Sulfidation of Silver Nanoparticles: Natural Antidote to Their Toxicity

Abstract

Nanomaterials are highly dynamic in biological and environmental media. A critical need for advancing environmental health and safety research for nanomaterials is to identify commonly occurring physical and chemical transformations affecting nanomaterial properties and toxicity. Silver nanoparticles, one of the most ecotoxic and well-studied nanomaterials, readily sulfidize in the environment. Here, we show that very low degrees of sulfidation (0.019 S/Ag mass ratio) universally and significantly decreases the toxicity of silver nanoparticles to four diverse types of aquatic and terrestrial eukaryotic organisms. Toxicity reduction is primarily associated with a decrease in Ag+ availability after sulfidation due to the lower solubility of Ag2S relative to elemental Ag (Ag(0)). We also show that chloride in exposure media determines silver nanoparticle toxicity by controlling the speciation of Ag. These results highlight the need to consider environmental transformation of NPs in assessing their toxicity to accurately portray their potential environmental risks.

Speciation analysis of silver sulfide nanoparticles in environmental waters by magnetic solid-phase extraction coupled with ICP-MS

“…For the WWTP effluent, however, the spiked recoveries were in the range of 106.2-149.9%, which can be attributed in part to the transformation of AgNPs to Ag 2 S NPs that commonly occur in WWTP. 10,[14][15][16] Overall, the results were good in view of the low spiking levels and matrix complexity, indicating that the proposed method is capable of the speciation analysis of Ag 2 S NPs in environmental samples. However, further studies are needed to obtain more satisfactory recoveries.…”

Particulate and colloidal silver in sewage effluent and sludge discharged from British wastewater treatment plants

“…However, the risks of particulate and nanosilver in the environment may be less than expected due to the favorable reaction of silver with sulphide (a common ion in sewage) to form precipitates and complexes which are stable even in oxidizing conditions (Choi et al, 2009;Kim et al, 2010;Kaegi et al, 2011) and importantly reducing the release of the toxic Ag ion (Levard et al, 2011). This form appears to reduce the toxicity of silver (Levard et al, 2013). It remains to be seen to what extent the diversion of silver to land through sewage sludge poses environmental risks.…”

Antibacterial activity of silver nanoparticles: A surface science insight

“…The toxicity reduction has thus been associated to the formation of an insoluble precipitate that scavenges most of the Ag + ions from the solution and hence lowers their availability and action. Presence of sulfides is one of the most notable cases, due to the very low solubility of Ag 2 S. Several studies showed that presence of traces of this ion almost suppressed the biocidal activity of silver containing-systems, as seen in Fig. 2A [57][58][59]. Furthermore, both Reinsch et al [58] and Levard et al [59] showed an inhibition of the effect for S 2− /Ag molar ratio below 0.5 (which corresponds to the stoichiometric conditions).…”

“…Presence of sulfides is one of the most notable cases, due to the very low solubility of Ag 2 S. Several studies showed that presence of traces of this ion almost suppressed the biocidal activity of silver containing-systems, as seen in Fig. 2A [57][58][59]. Furthermore, both Reinsch et al [58] and Levard et al [59] showed an inhibition of the effect for S 2− /Ag molar ratio below 0.5 (which corresponds to the stoichiometric conditions). This was explained by the formation of an insoluble Ag 2 S layer around the Ag NPs, preventing further dissolution and hence activity.…”