Distribution of sulfidized silver nanoparticles across abiotic and biotic environmental compartments: a long-term floodplain mesocosm study

In environmental research, the application of sulfidized silver nanoparticles (S-Ag-NPs) prepared by sulfidation of silver nanoparticles (Ag-NPs) will more realistically simulate the release routes of these nanoparticles and their fate in natural compartments compared to the frequently used pristine Ag-NPs or silver sulfide nanoparticles (Ag₂S-NPs) prepared by synthesis from dissolved silver which do not fully reflect the environmentally relevant state. Furthermore, the information on the accumulation of S-Ag-NPs in sediments, floodplain soils, biofilms, amphipods, and filter feeding organisms – bivalves – is extremely limited. In this study, we evaluated the distribution of S-Ag-NPs in abiotic and biotic compartments using indoor mesocosms simulating the aquatic-terrestrial transition zone and considering typical dynamics in floodplain areas. High accumulation of silver in sediments and biofilms observed in this study indicates that these compartments represent the most effective sinks for S-Ag-NPs in rivers. In the presence of mussels, immobilization of silver in sediment increased, most likely due to the rejection of nanoparticles as pseudo-feces by mussels. The enrichment of silver originating from S-Ag-NPs in/on biofilms, amphipods, mussels, and leaves suggests an enhanced risk of trophic transfer of these environmentally relevant nanoparticles. While some properties of nanoparticles are different for sulfidized and pristine Ag-NPs such as lower affinity of S-Ag-NPs to biofilms and leaves compared to Ag-NPs, other properties are similar for both nanoparticles such as high accumulation in sediments and soils. Furthermore, the high mobility of a residual nanoparticle fraction in river water seems to be representative for S-Ag-NPs and Ag-NPs indicating an enhanced risk for their long-distance transport in rivers.