By Roberta Attanasio
The debate on the safety of titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles contained in sunscreen products is still on. Some scientists have raised concerns about the negative impact that these tiny particles — generally between one and 100 nanometers (between one and 100 billionths of a meter) across — may have on human health. Due to their small size, nanoparticles might do harm to humans by seeping through the skin and into the bloodstream. A few months ago, despite the widespread safety concerns, Paul Wright (a toxicology expert at RMIT University) told The Guardian that sunscreen nanoparticles don’t get past the outermost dead layer of human skin cells. In contrast, Paul Westerhoff (a professor at Arizona State University’s School of Sustainable Engineering and the Built Environment) told The New York Times that the products have not been thoroughly studied and are minimally regulated — he concluded: “I’m just saying we need to figure out if we should worry.”
We need to figure out if we should worry not only in terms of human health, but also in terms of toxicity to the environment.
About a year ago, Antonio Tovar-Sánchez (Department of Global Change Research, Mediterranean Institute for Advanced Studies, Esporles, Balearic Island, Spain) and collaborators reported the potential effects of commercial sunscreens released in nearshore waters by beachgoers. The researchers sampled surface nearshore waters of three beaches around Majorca Island and demonstrated that sunscreen products are a significant source of organic and inorganic chemicals that reach the sea with potential ecological consequences on the coastal marine ecosystem, inhibiting the growth of some species of marine phytoplankton or adding essential micronutrients that may stimulate the growth of others.
In a new study published July 28, 2014 (Sunscreens as a Source of Hydrogen Peroxide Production in Coastal Waters), Antonio Tovar-Sánchez and his collaborator David Sánchez-Quiles show that titanium dioxide and zinc oxide nanoparticles — when exposed to solar radiation — produce significant amounts of hydrogen peroxide (H2O2), a strong oxidizing agent able to generates high levels of stress on phytoplankton, the microscopic organisms that feed marine animals, from small fish to shrimp to whales..
The 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, they concluded that titanium dioxide nanoparticles contained in sunscreen products are largely responsible for a dramatic summertime spike in hydrogen peroxide levels in coastal waters.
The researchers point out, in a press release, that other than staying indoors, slathering on sunscreen is currently the best way to protect the skin from the sun’s harmful rays. However, when sunbathers splash into the ocean to cool off, some of their lotions and creams get rinsed into the water, react with ultraviolet light from the sun and form new compounds (such as hydrogen peroxide) that could be toxic.
Back in 2010, Johannes Jacobs and collaborators argued that the marketing of sunscreens containing titanium dioxide nanoparticles constitutes a morally unacceptable societal experiment — it is a large scale societal experiment due to the introduction of the technology before the hazards of the technology can be fully assessed and it is morally unacceptable as it violates four reasonable moral conditions for societal experimentation. They proposed a set of actions to move towards acceptability:
- Closing the existing information gap.
- Setup of monitoring tools and gathering data from the conducted societal experiment.
- Start continuous evaluation of available quantitative risk and benefits.
- Ongoing engineering design for safety.
- Altering legislation so that it incorporates the experimental nature of introducing novel technologies into society.
Sadly, not much has been done by regulators during the past years as it relates to the proposed set of actions. Although the new study on the release of hydrogen peroxide at levels hazardous for sea life in coastal waters helps to attenuate the information gap, much more research must be carried out in a timely fashion to address the concerns raised by the widespread use of sunscreen products containing titanium dioxide nanoparticles.