Stable Isotope Tracer To Determine Uptake and Efflux Dynamics of ZnO Nano- and Bulk Particles and Dissolved Zn to an Estuarine Snail

Zinc oxide nanoparticles (ZnO NPs) are among the most commercialized engineered nanomaterials. Their biological impact in aquatic organisms has been associated with dissolution, but there is also evidence of nanospecific effects. In this study the waterborne uptake and efflux kinetics of isotopically labeled (ZnO)-Zn-68 NPs (7.8 +/- 1.2 nm), in comparison to aqueous Zn-68 and (ZnO)-Zn-68 bulk particles (up to 2 mu m), were determined for the estuarine snail Peringia ulvae following a 7 d exposure (nominally 20 mu g Zn-68 L-1) and 28 d depuration. Detection of the Zn-68 label was achieved by high precision multiple collector ICP-MS (MC-ICP-MS). Previous characterization in artificial estuarine water revealed that the NPs underwent initial aggregation and solubilized up to 60% within 12 days. Bulk and aqueous forms were significantly more bioavailable than (ZnO)-Zn-68 NPs (p < 0.05), but after correcting for dissolution, aqueous (0.074 L-1 g(-1) d(-1)) and NP (0.070 L-1 g(-1) d(-1)) uptake rate constants were highly comparable. The rate constant of loss for Zn-68 aqueous (0.012 +/- 0.005 d(-1)) and (ZnO)-Zn-68 NPs (0.012 +/- 0.007 d(-1)) were identical. These results strongly suggest that in this exposure scenario the bioaccumulation of Zn from ZnO NPs is primarily dependent upon solubility.