Antibacterial Activity Comparison of Three Metal Oxide Nanoparticles and their Dissolved Metal Ions

The potential ecotoxicity of three metal-oxide nanoparticles (NPs) toward Escherichia coli (E. coli) was investigated, including titanium dioxide (TiO2), copper oxide (CuO), and zinc oxide (ZnO). The true particle sizes of NPs in medium were significantly larger than the advertised sizes. Bacterial toxicity tests showed that the three NPs were harmful to varying degrees. The toxicity of CuO toward E. coli increased with the increasing concentration of CuO. The toxicity of ZnO and TiO2 toward E. coli was highest at NP concentration of 5 and 20 mg/L, respectively, but decreased when the NP concentration was higher, which is closely related with the nanoparticle sizes. Ion toxicity further demonstrated that dissolved metal ions were also responsible for the toxicity of CuO and ZnO. These results highlight the need for caution during the use and disposal of such manufactured nanomaterials to prevent unintended environmental impacts.