Stability of titania nanoparticles in soil suspensions and transport in saturated homogeneous soil columns

The stability of TiO2 nanoparticles in soil suspensions and their transport behavior through saturated homogeneous soil columns were studied. The results showed that TiO2 could remain suspended in soil suspensions even after settling for 10 days. The suspended TiO2 contents in soil suspensions after 24 h were positively correlated with the dissolved organic carbon and clay content of the soils, but were negatively correlated with ionic strength, pH and zeta potential. In soils containing soil particles of relatively large diameters and lower solution ionic strengths, a significant portion of the TiO2 (18.8–83.0%) readily passed through the soils columns, while TiO2 was significantly retained by soils with higher clay contents and salinity. TiO2 aggregate sizes in the column outflow significantly increased after passing through the soil columns. The estimated transport distances of TiO2 in some soils ranged from 41.3 to 370 cm, indicating potential environmental risk of TiO2 nanoparticles to deep soil layers.