CeO₂ nanoparticles alter the outcome of species interactions

Abstract

Despite considerable research on the environmental impacts of nanomaterials, we know little about how they influence interactions between species. Here, we investigated the acute (12 d) and chronic (64 d) toxicities of cerium oxide nanoparticles (CeO₂ NPs) and bulk particles (0–200 mg/L) to three ciliated protist species (Loxocephalus sp., Paramecium aurelia, and Tetrahymena pyriformis) in single-, bi-, and multispecies microcosms. The results show that CeO₂ NPs strongly affected the interactions between ciliated protozoan species. When exposed to the highest CeO₂ NPs (200 mg/L), the intrinsic growth rates of Loxocephalus and Paramecium were significantly decreased by 18.87% and 88.27%, respectively, while their carrying capacities declined by more than 90%. However, CeO₂ NP exposure made it difficult to predict outcomes of interspecific competition between species. At higher NP exposure (100 and 200 mg/L), competition led to the extinction of both species in the Loxocephalus and Paramecium microcosms that survived in the absence of competitors or CeO₂ NPs. Further, the presence of potential competitors improved the survival of Loxocephalus to hundreds of individuals per milliliter in microcosms with Tetrahymena where Loxocephalus would otherwise not be able to tolerate high levels of NP exposure. This result could be attributed to weakened NP adsorption on the cell surface due to competitor-caused reduction of NP surface charge (from −18.52 to −25.17 mV) and intensified NP aggregation via phagocytosis of NPs by ciliate cells. Our results emphasize the need to explicitly consider species interactions for a more comprehensive understanding of the ecological consequences of NP exposure.

Keywords:

• CeO₂ nanoparticles
• ciliate protists
• interspecific competition
• population abundance
• toxicity

Acknowledgements

This study was supported by the US National Science Foundation Grant CBET-1235166, DEB-1257858, and DEB-1342754, National Natural Science Foundation of China Grant 31361123001, and China Scholarship Council Grant 201406320074.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported by the US National Science Foundation Grant CBET-1235166, DEB-1257858, and DEB-1342754, National Natural Science Foundation of China Grant 31361123001, and China Scholarship Council Grant 201406320074.