People have been told to use sunscreen to limit their exposure to the sun. Several locations have recently banned the use of sunblocks by beachgoers. The bans were put in place after local waters were found to have high levels of some of the chemicals in sunblock, which was associated with the lower health of nearby coral reefs.
Several studies have shown that the root of the problem is a chemical called oxybenzone. It was not clear how oxybenzone could harm corals. It is difficult to tell which sunblocks pose a risk without that understanding.
The problem has been identified by researchers from the university. After being exposed to UV, the corals convert oxybenzone from a harmlessly absorbing UV light to one that damages biological molecules. The coral is less able to survive coral bleaching makes matters worse.
The researchers did most of their work on the anemone instead of working with corals. They started by testing growth under various conditions to confirm that oxybenzone was a problem in these organisms. The healthy anemones were exposed to a day-night light cycle. It took just over two weeks for all the anemones to die.
The day-night cycle did not affect anemone survival. The animals were killed by the UV light and the chemical. This result doesn't make sense. We use oxybenzone as a sunblock because it is harmless from UV radiation. UV was turning the chemical into a killer in these animals.
The researchers thought that oxybenzone was not the killer. A related chemical is created when many chemicals come in contact with each other. In some cases, the enzymes are used to remove related chemicals. In some cases, it is an accident caused by two chemicals that are very similar. The chemical that goes into cells may not be the chemical that changes the behavior of the cells.
AdvertisementTo find out if that was the case, the researchers ground up the anemones and looked for any related chemicals in their contents. They found that most of the chemical was attached to the substance.
In test tubes, oxybenzone does not do any damage to biomolecules. UV light leads to the creation of a couple of biomolecules when the Glucose is attached. It did so in a way that it didn't consume the glucose-oxybenzone in the process. It doesn't take much to do a lot of damage.
While looking for the chemical derivatives of oxybenzone, the researchers noticed that much of the material wasn't in the anemone cells, but in the symbiotic microorganisms associated with the anemone. The presence of the symbiotes may have protected the anemones from the toxic effects of oxybenzone.
To confirm this, they looked at a coral species that can lose its symbiotes. When the symbiotes were present, they took up enough of the oxybenzone to protect the coral from the harmful effects of UV radiation. In a bleached version of the same coral, the glucose-oxybenzone is once again lethal. The result raises the risk that sunscreen is dangerous in the wake of a coral bleaching event.
The researchers think that this is a big accident. The way in which the sugar is added to this chemical evolved as a way to make it easier to get rid of toxins. The fact that oxybenzone is great at absorbing UV light makes it a great sunscreen and it is more likely to use that energy in unfortunate ways once it is modified.
We have a better chance of detecting other chemicals that could cause similar problems now that we have identified the mechanism at play. It could allow us to design sunscreens that are less likely to have side effects.
Science in 2022. About the DOIs is available on the science.abn2600.
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