Toxicity of TiO(2) Nanoparticles to Escherichia coli: Effects of Particle Size, Crystal Phase and Water Chemistry

Controversial and inconsistent results on the eco-toxicity of TiO(2) nanoparticles (NPs) are commonly found in recorded studies and more experimental works are therefore warranted to elucidate the nanotoxicity and its underlying precise mechanisms. Toxicities of five types of TiO(2) NPs with different particle sizes (10∼50 nm) and crystal phases were investigated using Escherichia coli as a test organism. The effect of water chemistry on the nanotoxicity was also examined. The antibacterial effects of TiO(2) NPs as revealed by dose-effect experiments decreased with increasing particle size and rutile content of the TiO(2) NPs. More bacteria could survive at higher solution pH (5.0–10.0) and ionic strength (50–200 mg L(−1) NaCl) as affected by the anatase TiO(2) NPs. The TiO(2) NPs with anatase crystal structure and smaller particle size produced higher content of intracellular reactive oxygen species and malondialdehyde, in line with their greater antibacterial effect. Transmission electron microscopic observations showed the concentration buildup of the anatase TiO(2) NPs especially those with smaller particle sizes on the cell surfaces, leading to membrane damage and internalization. These research results will shed new light on the understanding of ecological effects of TiO(2) NPs.