Sunscreen: Protection from the Sun, but not from the Coral Reefs

Written by Tyler Wilson

On Wednesday, February 19th, Dr. Carys Mitchelmore gave a lecture at St. Mary’s College of Maryland on  whether or not sunscreen is killing our coral reefs. Mitchelmore works as a professor at the University of Maryland Center for Environmental Science and is an environmental toxicologist.

Mitchelmore started off by providing some background to the general question she would be addressing. She talked about how coral reefs are a keystone species, essential to their ecosystem’s survival. Then she described how coral reefs are dying off, which can largely be attributed to climate change, with warming oceans and acidification being the main reason for the decline. However, she also mentioned that there are other factors that may be involved, such as chemical contaminants. One of the possible chemical contaminants is sunscreen, which is used in abundant supply on beaches near coral reefs. 

Dr. Mitchelmore then talked about how the marketing of sunscreens has been very misleading. First of all, some sunscreens are labeled as “organic,” because they contain materials such as oxybenzone or “inorganic” because they contain materials such as zinc oxide, but in reality no product is organic. Just because ingredients like oxybenzone are biodegradable does not mean that they are not harmful. Secondly, there have been very few studies on the effect of sunscreen on coral reefs, so one study conducted by Dr. Craig Downs in 2016 is seen as the basis for making policy decisions about sunscreen. The study found that near a coral reef, oxybenzone levels were above the threshold of toxicity. After the study, there was a sign at a beach that said sunscreen with oxybenzone was harmful for coral reefs solely based on Downs’ study. As Mitchelmore explained, one study is never enough to justify major policy decisions. The whole theory behind the scientific method is that studies should be checked by other studies to help the scientific community get a clear picture of the issue at hand. 

Based on the lack of research on the topic, Mitchelmore decided to take matters into her own hands, and went out with a team to the Hawaii Institute of Marine Biology, where she tested the toxicity of 13 UV filters at 19 sites. Some of these sites were more highly populated than others, causing the toxicity of the UV filters to vary spatially, but she was still able to make general conclusions about her data. On average, she found that oxybenzone levels were below the toxicity threshold, but some of the other contaminants examined were toxic to the environment.  Mitchelmore concluded that while the results contradicted Downs’ study, oxybenzone is still something that should be used with caution, and more studies are needed to produce clear results that influence policy. However, there was one ingredient that she said was the most toxic of all: zinc oxide, the “inorganic” ingredient in sunscreen. This exposes the dangers on basing a public statement on little evidence; people going to the beach could have seen the sign about oxybenzone and switched to another sunscreen with zinc oxide, which would have hurt the coral reefs even more. 

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