Influence of silver nanoparticles on settling of suspended sediments

Interaction of silver nanoparticles with marine/lake snow in early formation stage

Marine and lake snows play an important ecological role in aquatic systems, and recent researches have also revealed their interactions with various pollutants. In this paper, the interaction of silver nanoparticles (Ag-NPs), a typical nano-pollutant, with marine/lake snow in the early formation stage was investigated by roller table experiments. Results indicated Ag-NPs promoted the accumulation of larger marine snow flocs while inhibited the development of lake snow. The promotion effect of AgNPs might be attributed to their oxidative dissolution into low-toxic silver chloride complexes in seawater, and the subsequent incorporation into marine snow, which would enhance the rigidity and strength of larger flocs and favor the development of biomass. Conversely, Ag-NPs mainly existed in the form of colloidal nanoparticles in lake water and their strong antimicrobial effect suppressed the growths of biomass and lake snow. In addition, Ag-NPs could also affect the microbial community of marine/lake snow, including impact on microbial diversity, and elevation on abundances of extracellular polymeric substances (EPS) synthesis genes and silver resistance genes. This work has deepened our understanding of the fate and ecological effect of Ag-NPs via the interaction with marine/lake snow in aquatic environments.

Effect of Nano-Silver on Formation of Marine Snow and the Underlying Microbial Mechanism

Roller experiments were conducted to explore the effect of nano-silver on the formation of marine snow and the underlying microbial mechanism. With the increasing concentration of nano-Ag from 1 ng/L to 1 mg/L, the formation and aggregation of marine snow particles were solidly suppressed in a dose-dependent pattern. Moreover, the formed marine snows tended to be thinner fibrous particles with smaller size and increased edge smoothness and compactness in the presence of nano-Ag. The microbial analyses indicated that nano-Ag not only inhibited the development of biomass but also changed the species composition and functional profile of the microbial community. Nano-Ag obviously inhibited most of the abundant species, except for some myxobacteria, which is unfavorable for the microbial community stability. For the microbial functions, some major biological processes including the growth, metabolic, and cellular processes were also inhibited by the high dosage of nano-Ag. The strong microbial inhibition of nano-Ag would contribute to the suppression on the formation of marine snow. Specifically, the function genes of extracellular polymeric substance synthesis and secretion were significantly reduced by nano-Ag, which might be the key and straight microbial factor in suppressing the formation of marine snow.

Current trends and challenges in analysis and characterization of engineered nanoparticles in seawater

With the increasingly wide use of engineered nanoparticles (ENPs), their release into the environment makes it important to determine in what quantitates they occur in aquatic systems and to understand their fate therein. In particular, detection and quantification of ENPs in seawater is challenging and often requires analytical methods to perform close to the feasibility confines. This review is aimed at critical analysis of current and emerging capabilities of analytical methods as have been employed for the analysis and characterization of ENPs in seawater in the last decade. An emphasis is given to the most reliable experimental strategies focused on avoiding the high-salt matrix effect and isolation and enrichment of the nanoparticulate fraction prior to analysis. Advanced analytical methodology in use basically relies on the application of elemental mass spectrometry to determine various particle-core metals and its single-particle mode to characterize the seawater-mediated transformation of ENPs, including dissolution, aggregation, etc. On the other hand, common microscopy, light scattering or X-ray based techniques are not sensitive enough to acquire the transformation information from real seawater samples. Finally, attention is pinpointed upon an acute shortcoming of the current research which is in the overwhelming majority of cases restricted to samples spiked with ENPs and often at excessive concentration levels.