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% 109Ag. In addition to conducting reactivity and dissolution studies, we assessed the bioavailability and toxicity of these isotopically modified Ag nanoparticles (109Ag NPs) to a freshwater snail under conditions typical of nature. We showed that accumulation of 109Ag from 109Ag NPs is detectable in the tissues of Lymnaea stagnalis after 24-h exposure to aqueous concentrations as low as 6ngL–1 as well as after 3h of dietary exposure to concentrations as low as 0.07μgg–1. Silver uptake from unlabelled Ag NPs would not have been detected under similar exposure conditions. Uptake rates of 109Ag from 109Ag 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 109Ag concentration in L. stagnalis at exposures <0.1µgL–1 originated from the newly solubilised Ag. Above this concentration, we predicted that 80% of the bioaccumulated 109Ag concentration originated from the 109Ag NPs. It was not clear if agglomeration had a major influence on uptake rates.