| dc.description.abstract | The production, use and disposal of silver nanoparticles (AgNPs) 3⁄4 one of the most common man-made nanoparticles in consumer products 3⁄4 will inevitably result in the
release of these novel materials into the environment. From an environmental point of view, the stability of AgNPs will subsequently be affected by certain environmental factors, such as molecular oxygen, natural organic matter (NOM), and complexing agents, thereby affecting the eventual bioavailability of AgNPs. Previous studies have demonstrated that AgNPs can exhibit significant bactericidal activity under aerobic conditions due to oxidative dissolution of AgNPs to Ag(I) by dissolved oxygen and then the uptake of Ag(I) by cells. The resulting intracellular Ag(I) will interfere with the functions of thiol-containing proteins, leading to the cells subject to oxidative stress. However, few studies have been conducted to investigate the conversion of AgNPs in the absence of dissolved oxygen, in particular the interactions between AgNPs and certain chemical species that are normally encountered in the anoxic environment. In this study, synthetic citrate-coated AgNPs were used to explore the effect of metabolic denitrifying species, chloride and NOM (using humic acid, HA, as the model species) on AgNP transformation under deoxygenated conditions. Ag(I) was separated from AgNPs by centrifugal ultrafiltration or 0.02 μm membrane filter and quantified by ICP- OES. Results show that increases in chloride alone was able to result in elevated Ag(I) production. Compared to nitrite that significantly oxidize AgNPs to Ag(I), nitrate had little effect on AgNP oxidation. Thiols could also convert AgNPs to Ag(I), and the higher the Ag/ligand molar ratio, the more Ag(I) formation. HA and AQDS (a quinone representative compound) were observed to reduce the extent of AgNPs transformed into Ag(I), implying that humic substances may help mitigate the toxicity of AgNPs to microbes. Results obtained in this study may help assess and manage the risk of AgNPs in the environment. | en_US |