AGGREGATION AND TRANSPORT OF TIO2 NANOPARTICLES IN POROUS MEDIA

Engineered titanium dioxide (TiO₂) nanoparticles have become ubiquitous in industry due to their practical applications as catalysts and white pigments. Nano-sized TiO₂ is reasonably likely to enter the environment in significant concentrations. Studies confirmed that nano-sized particles are released into waterways in wastewater effluents with concentrations of up to 15 µg/L, though larger TiO₂ particles are filtered out by wastewater treatment plants. The toxic effects of TiO₂ nanoparticles to microbes are known, but their geochemical fate has not yet been extensively studied. The goal of this study is to collect information about the geochemical fate of TiO₂ nanoparticles. Our objective is to determine the ability of TiO₂ nanoparticles to move within soil environments. This requires a chemical characterization of TiO₂ nanoparticles and their aggregates as well as measurement in soil column experiments.

Preliminary data were collected with dynamic light scattering analysis, and aggregates above 1 µm in size were observed to form within 5 minutes of suspension. Scanning electron microscopy (SEM) was used to image TiO₂ nanoparticle aggregates. The SEM data we collected indicate decreased aggregate size when TiO₂ is suspended in acidic solvent, likely due to electrostatic repulsion caused by low pH. To determine the effect of this smaller aggregate size on movement, glass chromatography columns are being used to measure transport behavior of TiO₂ nanoparticles. Experiments are being performed in silica sand and various soils, and the sorption and breakthrough of TiO₂ in suspension will be determined.

If smaller aggregates are more able to be transported through soil, the risks associated with TiO₂ nanoparticle contamination will vary with soil acidity. Implications include higher risks to microbial communities in naturally acidic soils, as well as in environments where anthropogenic factors have lowered pH.