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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SOS-Nano (Structure â€“ Oxidative Stress relationships of metal oxide nanoparticles in the aquatic environment)

Teaser

Summary

The SOS-Nano project addressed one of the most pressing cutting-edge issues of econanotoxicology: to find a structural property of nanoparticles (NPs) to predict their potential toxicity in marine aquatic environments. By using an in vivo exposure system, the SOS-Nano project tested the suitability of two paradigms for ranking the hazard of metal oxide NPs: 1) NPs physical-electrochemical properties (i.e. bandgap energy and dissolution) for predicting oxidative stress potential, and 2) oxidative stress generation for predicting biological impact.
The specific goals during the project to reach the main objective were:
â€¢ To screen the validity of Bandgap-Dissolution Paradigms over a set of model- metal oxide NPs;
â€¢ To assess the influence of natural organic matter (NOM) on the potential for metal oxide NPs to promote oxidative stress in aquatic environments;
â€¢ To explore the influence of salinity on the potential for metal oxide NPs to generate oxidative stress in aquatic environments.
â€¢ To estimate the longer-term hazard of metal oxide NPs in aquatic environment under realistic scenarios.
The results obtained by SOS-Nano are of high impact for the European Union policy and the overall society. Nanotechnology is one of the six EU Key Enabling Technologies selected by the EU Commission to address the industrial-economic competitiveness and the grand societal challenges in Europe by 2020. The SOS-Nano results add important new information to enable the establishment of a suitable risk assessment of these nanomaterials in the natural environment.

Work performed

The SOSâ€“Nano experimental program was based on short-term in vivo exposures assessing the relationships between the physical-chemical properties of three model nanoparticles (NPs) and the oxidative stress generated under different realistic scenarios. The test NPs (i.e. ZnO NPs, MnO2 NPs and CeO2 NPs) specifically represent three different modes-of-action (dissolution, bandgap i.e. potential for electron transfer with biological substrates, and generation of reactive oxygen species via Fenton like reaction, respectively).
The acute exposures specifically assessed the role of salinity and organic matter in the overall environmental and toxicological behaviour of NPs. In order to find predictive relationships between the NPsâ€™ physico-chemical properties and their toxicological activity, NPs were fully characterized for their intrinsic features and for those acquired once dispersed in seawater. The exposed organisms underwent a multi-parameter oxidative stress screening highlighting the expression of target genes and the induction of cytotoxic effects and pathogenesis. Finally, the effective ingestion and cellular internalization of NPs was traced by the use of the highest resolution imaging techniques and the actual functioning of the NPsâ€™ mode of action was assessed via dissolution tests and/or abiotic probes of redox activity.
The inclusive picture obtained through this comprehensive approach pointed out that oyster larvae are potentially exposed to NPs released in their environment and subject to their toxicological activity. Oyster larvae effectively internalised the NPs filtered from the surrounding into the cells of the post absorptive organs. This crucial aspect was explored in greater depth through an additional experiment designed to explore the fate of NPs ingested by the larvae.
As regards to the toxicological impact of these exposures, we obtained different outcomes for the three model NPs, consistently with the different resilience of their mode of action to the transformation driven by the salinity and organic matter. Briefly, the NPs releasing toxic metal ions (i.e. ZnO NPs) induced high toxicity in the oyster larvae as their dissolution was not stopped by seawater. However, we observed that this mode of action can be mitigated by organic matter present in seawater. In contrast, those nanomaterials whose toxicological mechanisms rely on their surface reactivity (MnO2 NPs and CeO2 NPs) were not toxic under all the exposure scenarios. The supporting information provided by the assessment of their physico-chemical propriety and oxidation reactivity under the exposure conditions suggested that salinity could be a key factor in the actual toxicological behaviour in marine environments (via sorption of ions at reactive sites).
The overall scientific outcome of the SOS-Nano project was disseminated through 1) two platform presentations at international conferences (SETAC 2017 - Europe 27th Annual Meeting, Brussels; ICEENN 2017 - 12th International Conference on the Environmental Effects of Nanoparticles and Nanomaterials, Birmingham), 2) three high-impact peer reviewed publications (under review/in preparation), and 3) two poster presentations at international meetings (SETAC 2016 - Europe 26th Annual Meeting, Nantes; 2017 symposium on the current trends in nanotoxicology: implications for environmental & human health, Plymouth).
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Final results

The relevant research outcome of the SOS-Nano project responded to some of the most pressing scientific needs to achieve appropriate NPs risk assessment, a fundamental goal of the EU policies toward the safe development of nanotechnology. The specific impact of each result on economical-regulatory aspects of EU policies is detailed below.
â€¢ Mechanistic understanding of metal oxide NPs hazard in real aquatic environments. This can support the prediction of the toxicological impact of other metal oxide NPs sharing some proprieties found as pivotal for the actual toxicological activity in seawater. Furthermore, it can support the design a future generation of nanomaterials whose intrinsic structure guarantees the missing of their toxicological potential once in the environment.
â€¢ Novel paradigms for predicting the toxicological impact of metal oxide NPs in the environment. The research evidence obtained for the bandgap model NPs calls for the reappraisal of this paradigm within the scope of the environmental risk assessment. The mechanistic understanding of the role of the sorption capacity on the overall oxidation potential of NPs can lead the formulation of a new paradigm or to the correction of the bandgap paradigm when specifically applied to the marine environment.
â€¢ Experimental data on NPs behaviour, fate and impact under realistic scenarios. The SOS-Nano project collected a comprehensive database crossing the primary physico-chemical proprieties of three NPs with 1) their secondary proprieties and oxidation activity in seawater, 2) their actual ingestion and cellular internalization, and 3) their toxicological effects in oyster embryo-larvae. This inclusive database is available to the research and regulatory community for all purposes (including modelling).
â€¢ Innovative multi-tier testing strategy for ranking NPs hazard. The multi-tier testing strategy set by the SOS-Nano project is available to the research and regulatory communities for use. Thanks to its flexible structure, it allows for future improvement and/or tailoring toward more specific toxicological responses.
â€¢ High-throughput exposure designs for screening NPs toxic potential in vivo. The SOS-Nano highlighted high potential for NPs exposure and a remarkable sensitivity of oyster embryo-larvae, making this model a valuable candidate for regulatory testing.