Effect and mechanism of silver nanoparticles on nitrogen transformation in water-sediment system of a hypereutrophic lake

Industrialization and urbanization are expected to increase the release of silver nanoparticles (AgNPs) into aquatic ecosystems. However, it remains to be determined how AgNPs influence nitrogen transformation and the underlying mechanism in natural water bodies. Here, the impact of AgNPs on nitrogen cycling in water-sediment system of a hypereutrophic lake was studied and the mechanism of nitrogen transformation was investigated in terms of the nitrogen functional enzymes and genes. Following 7 days of water-sediment microcosm experiments, the levels of total nitroten (TN) and organic nitrogen (Org-N) were significantly increased by 50 mg/L Ag+ treatment when compared with the non-Ag control (P < 0.05). In contrast, the levels of TN and Org-N were both slightly decreased by AgNPs treatments (0.5 and 50 mg/L). Additionally, the levels of NO3--N were evidently reduced with the presence of AgNPs (P < 0.05). Further, our data proved that enzymes and those enzyme encoding genes involved in the nitrogen transformation may directly responsible for the alterations of nitrogen transformation. Overall, our work suggested that the short-term exposure to AgNPs might cause hormetic effects on nitrogen-transforming microorganisms in hypereutrophic lakes, and have a potential to result in non-negligible changes in the nitrogen cycling of hypereutrophic lakes. (C) 2020 Elsevier B.V. All rights reserved.