With increasing emission of silver nanoparticles (AgNPs) into the environment,it is important to understand the effects of ambient concentration of AgNPs.The biological effects of AgNPs on Scenedesmus obliquus,a ubiquitous freshwater microalgae,was evaluated.AgNPs exerted a minor inhibitory effect at low doses.Non-targeted metabolomic studies were conducted to understand and analyze the effect of AgNPs on algal cells from a molecular perspective.During the 48 hr of exposure to AgNPs,30 metabolites were identified,of which nine had significant changes compared to the control group.These include D-galactose,sucrose,and D-fructose.These carbohydrates are involved in the synthesis and repair of cell walls.Glycine,an important constituent amino acid of glutathione,increased with AgNP exposure concentration increasing,likely to counteract an increased intracellular oxidative stress.These results provide a new understanding of the toxicity effects and mechanism of AgNPs.These metabolites could be useful biomarkers for future research,employed in the early detection of environmental risk from AgNPs.