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The widespread use of commercial silver nanoparticles (Ag NPs) inevitably results in their increased release into natural waters and subsequent deposition in sediments, requiring the environmental impact of such deposition to be closely investigated. Hence, the effects of Ag NPs, polyvinylpyrrolidone (PVP)-Ag NPs, and sliver sulfide nanoparticles (Ag 2 S NPs) on denitrification-induced gas production (N 2 O and 15 N-N 2 ), and denitrifying microbes in freshwater sediments were investigated. Slurry experiments (8 h) combined with a 15 NO 3 - addition technique were performed to determine the gaseous production. The abundance of relative functional genes (nirK, nirS and nosZ) and the composition of functional community were determined through RT-PCR and high-throughput sequencing, respectively. The obtained results showed that the toxicity of NPs on denitrification depended on their type (Ag +  > Ag NPs > PVP-Ag NPs > Ag 2 S NPs) and concentration, e.g., all 1 mg/L NPs exhibited no effects on denitrification, whereas evident hormesis effect-induced acceleration was observed in the case of Ag + . Conversely, 10 mg/L Ag + and Ag NPs significantly inhibited the release rates of N 2 O and N 2 by decreasing the abundance of functional genes (nirK and/or nirS) and the predominant bacteria Paracoccus. PVP-Ag and Ag 2 S NPs had no effects on N 2 release rates and the composition of denitrifiers, however, inhibited the emission of N 2 O (by reducing the abundance of nirK), suggesting that normal denitrification-induced N 2 formation in sediments could still be sustained when the N 2 O production decrease lied within a certain range. Further, the inhibiting ability of Ag-containing NPs was caused by their intrinsic nanotoxicity to functional microbes rather than by the general toxicity of Ag + . Besides, Ag 2 S NPs (as a main detoxification form of AgNPs) were revealed to be intrinsically nanotoxic to denitrifiers, albeit showing the lowest inhibitory effect among the three tested NPs. Thus, this study demonstrated that the inhibitory effect of Ag-containing NPs on denitrification in sediments depends on their morphology and type, implying that the stability and toxicity of Ag-containing NPs should be considered with caution., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

With the accelerated application of CeO 2 nanoparticles (NPs), wastewater treatment plants will increasingly receive CeO 2 NPs, thus inevitably causing CeO 2 NPs to encounter microaggregates. Here, we comprehensively elucidate the responses in the structural, physicochemical and microbial properties of wastewater biofilms to chronic exposure (75 days) to different CeO 2 NPs concentrations, with a particular emphasis on the protective mechanisms of stratified extracellular polymeric substances (EPSs). Chronic exposure to 0.1 mg/L CeO 2 NPs boosted the content and broadened the distribution of α-d-glucopyranose polysaccharides (PS), while the sharply increased production and breadth of β-d-glucopyranose PS, forming a formidable shield, was a response to 10 mg/L CeO 2 NPs. After the bacteria were exposed to CeO 2 NPs, loosely bound EPSs (LB-EPSs) aggregated into macromolecules (increasing in apparent molecular weight (AMW)) but at a lower abundance, whereas the average AMW in tightly bound EPSs (TB-EPSs) decreased. The acetyl content and (α-helix+3-turn helix)/β-sheet value of TB-EPSs increased to resist CeO 2 NPs. Furthermore, long-term exposure to CeO 2 NPs decreased cell viability, reduced microbial diversity and shifted the microbial composition. N-acylated-l-homoserine lactone concentrations increased with increased density of Pseudomonas, which was associated with PS-regulated control, thus promoting PS production in EPSs in response to CeO 2 NPs. These results expand the understanding of how microaggregates resist environmental stress caused by NPs., (Copyright © 2018 Elsevier Ltd. All rights reserved.)