The SOS–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 NPs’ 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 NPs’ 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).
