Thanks to Lynn L. Bergeson’s Sept. 21, 2016 posting for information about the US Environmental Protection Agency’s (EPA) research into what happens to the nanoparticles when your nanosunscreen washes off into a swimming pool. Bergeson’s post points to an Aug. 15, 2016 EPA blog posting by Susanna Blair,
… 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 [open access paper but you need to register for free] … But before I delve into that, let’s talk a bit about sunscreen chemistry and nanomaterials….
Blair goes on to provide a good brief description of nanosunscreens before moving onto her main topic,
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 [emphasis mine] 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.
Blair finishes by explaining that research is continuing as the EPA researches the whole life cycle of engineered nanomaterials.