In view of persistent heat waves, Australians reach sunscreen. But you may have heard some mixed messages about its environmental damage – especially for coral reefs.
In July 2018, Hawaii adopted a law to ban the future sale of sunscreen containing benzophen-3 and octinoxate and claimed these two chemicals increase coral bleaching and have significant detrimental effects on Hawaii's marine environment.
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In October 201
Key West in Florida may be the latest area to follow This trend with a proposal to be reconciled in early February.
However, medical and skin cancer specialists have warned of the health risks of a ban on commonly used sunscreen and describe the prohibition as risky and unjustified, partly because the few studies that have treated the environmental effects of sunscreen experimentally "are not representative of real world conditions. ".
For example, the way in which coral tissue is exposed to sunscreen in experiments does not mimic the proliferation and dilution of contaminants from a tourist skin (and other sources) into reef colors and on corals growing in nature.
Experiments which expose corals to sunscreen chemicals typically use much higher concentrations than ever been measured on a real reef. A recent review of the amount of benzophen-3 in reef waters showed that concentrations are typically almost non-detectable – usually a few parts per minute. Trillions. A much higher report of 1.4 parts per Million, in the US Virgin Islands, is based on a single water sample.
The environmental concern over sun protection on coral reefs is centered mainly on only two studies. The first published in 2008 noted that there was no previous scientific evidence of the effect of sunscreens on coral reefs.
This study exposed small fragments of coral (branch tips) to high levels of benzophenone-3 and other chemicals by incubating them for a few days inside plastic bags. The fragments in the bags quickly became ill with the virus and bleached. The authors concluded that up to 10% of world reefs are potentially threatened by sunscreen-induced coral bleaching.
Bleaching is a stress response to corals where they become weak due to a decrease in the symbiotic microalgae living inside their tissues. You can experimentally coral bleach by torturing it in a number of ways. However, coral bleaching on a global and regional scale is due to anthropogenic warming, not sunscreen. We know that the bleaching footprint on the Great Barrier Reef in 1998, 2002, 2016 and 2017 is closely matched to where the water was hottest longest in each event.
Even the farthest reefs are vulnerable to heat flow. The physiological mechanisms and time scales for thermal bleaching due to global warming are very different from the rapid reactions of corals to experimental exposure to high concentrations of sunscreen chemicals.
The second and most widespread study of sunscreen toxicity on corals is also laboratory-based. Released in 2016, it focused primarily on the responses of the day-old larvae of a coral species, as well as isolated coral cells. This study did not investigate intact coral colonies.
The larvae were placed in 2-3 centiliters of artificial seawater containing a range of concentrations of sunscreen chemicals and a solvent for spreading them. After a few hours, the coral larvae bleached (bleached) with higher concentrations of oxybenzene.
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This study also measured the concentration of benzophenone in seawater in six locations in Hawaii. These samples were not replicated (one per site) and all had irresistible amounts of sunscreen chemicals. In the US Virgin Islands, the authors found higher concentrations of benzophenone in four out of ten sites, although they did not report the results for any blank samples (to check for contamination). The study concluded that oxybenzone threatens coral reef resistance to climate change.
In summary, there is actually no direct evidence to show that bleaching due to global warming is exacerbated by polluting sunscreen. Similarly, there is no evidence that recovery from thermal bleaching is weakened by sunscreen, or sunscreen causes coral bleaching in nature.