While governments and businesses are racing ahead with brands and labels, scientists are still pondering the effects of sunscreens on corals in the lab.
Did you know that the sunscreen you apply before your swim contains chemicals that can be deleterious to coral life?
In Australia, it’s easy to find someone who’ll sell you “reef-safe” sunscreens to dodge this problem, which you can wear with impunity during your snorkel.
Except you can’t. The reef-safe tag on a sunscreen bottle is meaningless.
Unlike the term “SPF”, which requires dozens of tests on human volunteers to earn, there are no formal requirements for the phrase “reef-safe” in Australia. Any brand could, theoretically, pop it on their bottles, regardless of the ingredients.
In reality, most sunscreen vendors do explain why they’ve labelled their product “reef-conscious” somewhere on their websites: unfortunately, each brand seems to have its own reasons for deeming a product safe for marine life.
They may have just dodged the two active ingredients with the most evidence mounting against them: oxybenzone and octinoxate. Or, perhaps they’ve avoided organic ingredients entirely (so-called because they’re carbon-based, not because they’re more ‘natural’), opting instead for inorganic zinc oxide or titanium dioxide.
Perhaps the zinc and titanium are even present in a non-nanoparticle form – less comfortable and attractive to wear, but also, probably, less likely to penetrate corals.
Every single ingredient in the bottle might have been scrutinised, or perhaps the manufacturer has focussed just on the active ingredients: the things that are filtering out UV light.
A handful of countries and territories have regulated sunscreens to protect marine life, but the rules are as jumbled as the options on sale. The US state of Hawaii has banned the sale and use of sunscreens with oxybenzone and octinoxate, while Palau has blacklisted 10 active ingredients. Thailand has banned the use of four sunscreen ingredients in national parks, and in parts of Mexico, sunscreens have been restricted since the 1980s. A few other places, including the US Virgin Islands, Aruba, and Bonaire, have different rules still.
The real problem is that science is still some distance from a consensus on sunscreens and marine life.
The alarm on sunscreens and corals was first raised in the 2000s, and laboratory studies have been piling up ever since. Among other things, corals incubated with sunscreens can have low or no growth, more viral infections, and, ultimately, get bleached. A particularly prominent fear is ‘zombie corals’: corals that are alive, but can’t grow or reproduce – slowly but surely draining the environment of new growth.
Other research has shown sunscreen traces popping up in oceans everywhere, from Hong Kong to the Arctic. The ingredients are present in touristy spots, but drains and wastewater are also major sources of sunscreen contamination: after all, sunscreen is designed not to dissolve in water while you’re wearing it.
“A lot of the sunscreens that get into the water actually come from when we wash the sunscreens off, because we use soaps and detergents to get it out of our skin,” explains Associate Professor Nial Wheate, a chemist at the University of Sydney.
But these sunscreen traces might not necessarily cause harm.
“There’s a saying I like to teach my students: it’s the dose that makes the poison,” says Wheate.
“Everything is safe in the right dose, and everything is unsafe in the wrong dose.”
Wheate published a review on sunscreens and marine life in the Australian Journal of Chemistry. His conclusion was that sunscreen rarely, if ever, reached concentrations high enough to worry about.
“There are studies that show that these chemicals can cause damage to animals and plants when they’re at milligram and microgram doses, but we don’t find the chemicals at microgram or milligram doses. We find them at nanogram doses, and that’s not enough to do the damage that people are looking at.”
For Wheate, this is enough of a cue to move the lens off sunscreens, and turn it to much bigger threats to corals, like warming-induced bleaching and agricultural runoff.
But not every researcher agrees.
“The absence of evidence is not evidence of absence: half the time, you just don’t have the data,” says Professor Bob Richmond, director of the Kewalo Marine Laboratory at the University of Hawai’i at Mānoa, US.
Richmond is a member of a study committee on a 2022 US National Academies of Sciences, Engineering and Medicine report about UV filters (sunscreens) and marine life. He is now aiming to help the US Environment Protection Authority (EPA) set up an environmental risk assessment into the effects of these UV filters, as the report firmly urged.
This risk assessment would collect enough information to bridge the gap between the low doses of sunscreens found in the environment, and the higher-dose laboratory studies on corals. Beyond the total amount of sunscreen in use, there are some key differences between the conditions a coral experiences in a lab, and the conditions it sees in the wild.
“In the wild, we know that sunscreen concentrations go up during the day and down during the night, and they go up in summer and down in winter – so the tests they do aren’t even representative of what happens in the real world,” says Wheate.
“Well, that’s just obfuscation,” counters Richmond. “If you want to know the effect of a specific chemical, the only way you can set up a carefully controlled experiment is in the laboratory. You can’t do a controlled experiment in the field, because there’s so much variability in currents and tides and temperature, and two sites will never be exactly alike.”
The lab work, says Richmond, is crucial to understanding why sunscreens might be damaging.
“As a coral scientist, I can say this with a straight face: corals are notorious liars,” says Richmond.
“They lie about their taxonomy, they lie about their age, they just lie. And how do you hold a coral to being true? The things they can’t lie about are cellular processes. So that’s where a lot of the coral research is going on.”
I took a Great Barrier Reef visit off my bucket list last year. I only had time for a typical tourist jaunt – one of dozens for sale in north Queensland. They took a boat of us far out to sea, armed us with snorkels and sent us exploring the extraordinary reef.
When we surfaced for lunch, one of the guides picked up a photo of a bleached coral and explained to us, in a faltering voice, the threats the reef was facing.
“But,” she added brightly, “there are things you can do to help!”
She paused for dramatic effect.
“How many of you looked up reef-safe sunscreens before you came with us today?”
Stuck in a tiny boat, bobbing alone in the huge ocean, I’m not sure it was possible to feel less empowered by the speech.
Both Wheate and Richmond agree on this: sunscreens are not responsible for mass bleaching events on the Great Barrier Reef. For those, we can thank our old friend climate change.
But could sunscreens be an extra source of aggravation on corals worldwide? For now, that’s still a yes, no, or maybe, depending on who you ask. Richmond is hoping that the EPA will, eventually, provide some more authoritative answers.
“The role of science is to inform the decision-making process, stakeholders, elected leaders, and traditional leaders. Our responsibility is to make sure that we’re getting accurate data, we’re getting adequate data, and we’re translating it in a format that decision makers can use,” says Richmond.
And when he’s in the field, he opts for wetsuits, rashguards and skullcaps: as well as reducing the amount of sunscreen you need to use, these provide stouter UV protection.
“In a world where coral reefs have such incredible value economically, ecologically, culturally – why aren’t we doing everything we can to improve the environment in which these corals exist?” says Richmond.
Science is likely to reach a firmer conclusion on sunscreens and corals, but we’ll have to be patient.
In the meantime, while you should still absolutely apply your sunscreen where needed, a rashie will – at the very least – save you some money.
As will a healthy level of suspicion for any product that seems to be trading very hard on “reef-safe”.
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Originally published by Cosmos as How reef-safe are reef-safe sunscreens, really?
Ellen Phiddian is a science journalist at Cosmos. She has a BSc (Honours) in chemistry and science communication, and an MSc in science communication, both from the Australian National University.