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

Abstract

Environmental context. Predicting the environmental implications of nanotechnology is complex in part because of the difficulty in studying nanoparticle uptake in organisms at environmentally realistic exposures. Typically, high exposure concentrations are needed to detect accumulation and effects. We use labelled Ag nanoparticles to determine whether Ag bioaccumulation responses are linear over concentrations likely to occur in the environment, and whether concentration-dependent changes in agglomeration and dissolution affect bioavailability.Abstract. A major challenge in understanding the environmental implications of nanotechnology lies in studying nanoparticle uptake in organisms at environmentally realistic exposure concentrations. Typically, high exposure concentrations are needed to trigger measurable effects and to detect accumulation above background. But application of tracer techniques can overcome these limitations. Here we synthesised, for the first time, citrate-coated Ag nanoparticles using Ag that was 99.7 % 109 Ag. In addition to conducting reactivity and dissolution studies, we assessed the bioavailability and toxicity of these isotopically modified Ag nanoparticles ( 109 Ag NPs) to a freshwater snail under conditions typical of nature. We showed that accumulation of 109 Ag from 109 Ag NPs is detectable in the tissues of Lymnaea stagnalis after 24-h exposure to aqueous concentrations as low as 6 ng L À1 as well as after 3 h of dietary exposure to concentrations as low as 0.07 mg g À1. Silver uptake from unlabelled Ag NPs would not have been detected under similar exposure conditions. Uptake rates of 109 Ag from 109 Ag NPs mixed with food or dispersed in water were largely linear over a wide range of concentrations. Particle dissolution was most important at low waterborne concentrations. We estimated that 70 % of the bioaccumulated 109 Ag concentration in L. stagnalis at exposures ,0.1 mg L À1 originated from the newly solubilised Ag. Above this concentration, we predicted that 80 % of the bioaccumulated 109 Ag concentration originated from the 109 Ag NPs. It was not clear if agglomeration had a major influence on uptake rates.

Transformation kinetics of silver nanoparticles and silver ions in aquatic environments revealed by double stable isotope labeling

“…[27][28][29] The stable isotope labeling method has been used to detect the toxicity and bioaccumulation of several types of NPs with high sensitivity and reliability. 27,28,[30][31][32][33][34] In this study, we synthesized isotopically AgNO 3 and 3.7 mL of 34 mmol L −1 trisodium citrate dihydrate were added into 100 mL of boiling distilled water, and then 1 mL of 50 mmol L −1 sodium borohydride was added drop-wise into the solution with vigorous stirring. The solution turned from colorless to yellow immediately, and the color deepened with further addition of sodium borohydride.…”

“…37 Very limited silver (about 0.13% of the total silver content in the system) was detected by ICP-MS, showing that silver losses to the walls of the 500 mL FEP bottles were insignificant. An isotope tracing technique was employed to track two tracers, 107 Ag and 109 Ag, as described by Croteau et al 33 Since the concentration of silver in the reagents and container blanks was below the limit of detection of the ICP-MS, we assume that the silver present in the system was only from the two isotopes we added. 29 showing the obtained data were convincing.…”

Stable silver isotope fractionation in the natural transformation process of silver nanoparticles

“…We inferred the underlying pathways from the apparent isotope fractionation effects. In contrast to methods that use isotopically enriched materials as tracers 27,28 , this method employs natural variations of the stable isotope ratios and does not require any artificial tracers. However, it should be noted that extensive sample purification would be necessary before analysis of the Ag isotope ratios of samples from the natural environment 16 .…”

Bioavailability and toxicity of manufactured nanomaterials

“…Methodological advances such as stable isotope tracing techniques are helping to increase our ability to quantify and model bioaccumulation of MNMs. Croteau et al [7] demonstrate how the use of stable isotope labelled Ag MNMs allows for quantification of bioaccumulation at more environmentally realistic concentrations than has been possible in previous studies. Their study showed that the relative importance of uptake of dissolved Ag released from the MNMs at low, environmentally relevant, concentrations was greater than that at high Ag MNM concentrations.…”