Understanding how sunscreens damage coral

Date:
May 5, 2022
Source:
Stanford University
Summary:
Researchers reveal a mechanism by which oxybenzone, a common
sunscreen component, damages corals. The surprising findings
could help guide the development and marketing of effective,
coral-safe sunscreens.



FULL STORY ==========================================================================
You can love something to death. That is one way of thinking about a new Stanford University study that reveals how a common component of many sunscreens worn by coral reef-exploring tourists may hasten the demise
of these endangered ecosystems. The surprising findings, published May 6
in Science, could help guide the development and marketing of effective, coral-safe sunscreens.


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"It would be a sad irony if ecotourism aimed at protecting coral reefs
were actually exacerbating their decline," said study lead author Djordje Vuckovic, a PhD student in civil and environmental engineering. "My hope
is that our research will help lead the way to developing coral-safe sunscreens." Up to 6,000 tons of sunscreen -- more than the weight of
50 blue whales -- wash through U.S. reef areas every year, according to
the National Park Service.

Scientists have known for some time that oxybenzone, an organic compound
found in many sunscreens, can damage corals. As a result, sunscreens with
this compound have been banned in the U.S. Virgin Islands and Hawaii,
the island nation of Palau, and Bonaire, an island municipality of the Netherlands, among other places.

However, the mechanisms by which oxybenzone does harm have largely
remained a mystery, making it difficult to ensure that sunscreen
components proposed as alternatives are truly safer for corals.

William Mitch, a professor of civil and environmental engineering at
Stanford, became interested in the issue several years ago when he
heard about Hawaii's then-pending ban. With funding from the Stanford
Woods Institute for the Environment, he and John Pringle, a professor of genetics in the Stanford School of Medicine, began work to characterize
the chemical and biological mechanisms by which oxybenzone harms corals.

Protection for humans, damage for corals In their new study, Mitch,
Pringle, Vuckovic, and other Stanford researchers used anemones as
surrogates for corals, which are harder to experiment with, as well as
mushroom corals. Exposed to oxybenzone in artificial seawater under
simulated sunshine, the anemones all died within 17 days, whereas
anemones exposed to oxybenzone in the absence of simulated sunlight
remained viable.



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"It was strange to see that oxybenzone made sunlight toxic for corals --
the opposite of what it is supposed to do," said Mitch. "The compound is
good at absorbing light within the waveband we tested, which is why it's
so common in sunscreens." After absorbing ultraviolet light, oxybenzone
is designed to dissipate the light energy as heat, preventing sunburn. The anemones and corals, however, metabolized oxybenzone in such a way that
the resulting substance formed damaging radicals when exposed to sunlight.

In addition to this vulnerability, the researchers found evidence for a
coral defense mechanism. Symbiotic algae in corals appeared to protect
their hosts by sequestering within themselves the toxins that corals
produced from oxybenzone.

As ocean waters warm, stressed corals expel their algae partners,
exposing bone-white coral skeletons. Thus, in addition to being more
vulnerable to disease and environmental shocks, such "bleached" corals
would be more vulnerable to the depredations of oxybenzone without their
algae to protect them.

Ensuring sunscreens are safe for corals and other marine species
Oxybenzone may not be the only sunscreen ingredient of concern, the
researchers warn. The same metabolic pathways that appear to convert
oxybenzone into a potent toxin for corals may do something similar with
other common sunscreen ingredients, many of which share similar chemical structures and so could form similar phototoxic metabolites.



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Many sunscreens marketed as coral-safe are based on metals, such as zinc
and titanium, rather than organic compounds, such as oxybenzone. Although
these sunscreens are fundamentally different in how they function, it
is not clear whether they are actually safer for corals, according to
the researchers, who are planning to investigate the matter further.

"In environmental science, as in medicine, a sound understanding of
basic mechanisms should provide the best guidance for the development
of practical solutions," said Pringle. "Our study also illustrates the
enormous power of collaborations between scientists with very different backgrounds and expertise," said Mitch.

Co-authors of the study also include Amanda Tinoco, a research technician
at Stanford School of Medicine at the time of the research; Lorraine
Ling, a postdoctoral scholar in genetics at the time of the research;
and Christian Renicke, a postdoctoral research scientist in genetics.

The research was funded by the Stanford Woods Institute for the
Environment's Environmental Venture Projects program and the National
Science Foundation.


========================================================================== Story Source: Materials provided by Stanford_University. Original written
by Rob Jordan.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Djordje Vuckovic, Amanda I. Tinoco, Lorraine Ling, Christian
Renicke,
John R. Pringle, William A. Mitch. Conversion of oxybenzone
sunscreen to phototoxic glucoside conjugates by sea anemones and
corals. Science, 2022; 376 (6593): 644 DOI: 10.1126/science.abn2600 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/05/220505143215.htm

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