Discerning the Sources of Silver Nanoparticle in a Terrestrial Food Chain by Stable Isotope Tracer Technique

The increasing use of silver-containing nanoparticles (NPs) in commercial products has led to NP accumulation in the environment and potentially in food webs. Identifying the uptake pathways of different chemical species of NPs, such as Ag₂S-NP and metallic AgNPs, into plants is important to understanding their entry into food chains. In this study, soybean Glycine max L. was hydroponically exposed to Ag₂S-NPs via their roots (10-50 mg L^-1) and stable-isotope-enriched ¹⁰⁹AgNPs via their leaves [7.9 μg (g fresh weight)^-1]. Less than 29% of Ag in treated leaves (in direct contact with ¹⁰⁹AgNP) was accumulated from root uptake of Ag₂S-NPs, whereas almost all of the Ag in soybean roots and untreated leaves sourced from Ag₂S-NPs. Therefore, Ag₂S-NPs are phytoavailable and translocate upward. During trophic transfer the Ag isotope signature was preserved, indicating that accumulated Ag in snails most likely originated from Ag₂S-NPs. On average, 78% of the Ag in the untreated leaves was assimilated by snails, reinforcing the considerable trophic availability of Ag₂S-NPs via root uptake. By highlighting the importance of root uptake of Ag₂S-NPs in plant uptake and trophic transfer to herbivores, our study advances current understanding of the biogeochemical fate of Ag-containing NPs in the terrestrial environment.