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According to Coral.org (and many other websites):

This June, many of the world’s top coral reef scientists met at the International Coral Reef Symposium in Hawaii to discuss the challenges facing coral reefs. Sunscreen and other personal care product ingredients were hot topics. Of particular concern to scientists was oxybenzone, a chemical used in sunscreens to protect our skin from damaging UV light. Increasing a coral’s susceptibility to bleaching

  • Damaging coral DNA which interferes with reproduction
  • Causing deformities and growth anomalies
  • Disrupting a coral’s hormonal processes for growth and reproduction

Perhaps most alarming is that all of this can happen with very low doses of the chemical, only 62 parts per trillion (equivalent to one drop of water in 6.5 Olympic swimming pools)!

Are the above statements true? Can sunscreen worn by beachgoers really cause damage coral reefs? My skepticism is due to the fact that the amounts leached into the water would be extremely tiny and quickly diluted by the ocean, especially when compared to other sources of pollution.

For an additional source, see this page from the NOAA.

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    Found an interesting blog post that breaks this down: labmuffin.com/…. If no one posts an answer in the next couple of days I'll add my own. – JonathanReez Jan 21 at 10:05
  • Also American sunscreen may damage coral reefs — unlike sunscreen you can buy overseas. -- WaPo. Some interesting bits there "In 2014, the U.S. government passed the Sunscreen Innovation Act to encourage the development of new ingredients, but the FDA hasn’t approved any. As of 2019, the FDA has approved only three broad-spectrum sunscreens for the United States, which happen to be the ones to be banned in Hawaii." – Fizz Jan 21 at 10:27
  • One drop in 6½ swimming pools does not seem much in the context of an ocean, but water moves in currents before being uniformly dispersed. The idea that anything "thrown in to the sea" will vanish has long been disproved. – Weather Vane Jan 21 at 12:46
  • On the other hand, given the enormous amounts of material and chemicals that we are dumping into the ocean, I am not sure if sunscreen specifically makes that much of a difference... not that this would be a reason to take the subject likely, but in perspective. – DevSolar Jan 21 at 13:16
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    62 parts in a trillion!? Instances like these make me wish million billion and trillion didn't all sound like the same word. PPM, as in parts per million, is the typical scientific measure. So that's 0.000062 PPM? I greatly share your skepticism. – fredsbend Jan 21 at 17:00
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Can the oxybenzone and similar UV filters in sunscreen damage corals? The answer is clearly yes, they can.

Is the current level of exposure from swimmers coated with sunscreens using the chemicals in question sufficient to cause damage? Possibly, and the issue remains a subject of current research and debate over how great the effect is compared to other environmental stressors.

A 2020 paper title "Adding insult to injury: Effects of chronic oxybenzone exposure and elevated temperature on two reef-building corals" from researchers at Wageningen University and Research delves into state of knowledge of the issue to set up the background for their experimental results.

Organic UV filters such as oxybenzone (benzophenone-3) can be harmful to corals and their larvae (Danovaro et al., 2008; Downs et al., 2016; He et al., 2019).

Although the mechanisms underlying oxybenzone toxicity to corals are still unclear, it may involve formation of tissue damaging reactive oxygen species (ROS) (Hanson et al., 2006; He et al., 2019). This mechanism seems similar to the effects elevated seawater temperatures and high light intensity (Dove et al., 2006).

While a ban on oxybenzone and similar UV filters has been imposed in several places following the precautionary principle (Sirois, 2019), such as Bonaire, Hawaii and Palau, it is yet unknown to what extent field-relevant oxybenzone concentrations affect coral reefs.

For their experiment, the Wageningen researchers set up flow-through aquaria where coral were stressed by heat waves and half of the aquaria were exposed to levels of oxybenzone found in some field locations. They did find an impact, and suggested further research.

Taken together, our results support the current view that semi-chronic exposure to field-relevant levels of oxybenzone can cause subtle adverse effects on coral health, and a pronounced impact on the coral microbiome. Therefore, oxybenzone adds insult to injury by further weakening corals in the face of climate change.

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  • Group snorkeling at coral reefs with oxybenzone sunscreen might actually lead to some higher concentration there (not aware of any studies about that though) – lalala Jan 30 at 12:14

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