Trophic transfer of CuO NPs from sediment to worms (Tubifex tubifex) to fish (Gasterosteus aculeatus): a comparative study of dissolved Cu and NPs enriched with a stable isotope tracer (65Cu)

Abstract

Metal nanoparticles (NPs) released into the aquatic environment will likely accumulate in sediment and be available for sediment-dwelling invertebrates that serve as food for other organisms, such as fish. The aim of the present study was to investigate trophic transfer of copper oxide (CuO) NPs and dissolved Cu (CuCl₂) from natural sediment to the sediment-dwelling worm Tubifex tubifex, and then to the predatory fish Gasterosteus aculeatus (three-spined stickleback). Cu enriched in the stable isotope ⁶⁵Cu was used to increase detection and discriminate newly added/assimilated Cu from background Cu levels. Worms were exposed to sediment spiked with ⁶⁵CuCl₂ or ⁶⁵CuO NPs (∼20 nm) at environmentally relevant concentrations for 7 days and subsequently fed to fish for 7 days. Worms accumulated ⁶⁵Cu during sediment exposure to both ⁶⁵CuCl₂ and ⁶⁵CuO NPs (0.7 and 1.1 μg ⁶⁵Cu per g dw tissue, respectively), resulting in ⁶⁵Cu body burdens significantly different from control. Furthermore, significantly more ⁶⁵Cu was released from the sediment into the overlying water in the ⁶⁵CuO NP exposures compared to the ⁶⁵CuCl₂ exposures. ⁶⁵Cu accumulation in fish feeding on ⁶⁵CuCl₂ and ⁶⁵CuO NP-exposed worms was limited (intestinal tissue: 80 and 65 ng g⁻¹ dw; fish carcass: 7 and 10 ng g⁻¹ dw, and liver: 50 and 10 ng g⁻¹ dw, respectively). Glutathione peroxidase (gpx) mRNA expression was significantly higher in fish feeding on ⁶⁵CuCl₂-exposed worms compared to ⁶⁵CuO NP-exposed worms (though ⁶⁵Cu tissue concentrations were similar). No significant effects were detected for the other investigated genes (ctr1, mta, gcl, gr, sod, cat, zo-1). Our results show that NP-derived Cu can enter freshwater food webs, but bioaccumulation and trophic transfer under environmentally realistic exposures is low (detectable with a tracer) and not different from that of dissolved Cu.