Influence of Aging on Bioaccumulation and Toxicity of Copper Oxide Nanoparticles and Dissolved Copper in the Sediment-Dwelling Oligochaete Tubifex tubifex : A Long-Term Study Using a Stable Copper Isotope.

For engineered metal nanoparticles (NPs), such as copper oxide (CuO) NPs, the sediment is recognized as a major compartment for NP accumulation. Sediment-dwelling organisms, such as the worm , will be at particular risk of metal and metal NP exposure. However, a range of complex transformation processes in the sediment affects NP bioavailability and toxicity as the contamination ages. The objective of this study was to examine bioaccumulation and adverse effects of CuO NPs in compared to dissolved Cu (administered as CuCl) and the influence of aging of spiked sediment. This was done in a 28-day exposure experiment with incubated in clean sediment or freshly spiked sediment with different concentrations of dissolved Cu (up to 230 μg g dw) or CuO NPs (up to 40 μg g dw). The experiment was repeated with the same sediments after it had been aged for 2 years. To obtain a distinct isotopic signature compared to background Cu, both Cu forms were based on the stable isotope Cu (>99%). The 28-day exposure to sediment-associated dissolved Cu and CuO NPs resulted in a clear concentration-dependent increase in the Cu body burden. However, despite the elevated Cu body burdens in exposed worms, limited adverse effects were observed in either of the two experiments (e.g., above 80% survival in all treatments, low or no effects on the growth rate, feeding rate, and reproduction). Organisms exposed to aged sediments had lower body burdens of Cu than those exposed to freshly spiked sediments and we suggest that aging decreases the bioavailability of both Cu forms. In this study, the use of a stable isotope made it possible to use environmentally realistic Cu concentrations and, at the same time, differentiate between newly accumulated Cu and background Cu in experimental samples despite the high background Cu concentrations in sediment and tissue. Realistic exposure concentrations and aging of NPs should preferably be included in future studies to increase environmental realism to accurately predict the environmental risk of metal NPs.