a b s t r a c tWe examined the short-term toxicity of AgNPs and AgNO 3 to Daphnia magna at sublethal levels using 1 H NMR-based metabolomics. Two sizes of polyvinylpyrrolidone-coated AgNPs (10 and 40 nm) were synthesized and characterized and their Ag þ release was studied using centrifugal ultrafiltration and inductively coupled plasma mass spectrometry. Multivariate statistical analysis of the 1 H NMR spectra showed significant changes in the D. magna metabolic profiles following 48 h exposure to both AgNP particle sizes and Ag þ exposure. Most of the metabolic biomarkers for AgNP exposure, including 3-hydroxybutyrate, arginine, lysine and phosphocholine, were identical to those of the Ag þ -exposed groups, suggesting that the dominant effects of both AgNPs were due to released Ag þ . The observed metabolic changes implied that the released Ag þ induced disturbance in energy metabolism and oxidative stress, a proposed mechanism of AgNP toxicity. Elevated levels of lactate in all AgNP-treated but not in Ag þ -treated groups provided evidence for Ag-NP enhanced anaerobic metabolism. These findings show that 1 H NMR-based metabolomics provides a sensitive measure of D. magna response to AgNPs and that further targeted assays are needed to elucidate mechanisms of action of nanoparticle-induced toxicity.