Extracellular polymeric substances from the diatom Cyclotella meneghiniana adsorb onto citrate-coated nAg, forming an eco-corona and reducing nanoparticle dissolution and aggregation.

Methods to differentiate surface-bound and internalized Ag in phytoplankton are essential for understanding bioaccumulation but remain limited, especially for studies involving silver nanoparticles (AgNPs). To address this, we assessed biologically relevant ligands for extracting adsorbed Ag from Chlamydomonas reinhardtii and Cyclotella meneghiniana exposed to Ag⁺ or AgNPs, focusing on ligand type, concentration, and extraction time. Additionally, we examined the impact of these agents on AgNP stability and microalgal membrane integrity. The ligands l-histidine, l-glutamine, l-cysteine, and d-penicillamine were tested. The thiol-containing d-penicillamine, tested for the first time, showed the highest efficiency in desorbing Ag⁺ from Ag⁺-treated cells, followed by l-cysteine. Optimal conditions were 1 mmol L⁻¹ ligand concentration and 5 min contact time. For AgNP-exposed cells, two sequential cell resuspensions in Ag-free medium were sufficient to detach loosely bound AgNPs. Then, hydrogen peroxide (H₂O₂), a biologically relevant oxidant, was introduced for the first time in the extraction procedure to facilitate the oxidative dissolution of nanoparticles. A combination of 0.5 mmol L^-1 H₂O₂ with a 1 mmol L^-1l-cysteine or d-penicillamine effectively removed Ag from the cell walls of C. meneghiniana and C. reinhardtii. The tested extraction agents did not affect unexposed phytoplankton cells. However, AgNP-exposed cells treated with H₂O₂ showed slightly increased cell membrane damage in diatoms. A dissolution of AgNP was found in the presence of l-histidine and d-penicillamine and H₂O₂. These findings highlight the need to develop species-specific washing methodologies in AgNPs bioaccumulation studies and provide insight into optimized extraction methods for assessing AgNP adsorption, internalization, and toxicity.

Silver nanoparticles (AgNPs) are widely used nanomaterials, and understanding their effects on phytoplankton is essential for assessing ecological risks. While AgNP toxicity has been extensively studied in single species, the role of interspecies interactions on toxicity outcomes remains poorly understood. This study investigates the effects of AgNPs and Ag⁺ on phytoplankton, focusing on species-specific responses and interspecies interactions within artificial assemblages. Monocultures and assemblages of Chlamydomonas reinhardtii, Cyclotella meneghiniana, and Synechocystis sp. were exposed to AgNPs (1-3000 µg L^-1) and Ag⁺ (0.05-300 µg L^-1) to assess growth inhibition, photosynthetic efficiency, and pigment fluorescence. Spectral flow cytometry enabled high-resolution, single-cell monitoring of cell abundance and pigment fluorescence in the assemblages. Results revealed species-specific toxicity, with Synechocystis sp. being most affected by AgNPs, while C. meneghiniana showed greater tolerance. Ag⁺ exposure triggered rapid effects, including reduced photosynthetic efficiency within 2 h, whereas AgNPs caused delayed but persistent toxicity. Experiments with artificial assemblages revealed that interspecies interactions modulated silver toxicity. Co-occurrence of species alleviated AgNP stress, resulting in significantly higher 72h-EC₅₀ for some species and sustained photosynthetic performance in the cohabiting eukaryotes. These findings demonstrated that phytoplankton assemblages' composition strongly influences AgNP toxicity and highlighted spectral flow cytometry as a powerful tool for resolving species-specific responses within complex assemblages. The study emphasized the importance of integrative, assemblage-based approaches in ecotoxicology to more accurately predict ecosystem-level impacts of pollutants.

Sub-lethal exposure to dissolved and nanoparticulate silver induces distinct and substantial alterations in diatom metabolism, with central carbon and nitrogen metabolic pathways exhibiting particularly pronounced perturbations.

Silver nanoparticles (AgNPs) are extensively utilized engineered nanomaterials that inevitably find their way into the aquatic environment [1].

Silver nanoparticles (AgNPs), widely used in consumer products, are inevitably released into aquatic environments. In the water column, AgNPs undergo physicochemical transformations, notably oxidative dissolution, releasing ionic silver (Ag⁺). Both nanoparticulate and ionic Ag species can be toxic to phytoplankton, primarily through bioaccumulation. However, the mechanisms governing Ag bioaccumulation remain poorly understood due to the coexistence of multiple Ag forms and particle sizes, as well as the structural diversity across phytoplankton communities.In this study, we employed a recently proposed methodology to investigate the interactions of Ag⁺ and AgNPs (5 and 20 nm) with two freshwater phytoplankton species exhibiting distinct cellular architectures: the green alga Chlamydomonas reinhardtii and the diatom Cyclotella meneghiniana. Bioaccumulation and adsorption kinetics varied with Ag form, particle size, and cellular architecture. Rapid Ag bioaccumulation was observed during exposure to Ag⁺, whereas accumulation under AgNP exposure was more gradual and sustained. Smaller nanoparticles (5 nm) resulted in higher Ag bioaccumulation in both organisms, with greater dissolution and stronger cell adsorption compared to 20 nm AgNPs.The diatom exhibited higher uptake rates and Ag association than the green alga, consistent with transmission electron microscopy (TEM) observations.AgNPs were embedded in the frustule and detected within cellular compartments of C. meneghiniana, while, in C. reinhardtii, they were mainly observed as aggregates outside the cells, associated with the cell wall and palmelloid enveloppe. We demonstrate that Ag bioaccumulation is strongly influenced by silver speciation, particle size, and cellular architecture, highlighting the need to integrate these factors in environmental risk assessments.