Tracing Bioavailability of ZnO Nanoparticles Using Stable Isotope Labeling

Abstract

Zinc oxide nanoparticles (ZnO NPs) are widely used in commercial products and knowledge of their environmental fate is a priority for ecological protection. Here we synthesized model ZnO NPs that were made from and thus labeled with the stable isotope (68)Zn and this enables highly sensitive and selective detection of labeled components against high natural Zn background levels. We combine high precision stable isotope measurements and novel bioimaging techniques to characterize parallel water-borne exposures of the common mudshrimp Corophium volutator to (68)ZnO NPs, bulk (68)ZnO, and soluble (68)ZnCl(2) in the presence of sediment. C. volutator is an important component of coastal ecosystems where river-borne NPs will accumulate and is used on a routine basis for toxicity assessments. Our results demonstrate that ionic Zn from ZnO NPs is bioavailable to C. volutator and that Zn uptake is active. Bioavailability appears to be governed primarily by the dissolved Zn content of the water, whereby Zn uptake occurs via the aqueous phase and/or the ingestion of sediment particles with adsorbed Zn from dissolution of ZnO particles. The high sorption capacity of sediments for Zn thus enhances the potential for trophic transfer of Zn derived from readily soluble ZnO NPs. The uncertainties of our isotopic data are too large, however, to conclusively rule out any additional direct uptake route of ZnO NPs by C. volutator.

Biokinetics of zinc oxide nanoparticles: toxicokinetics, biological fates, and protein interaction

“…This is consistent with the in vivo ZnO nanoparticle fate determined by Paek et al 26 The bioavailability fate of isotope-labeled ZnO nanoparticles was traced by coherent anti-Stokes Raman scattering and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy in mud shrimp (Corophium volutator); 42 ionic zinc from particles in an aqueous environment was determined primarily to contribute to the uptake and bioavailability fate of ZnO nanoparticles. Although the particulate form affects the kinetics and toxicity of ZnO nanoparticles, it appears that the fate of ZnO nanoparticles in tissues or cells is primarily as ionic zinc, which should be considered in underlying the mechanisms of their in vitro and in vivo toxicity (Table 1 and Figure 3).…”

Isotopically modified silver nanoparticles to assess nanosilver bioavailability and toxicity at environmentally relevant exposures

“…[21,[26][27][28] Recently, enriched stable metal isotopes have been used in the synthesis of nanoparticles composed of the essential metals Cu and Zn, which provided enhanced sensitivity when evaluating the rates at which these particles delivered Cu and Zn to humans, [29] and to invertebrates. [15,16,27,30,31] Here we describe for the first time stable isotope labelling for citrate-coated Ag nanoparticles using Ag that was 99.7 % 109 Ag ( 109 Ag NPs). We used the freshwater snail (Lymnaea stagnalis) to characterise their bioaccumulation and toxicity at concentrations orders of magnitude lower than that employed in many previous studies, thereby demonstrating that stable isotope labelling can enhance detection sensitivity of Ag uptake.…”

Aquatic toxicity of manufactured nanomaterials: challenges and recommendations for future toxicity testing

“…Biodynamic modelling of Zn accumulation in the estuarine snail Peringia ulvae revealed comparable uptake and efflux rates of Zn 2þ and ZnO NMs suggesting that Zn 2þ was the bioavailable fraction. [175] Together these studies strongly indicated that the behaviour of ZnO NMs in the environment, even during relatively short periods (10 days in the study of Larner et al [174] ) may be little different from Zn 2þ . Although these studies have undoubtedly demonstrated the important role of Zn 2þ release in the toxicity of ZnO NMs, the high NM dissolution rates may potentially obscure other important facets of toxicity, including nanoscale specific properties.…”

“…Where the uptake of ZnO NMs has been measured directly, accumulation of Zn by aquatic organisms appears to be strongly correlated with Zn 2þ , including in benthic organisms where sedimentation could lead to elevated localised concentrations of ZnO NMs. Using a mass balance approach to the partitioning of 68 Zn-labelled ZnO NMs in a simplified marine system with the benthic invertebrate Corophium volutator, Larner et al [174] reported that 97 % of 68 Zn was associated with the sediment with relatively little in water (2.5 %). Less than 0.5 % was accumulated in C. volutator after 10 days.…”