Surface Interactions Affect the Toxicity of Engineered Metal Oxide Nanoparticles toward Paramecium

To better understand the potential impacts of engineered metal oxide nanoparticles (NPs) in the ecosystem, we investigated the acute toxicity of seven different types of engineered metal oxide NPs against Paramecium multi-micronucleatum, a ciliated protozoan, using the 48 h LC50 (lethal concentration, 50%) test. Our results showed that the 48 h LC50 values of these NPs to Paramecium ranged from 0.81 (Fe2O3 NPs) to 9269 mg/L (Al2O3 NPs); their toxicity to Paramecium increased as follows: Al2O3 < TiO2 < CeO2 < ZnO < SiO2 < CuO < Fe2O3 NPs. On the basis of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, interfacial interactions between NPs and cell membrane were evaluated, and the magnitude of interaction energy barrier correlated well with the 48 h LC50 data of NPs to Paramecium; this implies that metal oxide NPs with strong association with the cell surface might induce more severe cytotoxicity in unicellular organisms.