Ambivalent effects of dissolved organic matter on silver nanoparticles/silver ions transformation: A review

The numerous applications of silver nanoparticles (AgNPs) lead to their spread in aquatic systems and the release of silver ions (Ag+), which brings potential risks to environment and human health. Owing to the different toxicity, the mutual transformations between AgNPs and Ag+ has been a hot topic of research. Dissolved organic matter (DOM) is ubiquitous on the earth and almost participates in all the reactions in the nature. The previous studies have reported the roles of DOM played in the transformation between AgNPs and Ag+. However, different experiment conditions commonly caused contradictory results, leading to the difficulty to predict the fate of AgNPs in specific reactions. Here we summarized mechanisms of DOM-mediated AgNPs oxidation and Ag+ reduction, and analyzed the effects of environmental parameters. Moreover, the knowledge gaps, challenges, and new opportunities for research in this field are discussed. This review will promote the understanding of the fate and risk assessments of AgNPs in natural water systems.