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, including 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 µg 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.

Insight into the Crucial Role of Secondary Mineral Phases in the Transfer of Gold Nanoparticles through a Sand Column Using Online ICP-MS/spICP-MS Monitoring.

Investigating the transport of engineered nanoparticles through representative soils is an important issue in assessing their mobility and fate in the environment. In this study, successive injections of gold nanoparticles (AuNPs) were performed in a quartz sand column with an eluent composed of 10-2 M NaCl at a pH of 7.5. After this series of injections, remobilization of the AuNPs was examined by raising the eluent pH to 10. 197Au and the conservative ionic tracer 79Br were monitored simultaneously by online inductively coupled plasma mass spectrometry (ICP-MS), and the particulate nature of gold eluting from the column was confirmed by setting the ICP-MS in the "single particle" mode. The extent of AuNP attachment was greater than predicted by DLVO theory considering quartz as the sole collector, decreased with the number of injections and with particle size. In contrast with the repulsive interaction energy between the particles and the quartz surface, kaolinite, a secondary mineral of the sand, provided favorable conditions for particle attachment. The superimposed signals of 197Au and 27Al in the column effluent after pH increase suggest that gold nanoparticles were essentially remobilized as heteroaggregates with the kaolinite colloids they were attached to when favorable conditions for clay detachment from the sand grains were encountered.