Sunscreen chemicals may harm corals, but they're the tiniest player among reef threats

The dangers of certain sunscreens to coral reefs are believed by some Hawai`i legislators to be so dangerous that they are considering banning it.

Can they really be that bad? If they were, wouldn’t reefs where nobody swims be far healthier than those frequented by oil-slathered masses?

In our review of the science, it’s true that some of the chemicals in some sunscreens are harmful to reef organisms.

But as usual, this issue is complicated. 

While there has been much breathless prose arguing the hazards of sunscreens on reefs, there is also another side to this story. The other side is, essentially, that it is an issue, but a very minor one compared to the other challenges.

Also, even though folks worried about certain sunscreen products recommend using other products, some of those others may be dangerous to reefs too. And still more may use compounds that have not yet been thoroughly tested.

A 2008 research effort by Italian scientist Robert Danovaro argues that sunscreens can promote viral infections in tiny algae called zooxanthellae, and that can cause coral bleaching. Danovaro’s team looked at various components of sunscreens and found that in the laboratory, these had the strongest impact on coral bleaching: butylparaben, ethylhexylmethoxycinnamate, benzophenone-3 and 4-methylbenzylidene camphor.

Another of the key studies on the subject was published last year in the Archives of Environmental Contamination and Toxicology. The lead author was Craig Downs. It found that if certain corals were exposed to the active ingredient in many sunscreens, oxybenzone or benzophenone-3, they could harm corals and cause coral bleaching.

Oxybenzone is one of the chemicals in many sunscreens that shields your skin against ultraviolet radiation from the sun. And that reduces skin cancer risk.

Researchers found that if you expose coral cells to enough oxybenzone, it will kill them. At lower levels it will deform them, and will cause reef corals to expel their food-giving algae. When the algae are gone, the corals go white, a process called bleaching. Eventually the coral polyps can starve and die.

The study found that there can be impacts on coral larvae and cells at oxybenzone concentrations in the higher ranges found on Hawai`i beaches—notably heavily populated O`ahu beaches.

Thus, the authors wrote, “Oxybenzone poses a hazard to coral reef conservation and threatens the resiliency of coral reefs to climate change.”

But there’s more to it than that. 

We’re still waiting for studies that link the health of reefs where there is a lot of sunscreen-drenched swimming compared to similar reefs that are pristine.

Coral reefs are being hit by all kinds of attacks, and coral reefs are bleaching in the Main Hawaiian Islands as well as in the Northwestern Hawaiian Islands, many of which are uninhabited and sunscreen-free.

Hawai`i is taking coral reef degradation seriously. Earlier this year, the Department of Land and Natural Resources released its Coral Bleaching Recovery Plan. It focuses on a number of reef threats, primarily warming waters.

It does not consider sunscreen issues.

That doesn’t mean sunscreen is invisible to the state. The state Division of Aquatic Resources has issued a statement of concern that “Researchers have found oxybenzone concentrations in some Hawaiian waters at more than 30 times the level considered safe for corals.”

Rather than slathering on sunscreens with oxybenzone (read the label), the state recommends other alternatives to prevent sunburn: “water resistant sunscreens, which are more likely to stay on your skin, and sunscreens that use mineral filters, such as zinc oxide or titanium dioxide. Also, rash guards or wet suits will reduce the area of exposed skin, and thus the amount of sunscreen needed for protection.”

But switching to any other sunscreen may not be the best answer. It depends on which one. Zinc oxide and titanium dioxide are also potential reef problems. This study suggests that titanium dioxide, as it breaks up in the marine environment, can be toxic to marine algae. Zinc oxide is believed to have similar impacts.

If you care about reefs, limiting your participation in adding harsh chemicals to the surf is important. But you should also be paying attention to some of the more serious threats to reefs—including climate change, sedimentation from the land and overfishing. 

This 2012 study looked at all the known causes of a 27-year decline in coral cover on the massive Australian Great Barrier Reef. None of them was sunscreen. 

The big culprits, after tropical cyclones, crown-of-thorns starfish and climate-related bleaching: “their high sensitivity to rising seawater temperatures, ocean acidification, water pollution from terrestrial runoff and dredging, destructive fishing, overfishing, and coastal development.”

 

© Jan TenBruggencate 2017