Transport of nanoparticulate TiO2 UV-filters through a saturated sand column at environmentally relevant concentrations

The fate of sunscreen residues released during bathing activities around recreational areas is an emerging concern regarding the potential ecotoxicity of some of their ingredients, induding nanoparticulate TiO2 UV-filters. To assess the extent of contamination in the natural medium, sand-packed column experiments were carried out with bare TiO2 engineered nanoparticles (ENPs) and two commercial nano-TiO2 UV-filters coated with either SiO2 (hydrophilic) or a combination of Al2O3 and simethicone (amphiphilic). The high sensitivity of (single particle)ICPMS online monitoring of the breakthrough curves made it possible to inject the ENPs at trace levels (2-100 mu g L-1) in eluents composed of 10(-3) and 10(-2) M NaCl and pHs of 5.7 and 7.8. The deposition of all ENPs in the sand increased with the ionic strength and decreased with the pH of the carrier. Both bare and SiO2-coated ENPs showed a clear control by the electrostatic interactions between the particles and the quartz grains surfaces, in partial agreement with classical DLVO theory. Unexpectedly high rates of transfer were observed with the amphiphilic UV-filter, which could be explained by the addition of a contribution to the DLVO model to account for the steric repulsion between the sand collector and the polysiloxane surface layer of this ENP. These results demonstrate the major role played by the coating of UV-filters regarding their fate in porous media like soils, sediments and aquifers.

Automated summary

This study demonstrates the significant role played by the coating of UV-filters in determining their fate in porous media such as soils, sediments and aquifers. The deposition of nanoparticles in sand is influenced by changes in electrolyte concentration and carrier pH. Both bare ENPs and SiO2-coated ENPs are controlled by electrostatic interactions, while the high transfer rate of the hydrophobic UV-filter may be attributed to steric repulsion between the sand collector and the polysiloxane surface layer of the ENP.