Cerium oxide nanoparticles (nCeO) are currently used in many sectors of our economy, for instance as fuel additives and in ceramics for catalytic converters. As a result, there are concerns about their release and resulting toxicity in the aquatic environment. The purpose of this study was to examine the bioavailability and toxicity of nCeO and Ce(IV) in zebra mussels (Dreissena polymorpha) in various types of surface water differing in organic matter, conductivity and pH. Mussels were exposed to 100 μg/L Ce as either nCeO or Ce(IV) for 96 h in 4 types of water: 1) green water (high conductivity and low total organic carbon), 2) brown water (low conductivity and high natural total organic matter), 3) 10% municipal effluent (high conductivity and high anthropogenic organic matter) and 4) controls, which consisted of dechlorinated tap water. After the exposure period, the mussels were analyzed for morphological changes, resistance to survive in air, triglycerides (fat reserves), oxidative stress (arachidonate cyclooxygenase and lipid peroxidation) and DNA damage. Evidence of aggregation was observed with nCeO in most types of water, with the exception of the diluted municipal effluent. The data revealed that some of the effects of nCeO were influenced by surface water properties. The mussels were more sensitive to air emersion when exposed to nCeO in green water but not in the other water types and Ce(IV) to all types of water, although a marginal decrease was observed in mussels co-exposed to the diluted municipal effluent. A general decrease in oxidative stress and lipid levels was observed with both forms of Ce and all water types. Ce(IV) in brown water did not reduce the levels of DNA strand breaks compared with the controls. In conclusion, the sublethal toxicity of nCeO could be modulated by the surface water from which the nanoparticle is suspended.
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