Slathering on sunscreen to protect your skin on a beach vacation may come with an environmental hitch, scientists say.
Certain sunblock ingredients wash off skin and into the sea, and they can become toxic to some of the ocean's tiniest inhabitants, which are the main course for many other marine animals, scientists have found.
When sunbathers splash into the ocean to cool off, some of their lotions and creams get rinsed into the water.
Titanium dioxide and zinc oxide nanoparticles, which are common ingredients in sunblock, can react with ultraviolet light from the sun and form new compounds, such as hydrogen peroxide, that could be toxic, researchers said.
High amounts of hydrogen peroxide can harm phytoplankton, the microscopic algae that feed everything from small fish to shrimp to whales.
In the study published in the ACS journal Environmental Science & Technology, scientists wanted to figure out just how serious of an impact beachgoers could be having on life in coastal waters.
To investigate the matter, researchers went to Majorca Island's Palmira beach on the Mediterranean along with about 10,000 beachgoers, a small portion of the more than 200 million tourists that flock to Mediterranean shores every year.
Based on lab tests, seawater sampling and tourism data, the researchers concluded that titanium dioxide from sunblock was largely responsible for a dramatic summertime spike in hydrogen peroxide levels in coastal waters - with potentially dangerous consequences for aquatic life.
