Toxicokinetics of pristine and aged silver nanoparticles in Physa acuta

Abstract

Aquatic environments, particularly sediments, can be important final sinks for engineered nanoparticles (ENPs), with benthic biota being potentially exposed. There is an increasing need for hazard data to improve the environmental risk assessment of ENPs regarding aquatic systems. The aim of this study was to determine the toxicokinetics of several pristine (as manufactured) Ag-NPs, Ag₂S-NPs (used to simulate environmental aging of silver nanoparticles) and AgNO₃ as the ionic counterpart, in the freshwater snail Physa acuta. Snails were exposed through 1) contaminated water (without sediment), 2) contaminated water and clean sediment, and 3) contaminated sediment. Bioavailability of Ag to the snails was greatly influenced by Ag characteristics, as different uptake and elimination kinetics were found for the different Ag forms within the same exposure route. Snails exposed via water revealed, in general, similar uptake kinetics, differing from exposure via contaminated sediment, suggesting that exposure route also had a determining role in Ag bioavailability. The simulated aged form (Ag₂S-NPs) revealed fast uptake and depuration in snails from all experiments. When considering the double exposure route, which provides a more realistic contamination scenario, water was the main route, except for Ag₂S-NPs, for which sediment was more important. The remarkably low elimination and high stored fraction of Ag in some exposures emphasizes the bioaccumulation ability of P. acuta and may raise concerns about possible trophic transfer. Snail shells accumulated low amounts of Ag. The present study highlights the need for a proper examination of the overall exposure scenario of Ag-NPs to benthic organisms. Our results contribute to the environmental risk assessment of Ag-NPs in benthic environments.