Among all environmental contaminants, those emerging from nanotechnologies constitute one of the most critical challenges for the coming years. The new properties of nanoparticles are at the heart of current scientific advances and the growing interest in harnessing them brings awareness of potential impacts that we cannot ignore. To date, scientists and industrialists have focused on the manufacture of nanomaterials more than on the assessment of the risks for humans and ecosystems. Few databases exist regarding the amounts released within ecosystems and no specific procedure of recycling has yet been established. However, nanoparticles cannot be considered as molecular pollutants or larger particles, and careful consideration is needed to establish a legal system that is specific. Their novel properties, surface energy and reactivity make it impossible to simply transfer our physicochemical, thermodynamic and toxicological knowledge from the micronscale to the nanoscale. This article highlights, nonexhaustively, the strong relationship existing between the unique properties of metallic and metal oxide nanoparticles and their biological effects on aquatic organisms.

Cerium dioxide nanoparticles (C_eO₂ ENPs) are on the priority list of nanomaterials requiring evaluation. We performed in vitro assays on mature mouse oocytes incubated with C_eO₂ ENPs to study (1) physicochemical biotransformation of ENPs in culture medium; (2) ultrastructural interactions with follicular cells and oocytes using Transmission Electron Microscopy (TEM); (3) genotoxicity of C_eO₂ ENPs on follicular cells and oocytes using a comet assay. DNA damage was quantified as Olive Tail Moment. We show that ENPs aggregated, but their crystal structure remained stable in culture medium. TEM showed endocytosis of C_eO₂ ENP aggregates in follicular cells. In oocytes, C_eO₂ ENP aggregates were only observed around the zona pellucida (ZP). The comet assay revealed significant DNA damage in follicular cells. In oocytes, the comet assay showed a dose-related increase in DNA damage and a significant increase only at the highest concentrations. DNA damage decreased significantly both in follicular cells and in oocytes when an anti-oxidant agent was added in the culture medium. We hypothesise that at low concentrations of C_eO₂ ENPs oocytes could be protected against indirect oxidative stress due to a double defence system composed of follicular cells and ZP.