Fate and bioavailability of commercial silver nanoparticles to the polychaete, Capitella teleta

1. Membrane filter Resin gel Diffusive gel Lina Dai1, Gary T Banta1, Henriette Selck1 and Valery E Forbes1,2 1Department of Environmental, Social and Spatial Change, Roskilde University, Universitetsvej 1, DK-4000 Roskilde, Denmark. 3School of Biological Sciences, University of Nebraska Lincoln, 348 Manter Hall, Lincoln. E-mail contact: ldai@ruc.dk • Introduction • The environmental behavior and bioavailability of engineered nanoparticles (ENPs) have received increasing attention. One of the focuses is whether they exist as particles or as dissolved ions in the environment. However, little information is available about the fate and bioavailability of ENPs in a complex environment, such as sediment, which is believed to be the final sink for released ENPs. The hypothesis in this study is that dissolved Ag+ ions released from AgNPs are a main source of bioavailable Ag to the deposit feeder, Capitella teleta. Two exposure systems (seawater-only vs. sediment) were used and diffusive gradient in thin films (DGT) devices were added to both exposure systems as a means to estimate the bioavailable Ag+ to Capitella teleta. Results Fate and bioavailability of commercial silver nanoparticles to the polychaete, Capitella teleta Table 1. Initial concentrations of Ag and bioaccumulation factor (BAF) of Capitella teleta in exposure systems, . Mortality: In seawater-only exposure, all worms were dead on day 2 (Table 1). But no significant mortality was observed in worms in the sediment exposure. DGT bound Ag: Ag was detected in DGT in both seawater- only and sediment exposures (Fig. 4, left). Biovailability: both Ag and AgNP were detected in exposed C. teleta (Fig. 4, right). What’s DGT? DGT – diffusive gradient of thin films, is a novel technique to measure metal ions. The structure is shown in Fig. 3. Experimental setup Commercial Ag nanoparticles (20nm with PVP-coating, Fig. 1) and aqueous Ag (AgNO3) were either added seawater-only (30‰) or spiked into sediment. C. teleta was exposed to seawater-only Ag or sediment-associated Ag. In addition. DGTs were deployed in parallel beakers (Fig. 2). No Ag was detected in the water overlying the sediment phase (GAAS). Endpoints: Mortality and Ag body burden. Structure of Diffusive gradient of thin films: ---0,45 µm pore size; ---2-5nm pore space; ---Ag binding layer. Ag+ Fig. 4 The Ag measured in DGT devices (left), and body burden of silver in the deposit-feeding polychaete, Capitella teleta (right). Note that no body burden data were avaialble in the seawater-only exposure due to mortality. Fig. 3 The structure of a DGT unit. When a DGT unit is deployed in Ag solution, Ag will diffuse through the membrane, hydrogel and bind to resin. The amount of Ag bound in DGT is proportional to the concentration of Ag+ in the deployed media. Fig. 1 characterization of 20nm AgNP (PVP coating) by TEM at 100kV (A) 50nm, (B) 20nm, (C) 1µm and (D) 50nm (Cong et al, 2011 in prep.) • Conclusions • Less Ag was bound in DGT in the system where AgNP was mixed in the sediment compared to the system with aqueous Ag mixed into seawater. • Bioavailability was higher in sediment with aqueous Ag than in sediment with AgNP although the difference was less than expected based on DGT data alone. • Results indicates that both aqueous Ag and AgNP were bioavailable to some degree to C. teleta. The mechanisms controlling uptake of AgNP in C. teleta and the relative importance of Ag+ ions and AgNPs for the body burden still remain to be examined. • Test organism - Capitella teleta • Capitella teleta, formerly asCapitella species I, is a relevant test species due to the following characters: • Feeding mode: deposit feeding, on organic matter; • Habitat: marine sediment; • Abundant: up to 400,000 individuals per m2; • A dominant organism in highly polluted sediment; • High sediment processing rate (i.e., high potential exposure to sediment pollutants). Fig. 2 Exposure of Capitella teleta (left beaker) and DGT (right beaker, face down) to sediment-associated Ag. No Ag was detected in the overlying water phase by GAAS. Acknowledge - The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 214478 (NanoReTox)