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Does sunscreen kill marine life? New research shows just how quickly it can become toxic in the ocean.

How sunscreen can harm marine life
New research shows just how quickly sunscreen can become toxic in the ocean 01:31

Sunscreen is essential in protecting humans from UV rays that can lead to skin cancer and other issues. But while it's proven to save people, in many cases, it's also killing coral reefs. Now, new research shows just how deadly sunscreen can be to marine life. 

It's been known for years that sunscreens containing oxybenzone are the likely culprit of the damages suffered by coral reefs. The chemical is highly effective at blocking UV rays from human skin, but once it's in the ocean, it's no longer harmless to other forms of life, a fact that has led to the banning of certain sunscreen formulas in reef-heavy areas, such as Hawai'i, the U.S. Virgin Islands, Palau and Bonaire. 

But what wasn't known was just how that chemical ended up being so toxic to the marine environment, and without that information, there's no guarantee that sunscreen alternatives are any safer.

That's the information gap a new study, published in the journal Science on Thursday, sought to close. 

They placed 21 anemones in seawater under a lightbulb that emits a full spectrum of sunlight, with five of the animals being covered with a box that blocks the UV light that usually interacts with oxybenzone. The animals were then exposed to 2 mg of oxybenzone per liter of seawater.

"Anemones, like corals, have a translucent surface, so if oxybenzone were acting as a phototoxin, the UV rays hitting the light group would trigger a chemical reaction and kill the animals – while the dark group would survive," researchers said in an article they wrote explaining their findings. 

And that's exactly what happened. 

All it took was six days for the first anemone that had been exposed to oxybenzone and left in UV light to die. Ten days later, all of the light-covered anemones were dead, while all of the anemones that weren't hit by the UV rays were alive. 

The researchers discovered that the anemones' bodies automatically treated oxybenzone as a foreign substance, kickstarting metabolic processes that altered the chemical makeup of the oxybenzone. This is a common process that plants and animals do to make foreign substances less toxic, but in the case of this particular chemical, it just made the foreign substance deadly.

"It holds on to the energy it absorbs from UV light and kicks off a series of rapid chemical reactions that damage cells. Rather than turning the sunscreen into a harmless, easy-to-excrete molecule, the anemones convert oxybenzone into a potent, sunlight-activated toxin," researchers said. 

Some forms of marine life have built-in protection, the researchers found. When they repeated their experiment on mushroom corals, they found that those phototoxins were being stored in the algae that live within the coral. Without that algae, it's suspected the coral would have met the same fate as the tested anemones. 

In fact, when scientists ran the test yet again on anemones that didn't have any algae, they died roughly twice as fast and had almost three times as many phototoxins in their cells compared to anemones that had the algae. 

While seeing the protection algae can provide does offer some hope, the research also comes at a time when bleaching is devastating coral reefs around the world. When coral bleaching occurs, algae is expelled from the coral in which it resides, leaving the marine animals without their primary source of food and more susceptible to disease. 

As Earth nears 1.5°C of global warming, researchers have warned that more than 90% of coral reefs will suffer from an "intolerable level of thermal stress," as extreme heat events – a cause of coral bleaching – become more frequent and more intense. 

This means that without better sunscreen formulas, a summer dip in the ocean could only worsen the situation for the vital coral reef ecosystems, especially given the amount of sunscreen that enters the ocean's waters. 

Every year, between 4,000 and 6,000 tons of sunscreen enter coral reefs, according to the National Park Service. With 90% of of snorkeling and diving tourists exploring the waters on 10% of the world's reefs, the service said, it's the planet's most popular and beautiful underwater scenes that are bearing the brunt of the toxicity.

"It would be a sad irony if ecotourism aimed at protecting coral reefs were actually exacerbating their decline,"  study lead author Djordje Vuckovic said in a statement

Today, many alternative sunscreen formulas thought to be safer for marine life have chemicals similar to oxybenzone, meaning that they could just be adding to, rather than solving, the problem. But the latest research provides a vital piece of the puzzle of information, and with summer approaching and efforts to mitigate the effects of climate change ongoing, the researchers' findings could help create a sunscreen formula that protects and remains harmless to all forms of life.

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