Swimmers' sun creams deposit titanium dioxide nanoparticles into the sea, where their protective coatings may be washed away, according to a French study.
Last year, a team led by Dr Jérôme Labille from Aix-Marseille Université analysed titanium dioxide levels in the water off three French beaches. Their social scientist colleagues counted the number of beach users, asked them about their sun cream use and scrutinised their sun cream labels.
Many sun creams contain titanium dioxide nanoparticles, which tend to be coated with a thin layer of aluminium oxide or silica. This coating prevents the particles acting as light-activated catalysts (as used in self-cleaning windows).
Overall, the team estimated that about 68kg of sun cream could be used daily by 3,000 people on a small beach and detected up to 45 micrograms titanium dioxide per litre of water. The levels measured were lower than predicted from total sun cream use, however, so the team repeated the beach experiments this summer to see what proportion of the particles adsorb to the seabed. The results have yet to be analysed.
The work is part of a project called ECO-Sun, funded by a French consortium called LabEx Serenade (Laboratory of Excellence for Safe(r) Ecodesign Research and Education applied to Nanomaterial Development), which has 11 academic and two industrial partners. The project aims to help develop sun creams that are "safe by design".
"By considering each development stage of the sunscreen, from the choice of UV-blocker and its integration into a cosmetic formulation, to the knowledge of the risk involved in this choice all along the product lifecycle, a safe-by-design approach can be achieved and risk can be minimised," says Dr Labille.
Under the project, Dr Labille's team has created a number of model sun cream systems, some of which contain titanium dioxide coated with aluminium oxide or silica.
To simulate sun cream ageing, they agitated the products in either sea water or fresh water and were surprised to discover that some of the silica-coated particles soon shed their protective coatings. Removing the coating will affect nanoparticle toxicity, by exposing the pure photo-catalytic product to the environment, suggests Dr Labille.
He now hopes to gain funding for the next step of his research, which will investigate titanium dioxide levels in rivers and closed basins. He would also like to introduce organic UV filters into his research.