Structural characterization, solution stability, and potential health and environmental effects of the Nano-TiO2 bioencapsulation matrix and the model product of its biodegradation TiBALDH

Abstract

Dispersions of small TiO₂ nanoparticles in alcohol, stabilized by surface complexation with protonated triethanolamine ligands, are proposed as bio-encapsulation matrices. They were characterized by TEM and EXAFS spectroscopy, and DLS was used to investigate the nanoparticles stability over time in their pure form and after insertion into aqueous medium. This study reveals unusual structural features that explain the recently demonstrated facile formation of dense encapsulates on the surface of biological objects. In the view of the potentially broad application of this already industrially available material in agriculture as an encapsulation matrix for biocontrol organisms, its potential health and environmental effects were characterized by employing a number of model systems. The potential health effects of the produced stable aqueous dispersions were studied in vitro using A549 and U1810 lung carcinoma cell lines. The nanotitania in the environment is partly bio-digested with the formation of citrate and lactate complexes. The effects on the growth of tobacco pollen grains by the nanotitania and of the ammonium lactato-oxo-titanate (TiBALDH, a product already broadly used in biomineralization studies) were investigated to gain insight into the impact of these materials on the environment and specifically on plant reproduction. TiBALDH was used as a model product of the bio-digestion and its structure has been probed in this work by X-ray powder diffraction and EXAFS spectroscopy. No acute negative bio-effects could be observed for the studied materials at significantly high concentrations, such as 50 μg ml⁻¹ for the viability of human lung cancer cells and up to about 120 μg ml⁻¹ for the growth of pollen grains, corresponding to the conditions of proposed field applications. This observation was contrasted by the apparently high toxicity of the LaAlO₃ based nanophosphor which was applied as a positive control.