Sunscreen can cause decline of coral reefs

When I found out that reef-safe sunscreen existed, I was very intrigued. Does this mean that my current sunscreen is not safe for the corals? Sadly, the answer is most likely yes. As someone who loves to snorkel and marvel at the underwater world, it would be such a great sin if I contributed to the decline of the reefs.

Coral reefs in Bocas del Toro, Panama

The main reason behind the damaging effects is oxybenzone, a common chemical found in sunscreen. The adverse impact is strongest in coral larvae. A low concentration of the chemical is sufficient to cause coral bleaching (where they expel their symbiotic photosynthetic algae zooxanthellae) to occur at a lower temperature. Oxybenzone is also genotoxic and can cause mutation in the corals' DNA. Furthermore, oxybenzone can behave as an endocrine disrupter not only in corals but other marine invertebrates like shrimps as well. For example, it is estrogenic in fish and can cause them to acquire traits of the opposite sex. For corals, it will induce coral larvae to encase itself in skeleton and die. Oxybenzone can bioaccumulate, hence magnifying its toxic effects.

Sunscreen enters the waters via two main mechanisms: directly leeching into the sea or through sewage. Sunscreen can be washed off the bodies of tourists and visitors as they swim. Thus, famous snorkelling areas experience the greatest damage. For example, Hawaii has sought to ban oxybenzone in sunscreens. Sunscreen can also be washed into the sewage when bathing. If the sewage system is not well-developed and waste is dumped directly into the sea, the chemicals will become pollution. When I was in Bocas del Toro, the houses which were built over the water have no sophisticated sewage system and drains into the sea.

This article from Mashable argues that the effect of oxybenzone is probably negligible as compared to stronger drivers like climate change and improper discharge of sewage. Nevertheless, I believe that every bit of effort helps.

Are reef-safe sunscreens viable alternatives then? MarineSafe states that oxybenzone is not the only toxic chemical which used in sunscreens. Others, such as plant-based oils and zinc oxide nanoparticles, can be damaging to the marine environment too. Where possible, I suggest wearing UV-protective clothing. They also have the benefits of reusability. By putting in more thoughts about the products we consume, we can become more responsible tourists and help to preserve nature's treasures.

Sources:

http://www.marinesafe.org/blog/2016/03/18/sunscreen-pollution/

https://www.dermveda.com/learn/sun-care/sunscreen/environmental-impact-of-sunscreens

https://www.theguardian.com/environment/2015/oct/21/sunscreen-contributing-to-decline-of-coral-reefs-study-shows

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2291018/

https://www.nature.com/news/hawaii-seeks-to-ban-reef-unfriendly-sunscreen-1.21332