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 multimicronucleatum, a ciliated protozoan, using the 48 h LC₅₀ (lethal concentration, 50%) test. Our results showed that the 48 h LC ₅₀ values of these NPs to Paramecium ranged from 0.81 (Fe ₂O₃ 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.