The effects of varying concentrations of Ag NPs on coupled nitrification and denitrification (CND) in two suspended sediments (SPSs) sizes were investigated using isotopic tracer method. In general, 0.5 and 5 mg/L Ag NPs had less effect on CND, while 2 and 10 mg/L Ag NPs exhibited the improvement and inhibition effect, respectively. The CND improvement by 2 mg/L NPs was mainly due to the enhanced nitrifying and denitrifying enzyme activity. However, 10 mg/L Ag NPs inhibited NH4+ oxidation by directly reducing the AMO activity and AOB abundance. The inhibition on NAR and NIR activity and their encoding narG and nirK gene abundance further inhibited NO3- and NO2- reduction, leading to a dramatic decrease in the 15N-N2 production. The above inhibition effects were attributed to the nano-effects of Ag NPs, which led to the excessive ROS amount and the decreased T-AOC level in microbial systems. But the connection between nitrification and denitrification was not broken after Ag NPs exposure. Moreover, the results indicated that N-cycling in clay and silt-type SPS systems could be more sensitive than sand-type SPS systems to NP exposure. The findings provide a basis for evaluating the environmental risks of Ag NPs in water-sediment systems.

中文翻译：

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银纳米颗粒对悬浮沉积物中耦合硝化-反硝化作用的影响。

使用同位素示踪法研究了不同浓度的银纳米颗粒对两种悬浮沉积物（SPSs）大小的耦合硝化和反硝化（CND）的影响。通常，0.5和5 mg / L的Ag NPs对CND的影响较小，而2和10 mg / L的Ag NPs分别表现出改善和抑制作用。CND改善2 mg / L NPs的主要原因是硝化和反硝化酶活性增强。然而，10 mg / L Ag NPs通过直接降低AMO活性和AOB丰度来抑制NH4 +氧化。对NAR和NIR活性的抑制及其编码的narG和nirK基因丰度进一步抑制了NO3-和NO2-的还原，从而导致15N-N2产量急剧下降。上述抑制作用归因于银纳米颗粒的纳米效应，这导致微生物系统中过量的ROS含量和T-AOC含量降低。但是，Ag NPs暴露后，硝化和反硝化之间的联系并未被破坏。此外，结果表明，粘土和淤泥型SPS系统中的N循环比NPS沙型SPS系统更敏感。研究结果为评估水沉积系统中银纳米颗粒的环境风险提供了基础。