Cerium oxide nanoparticles induce oxidative stress in the sediment-dwelling amphipod Corophium volutator

Cerium oxide nanoparticles (CeO₂ 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 CeO₂ 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 (Corophium volutator) grown in marine sediments containing CeO₂ NPs showed a significant increase in oxidative damage compared to those grown in sediments without NPs and those containing large-sized (bulk) CeO₂ 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⁻¹ CeO₂. Characterisation of the CeO₂ NPs dispersed in deionised or saline exposure waters revealed that more radicals were produced by CeO₂ NPs compared with bulk CeO₂. Electron energy loss spectroscopy (EELS) analysis revealed that both CeO₂ 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 CeO₂ consisted mainly of Ce(IV). These results support a model whereby redox cycling of CeO₂ NPs between Ce(III) and Ce(IV) is enhanced in saline waters, leading to sublethal oxidative damage to tissues in our test organism.