.

Not so radical, man: The sun’s ultraviolet (UV) rays are a major health risk: they easily penetrate through skin cells, damaging DNA and increasing the risk of skin cancer.

Oxybenzone in sunscreens works by absorbing UV light from the sun and giving it off as heat, protecting your skin.

“The compound absorbs light well in the waveband we tested, which is why it’s so common in sunscreens,” Mitch said.

But when anemones and mushroom corals are exposed to both oxybenzone and UV light, they metabolize the chemical in a way that turns it into a “potent photosensitizer,” the researchers wrote in their paper.

This caused harmful radicals to form, which were toxic to sea creatures.

The team also discovered that the coral’s symbiotic algae help protect them by absorbing toxins produced by metabolized oxybenzone. This means that already bleached corals, which have no protective algae, can even be After susceptible to sunscreen damage.

Protect the reef: Although the team may have revealed how a particular compound can kill coral, it did. not prove that reef-safe metal-based sunscreen does not cause any collateral damage on its own.

The impact of the various chemicals in sunscreens and other topical products on the ocean is still poorly understood, so what makes a sunscreen “reef safe” is not well defined. Researchers at National Academy of Sciences are conducting an extensive environmental impact study of commercial sunscreens, the results of which are expected later in 2022.

“I hope our research will contribute to the development of sunscreens that are less likely to harm reefs.”

Djordje Vuckovic

In the meantime, NOAA recommends using organic-free sunscreens, shade providers like hats and umbrellas, and UV-blocking shirts and leggings to help reduce the amount of sunscreen you use.

As ecotourism increases the number of visitors to the reefs, these steps can be crucial in ensuring there is always something underwater to see. “It would be a sad irony if ecotourism aimed at protecting coral reefs actually worsened their decline,” said PhD student Vuckovic, lead author of the study.

“I hope our research will contribute to the development of sunscreens that are less likely to harm reefs.”

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