Yet in water, this coating can dissolve, releasing the TiO2 and allowing it to react with sunlight and oxygen to form numerous compounds, one being hydrogen peroxide, or H2O2.
Though familiar to humans as an antiseptic, high levels of H2O2 can inhibit the growth of phytoplankton, tiny plants that are the base of many ocean food chains. This made Sánchez-Quiles worry about the impact such sunscreen ingredients may be having on his local beaches, in the tourist-packed Spanish Balearic Islands.
“Tourism is one of the world’s largest industries, and coastal tourism is in many countries the fastest-growing area of contemporary tourism,” said Sánchez-Quiles. “Europe is also the world’s most-visited region, according to the World Tourism Organization.”
Just as the number of visitors has increased, so has the use of products to prevent skin damage. “Sun care products have increased an average of 7 percent per year over the last five years,” said Sánchez-Quiles.
Along with a team of scientists, Sánchez-Quiles recently published a study in Environmental Science & Technology. The team found levels of both TiO2 and H2O2 to be high enough in the waterways tested to pose a threat to bacterial and base-level plankton populations.
Putting numbers in context
The team estimated that roughly 4 kilograms (8.8 pounds) of TiO2 slips off the skin of sun-seekers into coastal waters on an average summer day, yielding 400 times the normal rates of H2O2. Though these numbers seem alarming on their own, others disagree.
Craig Downs, executive director of the Haereticus Environmental Laboratory in Clifford, Va., part of the Global Coral Repository, has been looking at the effect of cosmetic chemical byproducts in coastal waters for years, in particular how they affect coral reefs. He said that although he was enthusiastic about the efforts of the study, he was reluctant to draw conclusions from its findings.
Initially tasked to investigate the decline of coral reefs in the Virgin Islands National Park, Downs said he explored different components that can stress coral life, from pesticides to sunscreen ingredients like TiO2.
“For two sites, sunscreen residue was readily visible, an iridescent sheen on the surface of water,” said Downs. He found major changes in baby coral caused by these chemical additions to the water, both during the lifetime of the organisms and beyond.
Yet even with clear levels of these chemicals and knowledge of the damage they pose, Downs realized the ultimate cause of decline in the corals preceded recorded climate effects. Most of the decline was due to local and regional pollution.
At several sites, Downs found—along with the nanoparticles in question—chemicals indicative of sewage from residential runoff, primarily personal care products.
A labeling dilemma
Some scientists, like Anna Sobek, an environmental scientist at Stockholm University in Sweden, believe these products are making their way into the environment and will continue to, despite the findings of scientists, because regulators don’t check for them.
She said Sánchez-Quiles’s paper is not the first to recognize the murky water produced by commercial use of nanoparticles like TiO2.
Sobek said E.U. regulatory efforts remain confused, which has allowed many cosmetic products to avoid labeling requirements and thus responsibility for environmental consequences, including risk assessments.
“In the E.U., nanoparticles are regulated under the E.U.’s chemical regulation and should thus be treated, tested, risk-assessed in the same way as industrial chemicals,” Sobek said. “However, it is still uncertain as to how this will happen.”
Sánchez-Quiles added that there is another problem. Assuming that sunscreen ingredients are found to be harmful, to propose phasing out these products implies there is an equal alternative. As with other chemicals, such as pesticides, this just isn’t true yet, he said.
On top of this, climate changes are predicted to increase use of almost all of these chemicals to prevent disease and skin damage and to increase crop demand.
Sánchez-Quiles said fixing the situation will require collaboration. “Environmental scientists and cosmetic companies must work together to get the right compromise between human and environmental health,” he said.
Only the start
Although critical of some aspects of the sunscreen research, Downs said, “I am very glad that someone is working on the issue of sunscreens and environmental impacts. No one in the U.S. is working on this, and what small studies do exist, society needs to encourage.”
Downs said he will focus his next studies to look at how climate change-imposed factors, such as rising sea temperatures, will amplify these chemicals’ effects.
Sánchez-Quiles said the question regulators and scientists will have to answer is what the trade-offs are between the economic benefits of tourism and personal health benefits of these chemicals and the harmful effects on the environment as a whole.
With the number of international visitors to the Mediterranean alone projected to rise from 202 million in 2013 to 264 million by 2030, Sánchez-Quiles sees plenty of questions left to be answered. In the future, he wants to scale up his work, to better understand how his findings apply on a global level.