Colloidal Stability of Carbonate-Coated Silver Nanoparticles in Synthetic and Natural Freshwater

To gain important information on fate, mobility, and bioavailability of silver nanoparticles (AgNP) in aquatic systems, the influence of pH, ionic strength, and humic substances on the stability of carbonate-coated AgNP (average diameter 29 nm) was systematically investigated in 10 mM carbonate and 10 mM MOPS buffer, and in filtered natural freshwater. Changes in the physicochemical properties of AgNP were measured using nanoparticle tracking analysis, dynamic light scattering, and ultraviolet–visible spectroscopy. According to the pH-dependent carbonate speciation, below pH 4 the negatively charged surface of AgNP became positive and increased agglomeration was observed. Electrolyte concentrations above 2 mM Ca²⁺ and 100 mM Na⁺ enhanced AgNP agglomeration in the synthetic media. In the considered concentration range of humic substances, no relevant changes in the AgNP agglomeration state were measured. Agglomeration of AgNP exposed in filtered natural freshwater was observed to be primarily controlled by the electrolyte type and concentration. Moreover, agglomerated AgNP were still detected after 7 days of exposure. Consequently, slow sedimentation and high mobility of agglomerated AgNP could be expected under the considered natural conditions. A critical evaluation of the different methods used is presented as well

Exposure of silver-nanoparticles and silver-ions to lung cells in vitro at the air-liquid interface

Background Due to its antibacterial properties, silver (Ag) has been used in more consumer products than any other nanomaterial so far. Despite the promising advantages posed by using Ag-nanoparticles (NPs), their interaction with mammalian systems is currently not fully understood. An exposure route via inhalation is of primary concern for humans in an occupational setting. Aim of this study was therefore to investigate the potential adverse effects of aerosolised Ag-NPs using a human epithelial airway barrier model composed of A549, monocyte derived macrophage and dendritic cells cultured in vitro at the air-liquid interface. Cell cultures were exposed to 20 nm citrate-coated Ag-NPs with a deposition of 30 and 278 ng/cm² respectively and incubated for 4 h and 24 h. To elucidate whether any effects of Ag-NPs are due to ionic effects, Ag-Nitrate (AgNO₃) solutions were aerosolised at the same molecular mass concentrations.Results Agglomerates of Ag-NPs were detected at 24 h post exposure in vesicular structures inside cells but the cellular integrity was not impaired upon Ag-NP exposures. Minimal cytotoxicity, by measuring the release of lactate dehydrogenase, could only be detected following a higher concentrated AgNO₃-solution. A release of pro-inflammatory markers TNF-α and IL-8 was neither observed upon Ag-NP and AgNO₃ exposures as well as was not affected when cells were pre-stimulated with lipopolysaccharide (LPS). Also, an induction of mRNA expression of TNF-α and IL-8, could only be observed for the highest AgNO₃ concentration alone or even significantly increased when pre-stimulated with LPS after 4 h. However, this effect disappeared after 24 h. Furthermore, oxidative stress markers (HMOX-1, SOD-1) were expressed after 4 h in a concentration dependent manner following AgNO₃ exposures only.Conclusions With an experimental setup reflecting physiological exposure conditions in the human lung more realistic, the present study indicates that Ag-NPs do not cause adverse effects and cells were only sensitive to high Ag-ion concentrations. Chronic exposure scenarios however, are needed to reveal further insight into the fate of Ag-NPs after deposition and cell interactions

Intracellular Silver Accumulation in <i>Chlamydomonas reinhardtii</i> upon Exposure to Carbonate Coated Silver Nanoparticles and Silver Nitrate

The intracellular silver accumulation ({Ag}_in) upon exposure to carbonate coated silver nanoparticles (AgNP, 0.5–10 μM, average diameter 29 nm) and silver nitrate (20–500 nM) was examined in the wild type and in the cell wall free mutant of the green alga <i>Chlamydomonas reinhardtii</i> at pH 7.5. The {Ag}_in was measured over time up to 1 h after a wash procedure to remove silver ions (Ag⁺) and AgNP from the algal cell surface. The {Ag}_in increased with increasing exposure time and with increasing AgNP and AgNO₃ concentrations in the exposure media, reaching steady-state concentrations between 10^–5 and 10^–3 mol L_cell^–1. According to estimated kinetic parameters, high Ag⁺ bioconcentration factors were calculated (>10³ L L_cell^–1). Higher accumulation rate constants were assessed in the cell wall free mutant, indicating a protective role of the cell wall in limiting Ag⁺ uptake. The bioavailability of AgNP was calculated to be low in both strains relative to Ag⁺, suggesting that AgNP internalization across the cell membrane was limited

Chemical Aspects of Nanoparticle Ecotoxicology

Nanoecotoxicology strives to understand the processes and mechanisms by which engineered nanoparticles (ENP) may exert toxic effects on aquatic organisms. Detailed knowledge of the chemical reactions of nanoparticles in the media and of their interactions with organisms is required to understand these effects. The processes of agglomeration of nanoparticles, of dissolution and release of toxic metal ions, and of production of reactive oxygen species (ROS) are considered in this article. Important questions concern the role of uptake of nanoparticles in various organisms, in contrast to uptake of ions released from nanoparticles and to nanoparticle attachment to organism surfaces. These interactions are illustrated for effects of silver nanoparticles (AgNP), cerium oxide (CeO2 NP) and titanium dioxide (TiO2 NP), on aquatic organisms, including algae, biofilms, fish cells and fish embryos