Toxicity of mixtures of zinc oxide and graphene oxide nanoparticles to aquatic organisms of different trophic level: particles outperform dissolved ions

Abstract

Concomitant releases of various engineered nanoparticles (NPs) into the environment have resulted in concerns regarding their combined toxicity to aquatic organisms. It is however, still elusive to distinguish the contribution to toxicity of components in NP mixtures. In the present study, we quantitatively evaluated the relative contribution of NPs in their particulate form (NP_(particle)) and of dissolved ions released from NPs (NP_(ion)) to the combined toxicity of binary mixtures of ZnO NPs and graphene oxide nanoplatelets (GO NPs) to three aquatic organisms of different trophic levels, including an alga species (Scenedesmus obliquus), a cladoceran species (Daphnia magna), and a freshwater fish larva (Danio rerio). Our results revealed that the effects of ZnO NPs and GO NPs were additive to S. obliquus and D. magna but antagonistic to D. rerio. The relative contribution to toxicity (RCT) of the mixture components to S. obliquus decreased in the order of RCT_{GO NP(particle)} > RCT_{ZnO NP(particle)} > RCT_{ZnO NP(ion)}, while the RCT of the mixture components to D. magna and D. rerio decreased in the order of RCT_{ZnO NP(particle)} > RCT_{GO NP(particle)} > RCT_{ZnO NP(ion)}. This finding also implies that the suspended particles rather than the dissolved Zn-ions dictated the combined toxicity of binary mixtures of ZnO NPs and GO NPs to the aquatic organisms of different trophic level. The alleviation of the contribution to toxicity of the ionic form of ZnO NPs was caused by the adsorption of the dissolved ions on GO NPs. Furthermore, the ZnO NP_(particle) and GO NP_(particle) displayed a different contribution to the observed mixture toxicity, dependent on the trophic level of the aquatic organisms tested. The difference of the contributions between the two particulate forms was mainly associated with differences in the intracellular accumulation of reactive oxygen species. Our findings highlight the important role of particles in the ecological impact of multi-nanomaterial systems.

Keywords:

• Zinc oxide nanoparticles
• graphene oxide
• aquatic organisms
• mixture toxicity
• relative contribution to toxicity

Acknowledgements

We also thank the anonymous reviewers for helping to improve the manuscript.

Disclosure statement

The authors declare there are no competing financial interests.

Additional information

Funding

This study was supported by the National Natural Science Foundation of China [Grant No. 21407080, 41601519] and the Natural Science Foundation of Jiangsu Province [Grant No. BK20150891]. The research described in this work was supported by the European Union’s Horizon 2020 research and innovation program “FUTURENANONEEDS” under grant agreement number [604602].