John Wiley & Sons, Ltd.

Uptake routes and toxicokinetics of silver nanoparticles and silver ions in the earthworm Lumbricus rubellus

Current bioavailability models, such as the free ion activity model and biotic ligand model, explicitly consider that metal exposure will be mainly to the dissolved metal in ionic form. With the rise of nanotechnology products and the increasing release of metal‐based nanoparticles (NPs) to the environment, such models may increasingly be applied to support risk assessment. However, it is not immediately clear whether the assumption of metal ion exposure will be relevant for NPs. Here using an established approach of oral gluing we have conducted a toxicokinetics study to investigate the routes of Ag NP and Ag+ ion uptake in the soil dwelling earthworm Lumbricus rubellus. Results indicated a significant part of the Ag uptake in the earthworms is through oral/gut uptake for both Ag+ ions and NPs. Thus, sealing the mouth reduced Ag uptake by between 40‐75%. An X‐ray analysis of the internal distribution of Ag in transverse sections confirmed the presence of increased Ag concentrations in exposed earthworm tissues. For the Ag NPs but not the Ag+ ions, high concentrations were associated with the gut wall, liver‐like chloragogenous tissue and nephridia, which suggest a pathway for Ag NP uptake, detoxification and excretion via these organs. Overall our results indicate that Ag in ionic and NP form is assimilated and internally distributed in earthworms and that this uptake occurs predominantly via the gut epithelium and less so via the body wall. The importance of oral exposure questions the application of current metal bioavailability models, which implicitly consider that the dominant route of exposure is via the soil solution, for bioavailability assessment and modelling of metal‐based NPs. This article is protected by copyright. All rights reserved

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