Sunscreen and Sun Safety: Just One Piece of the Story

By Susanna Blair

Blue towel and sunscreen lotion near the poolIt’s the end of summer, and you know what that means: it is hot and sunny! (And if you’re in DC like me, it also feels like a swamp.) Going to the pool is one of my favorite things to do to help beat the heat, and because UV radiation is a known carcinogen, I make sure to bring the items CDC recommends for sun protection:  protective clothing, a hat, sunglasses, and loads of sunscreen.

But where does all of that sunscreen go? It’s not surprising that sunscreens are detected in pool water (after all, some is bound to wash off when we take a dip), but certain sunscreens have also been widely detected in our ecosystems and in our wastewater. So how is our sunscreen ending up in our environment and what are the impacts?

Well, EPA researchers are working to better understand this issue, specifically investigating sunscreens that contain engineered nanomaterials and how they might change when exposed to the chemicals in pool water. But before I delve into that, let’s talk a bit about sunscreen chemistry and nanomaterials….

The best protection from UV radiation is a physical block, such as titanium dioxide, which is a common ingredient in sunscreen. This type of physical sunblock is often in the form of engineered nanomaterials , which are materials with dimensions between 1 and 100 nanometers engineered with unique properties for specific uses.  (To put a nanomaterial’s size into perspective, just take a look at the hair on your head – a single strand is between 80,000-100,000 nanometers thick.)

Many sunscreens contain titanium dioxide (TiO2) because it absorbs UV radiation, preventing it from damaging our skin. But titanium dioxide decomposes into other molecules when in the presence of water and UV radiation. This is important because one of the new molecules produced is called a singlet oxygen reactive oxygen species. These reactive oxygen species have been shown to cause extensive cell damage and even cell death in plants and animals. To shield skin from reactive oxygen species, titanium dioxide engineered nanomaterials are often coated with other materials such as aluminum hydroxide (Al(OH)3).

EPA researchers are testing to see whether swimming pool water degrades the aluminum hydroxide coating, and if the extent of this degradation is enough to allow the production of potentially harmful reactive oxygen species. In this study, the coated titanium dioxide engineered nanomaterials were exposed to pool water for time intervals ranging from 45 minutes to 14 days, followed by imaging using an electron microscope.  Results show that after 3 days, pool water caused the aluminum hydroxide coating to degrade, which can reduce the coating’s protective properties and increase the potential toxicity.  To be clear, even with degraded coating, the toxicity measured from the coated titanium dioxide, was significantly less than the uncoated material. So in the short-term – in the amount of time one might wear sunscreen before bathing and washing it off — these sunscreens still provide life-saving protection against UV radiation. However, the sunscreen chemicals will remain in the environment considerably longer, and continue to degrade as they are exposed to other things.

This study provides evidence that when released into the environment, nanomaterials undergo physical and/or chemical transformations – an important consideration when measuring the impact of these materials on public health and the environment. EPA researchers continue to do work to better understand the life cycle of engineered nanomaterials and the potential transformation of these products when they are no longer working to protect our skin.

 

About the author: Susanna Blair is a physical scientist in the Chemical Safety for Sustainability Research Program in the Office of Research in Development. Her primary role is to translate and disseminate EPA’s chemical safety research.

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