Investigation of the life cycle of nanoparticles by means of [44,45Ti]TiO2 and [110mAg]Ag0 – Research project NanoTrack

Production and application of nanocomposites such as functional surface coatings have significantly increased in recent years. Nanoparticle (NPs) coatings are used in a wide array of applications ranging from self-cleaning and scratch resistant surfaces to biocidal coatings. The current database for risk evaluation of NPs containing surface coatings (e.g. TiO2, Ag0) is still insufficient. Tools are currently lacking with which to assess the impact of TiO2 and Ag0 NPs. Radiolabeling of the NPs provides a method to sensitively detect NPs and is feasible for qualitative and quantitative fate and effects determination. With this detection method, evaluation of NPs fate during aging and abrasion of nanocomposites, estimation of release rates, transport of NPs in the environment and up-take and effects with organisms can be studied in great detail.
The joint research project NanoTrack uses model surface coatings in an acrylate-based formulation containing TiO2 (d = 21 nm, P25, Evonik Industries) and Ag0 NPs (d < 100 nm, Sigma Aldrich). Coatings were produced by application of 25 µm thick nanocomposite layers (thickness of wet coat) on a substrate followed by curing and later weathered under laboratory standard test conditions. Due to the low resistivity of this model system, the organic matrix of the surface coating was severely degraded and nanoparticles were partly released. Scanning electron microscopy showed that mostly aggregates and agglomerates of NPs were released and only a small fraction of primary NPs can be expected to be discharged. Nevertheless, further environmental processes can also lead to disaggregation and stabilization of smaller NPs composites.
Current studies on the environmental fate and effects of nanoparticles are limited by our inability to detect and quantify nanoparticles in complex environmental test systems and radiolabeling nanoparticles may provide a solution to this limitation. Isotopic labeling was carried out via a low-temperature diffusive implementation of radionuclides resulting in [44Ti]TiO2 and [110mAg]Ag0 NPs (Hildebrand & Franke, 2012). Chemical composition, particle size distributions and morphology of the radiolabeled NPs remained unaltered compared to the original material. Upon suspension in various test solutions, [44Ti] from TiO2 and [110mAg] from Ag0 NPs did not leach from the NPs and remained within the lattice framework of the NPs. Within the project, interactions of the NPs with environmental geological media (such as humic acids or sediments) and transport in flow through systems are under study.
Another important aspect is the ecotoxicological impact of the released NPs. In case of entry of the NPs in aquatic systems, interactions with living organisms become very likely. Biofilms are considered as potential receptor of industrial nanoparticles in the environment and as an important part of aquatic ecosystems it is not yet known if these NPs may end up in higher organisms via the food chain transfer. Systematic studies of NPs behavior in aquatic systems are carried out to gain knowledge of their fate and transport and potential risks for ecosystems.
The integrated examination of NPs in surface coatings in terms of production, aging and abrasion, NP release and their fate and transport in the environment provides a data base for risk assessment and validation or possibly adaptation of new nanocomposite production.

Hildebrand H and Franke K (2012) J Nanopart Res 14:1142.