Uptake of Silver-Containing Nanoparticles in an Estuarine Plant: Speciation and Bioaccumulation

Understanding the bioaccumulation of silver-containing nanoparticles (Ag-NPs) with different species, concentrations, and sizes in estuarine plants is critical to their related environmental risk. Herein, the distribution of Ag-NPs in tidewater, sediments, and plants (Scirpus triqueter) of field-constructed mesocosm was investigated, where tidewater was exposed to Ag⁰-NPs and Ag⁺ at environmentally relevant concentrations. Particle number concentrations (PNCs) and sizes of Ag-NPs with various species were analyzed using a multistep selective dissolution method followed by the single-particle- inductively coupled plasma mass spectrometry technique. After 30 days of exposure, more than half of Ag⁰-NPs were dissolved to Ag⁺ and about 1/4 of Ag⁺ were transformed into Ag⁰-/AgCl-NPs in tidewater. Ag-NPs in stems exposed to Ag⁰-NPs were found to be dominated by metallic Ag, while Ag⁺ exposure led to more Ag₂S-NPs in stems. In roots, 71% and 51% of Ag-NPs were found as Ag₂S-NPs for Ag⁰-NPs and Ag⁺ treatment groups, respectively. Plant stems had a significantly higher enrichment of Ag-NPs than roots. Based on both random forests and structure equation models, it is suggested that salinity of tidewater can regulate Ag⁰-NPs in tidewater indirectly by influencing AgCl-NPs in tidewater and further affect the total PNCs of Ag-NPs in plant stems. Moreover, elevated sulfate-reducing bacteria (SRB) result in more Ag₂S-NPs in rhizosphere sediments, thereby enhancing the bioaccumulation of Ag-NPs by roots.