Generation and characterization of stable, highly concentrated titanium dioxide nanoparticle aerosols for rodent inhalation studies

Abstract

The intensive use of nano-sized titanium dioxide (TiO2) particles in many applications worldwide necessitates studies on their risk assessment as there are still open questions on their safe and sustainable handling and utilisation. For reliable risk assessment, the interaction of TiO2 nanoparticles (NP) with biological systems needs to be investigated using physico-chemically uniform and well characterized NP. Here we describe the reproducible production of TiO2 NP aerosols using spark ignition technology. Since there are no data existing on inhaled NP of 10-50 nm size range the emphasis was to generate NP as small as 20 nm for inhalation studies in rodents. For anticipated in vivo dosimetry analyses TiO2 NP were radio-labeled with 48V by proton irradiation of the titanium electrodes of the spark generator. The dissolution rate of the 48V label was about 1% within the first day. The highly concentrated, polydisperse TiO2 NP aerosol proved to be constant over several hours in terms of its count median diameter, its geometric standard deviation and number concentration. Extensive NP characterization of chemical composition, physical structure, morphology and specific surface area was performed. The originally generated amorphous TiO2 NP were converted into polycrystalline anatase TiO2 NP by thermal annealing at 950°C. Both polycrystalline and amorphous 20-nm TiO2 NP were chain-agglomerated/-aggregated consisting of primary particles in the range of 5 nm. Disintegration of the deposited TiO2 NP in lung tissue was not detectable within 24 hours.