Spanish researchers have reportedly determined that the titanium dioxide in sunscreens that are rinsed off human skin in coastal waters could cause damage to the marine environment because the substance interacts with solar radiation to produce “significant amounts of hydrogen peroxide, a strong oxidizing agent that generates high levels of stress on marine phytoplankton.” David Sánchez-Quiles and Antonio Tovar-Sánchez, “Sunscreens as a Source of Hydrogen Peroxide Production in Coastal Waters,” Environmental Science & Technology (2014). The researchers studied Palmira beach on the Spanish island of Majorca, visited by some 10,000 beachgoers who wash 4 kilograms of titanium dioxide into the water each day, producing an additional 270 nM of hydrogen peroxide daily, significantly above the natural levels of 100 nM. This was apparently a conservative estimate, based on each adult using just half of the recommended amount of sunscreen. See conservationmagazine. org, August 27, 2014; cosmeticobs.com, September 5, 2014.