Cerium oxide nanoparticles induce oxidative stress in the sediment-dwelling amphipod <i>Corophium volutator</i>

<p>Cerium oxide nanoparticles (CeO<sub>2</sub> NPs) exhibit fast valence exchange between Ce(IV) and Ce(III) associated with oxygen storage and both pro and antioxidant activities have been reported in laboratory models. The reactivity of CeO<sub>2</sub> NPs once they are released into the aquatic environment is virtually unknown, but this is important to determine for assessing their environmental risk. Here, we show that amphipods (<i>Corophium volutator</i>) grown in marine sediments containing CeO<sub>2</sub> NPs showed a significant increase in oxidative damage compared to those grown in sediments without NPs and those containing large-sized (bulk) CeO<sub>2</sub> particles. There was no exposure effect on survival, but significant increases in single-strand DNA breaks, lipid peroxidation and superoxide dismutase activity were observed after a 10-day exposure to 12.5 mg L<sup>−1</sup> CeO<sub>2</sub>. Characterisation of the CeO<sub>2</sub> NPs dispersed in deionised or saline exposure waters revealed that more radicals were produced by CeO<sub>2</sub> NPs compared with bulk CeO<sub>2</sub>. Electron energy loss spectroscopy (EELS) analysis revealed that both CeO<sub>2</sub> NPs were predominantly Ce(III) in saline waters compared to deionised waters where they were predominantly Ce(IV). In both types of medium, the bulk CeO<sub>2</sub> consisted mainly of Ce(IV). These results support a model whereby redox cycling of CeO<sub>2</sub> NPs between Ce(III) and Ce(IV) is enhanced in saline waters, leading to sublethal oxidative damage to tissues in our test organism.</p>